MULTI-BAND ANTENNA FEED ARRANGEMENT

TECHNICAL FIELD The present disclosure relates to multi-band antennas and antenna feed arrangements. The disclosed feed arrangements enable feeding of radio frequency signals in a plurality of radio frequency bands to an antenna via a single integrally formed feed arrangement.

BACKGROUND

Wireless communication networks comprise radio frequency transceivers, such as radio base stations used in cellular access networks, microwave radio link transceivers used for, e.g., backhaul from an access point into a core network, and satellite transceivers which communicate with satellites in orbit.

Radio transceivers, in general, comprise antenna devices. There is often one radio branch connected to the antenna device arranged for transmission, and another radio branch connected to the antenna device arranged for reception. A key element in antenna design is the design of the feed arrangement which acts as interface between the radio branches and the physical antenna. For instance, a directive dish antenna used for satellite communication use feed arrangements to transmit and to receive electromagnetic radiation via the dish. In the same manner, in an array antenna solution, the array comprises elements which each have to operate with a certain electromagnetic performance in order for the array to work properly.

Some wireless communication systems use several different frequency bands for communication. For instance, satellite communications may comprise communication over the Ka band as well as over the Ku band or X band. This complicates the design of the feed arrangement, since the different frequency bands are ideally designed with different antenna feed geometries in order to provide good antenna performance, e.g., in terms of return loss, directivity pattern performance, and co- polar and cross-polar performance.

Dual-band antenna feed arrangements in general are known, for instance; US5003321 A discloses a dual frequency feed arrangement.

US6714165B2 discloses a Ka/Ku dual band feed horn and orthomode transducer.

A problem associated with antenna feed arrangements is the mechanical stability of the design, which must be high to ensure satisfactory performance of the antenna system. This is especially true at higher frequencies where wavelengths are small, and mechanics are therefore more sensitive to mechanical imperfections and manufacturing variations.

There is a need for cost effective high performance multi-band antenna feed arrangements.

Another issue related to multiband antenna feed solutions in which several feeding points are used is to design the different bands in such a way so that they in the final product work well together. A major parameter is then the return loss performance, i.e., the measure of how much power is transmitted from cable to air and received from air to cable in the antenna system for the various bands of operation.

SUMMARY

It is an object of the present disclosure to provide improved antenna feed arrangements. This object is obtained by an antenna feed arrangement for feeding a plurality of signals occupying different frequency bands to an antenna. The antenna feed arrangement comprises a first waveguide structure†L and a second waveguide structure fa arranged co-axially with respect to each other and symmetrically with respect to a symmetry axis of the antenna feed arrangement, whereby the first waveguide structure at least partially encloses the second waveguide structure. The first waveguide structure fa comprises a first feed port arranged radially with respect to the symmetry axis, the second waveguide structure fa comprises a second feed port arranged axially with respect to the symmetry axis. The antenna feed arrangement also comprises a dielectric element. The dielectric element comprises a first trough arranged to receive an end section of the first waveguide structure, thereby providing mechanical stability and sealing at least the first waveguide structure. This way, an antenna feed arrangement with mechanical robustness is obtained since the dielectric element provides stability to the structure. Also, the waveguides are sealed by the dielectric element and thereby protected from moisture and dirt entering the interiors of the waveguide structures. The dielectric element also provides a lens effect, which focuses electromagnetic energy and thus improved antenna performance.

According to aspects, troughs in the dielectric element are arranged to receive end sections of the waveguide structures, thereby providing mechanical stability. This mechanical stability can be further increased by fastening means as described herein.

According to aspects, matching surfaces can be arranged on the dielectric element in order to improve matching between waveguide structures and, e.g., a reflector arrangement.

There are also disclosed herein antenna arrangement, antenna arrays, and methods associated with the above mentioned advantages.

This improvement solves or alleviates both the problem with mechanical imperfections as well as the issues related to matching of the feed at various frequency bands.

The use of dielectrics in the feed section also solves another major issue with antennas which is to provide a natural radome, lense, sealing and shielding against dust and humidity which often degrade the antenna performance.

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 a schematically shows an antenna feed arrangement;

Figure 1 b shows details of an antenna feed arrangement;

Figure 1 c shows details of an antenna feed arrangement;

Figure 2 schematically shows an antenna feed arrangement;

Figure 3 illustrates examples of matching transitions in feed arrangements;

Figures 4-5 schematically show example waveguide geometries;

Figures 6-7 illustrate antenna arrangements;

Figure 8 schematically shows a multi-band antenna feed arrangement;

Figure 9 is a flowchart illustrating methods.

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.

