TECHNICAL FIELD

The present disclosure relates to antenna systems comprising a communication device and a dualreflector antenna.

BACKGROUND

The present disclosure is in the field of antenna systems. Such an antenna system may comprise a communication device and a dual-reflector antenna for transmitting and/or receiving electromagnetic waves. A dual-reflector antenna may be an antenna comprising two reflectors for transmitting and/or receiving electromagnetic waves.

SUMMARY

The following considerations are made by the inventors:

Nowadays, millimeter-wave, terahertz and optical wireless communications share similar motivations for the challenging requirements of a new generation of reflector antennas, that may be characterized by very high gain, extremely narrow beam and beam steering capability.

At millimeter-wave (MMW) in E-band and D-band, the backhaul radio-links exceeding distances of one kilometer may require antenna gain higher than 50dBi, suited for line-of-site long range link budgets, withstanding to any atmospheric condition; corresponding antennas, with beam-widths narrower than half degree, may need careful installation. Moreover, this class of large-diameter dish antennas is prone to high values of wind-loads and, in case they are mounted on high towers or masts, their pointing may be affected by deflections, sways and vibrations of supporting structures. When considering the typical case of an E-band backhaul antenna, operating at 71 to 86 GHz with a dish diameter of 2 feet (660mm), that is about 170 wavelengths, and the equivalent case of a D-band antenna, operating at 130 to 175GHz with a nominal dish diameter of one foot, both antennas may perform more than 50dBi of gain with a beam-width narrower than 0.4 degrees, such that one degree of deflection of the supporting structure may mispoint the antenna and downgrade its gain to 40dBi.

In view of the above, this disclosure aims to provide an antenna system that may deal with environmental influences on the antenna system, wherein the environmental influences cause deflections, sways and vibrations of the antenna system. An objective may be providing an antenna system that may deal with environmental influences on the antenna system in order to keep a sufficient gain of the antenna system. These and other objectives are achieved by the solution of this disclosure as described in the independent claims. Advantageous implementations are further defined in the dependent claims.

A first aspect of this disclosure provides an antenna system comprising: a communication device; a dualreflector antenna; and a gradient-index lens (GRIN lens). The communication device is configured to transmit primary plane electromagnetic waves to the GRIN lens, wherein the GRIN lens is configured to transform the transmitted primary plane electromagnetic waves to a Gaussian beam of radiation. The dual-reflector antenna is configured to transform the Gaussian beam of radiation to secondary plane electromagnetic waves and transmit the secondary plane electromagnetic waves outside the antenna system. The communication device is configured to change the direction of propagation of the transmitted secondary plane electromagnetic waves by changing the direction of propagation of the transmitted primary plane electromagnetic waves.

With other words, the first aspect proposes using a dual-reflector antenna and a GRIN lens in addition to a communication device for transmitting secondary plane electromagnetic waves, wherein the direction of propagation of the transmitted secondary plane electromagnetic waves may be changed by changing the direction of propagation of the transmitted primary plane electromagnetic waves.

That is, the communication device may be configured to perform beam steering of the secondary plane electromagnetic waves by changing the direction of propagation of the primary plane electromagnetic waves. Changing the direction of propagation of the primary plane electromagnetic waves may be referred to as beam steering of the primary plane electromagnetic waves. Changing the direction of propagation of the secondary plane electromagnetic waves or performing beam steering of the secondary plane electromagnetic waves corresponds to or comprises pointing (re-pointing) an antenna beam that may be transmitted (e.g. in the form of the secondary plane electromagnetic waves) by the antenna system to outside the antenna system. The term “beam scanning” may be used as a synonym for the term “beam steering”.

Therefore, the antenna system allows to compensate an effect of deflections, sways and/or vibrations (e.g. due to strong wind) on the antenna system, e.g. on a pointing of the antenna systems. Namely, the antenna system is configured for changing the propagation direction of the secondary plane electromagnetic waves and, thus, for re-pointing of the antenna system (i.e. the antenna beam of the antenna system). As a result, deflections, sway and vibration may have a reduced impact or no impact on the gain of the antenna system, so that the antenna system’s gain may be robust against environmental influences on the antenna system leading to deflections, sways and/or vibrations of the antenna system. As outlined above, the antenna system according to the first aspect enables full antenna beam steering (e.g. beam steering of the secondary plane electromagnetic waves within an angular sector (e.g. a limited angular sector)). The angular sector may be for example ±1.5 degrees (±1.5°). This allows the antenna system to be used for radio communication services. In addition or alternatively, the antenna system may be used for satellite telecommunication ground stations and/or for radio telescope antennas (e.g. large radio telescope antennas). The antenna system allows keeping a gain loss and other radiation patterns degradation, due to beam steering, as low as possible. For example, the antenna system may have a gain loss smaller than or equal to 1.5 dB (< 1.5dB). The antenna system may comply with ETSI Class 4, i.e. it may be an antenna system according to ETSI Class 4, as described in the European Norm document ETSI EN 302 217-4.

Using the dual-reflector antenna in combination with the GRIN lens allows changing the direction of propagation of the transmitted secondary plane electromagnetic waves and, thus, pointing (re-pointing) of the antenna beam that may be transmitted by the antenna system by changing the direction of propagation of the transmitted primary plane electromagnetic waves. Therefore, the antenna system according to the first aspect does not need to move the dual-reflector lens, the GRIN lens and/or the communication device (e.g. change the position and/or orientation of the dual-reflector lens, the GRIN lens and/or the communication device). As a result, means for motion of mechanical components of the antenna (e.g. one or more motors) are not needed. In other words, the dual-reflector antenna, the GRIN lens and the communication device may be kept fix at a respective place of installation (i.e. are not moved). This has the advantage that there is no wear out or deterioration due to motion of mechanical components and, thus, no risk of failure of the antenna system due to such wear out or deterioration. In addition, a movement of the dual-reflector lens, the GRIN lens and/or the communication device for repointing may limit the re-pointing speed of antenna beam steering. Thus, the antenna system according to the first aspect may achieve a high re-pointing speed of the antenna beam steering (i.e. changing the direction of the secondary plane electromagnetic waves). As a result, the antenna system may be configured for a high-speed tracking of a microwave beacon by means of a simple conical scan of the antenna beam. Since no means for motion of mechanical components of the antenna system are needed, the antenna system may have a low complexity and low costs.

The antenna system according to the first aspect may provide an electronic controlled steering of an antenna beam (e.g. the primary planes electromagnetic waves and, thus, secondary plane electromagnetic waves) for anti-sway compensation. The antenna system may be configured for an electronic controlled beam steering for a range of angle of beam scanning (e.g. limited angle of beam scanning) by means of the GRIN lens. By providing the antenna system according to the first aspect, this disclosure allows providing a very high gain antenna mixed assembly, where a dual-reflector antenna may be matched with a communication device (e.g. an array-feeder) by means of a graded index (GRIN) lens.

The gradient-index lens (GRIN lens) is a lens having a varying or changing refractive index within the lens itself. That is, the GRIN lens may be characterized by a non-homogeneous refractive index. The GRIN lens has a distributed material density for achieving the varying refractive index within the lens itself. The terms “index of refraction” and “refraction index” may be used as a synonym for the term “refractive index”. The term “graded index lens” may be used as a synonym for the term “gradient-index lens”, which may be abbreviated by the term “GRIN lens”. The Gaussian beam being transformed by the GRIN lens from the transmitted primary plane electromagnetic waves may be referred to as “primary Gaussian beam”.

The primary plane electromagnetic waves and the secondary plane electromagnetic waves may be radio waves (such as microwaves, millimeter- waves, or terahertz waves) or optical waves. The primary plane electromagnetic waves and the secondary plane waves may be abbreviated by the terms “primary plane waves” and “secondary plane waves”, respectively. That is, the term “electromagnetic wave(s)” may be abbreviated by the term “wave(s)”.

