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Title:
AN ANTENNA WITH REDUCED BACK-LOBE RADIATION
Document Type and Number:
WIPO Patent Application WO/2020/260045
Kind Code:
A1
Abstract:
A parabolic dish antenna (100) configured to radiate electromagnetic energy in a main axial direction (D), the dish antenna having a rim portion (110) extending circumferentially around a periphery of the dish antenna (100), wherein the rim portion (110) comprises a plurality of profile sections (120, 130), the profile sections being of at least a first and a second type, wherein a profile section of the first type has a cross- sectional shape different from a profile section of the second type, to cause a phase difference of an electromagnetic field propagating past the rim via the profile sections (120, 130), thereby suppressing a back-lobe radiation (B) of the parabolic dish antenna (100).

Inventors:
SCHÄFER THOMAS (SE)
STERN BJÖRN (SE)
HÅKANSSON DAVID (SE)
ÖSTLING TOMAS (SE)
Application Number:
PCT/EP2020/066421
Publication Date:
December 30, 2020
Filing Date:
June 15, 2020
Export Citation:
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Assignee:
LEAX ARKIVATOR TELECOM AB (SE)
International Classes:
H01Q15/16; H01Q17/00; H01Q19/02; H01Q1/42
Foreign References:
US9634373B22017-04-25
US3599219A1971-08-10
GB1205014A1970-09-09
US3140491A1964-07-07
US20120306712A12012-12-06
US3599219A1971-08-10
Attorney, Agent or Firm:
QAMCOM IPR TECHNOLOGY AB (SE)
Download PDF:
Claims:
CLAIMS

1. A parabolic dish antenna (100) configured to radiate electromagnetic energy in a main axial direction (D), the dish antenna having a rim portion (110) extending circumferentially around a periphery of the dish antenna (100), wherein the rim portion (1 10) comprises a plurality of profile sections (120, 130, 500), the profile sections being of at least a first and a second type, wherein a profile section of the first type has a cross-sectional shape different from a profile section of the second type, to cause a phase difference of an electromagnetic field propagating past the rim via the profile sections (120, 130, 500), thereby suppressing a back-lobe radiation (B) of the parabolic dish antenna (100).

2. The parabolic dish antenna (100) according to claim 1 , wherein the first and the second type of profile sections (120, 130, 500) are configured to extend different distances in the axial direction (D).

3. The parabolic dish antenna (100) according to any previous claim, wherein the first and the second type of profile sections (120, 130, 500) are configured to extend different lengths along the rim portion (1 10).

4. The parabolic dish antenna (100) according to any previous claim, wherein the first and the second type of profile sections are arranged alternating around the rim portion (1 10).

5. The parabolic dish antenna (100) according to any previous claim, wherein the first and the second type of profile sections (120, 130, 500) are made at least partly in materials having different dielectric constant values.

6. The parabolic dish antenna (100) according to any previous claim, wherein the profile sections arranged circumferentially along the rim portion (1 10) are selected in dependence of a frequency band of operation, or a center frequency of operation, associated with the antenna.

7. The parabolic dish antenna (100) according to any previous claim, wherein the profile sections (120, 130, 500) are at least partly made in an electrically non- conductive material and/or in an electromagnetically absorbing material.

8. The parabolic dish antenna (100) according to any previous claim, wherein the profile sections (120, 130, 500) are at least partly made in an electrically conductive material and/or in an electromagnetically shielding material.

9. The parabolic dish antenna (100) according to any previous claim, wherein adjacent profile sections (120, 130, 500) along the rim portion (1 10) are arranged to be releasably fastened to each other by fastening elements.

10. The parabolic dish antenna (100) according to any previous claim, wherein the profile sections (120, 130, 500) comprise a groove configured to hold a radome (340).

11. The parabolic dish antenna (100) according to any previous claim, wherein one or more of the profile sections (120, 130, 500) are at least partly hollow (360).

12. The parabolic dish antenna (100) according to any previous claim, wherein the phase difference is larger than 90 degrees, and preferably around 180 degrees.