Figure 1 a illustrates an antenna feed arrangement 100 for feeding a plurality of signals occupying different frequency bands to an antenna. The plurality of signals may for instance be radio frequency signals that are band-limited to different radio frequency bands. The radio frequency bands in which the antenna feed arrangement operates may for example be the Ka and Ku frequency bands used for, e.g., satellite communication. The radio frequency bands may also be parts of microwave frequency bands, such as E-band or V-band. The antenna feed arrangement has two feed ports 110, 120. These two feed ports lead to first†L and second fa waveguide structures which guide the signals towards the antenna. There is one waveguide per signal, i.e., one waveguide structure per frequency band. Thus, one waveguide is dimensioned for, e.g., the Ka band, while the other waveguide is dimensioned for, e.g., the Ku band.

The antenna operates as a transition of guided waves within, e.g., a coaxial cable transformed from the transverse electromagnetic mode (TEM) waveguide modes in the coaxial cable to the waveguide modes inside the waveguide which are matched with the appropriate dielectric to air transitions, led to either radiate directly from the antenna aperture or hitting a reflective surface which, according to aspects, is a metallization of a dielectric section which acts as an electromagnetic reflector.

The waveguide modes described above are circular waveguide modes for circular waveguides and rectangular waveguide modes for rectangular waveguides.

These waveguide modes are then added in such a way as to give an improved or optimal radiated antenna performance depending on the application. It may be that not only the dominant waveguides are propagating inside the dielectric sections. It is rather so that higher order modes may be generated inside the dielectric sections which added in correct phase and amplitude to the dominant mode gives a hybrid field propagating and giving rise to improved or optimal performance.

A key element in the antenna feed arrangement is a dielectric element 140 which is arranged in connection to end sections of the waveguide structures. In Figure 1 a, the end sections of the waveguide structures are the sections opposite from the feed port sections. This dielectric element 140 serves a plurality of purposes; it provides mechanical stability to the feed arrangement, it provides a seal which protects the waveguide structures from, e.g., moisture and dirt, and it also improves electromagnetical matching of the feed arrangement.

The antenna feed arrangement illustrated in Figure 1 a comprises a first waveguide structure fa and a second waveguide structure fa arranged co-axially with respect to each other and symmetrically with respect to a symmetry axis 130 of the antenna feed arrangement, whereby the first waveguide structure at least partially encloses the second waveguide structure. This enclosing provides a sandwich-like structure with increased structural integrity. The enclosing also implies that the second waveguide structure is protected from moisture and dirt by the first waveguide structure.

The first waveguide structure†L comprises a first feed port 110 arranged radially with respect to the symmetry axis 130, while the second waveguide structure†H comprises a second feed port 120 arranged axially with respect to the symmetry axis 130. Herein, a feed port arranged radially means that the feed port can be accessed from the side of the arrangement as shown in Figure 1 a. Arranged axially means that the feed port is located in an extension direction of the antenna feed arrangement 100, as illustrated in Figure 1 a. By arranging feed ports radially and axially, the two ports will be separated from each other, and will not interference structurally with each other. Arranging the two ports radially and axially provides for a convenient way of receiving and transmitting electromagnetic signals to and from the antenna.

Alternatively, both feed ports may be arranged radially, i.e., accessed from the side of the antenna feed arrangement.

As already mentioned above, the antenna feed arrangement comprises a dielectric element 140. This dielectric element comprises a first trough 141 arranged to receive an end section 151 of the first waveguide structure fi_. This trough can be a machined or a molded trough, i.e., a ditch or recess in the dielectric element. The end section 151 of the first waveguide structure is, according to some aspects, relatively narrow. The trough therefore does not need to have a large width, just enough to receive the end section of the first waveguide structure. According to some aspects, the trough is made slightly conical in order to better receive the end section, and to hold the end section in place due to the squeezing which results from the conical shape. This type of conical trough is illustrated in Figure 1 b. It is appreciated that the same effect is obtained if the end section is instead, or as a complement, also conical.

According to aspects, the trough also comprises a snap-lock mechanism 152 arranged to hold a corresponding lip of the end section to lock the waveguide structure to the dielectric element.

An optional reflector arrangement 190 is shown in Figure 1 a. This reflector 190 is arranged to reflect the plurality of signals in different frequency bands to and from the first†L and second†H waveguide structures from and in the pre-determ ined direction D, respectively. The antenna can be of different types as will be discussed in more detail below.

According to an example, the waveguide structure has a tube shape, and the first trough is then a circular recess machined in the dielectric element 140. According to another example, the waveguide structure has a rectangular shape, and the trough is then a rectangular shape recess in the dielectric element arranged to receive an end section of the rectangular waveguide structure. These shapes are illustrated in Figure 4 and Figure 5 respectively.

The trough arrangement provides for mechanical stability of the antenna feed arrangement. This is because the bond between the first waveguide structure and the mechanically stable dielectric element is strong due to the trough receiving the end section of the waveguide structure. The trough also serves to seal at least the first waveguide structure. Since the first waveguide structure at least partly encompasses the second waveguide structure, the second waveguide structure is also protected by the trough arrangement of the first waveguide structure.