Terahertz communications (THz communications), using THz waves as electromagnetic waves, allow bridging the gap between millimeter-wave and optical wireless communications. The electronic beam steering capability of high gain antennas at terahertz frequencies, which may be provided by the beam steering capability of the antenna system according to the first aspect, may enable a substantial extension of wireless communication distances. This allows fostering a plethora of applications to satisfy the ever increasing user demand of higher data rates.

Optical wireless communications, using optical waves as electromagnetic waves, like free-space optical (FSO) links, allow higher data rates, improve physical security and avoid electromagnetic interference. Stability and quality of the FSO link may be highly dependent on atmospheric factors such as rain, fog, dust and heat. Thus, the electronic beam steering capability, which may be provided by the beam steering capability of the antenna system according to the first aspect, is an advantage for optical wireless communications.

The primary plane electromagnetic waves may be referred to as primary radiation or primary beam of radiation and the secondary plane electromagnetic waves may be referred to as secondary radiation or secondary beam of radiation. The dual-reflector antenna, the GRIN lens and the communication device may be arranged such that they are not movable, i.e. they are mechanically fixed. For example, the GRIN lens and the communication device are arranged such that they are not movable for performing beam steering of the secondary plane waves. In other words, the communication device may be configured to change the direction of propagation of the secondary plane electromagnetic waves by changing the direction of propagation of the primary plane waves without moving the GRIN lens. For example, the antenna system may be configured to change the direction of propagation of the secondary plane electromagnetic waves by changing the direction of propagation of the primary plane electromagnetic waves without moving the GRIN lens and optionally the communication device. The antenna system may be configured to change the direction of propagation of the secondary plane electromagnetic waves by changing the direction of propagation of the primary plane electromagnetic waves without moving the dual-reflector antenna, the GRIN lens and the communication device.

The Gaussian beam of radiation may be spherical electromagnetic waves having an amplitude changing along the wave front according to a Gaussian distribution. The term “Gaussian beam of radiation” may be abbreviated by the term “Gaussian beam”.

The communication device of the antenna system according to the first aspect may be a transmitter. The terms “antenna feeder” and “feeder” may be used for referring to the communication device being a transmitter.

Optionally, the dual-reflector antenna may be configured to receive secondary plane electromagnetic waves from outside the antenna system and transform the received secondary plane electromagnetic waves to a Gaussian beam of radiation, wherein the GRIN lens may be configured to transform the Gaussian beam of radiation to primary plane electromagnetic waves. The communication device may be configured to receive the primary plane electromagnetic waves from the GRIN lens, and change the direction of propagation of the received secondary plane electromagnetic waves by changing the direction of propagation of the received primary plane electromagnetic waves. In other words, optionally, the communication device of the antenna system according to the first aspect may be a transceiver for transmitting and receiving electromagnetic waves (e.g. the primary plane electromagnetic waves). The description with regard to transmitted primary plane waves and transmitted secondary plane waves is correspondingly valid for received primary plane waves and received secondary plane waves, respectively. In case that the communication device of the antenna system according to the first aspect is a transceiver, the description of the antenna system according to the second aspect of the disclosure may be correspondingly valid for the antenna system according to the first aspect. In an implementation form of the first aspect, the communication device is a multi-channel communication device that is configured to change the direction of propagation of the transmitted primary plane electromagnetic waves by changing phases of two or more channels of the multi-channel communication device.

That is, the multi-channel communication device is configured to perform electronic beam steering of the secondary plane electromagnetic waves by changing the phases of the two or more channels of the multi-channel communication. Changing the phases of the two or more channels changes the direction of propagation of the primary plane electromagnetic waves (i.e. beam steering of the primary plane electromagnetic waves is performed). This changes the direction of propagation of the secondary plane electromagnetic waves and, thus, provides beam steering of the secondary plane electromagnetic waves. The channels of the multi-channel communication device may be configured to be phase-controlled by electronic means.

The multi-channel communication device may comprises multiple channels, i.e. two or more channels. For example, the multi-channel communication device may comprise an array of four channels or sixteen channels. The channels may be referred to as radio channels.

Optionally, the communication device may be a multi-channel communication device that is configured to change the direction of propagation of the received primary plane electromagnetic waves by changing phases of two or more channels of the multi-channel communication device. In other words, optionally, the multi-channel communication device of the antenna system according to the first aspect may be a transceiver for transmitting and receiving electromagnetic waves (e.g. the primary plane electromagnetic waves).

In an implementation form of the first aspect, the communication device comprises a single-channel communication device and a mirror. The single-channel communication device may be configured to transmit via the mirror the primary plane electromagnetic waves to the GRIN lens, wherein the communication device may be configured to change the direction of propagation of the transmitted primary plane electromagnetic waves by rotating the mirror.

In other words, the single-channel communication device may be configured to transmit the primary plane electromagnetic waves to the mirror; the mirror may be configured to reflect the transmitted primary plane electromagnetic waves to the GRIN lens; and the communication device may be configured to change the direction of propagation of the transmitted primary plane electromagnetic waves by rotating the mirror. The mirror may be a planar mirror. Optionally, the single-channel communication device may be configured to receive via the mirror the primary plane electromagnetic waves from the GRIN lens, wherein the communication device may be configured to change the direction of propagation of the received primary plane electromagnetic waves by rotating the mirror. In other words, optionally, the communication device, comprising a singlechannel communication device and a mirror, of the antenna system according to the first aspect may be a transceiver for transmitting and receiving electromagnetic waves (e.g. the primary plane electromagnetic waves).

In an implementation form of the first aspect, the dual-reflector antenna comprises a main reflector and a sub-reflector. The sub-reflector may be configured to reflect the Gaussian beam of radiation from the GRIN lens to the main reflector. The main reflector may be configured to transform the Gaussian beam of radiation to the transmitted secondary plane electromagnetic waves by reflecting the Gaussian beam of radiation.

The antenna system may be configured for a gain greater than 47 dBi. For this, the main reflector of the dual-antenna reflector may have an aperture extension of the secondary plane waves that is larger than 120 wavelengths and magnifying the primary plane electromagnetic waves that may be transmitted by the communication device. For example, the main reflector may be a main reflector dish with a diameter larger than 120 wavelengths of the secondary plane electromagnetic waves. For example, the antenna system may be an E-band microwave backhaul antenna configured to operate at a frequency between 71 and 86 GHz. The main reflector of the dual-reflector antenna may have an extension of 660 mm (e.g. be a reflector dish with a nominal diameter of 660 mm), which is about 170 wavelengths of the secondary plane waves, magnifying the primary plane electromagnetic waves that may be transmitted by the communication device. Alternatively, the antenna system may be a D-band antenna configured to operate at a frequency between 130 and 175 GHz. The main reflector of the dual-reflector antenna may have an extension of 360 mm (e.g. e.g. be a reflector dish with a nominal diameter of 360 mm). The antenna system may be configured to have a gain equal to or greater than 50 dBi of gain. The antenna system may be configured to transmit a beam (in the form of the secondary plane electromagnetic waves) with a beam width equal to or smaller than (i.e. narrower than) 0.4 degrees (0.4°)

In case the communication device of the antenna system according to the first aspect is a transceiver, the main reflector may be configured to transform the received secondary plane electromagnetic waves to the Gaussian beam of radiation by reflecting the received secondary plane electromagnetic waves to the sub-reflector. The sub-reflector may be configured to reflect the Gaussian beam of radiation from the main reflector to the GRIN lens. A second aspect of this disclosure provides an antenna system comprising: a communication device; a dual-reflector antenna; and a gradient-index lens (GRIN lens). The dual-reflector antenna is configured to receive secondary plane electromagnetic waves from outside the antenna system and transform the received secondary plane electromagnetic waves to a Gaussian beam of radiation, wherein the GRIN lens is configured to transform the Gaussian beam of radiation to primary plane electromagnetic waves. The communication device is configured to receive the primary plane electromagnetic waves from the GRIN lens and change the direction of propagation of the received secondary plane electromagnetic waves by changing the direction of propagation of the received primary plane electromagnetic waves.