13. A parabolic dish antenna (100) configured to radiate electromagnetic energy in a main axial direction (D), the dish antenna having a rim portion (1 10) extending circumferentially around a periphery of the dish antenna (100), wherein the rim portion (1 10) comprises a plurality of profile sections (120, 130, 500), the profile sections being of at least a first and a second type, wherein a collection of profile sections of at least the first and the second type arranged adjacent to each other around the rim portion (1 10) is modularly selectable to cause a phase difference of an electromagnetic field propagating past the rim via the profile sections (120, 130, 500), thereby suppressing a back-lobe radiation (B) of the parabolic dish antenna (100).

14. A parabolic dish antenna (100) configured to radiate electromagnetic energy in a main axial direction (D), the dish antenna having a rim portion (1 10) extending circumferentially around a periphery of the dish antenna (100), wherein the rim portion (1 10) comprises a plurality of profile sections (120, 130, 500), the profile sections being of at least a first and a second type, wherein a profile section of the first type comprises a material having a dielectric constant value different from a dielectric constant value of a profile section of the second type, wherein a collection of profile sections of at least the first and the second type arranged circumferentially adjacent to each other around the rim portion (1 10) is selectable to cause a phase difference of an electromagnetic field propagating past the rim via the profile sections (120, 130, 500), thereby suppressing a back-lobe radiation (B) of the parabolic dish antenna (100).

Description:
TITLE

AN ANTENNA WITH REDUCED BACK-LOBE RADIATION

TECHNICAL FIELD

The present disclosure relates to directive antennas, and in particular to parabolic dish antennas.

BACKGROUND

Parabolic dish antennas are configured to radiate electromagnetic energy in a forward axial direction. The direction of maximum radiation is often referred to as the main lobe direction of the antenna. The radiation pattern of most antennas is a pattern of lobes at various angles where the radiated signal power reaches a local maximum, separated by nulls at angles where the radiated signal power falls to some small value. A side lobe in the opposite direction from the main lobe, i.e., the reverse axial direction, is called the back lobe of the antenna.

It is often desired to reduce radiation in directions other than the main lobe direction, since energy radiated in these directions may cause interference to other systems and decrease antenna efficiency. Also, energy received from directions other than the main lobe direction may comprise unwanted signals which can interfere with the operation of the antenna system. The relationship between antenna gain in the main axial direction and gain in the reverse axial direction is referred to as the front-to-back ratio. It is desired to maximize this front-to-back ratio.

US 3,599,219 shows a dual-polarized antenna which employs a polygonal rim surrounding a round reflector, whereby an increase in front-to back ratio is obtained.

However, there is a continuing need for further improvements of parabolic dish antennas.

SUMMARY

It is an object of the present disclosure to provide an improved parabolic reflector antenna arrangement having a reduced front-to-back ratio. This object is obtained by a parabolic dish antenna configured to radiate electromagnetic energy in a main axial direction. The dish antenna has a rim portion extending circumferentially around a periphery of the dish antenna. The rim portion comprises a plurality of profile sections. The profile sections are of at least a first and a second type, wherein a profile section of the first type has a cross-sectional shape different from a profile section of the second type, to cause a phase difference of an electromagnetic field propagating past the rim via the profile sections, thereby suppressing a back-lobe radiation of the parabolic dish antenna.

The object is also obtained by a parabolic dish antenna configured to radiate electromagnetic energy in a main axial direction. The dish antenna has a rim portion extending circumferentially around a periphery of the dish antenna. The rim portion comprises a plurality of profile sections. The profile sections are of at least a first and a second type, wherein collection of profile sections of at least the first and the second type arranged adjacent to each other around the rim portion is modularly selectable to cause a phase difference of an electromagnetic field propagating past the rim via the profile sections, thereby suppressing a back-lobe radiation of the parabolic dish antenna.