According to some aspects, the end section of the first waveguide structure, when received by the first trough 141 , constitutes a water-proof seal, or gas-proof seal, thereby sealing the first and second waveguide structures (fL, fa) with respect to an exterior of the antenna feed arrangement.

The antenna feed arrangements illustrated in, e.g., Figures 1 and 2, are dual band feed arrangements allowing to feed an antenna in two separate frequency bands at the same time, which is an advantage. Flowever, multi-band feed arrangements can also be constructed using the same design principles. One such example is illustrated in Figure 8.

The dielectric element 140 serves a plurality of purposes beyond protecting the waveguide structures from dirt and moisture. It provides electromagnetic matching at the end sections of the first and second waveguide structures. It also provides a lens effect which focuses electromagnetic energy entering and leaving the antenna feed arrangement. These technical effects will be discussed in more detail below.

According to some aspects, the dielectric element 140 also comprises a second trough 142 arranged to receive an end section of the second waveguide structure fH, thereby providing further mechanical stability and sealing the second waveguide structure. This way there are two troughs arranged to receive respective end sections of both waveguide structures. The two troughs provide further improved mechanical robustness of the antenna feed arrangement. The second trough may optionally also be formed conically in order to better receive the end section and seal the second waveguide structure, as illustrated in Figure 1 b. The second trough 142 may also comprise the snap-lock mechanism illustrated in Figure 1 c.

As noted above, the dielectric element can be used to provide electromagnetic matching towards the first and second waveguide structures. Thus, according to some aspects, the dielectric element 140 comprises a first internal matching surface 150 arranged tapered with respect to an extension direction of the first waveguide structure to electromagnetically match a transition between the end section of the first waveguide structure and the dielectric element 140.

The dielectric element 140 may optionally also comprise a second internal matching surface 160 arranged tapered with respect to an extension direction of the second waveguide structure to electromagnetically match a transition between the end section of the second waveguide structure and the dielectric element 140.

It is appreciated that shapes other than a tapering can be used for the first and second internal matching. Flowever, a tapering is easily machined into the dielectric element in a cost-effective manner.

Even though the first and second waveguide structures are attached to the dielectric element by means of the troughs 141 , 142, further mechanical robustness can be obtained by an optional fastening device 180. Thus, according to aspects, the antenna arrangement comprises a first fastening device 180 arranged to fixedly attach the dielectric element 140 to the first waveguide structure†L when the first†L waveguide structure is received in the first 141 trough. This first fastening device is preferably a screw configured to engage with a thread that has been machined in the dielectric element or in the waveguide structure. The screw has an extension to engage with the first waveguide structure in order to fixedly attach the first waveguide structure to the dielectric element.

Figure 1 a also shows a second fastening device 185, which will be discussed below.

According to aspects, the dielectric element 140 comprises a lens surface 143 having a shape arranged as an electromagnetic lens, whereby the plurality of signals in different frequency bands are focused in a pre-determined direction D. The lens can, for instance, be configured to direct electromagnetic energy is a direction between the reflector 190 and a disc antenna. The shape of the lens can be determined based on computer simulation or laboratory experiments according to known methods for designing electromagnetic lenses. An example of a reflector type antenna is illustrated in Figure 6.

According to aspects, the dielectric element is a layered dielectric material, comprising layers or sections with different permittivity values, which layered or sectioned dielectric material can be used to achieve a more pronounced or advanced lens effect.

The reflector arrangement 190 is preferably fixedly attached in a structurally robust manner to the antenna feed arrangement. The reflector arrangement may be embedded in the dielectric material for increased mechanical strength. According to some aspects, the dielectric element 140 comprises a recess arranged to receive and to fixedly hold the reflector arrangement 190. According to other aspects, the dielectric element is arranged molded around the reflector arrangement, thus enclosing and fixedly holding the reflector arrangement 190.

To provide further mechanical strength, a fastening device similar to the first fastening device discussed above can be used. Thus, according to aspects, the antenna feed arrangement comprises a second fastening device 185 arranged to fixedly attach the dielectric element 140 to the reflector arrangement 190. This second fastening device is preferably also a screw arranged to engage with a machined thread in the reflector arrangement, or in the dielectric element, and to extend to the reflector arrangement, thereby fixedly holding the reflector arrangement.

A disc antenna arrangement 600 using an antenna feed arrangement 620 such as that shown in Figure 1 is illustrated in Figure 6. The antenna arrangement uses a disc 610 to focus radio transmission in a direction 630.