The above description of the antenna system according to the first aspect may be correspondingly valid for antenna system of the second aspect. For example, the description of the communication device, the GRIN lens and the dual-reflector antenna of the antenna system according to the first aspect may be correspondingly valid for the communication device, the GRIN lens and the dual-reflector antenna, respectively, of the antenna system according to the second aspect. The description with regard to transmitted primary plane waves and transmitted secondary plane waves is correspondingly valid for received primary plane waves and received secondary plane waves, respectively. The antenna system of the second aspect may be the antenna system of the first aspect. In this case, the communication device may be configured to transmit and receive primary plane electromagnetic waves. Thus, in this case, the communication device may be referred to as transceiver.

The antenna system of the second aspect and its implementation forms and optional features achieve the same advantages as the antenna system of the first aspect and its respective implementation forms and respective optional features.

In an implementation form of the second aspect, the communication device is a multi-channel communication device that is configured to change the direction of propagation of the received primary plane electromagnetic waves by changing phases of two or more channels of the multi-channel communication device. The channels of the multi-channel communication device may be configured to be phase-controlled by electronic means.

In an implementation form of the second aspect, the communication device comprises a single-channel communication device and a mirror. The single-channel communication device may be configured to receive via the mirror the primary plane electromagnetic waves from the GRIN lens, wherein the communication device may be configured to change the direction of propagation of the received primary plane electromagnetic waves by rotating the mirror. In other words, the mirror may be configured to reflect the primary plane electromagnetic waves from the GRIN lens to the single-channel communication device, the single-channel communication device may be configured to receive the primary plane electromagnetic waves; and the communication device may be configured to change the direction of propagation of the received primary plane electromagnetic waves by rotating the mirror. The mirror may be a planar mirror.

In an implementation form of the second aspect, the dual-reflector antenna comprises a main reflector and a sub-reflector. The main reflector may be configured to transform the received secondary plane electromagnetic waves to the Gaussian beam of radiation by reflecting the received secondary plane electromagnetic waves to the sub-reflector. The sub-reflector may be configured to reflect the Gaussian beam of radiation from the main reflector to the GRIN lens.

In an implementation form of the first aspect or of the second aspect, the main reflector and the subreflector are axis-symmetric with regard to a common axis.

That is, the dual-reflector antenna may be an on-set dual-reflector antenna. The terms “axis-symmetric dual-reflector antenna” and “on-set dual -reflector antenna” may be used as synonyms.

In an implementation form of the first aspect or of the second aspect, the main reflector is an axis- symmetric parabolic reflector, and the sub-reflector may be an axis-symmetric hyperbolic reflector or axis-symmetric elliptic reflector.

The terms “parabolic”, “elliptic” and “hyperbolic” may mean “quasi-parabolic”, “quasi-elliptic” and “quasi-hyperbolic”, respectively. The terms “elliptic” and “elliptical” may be used as synonyms. In other words, the dual-reflector antenna may be an on-set (i.e. axis-symmetric) Cassegrain dual-reflector antenna, wherein the main reflector is an axis-symmetric parabolic reflector and the sub-reflector is an axis-symmetric hyperbolic reflector. Alternatively, the dual-reflector antenna may be an on-set (i.e. axis- symmetric) Gregorian dual-reflector antenna, wherein the main reflector is an axis-symmetric parabolic reflector and the sub-reflector is an axis-symmetric elliptic reflector.

In an implementation form of the first aspect or of the second aspect, the dual-reflector antenna is an off-set dual-reflector antenna. That is, the dual-reflector antenna may comprise an off-set main reflector and an off-set sub-reflector.

In an implementation form of the first aspect or of the second aspect, the dual-reflector antenna is a Cassegrain dual-reflector antenna or a Gregorian dual-reflector antenna. The terms “Cassegrain antenna” and “Gregorian antenna” may be used for referring to a Cassegrain dual-reflector antenna and Gregorian dual-reflector antenna, respectively.

The Cassegrain dual-reflector antenna may comprise a parabolic main reflector and a hyperbolic subreflector. The Gregorian dual-reflector antenna may comprise a parabolic main reflector and an elliptic sub-reflector.

In an implementation form of the first aspect or of the second aspect, the dual-reflector antenna is an off-set Cassegrain antenna or an off-set Gregorian antenna. In other words, if the dual-reflector antenna is an off-set dual-reflector antenna, the dual-reflector antenna may be a Cassegrain antenna (i.e. off-set Cassegrain antenna) or a Gregorian antenna (i.e. off-set Gregorian antenna).

If the dual-reflector antenna is an off-set Cassegrain dual-reflector antenna, the main reflector may be a parabolic off-set reflector and the sub-reflector may be a hyperbolic off-set reflector. If the dual-reflector antenna is an off-set Gregorian dual-reflector antenna, the main reflector may be a parabolic off-set reflector and the sub-reflector may be an elliptic off-set reflector.

The dual-reflector antenna may be a bi-focal antenna (on-set or off-set) or a multi-focal antenna (on-set or off-set).

In an implementation form of the first aspect or of the second aspect, the main reflector and the subreflector are each a parabolic cylindrical off-set reflector. In other words, if the dual-reflector antenna is an off-set dual-reflector antenna, the main reflector and the sub-reflector may each be a parabolic cylindrical off-set reflector. The terms “parabolic cylindrical (off-set) reflector” and “cylindrical parabolic (off-set) reflector” may be used as synonyms.

The aforementioned off-set dual-reflector antenna comprising two parabolic cylindrical reflectors may be configured to transform the transmission of an axis-symmetric Gaussian beam (e.g. the Gaussian beam generated or transformed by the GRIN lens from the transmitted primary plane waves, which may be referred to as primary Gaussian beam) to an elliptic beam (may be referred to as elliptic secondary beam) in the form of the secondary plane waves that may be transmitted (e.g. radiated) to outside the antenna system. That is, the antenna beam that may be transmitted by the antenna system may be an elliptic beam due to the dual-reflector antenna comprising a main reflector and sub-reflector each being a parabolic cylindrical off-set reflector. This may be advantageous when a wider angle of beam steering in the vertical plane and a narrower angle of beam steering in the horizontal plane is desired, as it may occur in many antenna applications. The antenna beam being an elliptic beam provides an antenna beam which is wider in the vertical plane and narrower in the horizontal plane, as degradations due to beam steering may be equalized.

In an implementation form of the first aspect or of the second aspect, the parabolic curvature of the main reflector and the parabolic curvature of the sub-reflector belong to different planes, which are orthogonal to each other.

In an implementation form of the first aspect or of the second aspect, the GRIN lens has a plurality of elliptical contours defining regions of different material density.

That is, the GRIN lens may have a distributed material density by having a plurality of elliptical contours defining regions of different material density. The term “elliptical” may mean “quasi-elliptical”. The plurality of elliptical contours define regions of different refractive index of the GRIN lens by defining the regions of different material density. That is, the regions of different material density correspond to regions of different refractive index. This allows achieving a varying or changing refractive index within the GRIN lens. For example, the refraction index of the GRIN lens may be described by (e.g. constant) elliptical contours.

In an implementation form of the first aspect or of the second aspect, the GRIN lens comprises two surfaces, and at least one of the two surfaces has a refractive index greater than the refractive index of air.

Alternatively or additionally, at least one of the two surfaces may at least partly have a refractive index of air. The shape of the two surfaces may be ellipsoidal.