The object is furthermore obtained by a parabolic dish antenna configured to radiate electromagnetic energy in a main axial direction. The dish antenna has a rim portion extending circumferentially around a periphery of the dish antenna. The rim portion comprises a plurality of profile sections. The profile sections are of at least a first and a second type, wherein a profile section of the first type comprises a material having a dielectric constant value different from a dielectric constant value of a profile section of the second type. A collection of profile sections of at least the first and the second type arranged circumferentially adjacent to each other around the rim portion is selectable to cause a phase difference of an electromagnetic field propagating past the rim via the profile sections, thereby suppressing a back-lobe radiation of the parabolic dish antenna.

Thus, there is disclosed herein a plurality of different ways in which a rim portion of a disc antenna can be fitted with modular system of profile sections having different properties in terms of cross-sectional shape and/or dielectric properties. An electromagnetic field propagating past the rim will have different phases depending on if the field propagates past a profile section of the first type or the second type. There may also be further types arranged along the rim portion, i.e., a third type of profile section and/or a fourth type. When the electromagnetic field components are summed at the back of the disc antenna, the components add destructively due to the phase difference, resulting in a reduced back-lobe radiation from the antenna.

Preferably, the phase relationship between electromagnetic field components associated with the first type of profile sections along the rim portion and associated with the second type of profile section is about 180 degrees and the amplitude, power, or energy of the different components is approximately equal.

According to aspects, the first and the second type of profile sections are configured to extend different distances in the axial direction. By extending different distances in the axial direction the path lengths for propagating past the first type profile sections compared to propagating past the second type profile sections become different, thereby causing a suppressed back-lobe radiation from the antenna. The cross- sectional shapes can be configured such that the phase difference of the different electromagnetic components have phase differences greater than 90 degrees to cause destructive interference. Preferably the phase difference is about 180 degrees to cause maximum destructive interference, i.e., cancellation in case of similar amplitudes.

According to aspects, the first and the second type of profile sections are configured to extend different lengths along the rim portion. By extending different lengths along the rim portion the relative percentages of the different electromagnetic field components at the back of the antenna can be adjusted. This way the amplitude relationship between different phase components of the electromagnetic field can be made more even, resulting in improved suppression of the back-lobe radiation.

According to aspects, the first and the second type of profile sections are arranged alternating around the rim portion. This means that a profile section of the first type is configured adjacent to profile sections of the second type. This configuration provides for an even phase distribution and therefore improved back-lobe radiation suppression.

According to aspects, the profile sections are selected in dependence of a frequency band of operation associated with the antenna. By configuring the profile sections in dependence of frequency, the phase relationship between the electromagnetic field components at the back of the antenna can be further fine-tuned in order to enable further reductions in back-lobe radiation from the antenna. According to aspects, adjacent profile sections are arranged to be releasably fastened to each other by fastening elements. Thus, a modular system is provided which can be adapted to different types of antennas and to different types of frequency bands.

According to other aspects, adjacent profile sections are arranged to be fastened to each other by an adhesive such as a glue.

According to aspects, the profile sections comprise a groove configured to hold a radome, i.e., a protective enclosure used to protect the antenna from external factors such as rain and debris. This way the rim portion also functions as a radome holding means, which is an advantage.

According to aspects, one or more of the profile sections are at least partly hollow. This reduces weight of the antenna, which is an advantage.

To summarize, it has been realized that the rim portion of a disc antenna can be fitted with different profile sections arranged circumferentially to cause a reduction in back- lobe radiation in an efficient manner. The differentiating factor of the different profile shapes may, e.g., be an extension in the axial direction of the different sections. The differentiating factor may also be different types of material having different dielectric properties, and/or different extensions in the radial direction.

A rim portion having alternating profile section shapes around the periphery can be manufactured in an efficient manner, which is an advantage. The rim portion geometry can also be adapted to different types of antennas and to different operating frequency bands in a modular manner, which is an advantage. Also, the rim portion provides structural integrity to the overall antenna design and can be designed for a relatively low weight-addition to the overall antenna system.

According to aspects, the profile sections are at least partly made in an electrically non- conductive material or in an electromagnetically absorbing material. This is an advantage since electrically conductive materials are often heavier and may also be more costly. Electrically non-conductive materials such as plastics, nylon, or polytetrafluoroethylene (PTFE), can often be accurately molded into shape in a cost- efficient manner.