Figure 2 shows an alternative configuration of the antenna feed arrangement which does not comprise a reflector. Instead, the antenna feed arrangement 200 illustrated in Figure 2 is arranged to communicate directly in direction D, which then is a communication direction. According to some aspects, the dielectric material is arranged as electromagnetic lens 210 to focus electromagnetic energy in the direction D. An example of an antenna arrangement 700 using this type of feed arrangement 720, 710 is illustrated in Figure 7. Here radio transmission in a communication direction 730 is achieved using the lens effect of the dielectric material, as discussed above.

As mentioned above, the dielectric element 140 is an important component of the disclosed antenna feed arrangements. This dielectric component can be designed and manufactured in several different ways, using different materials, as will now be discussed.

According to some aspects, the dielectric element 140 is molded or machined in a single piece. This way there is a minimum of loose parts and assembly needed, which is an advantage. The single piece also provides improved protection from, e.g., moisture.

Regarding materials, the skilled person will appreciate that a wide range of dielectric materials may be selected from. Also, one or more different types of materials can be used to form the dielectric element. According to aspects, the dielectric element 140 is made of any of polytetrafluoroethylene, PTFE, fluorinated ethylene propylene, FEP, polyurethane, or poly vinyl chloride, PVC. It is appreciated that this list is not exhaustive. In general, any dielectric material can be used as long as the permittivity value agrees with the electromagnetical properties of the antenna feed arrangement. For instance, according to some aspects, the dielectric element 140 comprises a dielectric material having an relative electric permittivity value r in a range of 1 -10. According to aspects, the dielectric element 140 comprises a plurality of dielectric material layers, wherein each dielectric layer is associated with a respective absolute permittivity value absolute permittivity value e in a range of 1 -10 farad per meter.

With reference to Figure 3, according to some aspects, the transition between the end section of the first waveguide structure and the dielectric element 140 comprises a first feed horn arrangement 350, and/or wherein the transition between the end section of the second waveguide structure and the dielectric element 140 comprises a second feed horn 360 arrangement. These feed horn arrangements improve the electromagnetical properties of the interface between the dielectric element and the first and second waveguide structures. It is appreciated that the feed horn arrangements may be designed with different shapes from that illustrated in Figure 3. Figure 3 is just one example of how the effect of feed horn arrangements can be obtained.

The first and second waveguide structures may be circular or oval in shape, i.e., resembling tubes. Such waveguide structures are illustrated in Figure 4 from a top view perspective. Flowever, other shapes are equally possible. For instance, a square or rectangular waveguide shape is also applicable. Such as rectangular waveguide shape is illustrated in Figure 5, also from a top view perspective.

Figure 6 shows communication 630 using an antenna arrangement 600 comprising center feed reflector 620 and disc 610. The antenna feed arrangements discussed herein are applicable in these types of systems. As noted above, the antenna feed arrangement can also be used to communicate without reflector or disc. This type of application is illustrated in Figure 7. Flere, an antenna system 700 is used to communicate 730 in a communication direction by means of a waveguide feed arrangement 710 and a dielectric element used as lens 720.

With reference to Figure 8, it is appreciated that the above discussed techniques and concepts can be extended to antenna feed arrangements for more than two frequency bands. According to some aspects, the antenna feed arrangement comprises a third waveguide structure fM arranged co-axially in-between the first†L and the second fa waveguide structure. This third waveguide structure is dimensioned for radio signals band-limited to a third frequency band. The third waveguide structure fM is arranged with a third feed 810 arranged radially with respect to the symmetry axis 130. The dielectric element optionally comprises a third trough arranged to receive an end section of the third waveguide structure, thereby providing further mechanical stability and sealing the third waveguide structure from moisture and dirt.

The disclosed antenna feed arrangements can be used in a wide variety of antenna applications. For instance, the feed arrangements can be used in satellite transceiver antenna arrangements, in microwave radio link transceiver arrangements, or in antenna arrays.

Figure 9 is a flow chart illustrating methods according to the present disclosure. There is shown a method for feeding a plurality of signals in different frequency bands to an antenna. The method comprises configuring S1 a dielectric element 140 with a first trough 141 arranged to receive an end section of a first waveguide structure†L and a second trough 142 arranged to receive an end section of a second waveguide structure fa arranged co-axially with the first waveguide structure. The troughs and the end sections were discussed above in connection to, e.g., Figure 1.

The method also comprises sealing S2 the first and second waveguide structures by inserting the end section of the first waveguide structure fa into the first trough 141 and inserting the end section of the second waveguide section into the second trough 142, thereby providing mechanical stability and sealing the first and the second waveguide structure.

The method further comprises feeding S3 a signal in a first frequency band into the first waveguide structure fa via a first feed port 110 arranged radially with respect to the symmetry axis 130, and feeding S4 a signal in a second frequency band separated from the first frequency band into a second waveguide structure fa via a second feed port 120 arranged axially with respect to the symmetry axis 130.