In an implementation form of the first aspect or of the second aspect, the GRIN lens is configured to match a phase center of the Gaussian beam of radiation with a focal point of the dual-reflector antenna by having a distributed material density.

In other words, the GRIN lens may be configured such that the phase center of the Gaussian beam of radiation equals to/coincides with or is located close to the focal point of the dual-reflector antenna, in all cases of operation. The GRIN lens may be configured such that the phase center of the Gaussian beam of radiation nearly coincides with the focal point of the dual-reflector antenna, in all cases of operation. For example, when the primary plane electromagnetic waves travel in parallel in a direction of the optic axis of the GRIN lens, then the phase center of the Gaussian beam is matched (that is: nearly coincident) with the focal point of the dual-reflector antenna. Thus, the secondary plane electromagnetic waves travel along the boresight direction with respect to the radiating aperture of the main reflector. However, in case the primary plane electromagnetic waves travel in a direction that deviates from the optic axis of the GRIN lens by an angle greater than zero degrees (0°), then the phase center of the matched Gaussian beam is proportionally displaced from said focal point, such that the direction of propagation of the secondary plane electromagnetic waves is deviated too, according to a well-known proportionality relationship, where the factor of proportionality is defined as beam deviation factor (BDF).

The phase center of the Gaussian beam of radiation may be the focal point of the GRIN lens. The term “focus” and “focal point” may be used as synonyms.

There may be multiple focal points (i.e. multiple phase centers of Gaussian beams) associated with the GRIN lens, i.e. the GRIN lens may be multifocal. Each of the multiple focal points corresponds to a different direction of propagation of the primary plane electromagnetic waves.

The dual-reflector antenna may have a unique focal point. Such a dual-reflector antenna may be for example a dual parabolic cylindrical antenna, a Cassegrain antenna or a Gregorian antenna. The dualreflector antenna may be a bifocal or a multifocal dual-reflector antenna. In this case, the dual-reflector antenna may have two or more focal points. The GRIN lens may be configured to match its multiple focal points with the two or more focal points of the dual-reflector antenna by having the distributed material density, the dual-reflector antenna being a bifocal or multifocal dual-reflector antenna.

In an implementation form of the first aspect or of the second aspect, the communication device is configured to cause, via the GRIN lens, a displacement of the phase center of the Gaussian beam with respect to the focal point of the dual-reflector antenna by changing the direction of propagation of the transmitted primary plane electromagnetic waves or of the received primary plane electromagnetic waves.

The greater the change of the direction of the primary electromagnetic waves is, the greater the displacement of the phase center of the Gaussian beam with respect to the focal point of the dualreflector antenna is. The greater the displacement of the phase center of the Gaussian beam of radiation is, the greater the change of the direction of propagation of the secondary electromagnetic waves is.

In an implementation form of the first aspect or of the second aspect, the communication device is configured to cause the displacement of the phase center of the Gaussian beam such that, the greater the displacement of the phase center of the Gaussian beam with respect to the focal point of the dualreflector antenna is, the greater the change of the direction of propagation of the transmitted secondary plane electromagnetic waves or of the received secondary plane electromagnetic waves is. The greater the displacement of the phase center of the Gaussian beam with respect to the focal point of the dual -reflector antenna is, the greater the angle of beam steering of the secondary plane is.

In order to achieve the antenna system according to the first aspect of the disclosure, some or all of the implementation forms and optional features of the first aspect and second aspect, as described above, may be combined with each other. In order to achieve the antenna system according to the second aspect of the disclosure, some or all of the implementation forms and optional features of the first aspect and second aspect, as described above, may be combined with each other.

All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

BRIEF DESCRIPTION OF DRAWINGS

The above described aspects and implementation forms will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which

Fig. 1 schematically shows two examples of an antenna system according to an embodiment of this disclosure;

Fig. 2 schematically shows three different perspectives of an example of an implementation form of the antenna system of Figure 1;

Fig. 3 schematically shows an example of three different states of the antenna system of

Figure 1 (A);

Fig. 4 schematically shows an example of two different states of an example of an antenna system;

Fig. 5 schematically shows an example of two different states of the antenna system of

Figure 1 (B);

Fig. 6 schematically shows an example of a GRIN lens of an antenna system according to an embodiment of this disclosure; Fig. 7 shows an example of a graph showing the relationship between antenna radiation gain and an angle of beam steering for the two states of the antenna system of Figure 1 (A) shown in Figures 3 (A) and (B);

Fig. 8 and 9 schematically show two different perspectives of an example of an antenna system according to an embodiment of this disclosure;

Fig. 10 and 11 schematically show two different perspectives of an example of an implementation form of the antenna system of Figures 8 and 9;

Fig. 12 and 13 schematically show two different perspectives of an example of an implementation form of the antenna system of Figures 8 and 9;

Fig. 14 and 15 each show an example of a graph showing the relationship between antenna radiation gain and an angle of beam steering for two states of the antenna system of Figures 8 and 9;

Fig. 16 shows a diagram showing the focal point(s) of an example of a Cassegrain axis- symmetric dual-reflector antenna; and

Fig. 17 shows a diagram showing the focal point of an example of a dielectric lens.

In the Figures, corresponding elements are labelled by the same reference sign.

DETAILED DESCRIPTION OF EMBODIMENTS

Figure 1 schematically shows two examples of an antenna system according to an embodiment of this disclosure. The antenna systems of Figure 1 are examples of the antenna system according to the first aspect and/or second aspect of this disclosure. Therefore, the description of the antenna system according to the first aspect and second aspect of this disclosure may be correspondingly valid for the antenna systems of Figure 1.

The antenna system 1 of Figure 1 (A) comprises a communication device 2; a dual-reflector antenna 4; and a gradient-index lens 3 (GRIN lens). The GRIN lens 3 may have a proximal surface 3a and a distal surface 3b with regard to the communication device 2. The communication device 2 may be configured to transmit primary plane electromagnetic waves to the GRIN lens 3, wherein the GRIN lens 3 may be configured to transform the transmitted primary plane electromagnetic waves to a Gaussian beam of radiation. The dual-reflector antenna 4 may be configured to transform the Gaussian beam of radiation to secondary plane electromagnetic waves and transmit the secondary plane electromagnetic waves to outside the antenna system 1. The communication device 2 may be configured to change the direction of propagation of the transmitted secondary plane electromagnetic waves by changing the direction of propagation of the transmitted primary plane electromagnetic waves. As shown in Figure 1 (A), the dual-reflector antenna 4 may comprise a main reflector 4b and a subreflector 4a. The sub-reflector 4a may be configured to reflect the Gaussian beam of radiation from the GRIN lens 3 to the main reflector 4b. The main reflector 4b may be configured to transform the Gaussian beam of radiation to the transmitted secondary plane electromagnetic waves by reflecting the Gaussian beam of radiation.

As indicated in Figure 1 (A), the communication device 2 may be a multi-channel communication device 2a that is configured to change the direction of propagation of the transmitted primary plane electromagnetic waves by changing phases of two or more channels of the multi-channel communication device 2a. When the communication device 2 is a multi-channel communication device 2a (e.g. fed by a multichannel radio) with multiple channels (e.g. radio channels), the phase-shift relevant to each channel (e.g. radio channel) may be periodically aligned and calibrated. An accurate self-alignment of channel phases may already be implemented in or for the multi-channel communication device 2a, in order to cope with phase offsets (due to repeatability of technology processes) and with phase erratic drift (due to temperature and ageing). Therefore, such alignment capability may also be used for electronically controlling a change of the direction of propagation of the primary plane waves and, thus, electronic-controlled beam steering may be performed by the antenna system 1.