Optional material for use in the proposed profile sections comprise Polycarbonate (PC), Acrylonitrile Styrene Acrylate (ASA), Acrylonitrile Butadiene Styrene (ABS). Regarding the material of the alternating profile sections, one material that may be used is a stainless-steel compound plastic referred to as Beki-Shield® (trademark name), produced by Bekaert Fibre Technologies. This materiel has RF shielding properties, i.e. it is non-transmitting. It cannot be readily classified as being homogenous conductive nor being an absorbing material. Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will now be described more in detail with reference to the appended drawings, where:

Figure 1 schematically shows an antenna arrangement;

Figure 2 illustrates an example antenna radiation pattern;

Figures 3-5 show example rim profile cross-sectional shapes; and

Figure 6 illustrates an example communication system.

DETAILED DESCRIPTION

The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain aspects of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments and aspects set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout the description.

Figures 1 a and 1 b show different views of a parabolic dish antenna 100 configured to radiate electromagnetic energy in a main axial direction D. The antenna 100 comprises a feed arrangement (not shown in Figures 1 a and 1 b) and a parabolic reflector 101. Parabolic dish antennas are known in general and will therefore not be discussed in more detail herein.

The parabolic dish antenna 100 is associated with a radiation pattern diagram. An example 200 of such a pattern is illustrated in Figure 2. A main lobe 210 extends in a forward axial direction D at zero degrees. This is the direction of communication, i.e., a far end receiver is often located in this direction. The antenna is not perfect, which means that there are side-lobes 220 extending at angles other than the forward axial direction D. As is commonly the case with parabolic reflector antennas, there is a relatively strong back-lobe 230 extending in the reverse axial direction B, i.e., in direction opposite to the main lobe direction D. This relatively strong back-lobe appears due to symmetry effects associated with the parabolic reflector antenna.

The dish antenna 100 has a rim portion 1 10 extending circumferentially around a periphery of the dish antenna 100. Flere, the periphery is the extreme point of the dish antenna in a radial direction R perpendicular to the axial direction D. The rim portion 110 of the antenna 100 is ‘crenelated’, i.e., it comprises high profile sections interleaved by low profile sections distributed evenly around the periphery. In other words, the rim portion 1 10 comprises a plurality of profile sections. The profile sections are of at least a first and a second type. A profile section of the first type has a cross- sectional shape different from a profile section of the second type. The difference in cross-sectional shapes causes a phase difference of an electromagnetic field propagating past the rim via the different profile sections, thereby suppressing a back- lobe radiation (B) of the parabolic dish antenna.

Some example cross sectional shapes will be described below in connection to Figures 3A-3C, 4A-4C, and 5A-5C.

Due to the different profile shapes, the electromagnetic field travelling along a surface of the reflector antenna travels further as it propagates or diffracts via the profile section of the first type to the back-side of the antenna than it does when it propagates or diffracts via the second type profile sections. Now, if the geometry of the different sections is configured in dependence of a wavelength of the electromagnetic field, i.e., in dependence of a wavelength of a frequency band of operation associated with the antenna 100, then two types of field components will be generated. One type of field component will have one phase value and the other type of field component will have another phase value since the two components will have traveled along different geometry paths. In particular, when the two types of field components are summed at the back of the antenna 140, the two types of field component will add destructively, or at least not constructively, causing attenuation of the total electromagnetic field radiated from the back of the antenna, i.e., effectively reducing the power in the back- lobe. This way the front-to-back ratio of the antenna is increased, which is an advantage.

The same effect can also be obtained by using profile sections having different dielectric properties.

Maximum attenuation is of course obtained if two waveforms at the same delay are phase shifted by 180 degrees. It is also appreciated that, in order to obtain total cancellation of two waveforms, they need to be of the same amplitude value in addition to being shifted 180 degrees in phase.

In essence, the antenna rim is divided into sections, where each section spans a number of degrees along the rim of the disc antenna. Profile sections having different cross-sectional shapes are arranged along the antenna rim in a modular pattern causing phase differences in the electromagnetic field components at the back of the antenna. These phase differences reduce antenna back lobe power.