Alternatively, as shown in Figure 1 (B), the communication device 2 may comprise a single-channel communication device 2b and a mirror 2c. Optionally, the mirror 2c is a planar mirror. The singlechannel communication device 2b may be configured to transmit via the mirror 2c the primary plane electromagnetic waves to the GRIN lens 3, wherein the communication device 2 may be configured to change the direction of propagation of the transmitted primary plane electromagnetic waves by rotating the mirror 2c. Thus, the antenna system 1 of Figure 1 (B) corresponds to the antenna system 1 of Figure 1 (A), wherein Figure 1 (B) shows an example of a possible implementation form of the communication device 2. The description of the antenna system 1 of Figure 1 (A) is correspondingly valid for the antenna system 1 of Figure 1 (B).

In addition or alternatively, the dual-reflector antenna 4 of the antenna system 1 of Figure 1 (A) or (B) may be configured to receive secondary plane electromagnetic waves from outside the antenna system 1 and transform the received secondary plane electromagnetic waves to a Gaussian beam of radiation, wherein the GRIN lens 3 may be configured to transform the Gaussian beam of radiation to primary plane electromagnetic waves. Further, the communication device 2 may be configured to receive the primary plane electromagnetic waves from the GRIN lens 3, and change the direction of propagation of the received secondary plane electromagnetic waves by changing the direction of propagation of the received primary plane electromagnetic waves. For example, the main reflector 4b may be configured to transform the received secondary plane electromagnetic waves to the Gaussian beam of radiation by reflecting the received secondary plane electromagnetic waves to the sub-reflector 4a. The sub-reflector 4a may be configured to reflect the Gaussian beam of radiation from the main reflector 4b to the GRIN lens 3.

The communication device 2 of the antenna system of Figure 1 (A) may be a multi-channel communication device 2a that is configured to change the direction of propagation of the received primary plane electromagnetic waves by changing phases of two or more channels of the multi-channel communication device. The channels of the multi-channel communication device may be configured to be phase-controlled by electronic means.

The single-channel communication device 2b of the communication device 2 of the antenna system 1 of Figure 1 (B) may be configured to receive via the mirror 2c the primary plane electromagnetic waves from the GRIN lens 3, wherein the communication device 2 may be configured to change the direction of propagation of the received primary plane electromagnetic waves by rotating the mirror 2c.

As shown in Figure 1, the main reflector 4b and the sub-reflector 4a of the antenna systems 1 may be axis-symmetric with regard to a common axis. For example, the main reflector 4b may be an axis- symmetric parabolic reflector and the sub-reflector 4a may be an axis-symmetric hyperbolic reflector, as exemplarily shown in Figure 2.

For further information on the antenna systems 1 of Figure 1 reference is made to the description of the antenna system according to the first aspect and the second aspect.

Figure 2 schematically shows three different perspectives of an example of an implementation form of the antenna system of Figure 1. Figure 2 (B) shows a front view in the direction of the distal surface 3b of the GRIN lens 3 of the antenna system 1, Figure 2 (C) shows a side view of the antenna system 1, and Figure 2 (A) shows a view, when the antenna system is turned between the front view of Figure 2 (B) and the side view of Figure 2 (C). As outlined above, according to the example of Figure 2, the antenna system 1 of Figure 1 (A) or (B) may optionally be implemented such that the main reflector 4b may be an axis-symmetric parabolic reflector and the sub-reflector 4a may be an axis-symmetric elliptic reflector. The antenna system 1 of Figure 2 is an example of an antenna system 1 comprising a Cassegrain antenna as the dual -reflector antenna 4.

As indicated in Figure 2, the main reflector 4b may be arranged between the GRIN lens 3 and the communication device 2. Thus, the main reflector 4b may comprise an opening 5 through which the communication device may communicate primary plane electromagnetic waves (e.g. transmit primary plane waves and/or receive primary plane waves). Further, as may be derived from Figure 2, the main reflector 4b and the sub-reflector 4a may be axis-symmetric, sharing the same axis. For example, the dual-reflector antenna 4 (e.g. the main reflector 4b and the sub-reflector 4a), the GRIN lens 3 and optionally the communication device 2 may be axis-symmetric, sharing the same axis. They may be aligned along the same axis.

The Cassegrain configuration of the dual-reflector antenna 4 of Figure 2 is an axis-symmetric on-set dual-reflector antenna configuration. The antenna systems 1 of Figure 2 may be configured to perform a spot beam with a gain of 50 dBi and ± 1.5 degrees (± 1.5°) of beam steering in any plane, passing through the common axis of symmetry of the main reflector 4b and the sub-reflector 4a. If the dualreflector antenna 4 is axis-symmetric (i.e. the main reflector 4b and sub-reflector 4a are axis-symmetric to the same axis), the Gaussian beam of radiation may be transformed by the dual-reflector antenna 4 to a spot beam in the form of the transmitted secondary plane waves.

Figure 3 schematically shows an example of three different states of the antenna system of Figure 1 (A). In the Figures 3 to 5, rays representing primary plane electromagnetic waves are labelled by the reference sign “Wl” and rays representing secondary plane electromagnetic waves are labelled by the reference sign “W2”. The description of Figures 3 to 5 assumes, only by way of example, that the communication device 2 of the antenna system 1 is configured to transmit primary plane waves for transmitting secondary plane electromagnetic waves to the outside of the antenna system 1, wherein the communication device is configured to change the direction of propagation of the transmitted secondary plane waves by changing the direction of propagation of the transmitted primary plane waves. This description is correspondingly valid for the case that the communication device is, additionally or alternatively, configured to receive primary plane waves for receiving secondary plane waves from outside the antenna system 1.

In Figure 3 (A), the state is exemplary shown in which the communication device 2 does not perform beam steering of the primary plane waves and, thus, does not perform beam steering of the secondary plane waves. That is, the state is shown in which the communication device 2 is configured for transmitting a boresight beam (no beam scanning). Figures 3 (B) and 3 (C) show states in which the communication device 2 performs beam steering, that is in which the communication device 2 changes the direction of the secondary plane waves transmitted to outside the antenna system 1 by changing the direction of propagation of the transmitted primary plane waves. With regard to the state of Figure 3 (A) of no beam steering, in the state of Figure 3 (C) a greater beam steering is performed compared to the state of Figure 3 (B). The beam steering of the secondary plane waves by performing beam steering of the primary plane waves without a gain loss or with a reduced gain loss may be performed by the communication device 2 due to the presence of the GRIN lens 3 in addition to the dual-reflector antenna 4. This becomes clear when referring to the example of Figure 4 showing an antenna system comprising a dielectric lens 6 (i.e. lens with a homogenous dielectric material) instead of the GRIN lens 3. The transmitted primary plane waves hitting or impinging the proximal surface 3a of the GRIN lens 3 may be characterized by linear phase.

Figure 4 schematically shows an example of two different states of an example of an antenna system. The antenna system 1 of Figure 4 corresponds to the antenna system 1 of Figure 3, wherein the GRIN lens 3 is replaced by a lens 6 having a homogenous dielectric material. Thus, the description of Figures

1 to 3 may be correspondingly valid for the antenna system of Figure 4.

As indicated by Figure 4 (A), in case there is no beam steering, the function and performance of the antenna system 1 of Figure 4 may correspond to the function and performance of the antenna system 1 of Figure 3. That is, the state of Figure 4 (A) correspond to the state of Figure 3 (A). However, as shown in Figure 4 (B), when the communication device 2 performs beam steering of the primary plane waves, a gain loss may occur that is greater compared to the state of Figures 3 (B) and (C). Namely, as a result of using the dielectric lens 6 instead of the GRIN lens 3, some waves or rays W3 provided via the lens 6 do not impinge or hit the dual -reflector antenna 4, e.g. the sub-reflector 4a, as shown in Figure 4 (B). This leads to an energy loss of the transmission of the communication device and, thus, to a gain loss of the antenna system 1 of Figure 4. The transmitted primary plane waves hitting or impinging the proximal surface (with regard to the communication device 2) of the dielectric lens 6 (i.e. homogenous lens) may be characterized by constant phase.

Figure 5 schematically shows an example of two different states of the antenna system of Figure 1 (B). Figure 5 (A) shows an example of the antenna system of Figure 1 (B). The state of Figure 5 (B) corresponds to the state of Figure 3 (A) and the state of Figure 5 (C) corresponds to the state of Figure 3 (B). The description of Figure 3 is correspondingly valid for the antenna system 1 of Figure 5.

In Figure 5 (B), the state is exemplary shown in which the communication device 2 does not perform beam steering of the primary plane waves and, thus, does not perform beam steering of the secondary plane waves. That is, the state is shown in which the communication device 2 is configured for transmitting a boresight beam (no beam scanning). For this, the mirror 2c of the communication device

2 may be set, for example, to an angle of 45 degrees (45°) with regard to an optical axis of the GRIN lens. Figure 5 (C) shows a state in which the communication device 2 performs beam steering, that is in which the communication device 2 changes the direction of the secondary plane waves transmitted to outside the antenna system 1 by changing the direction of the transmitted primary plane waves. For this, the communication device 2 of the antenna system 1 of Figure 1 (B) is configured to change the direction of propagation of the transmitted primary plane waves by rotating the mirror 2c. That is, the mirror 2c may be rotated (e.g. slightly rotated) with regard to the state of the mirror 2c shown in Figure 5 (B). The beam steering of the secondary plane waves by performing beam steering of the primary plane waves without a gain loss or with a reduced gain loss may be performed by the communication device 2 due to the presence of the GRIN lens 3 in addition to the dual-reflector antenna 4.

Figure 6 schematically shows an example of a GRIN lens of an antenna system according to an embodiment of this disclosure.

Figure 6 (A) shows an example of an implementation form of the GRIN lens, e.g. of the GRIN lens 3 of the antenna systems of Figure 1 and/or the antenna system of Figures 8 and 9. The proximal surface and distal surface of the GRIN lens 3 with regard to the communication device 2 of the antenna system 1 when the GRIN lens 3 is arranged in the antenna system 1 are labelled by the reference signs “3a” and “3b” respectively. That is, the GRIN lens 3 may comprise two surfaces 3a and 3b. At least one of the two surfaces 3a and 3b may have a refractive index greater than the refractive index of air. Alternatively or additionally, at least one of the two surfaces 3a and 3b may at least partly have a refractive index of air. The shape of the two surfaces 3a and 3b may be ellipsoidal. As shown in Figure 6 (A), the GRIN lens 3 may optionally have multiple holes 3c arranged at its surface. This may set a refractive index at the surface of the GRIN lens 3.

As mentioned already above, the GRIN lens 3 is a lens having a varying or changing refractive index within the lens itself. That is, the GRIN lens 3 may be characterized by a non-homogeneous refractive index. The GRIN lens 3 has a distributed material density for achieving the varying refractive index within the lens itself.

For example, the GRIN lens 3 has a plurality of elliptical contours defining regions of different material density. That is, the GRIN lens 3 may have a distributed material density by having a plurality of elliptical contours defining regions of different material density. The term “elliptical” may mean “quasielliptical. The plurality of elliptical contours define regions of different refractive index of the GRIN lens by defining the regions of different material density. That is, the regions of different material density correspond to regions of different refractive index. This allows achieving a varying or changing refractive index within the GRIN lens. This is exemplarily shown in Figure 6 (B). Figure 6 (B) exemplarily shows different contours 3d (e.g. elliptical contours) defining different regions of refractive index. Examples of different values of refractive index are indicated on the right side of Figure 6 (B), which are valid for the whole respective contour 3d, i.e. also for the corresponding part of the respective contour 3d on the left side of Figure 6 (B). For example, in the middle of the GRIN lens 3 the refractive index of the GRIN lens 3 may be greater than at the side of the of the GRIN lens 3. For example, the refractive index may decrease from 1.4 to 1.2, as shown in Figure 6 (B). The GRIN lens 3, when arranged at fix position in the antenna system between the communication device 2 and the dual-reflector antenna 4 (e.g. characterized by quasi-elliptical contours of its index of refraction) enables an optimum focal point displacement for each direction of propagation of the primary plane waves. For this the primary plane waves impinging the proximal surface 3a of the GRIN lens 3 may be characterized by proper phase-fronts, which are linear or quasi-linear.

The capability of transforming a phase-front (e.g. quasi-linear phase) of the transmitted primary plane wave into a displacement of focal point of the Gaussian beam (primary Gaussian beam), corresponding to a change of direction of propagation of the transmitted primary plane waves, may be achieved by quasi-elliptical contours of different refractive index and/or correspondingly shaped surfaces, both proximal and distal surfaces, of the GRIN lens 3.

Figure 7 shows an example of a graph showing the relationship between antenna radiation pattern gain and an angle of beam steering for the two states of the antenna system of Figure 1 (A) shown in Figures 3 (A) and (B).

For the example of Figure 7, it is assumed that the dual-reflector antenna 4 of the antenna system of Figure 1 (A) is a 360 mm Cassegrain antenna that is optimized at a frequency of 150 GHz of electromagnetic waves to be transmitted and/or received. Further, the description of Figure 7 assumes, by way of example, that the communication device 2 of the antenna system 1 is configured to transmit primary plane waves for transmitting secondary plane electromagnetic waves to the outside of the antenna system 1, wherein the communication device 2 is configured to change the direction of propagation of the transmitted secondary plane waves by changing the direction of propagation of the transmitted primary plane waves. This description is correspondingly valid for the case that the communication device 2 is, additionally or alternatively, configured to receive primary plane waves for receiving secondary plane waves from outside the antenna system 1.

In Figure 7, the curve C 1 shows the antenna pattern of the antenna system in case of the state of Figure 3 (A), i.e. in case no beam steering is performed (i.e. the antenna radiation is at boresight). In this case the angle of the transmitted primary plane waves is 0 degrees (0°). That is, there is no change in the direction of propagation of the transmitted primary plane waves. The curve C2 shows the antenna pattern of the antenna system in case of the state of Figure 3 (B), i.e. in case beam steering is performed. For example, as shown in Figure 7, the steered beam may have an angle of 1.6 degrees (1.6°) with regard to the beam in case of no beam steering. With other words, it may be assumed that the communication device changes the direction of propagation of the transmitted primary plane waves such that the changed direction of propagation deviates by an angle of 1.6° from the direction of propagation of the transmitted primary plane waves in case of no beam steering. As shown in Figure 7, for both cases, i.e. no beam steering and beam steering by 1.6° of the primary plane waves, the peak gain of the antenna pattern may be greater than 52 dBi. That is, the reduction of the antenna radiation gain of the antenna system due to beam steering may be negligibly small. In addition, the curve C3 of Figure 7 shows the mask pattern for an ETSI class 4 antenna system. Thus, the antenna system 1 of Figure 1 (A) may fulfill the ETSI class 4 requirements for both cases, no beam steering and beam steering e.g. of 1.6°.

Figures 8 and 9 schematically show two different perspectives of an example of an antenna system according to an embodiment of this disclosure.

The antenna system of Figures 8 and 9 is an example of the antenna system according to the first aspect and/or second aspect of this disclosure. Therefore, the description of the antenna system according to the first aspect and the second aspect of this disclosure may be correspondingly valid for the antenna system of Figures 8 and 9. The antenna system of Figures 8 and 9 corresponds to the antenna system of Figure 1 (A), wherein the dual-reflector antenna of the antenna system of Figures 8 and 9 is differently implemented compared to the axis-symmetric dual-reflector antenna of the antenna system of Figure 1 (A). Thus, the description of Figures 1 to 6 is correspondingly valid for the antenna system of Figures 8 and 9 and in the following mainly the dual -reflector antenna of the antenna system of Figures 8 and 9 is described.