The example illustrated in Figures 1 a and 1 b shows 12 sections with a‘high’ profile (an example first type), and 12 sections with a‘low’ profile (an example second type). It is not necessary that there is an even number of first and second type profile sections. Also, there can be more than two types of elements, i.e., there may be a third type of element, a fourth type, a fifth type, and so on.

According to an example, the first and the second type profile sections cover 15 degrees each of the rim portion 1 10. However, another division in terms of degrees per profile section can be used to adjust or fine-tune waveform component relationships at the back of the antenna. For instance, the profile sections may alternate between being 16 degrees wide and 14 degrees wide. Other divisions are also possible depending on antenna design. An uneven circumferential length of the different types of profile sections can be used to modify field strength associated with the different phases at the back of the antenna. If the circumferential length of a given type of segment is increased then the relative percentage of electromagnetic field components associated with a given phase increases, and vice versa.

The number of antenna sections can be freely varied; more sections provide a finer resolution in terms of design options, but the section dimensions should be kept such that the periodicity does not come too close to the operating wavelength of the antenna If too few sections are used, i.e., too large sections spanning over large segments of the antenna rim, then the location relative to the electric field direction will have an impact which may be undesired.

The profile sections 120, 130 are optionally arranged to be releasably fastened to each other by fastening elements. This way the rim portion can be assembled from the different profile sections. As will be shown below, the arrangement can also be used to securely hold a circular shape radome to protect the dish antenna. The profile sections can also be glued together or attached by other methods.

According to some aspects, different types of rim portion sections can be assembled to calibrate the antenna radiation pattern according to some requirement or specification. Thus, there is provided herein a modular system where a selection of different type profile sections can be selected from in order to compose a collection of profile sections along the rim portion with the required properties. For instance, the collection can be selected in dependence of a frequency band of operation of the antenna, or in dependence of some external factor such as antenna mounting bracket geometry of objects in the near field of the antenna.

The profile sections may have different cross-sectional shapes. Some examples of various cross-sectional shapes will now be discussed in connection to Figures 3-5. Some example‘first type’ profile sections 310, 320, 330 are exemplified in Figures 3A, 3B, and 3C, while some‘second type’ profile sections 410, 420, 430 are shown in Figures 4A, 4B, and 4C. It is noted that the example first type profile shapes extend further in the axial direction D compared to the second type profile shapes. Figures 5A, 5B, and 5C illustrate some example‘third type’ profile sections 510, 520, 530 which extend further in the axial direction compared to the second type profile shapes 410, 420, but which have a smaller extension in the axial direction D compared to the first type profile sections 310, 320, 330.

It is appreciated that any selection of the example profile sections in Figures 3-5 can be combined along the rim portion 1 10, i.e., some profile sections along the rim portion may be those shown in Figure 3 or in Figure 4 and some others may be those shown in Figure 5.

The parabolic dish antenna may comprise alternating first and second type profile sections or alternating first and third type profile sections, or alternating second and third type profile sections, or a mix of different profile sections selected from the first, second, and third types. Other cross-sectional shapes are also possible; the disclosure is not limited to the examples given in Figures 3-5. The profile sections are, according to some aspects, designed with fixed cross-sectional shapes, which cross-sectional shapes alternate in a periodical manner along the rim portion 1 10 of the disc antenna.

According to aspects, the profile sections 310, 320, 330 comprise an angled portion 350 configured angled outwards in a radial direction R of the parabolic dish antenna 100.

The profile sections 310, 330, 530 may be hollow 360 , i.e., may comprise cavities to, e.g., reduce a weight of the rim portion 1 10. It has been found that these cavities may be present while still maintaining the back-lobe suppressing function of the rim portion 110. Thus, according to some aspects, one or more of the profile sections 120, 130, 500 are at least partly hollow 360.

Examples 310, 430, 510 comprise protrusions 370, 440 extending radially outwards from the rim portion. These protrusions 370, 440 have an effect on the diffractive properties of the rim portion 1 10.