The main reflector 4b and the sub-reflector 4a of the dual-reflector antenna 4 may each be a parabolic cylindrical off-set reflector, as indicated in Figures 8 and 9. Optionally, the parabolic curvature of the main reflector 4b and the parabolic curvature of the sub-reflector 4a belong to different planes, which are orthogonal to each other (not shown in Figures 8 and 9). Thus, the dual-reflector antenna 4 of the antenna system 1 may have a dual-offset configuration (i.e. it may be a dual-offset antenna), as shown in Figures 8 and 9. This is a different type of dual-reflector antenna 4 compared to the dual-reflector antenna 4 of the antenna system of Figure 2, which is a Cassegrain axis-symmetric antenna. The dualoffset configuration (as exemplarily shown in Figures 8 and 9) may enable a wider angle of beam steering or a higher efficiency and antenna gain compared to the Cassegrain axis-symmetric dualreflector antenna (as exemplarily shown in Figure 2).

According to the example of Figures 8 and 9, the main reflector 4b and the sub-reflector 4a are not axis- symmetric. This enables bi-dimensional beam steering with an angular sector of ± 10° degrees (± 10°) in elevation (vertical plane) and ± 2 degrees (± 2°) in azimuth (horizontal plane). This angular sector may be extended compared to the case of using a dual-reflector antenna 4 having a main reflector 4b and sub-reflector 4a that are axis-symmetric with regard to a common axis (e.g. using a Cassegrain antenna). If the dual-reflector antenna 4 is not axis-symmetric, as is shown in Figures 8 and 9, showing a dual-offset configuration, the Gaussian beam of radiation (primary Gaussian beam), which is still axis- symmetric, may be transformed by a parabolic cylindrical configuration of the main reflector 4b and sub-reflector 4a of the dual-reflector antenna 4 to an elliptical beam in the form of the transmitted secondary plane waves. An off-set dual-reflector antenna 4 (i.e. dual-reflector antenna having a dualoffset configuration) comprising a parabolic cylindrical main reflector 4b and a parabolic cylindrical sub-reflector 4a may be referred to as dual-reflector antenna having a dual parabolic cylindrical reflector configuration.

Figures 10 and 11 schematically show two different perspectives of an example of an implementation form of the antenna system of Figures 8 and 9. The description of Figures 8 and 9 is correspondingly valid for the antenna system of Figures 10 and 11. As shown in Figures 10 and 11, the dual-reflector antenna 4 may be an elliptical beam antenna, wherein the angular sector of steering of the antenna beam is rectangular. This example of dual parabolic cylindrical reflector configuration of the dual-reflector antenna 4 allows a beam steering by the antenna system 1 of e.g. ± 10° in elevation (vertical plane) and ± 2° in azimuth (horizontal plane). For this, the GRIN lens 3 of the antenna system 1 may be properly designed to manage the bi-dimensional displacement of the focus according to a beam steering requirement (e.g. ETSI class 4 requirements). The elliptical beam antenna 4 may be designed such that a focus displacement describes a locus characterized by rectangular-shaped edges. The shapes of the GRIN lens surfaces (both distal and proximal surfaces) may be ellipsoidal. Further, constant contours of different refractive index of the GRIN lens 3 may be elliptical contours or ellipsoidal.

Figures 12 and 13 schematically show two different perspectives of an example of an implementation form of the antenna system of Figures 8 and 9. The description of Figures 8 and 9 is correspondingly valid for the antenna system of Figures 12 and 13. As shown in Figures 12 and 13, the main reflector 4b of the dual-reflector antenna 4 may be parabolic cylindrical offset main reflector and the sub-reflector 4a of the dual-reflector antenna 4 may be a parabolic cylindrical offset sub-reflector. In the Figures 12 and 13, the communication device 2 is exemplarily shown as a multi-channel communication device comprising an array of sixteen channels. This is only by way of example. Thus, the communication device 2 may be a different communication device (e.g. a communication device comprising a singlechannel communication device and a mirror) or may comprise a different number of channels.

Figures 14 and 15 each show an example of a graph showing the relationship between antenna radiation pattern gain and an angle of beam steering for two states of the antenna system of Figures 8 and 9.

For the examples of Figures 14 and 15, it is assumed that the dual-reflector antenna 4 of the antenna system of Figures 8 and 9 is a dual-cylindrical antenna (e.g. off-set antenna configuration) that is optimized at a frequency of 150 GHz of electromagnetic waves to be transmitted and/or received. Further, the description of Figures 14 and 15 assumes, by way of example, that the communication device 2 of the antenna system 1 is configured to transmit primary plane waves for transmitting secondary plane electromagnetic waves to the outside of the antenna system 1, wherein the communication device is configured to change the direction of propagation of the transmitted secondary plane waves by changing the direction of propagation of the transmitted primary plane waves. This description is correspondingly valid for the case that the communication device 2 is, additionally or alternatively, configured to receive primary plane waves for receiving secondary plane waves from outside the antenna system 1.

Figure 14 shows the antenna pattern for an angular sector in elevation (vertical plane) and Figure 15 shows the antenna pattern for an angular sector in azimuth (horizontal plane).

In Figures 14 and 15, the curve Cl shows the antenna pattern of the antenna system in case no beam steering is performed (i.e. the antenna radiation is at boresight). In this case the angle of the transmitted primary plane waves in the vertical plane (cf. Figure 14) as well as in the horizontal plane (cf. Figure 15) is 0 degrees (0°). That is, there is no change in the direction of propagation of the transmitted primary plane waves. In Figures 14 and 15, the curve C2 shows the antenna pattern of the antenna system in case beam steering is performed. For example, as shown in Figure 14, in the vertical plane the steered beam may have an angle of 10 degrees (10°) with regard to the beam in case of no beam steering. With other words, it may be assumed that the communication device changes the direction of propagation of the transmitted primary plane waves in the vertical plane such that the changed direction of propagation deviates by an angle of 10° from the direction of propagation of the transmitted primary plane waves in case of no beam steering. For example, as shown in Figure 15, in the horizontal plane the steered beam may have an angle of 2.3 degrees (2.3°) with regard to the beam in case of no beam steering. With other words, it may be assumed that the communication device changes the direction of propagation of the transmitted primary plane waves in the horizontal plane such that the changed direction of propagation deviates by an angle of 2.3° from the direction of propagation of the transmitted primary plane waves in case of no beam steering.

As shown in Figure 14, for both cases, i.e. no beam steering in the vertical plane and beam steering by 10° of the secondary plane waves in the vertical plane, the peak gain of the antenna pattern may be greater than 48.5 dBi. That is, the reduction of the antenna radiation gain of the antenna system due to beam steering in the vertical plane may be negligibly small. As shown in Figure 15, for both cases, i.e. no beam steering in the horizontal plane and beam steering by 2.3° of the secondary plane waves in the horizontal plane, the peak gain of the antenna pattern may be greater than 50 dBi. That is, the reduction of the antenna radiation gain of the antenna system due to beam steering in the horizontal plane may be negligibly small. In Figures 14 and 15, the curve C3 shows the mask pattern for an ETSI class 4 antenna system. Thus, the antenna system 1 of Figures 8 and 9 may fulfill the ETSI class 4 requirements for both cases, no beam steering and beam steering in the vertical plane (e.g. of 10°) as well as in the horizontal plane (e.g. of 2.3°).

In the following an example of a design method for implementing an antenna system 1 according to Figures 1 (A) and (B) is described. This design method allows a step-by-step configuration of the overall antenna system. The design method may belong or be part of a computer-aided procedure.

In a first step (Step 1) of the design method, the dual-reflector antenna 4, comprising the sub-reflector 4a and the main reflector 4b, may be designed such that a desired low steering loss and low aberration effects are duly performed in the desired angle interval of beam steering. For example, the steering loss may be desired to be as low as 1.5 dB and aberration effects may be desired to not impair the ETSI Class 4 norms about the antenna radiation pattern envelope, while the angle interval desired for beam steering may be between -1.5° and +1.5°, i.e. [-1.5°, +1.5°].

In a second step (Step 2) of the design method, the communication device 2 may be designed in association with an auxiliary lens having a homogenous dielectric material (e.g. a planar-hyperbolic convergent lens made of homogeneous dielectric material). For this, the communication device 2 may be assumed to be a transmitter, for example an array-feeder, for providing or transmitting primary plane electromagnetic waves.

In a third step (Step 3) of the design method, the auxiliary lens may be replaced with a properly designed GRIN lens (i.e. the Grin lens 3). The GRIN lens may be characterized by elliptical (quasi-elliptical) contours of its index of refraction and, optionally, with properly shaped surfaces of the GRIN lens.

According to the first step (Step 1) of the design method, a computer-aided procedure may be set up dealing with an optimization of the dual-reflector antenna 4 of the antenna system 1. It may be assumed that the main reflector 4b of the dual-antenna reflector 4 is a parabolic (e.g. quasi-parabolic) main reflector dish and the sub-reflector 4a is a hyperbolic (e.g. quasi-hyperbolic) sub-reflector. Such reflectors may be designed as axis-symmetric surfaces of revolutions, in order to keep the complexity and cost of manufacturing as low as possible.

Further, it is assumed that the antenna system is optimized at a frequency of 150 GHz of electromagnetic waves to be transmitted and/or received so that the antenna system may comply with ETSI Class 4 norms. In a first sub-step (Step 1.1) of the first step (Step 1), the performance of a preliminary dualreflector antenna mechanical configuration may be evaluated. In a second sub-step (Step 1.2) of the first step (Step 1), an illumination taper at the edge of the sub-reflector may be gradually reduced to comply with ETSI Class 4. In a third sub-step (Step 1.3) of the first step (Step 1), the final antenna assembly of the dual-reflector antenna may be assessed with regard to a mechanical configuration and radiation performances of the dual-reflector antenna. At a fourth sub-step (Step 1.4) of the first step (Step 1), a constant product of antenna gain and maximum angle of beam steering (antenna gain x maximum angle of beam steering) of the antenna system may be assumed to be a constant product of 150000 = 50 dBi antenna gain x 1.5° maximum angle of beam steering. In case a larger beam steering is desired, a multifocal dual -reflector antenna with 45 dBi Gain x 5° maximum angle of beam steering may be assumed or implemented.

After the first step (Step 1) of the design method, the mechanical configuration of the dual -reflector antenna 4 of the antenna system may be completed. In other words, the surfaces of the main reflector 4b and the sub-reflector 4a of the dual-reflector antenna 4 may designed together with the position of the focal point, including also its optimum displacements performing the desired steering of the antenna beam (e.g. the secondary plane electromagnetic waves) and the re-pointing angle of the Gaussian beam towards the sub-reflector 4a.

The bundle of rays (e.g. the Gaussian beam) hitting the sub-reflector 4a start from a focal point, whose position is optimized to keep the gain loss, due to beam steering, as low as possible (e.g. < 1.5dB) and to minimize aberrations that may impair the compliance of a radiation pattern envelope with ETSI norms (e.g. Class 4). However, when the antenna radiation is at boresight (i.e. no beam steering is done), the bundle of rays is to start from a different focal point, positioned on the axis of symmetry of the dualreflector antenna.

With regard to transmitting electromagnetic waves by an antenna system, such as the antenna system of Figure 1, the focal point displacement, performing a best antenna beam steering, may be obtained by means of a mechanical rotation of the feeder assembly, e.g. made of a feeder-array (i.e. transmitter for electromagnetic waves) and an associated lens. Therefore, for each desired beam direction, there may exist an optimum focal point displacement.

After the dual-reflector antenna has been configured during the first step (Step 1) of the design method, the further design steps (Step 2 and Step 3) may follow. This following second step (Step 2) and third step (Step 3) of the design method are described in the following with regard to Figures 16 and 17. Figure 16 shows a diagram showing the focal point(s) of an example of a Cassegrain axis-symmetric dual-reflector antenna. Figure 17 shows a diagram showing the focal point of an example of a dielectric lens. Without lack of generality about the second step (Step 2) and third step (Step 3) of the design method, and merely for simplifying the description, these steps are exemplarily described considering a onedimensional case of a Cassegrain dual-reflector antenna, such as an on-set configuration of a parabolic main reflector 4b with an hyperbolic sub-reflector 4a (elliptical sub-reflector), both characterized by axial symmetry as shown in Figure 16. Equivalent considerations are applicable to many other dualreflector antenna configurations comprising either off-set Cassegrain or Gregorian, either Bi-focal or Multifocal (on-set and off-set) as well. That is, the following description is not limited to the case of the dual-reflector antenna being a Cassegrain dual-reflector antenna and, thus, may be correspondingly valid for other types of dual-reflector antennas.

In Figure 16, let 2a be the length of the parabolic reflector aperture and x an abscissa on it. Further, let u = 2TI/X sin(0) be an abscissa on the wavenumber axis, where 0 is the angle from broadside direction and X is the wavelength of operation. The radiation pattern G(u) and the aperture illumination function f(x) are related by the following Fourier Transformation:

Moreover, the equivalent focal of the Cassegrain dual-reflector antenna is as follows:

In the above equation, the term “F” is the focal of the parabolic reflector and the term “e” is the ellipticity of the sub-reflector. A feeder angle 0a of this Cassegrain optics may be computed from the following relationship: — 1 sin(0a) = a/F _e = a/F

Similarly, the one-dimensional case of an auxiliary convergent lens made of homogeneous dielectric material (e.g. a planar-hyperbolic convergent lens made of homogeneous dielectric material) may be considered, as shown in Figure 17. Such an auxiliary lens may be referred to as dielectric lens.

In Figure 17, let 2r be the diameter of the lens aperture and x’ an abscissa on it. Further, let u’ = 2TI/X sin(0’) be an abscissa on the wavenumber axis, where 0’ is the angle from broadside direction and X is the wavelength of operation. The radiation pattern G(u’) and the aperture illumination function f(x’) are related by the following Fourier Transformation:

The feeder angle 0r of this convergent lens may be related to the optical focal length as follows: sin(0r) = T/FL

Next, the aforementioned auxiliary lens may be combined “back-to-back” with the aforementioned Cassegrain dual-reflector antenna, such that the relevant focal points are matched together in the same point and the auxiliary lens focuses its illumination f(x’) while the Cassegrain dual-reflector antenna focuses its illumination function f(x). This may provide a mixed optical system formed by assembling or putting together dual-reflector optics (e.g. the dual-reflector antenna) and lens optics (e.g. the auxiliary lens). The latter may be properly matched, such that a magnifier may be obtained transforming the illumination f(x’) into illumination f(x), with a magnification factor p expressed by the following equation:

0 — 1 p = sin(0a) / sin(0r) = FL/F aJr

Assuming that this magnifier, as first approximation, performs the following linear transformation: f(x) = p f(x’), finally, the antenna radiation pattern becomes:

This antenna pattern is the Fourier Transform of the lens aperture illumination function f(x’) rescaled by the magnification factor p.

The lens aperture illumination function f(x’) is a complex-values function and may be expressed by means of two real-values functions (real part and imaginary part or by amplitude and phase). These two real-values functions may represent the primary plane electromagnetic waves, which may be radiated by the communication device 2, assuming that the communication device is configured for transmitting electromagnetic waves. The present disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.