The example profile sections 310, 320, 330, 410, 420, 430, 510, 520, 530 comprise an optional groove configured to hold a radome 340 of the parabolic dish antenna. This way the rim portion section not only reduces back-lobe radiation but also provide structural integrity to the antenna and serve as radome mounting means as well. In other words, the profile sections 120, 130, 500 optionally comprise a groove configured to hold a radome 340. The radome 340 may for example have a disc shape. According to some aspects, the profile sections 120, 130, 500 are at least partly made in an electrically non-conductive material or electromagnetically absorbing material.

According to some other aspects, the profile sections 120, 130, 500 are at least partly made in an electrically conductive material.

Figure 6 illustrates an example communication system 600 comprising at least one parabolic dish antenna 100 according to the above discussion.

The dielectric properties of the profile sections also affect the phase relationship between the electromagnetic field components associated with propagation past the different type profile sections.

Another alternative or complementary method to reduce the back-lobe radiation of the antenna is to achieve the phase difference of the electromagnetic field over the rim by letting parts of the radiation that contributes to the back-lobe pass through materials with different dielectric properties and hence have an extended optical path length.

To summarize the discussion above, there has been disclosed herein a parabolic dish antenna 100 configured to radiate electromagnetic energy in a main axial direction D, the dish antenna having a rim portion 1 10 extending circumferentially around a periphery of the dish antenna 100, wherein the rim portion 1 10 comprises a plurality of profile sections 120, 130, 500, the profile sections being of at least a first and a second type, wherein a profile section of the first type has a cross-sectional shape different from a profile section of the second type, to cause a phase difference of an electromagnetic field propagating past the rim via the profile sections 120, 130, 500, thereby suppressing a back-lobe radiation B of the parabolic dish antenna 100.

According to aspects, the first and the second type of profile sections 120, 130, 500 are configured to extend different distances in the axial direction D.

According to aspects, the first and the second type of profile sections 120, 130, 500 are configured to extend different lengths along the rim portion 1 10.

According to aspects, the first and the second type of profile sections are arranged alternating around the rim portion 1 10.

According to aspects, the profile sections are selected in dependence of a frequency band of operation associated with the antenna. According to aspects, the profile sections 120, 130, 500 are at least partly made in an electrically non-conductive material and/or or electromagnetically absorbing material.

According to aspects, the profile sections 120, 130, 500 are at least partly made in an electrically conductive material and/or an electromagnetically shielding material.

According to aspects, adjacent profile sections 120, 130, 500 are arranged to be releasably fastened to each other by fastening elements.

According to aspects, the profile sections 120, 130, 500 comprise a groove configured to hold a radome 340.

According to aspects, one or more of the profile sections 120, 130, 500 are at least partly hollow 360.

There was also disclosed a parabolic dish antenna 100 configured to radiate electromagnetic energy in a main axial direction D, the dish antenna having a rim portion 1 10 extending circumferentially around a periphery of the dish antenna 100, wherein the rim portion 1 10 comprises a plurality of profile sections 120, 130, 500, the profile sections being of at least a first and a second type, wherein a profile section of the first type has a cross-sectional shape different from a profile section of the second type, wherein a collection of profile sections of at least the first and the second type arranged adjacent to each other around the rim portion 1 10 is selectable to cause a phase difference of an electromagnetic field propagating past the rim via the profile sections 120, 130, 500, thereby suppressing a back-lobe radiation B of the parabolic dish antenna 100.

There was furthermore disclosed a parabolic dish antenna 100 configured to radiate electromagnetic energy in a main axial direction D, the dish antenna having a rim portion 1 10 extending circumferentially around a periphery of the dish antenna 100, wherein the rim portion 1 10 comprises a plurality of profile sections 120, 130, 500, the profile sections being of at least a first and a second type, wherein a profile section of the first type comprises a material having a dielectric constant value different from a dielectric constant value of a profile section of the second type, wherein a collection of profile sections of at least the first and the second type arranged circumferentially adjacent to each other around the rim portion 1 10 is selectable to cause a phase difference of an electromagnetic field propagating past the rim via the profile sections 120, 130, 500, thereby suppressing a back-lobe radiation B of the parabolic dish antenna 100.