Directional antenna system

Abstract

An apparatus comprising: a primary reflector; and a feed-in device, the feed-in device comprising: a multiband waveguide feed-in comprising a first waveguide feed-in for a first frequency band and a second waveguide feed-in for a second frequency band separated from the first frequency band, where the first waveguide feed-in and the second waveguide feed-in are coaxial and have a first aperture and a second aperture, respectively; and a secondary reflector configured as a feed for the primary reflector, the secondary reflector comprising at least one substantially concave hyperboloid reflective surface.

Description

Technical Field

[0001] Examples of the present disclosure relate to directional antenna systems. Background Art

[0002] The directional antenna system may include a main parabolic reflector; and

[0003] A feed arrangement includes a waveguide feed for an operating frequency band and a sub-reflector configured as a feed for a primary reflector.

[0004] It would be best to have a dual band antenna system. Summary of the invention

[0005] According to various but not necessarily all examples, there is provided an apparatus comprising:

[0006] a primary reflector; and

[0007] A feeding device, the feeding device comprising:

[0008] a multi-band waveguide feed comprising a first waveguide feed for a first frequency band and a second waveguide feed for a second frequency band separate from the first frequency band, wherein the first waveguide feed and the second waveguide feed are coaxial and have first and second apertures, respectively; and

[0009] A sub-reflector is configured as a feed for the main reflector, the sub-reflector comprising at least one generally concave hyperbolic reflective surface.

[0010] In some but not necessarily all examples, the hyperbolic reflective surface has a shape that can be formed by rotating a hyperbola about an aiming axis of symmetry of the primary reflector.

[0011] In some but not necessarily all examples, the generally concave hyperbolic reflective surface has a shape optimized to provide a phase center located at the focus of the primary reflector.

[0012] In some but not necessarily all examples, the primary reflector includes a generally concave parabolic reflective surface having a toroidal focus, wherein the generally concave hyperbolic reflective surface has a shape optimized to provide a phase center trajectory along the toroidal focus of the primary reflector.

[0013] In some but not necessarily all examples, the sub-reflector includes an outer surface with a different annular recess, wherein the outer surface and the annular recess have rotational symmetry about the aiming axis of the primary reflector.

[0014] In some but not necessarily all examples, the sub-reflector includes a first external conductive surface that is positioned farther away from the main reflector than the generally concave hyperbolic reflective surface and has one or more distinct first annular recesses having rotational symmetry about an aiming axis of the main reflector.

[0015] In some but not necessarily all examples, the sub-reflector includes an external dielectric surface that is positioned closer to the main reflector than one or more different first annular recesses and has one or more different second annular recesses having rotational symmetry about the aiming axis of the main reflector.

[0016] In some but not necessarily all examples, the first distinct annular notch is a deep notch having a depth greater than its width, and the second distinct annular notch is a shallow notch having a depth less than its width.

[0017] In some but not necessarily all examples, the size of the notch is optimized to maximize the linear electric field at a first frequency band, where the first frequency band is a lower frequency band than the second frequency band.

[0018] In some but not necessarily all examples, the generally concave hyperbolic reflective surface forms a front surface of an air-filled dielectric channel that widens radially from the line of sight of the primary reflector to an opening, wherein the opening of the channel is short-circuited by a dielectric material having a relative dielectric constant greater than 2.

[0019] In some but not necessarily all examples, the dielectric material has a variable thickness.

[0020] In some but not necessarily all examples, the second waveguide feed is a higher frequency feed and the first waveguide feed is a lower frequency feed, wherein the second waveguide feed is generally cylindrical and is an inner waveguide feed positioned within and coaxial with the outer first waveguide.

[0021] In some but not necessarily all examples, the first waveguide includes a constricted neck adjacent to the first aperture.

[0022] In some but not necessarily all examples, the first waveguide feed supports a lower frequency coaxial TE11 mode for both polarizations and the second waveguide feed supports a higher frequency circular TE11 mode for both polarizations.

[0023] In some but not necessarily all examples, the first waveguide feed is sized to transmit radio waves at a frequency less than 25 GHz, and the second waveguide feed is sized to transmit radio waves at a frequency greater than 30 GHz.

[0024] Examples are provided as claimed in the following claims according to various, but not necessarily all, examples.

[0025] The "Summary" section describes various features that may be characteristic of any of the described examples. A description of a function should also be considered to also disclose any means suitable for performing that function.

[0026] Although the examples and optional features of the above disclosure are described separately, it should be understood that they are provided in all possible combinations and arrangements and are included in the disclosure. It should be understood that the various examples of the disclosure may include any or all of the features described for other examples of the disclosure, and vice versa. In addition, it should be understood that any one or more or all of the features, in any combination, can be implemented / included in / can be performed by devices, methods, and / or computer program instructions as needed and appropriately by devices, methods, and / or computer program instructions. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Some examples will now be described with reference to the accompanying drawings, in which:

[0028] Figure 1 An example of the subject matter described herein is shown;

[0029] Figure 2 Another example of the subject matter described herein is shown;

[0030] Figure 3A Another example of the subject matter described herein is shown;

[0031] Figure 3B Another example of the subject matter described herein is shown;

[0032] Figure 3C Another example of the subject matter described herein is shown;

[0033] Figure 4 Another example of the subject matter described herein is shown;

[0034] Figure 5 Another example of the subject matter described herein is shown;

[0035] Figure 6 Another example of the subject matter described herein is shown.

[0036] These figures are not necessarily drawn to scale. For clarity and brevity, certain features and views in the figures may be shown schematically or enlarged in scale. For example, the size of certain elements in the figures may be enlarged relative to other elements to aid in illustration. Similar reference numerals are used in the figures to indicate similar features. For clarity, all reference numerals are not necessarily shown in all figures.

[0037] In the following description, reference numbers without subscript indexes (e.g., 10) may be used to refer to a class (or collection), reference numbers with numeric subscript indexes (e.g., 10_1) may be used to refer to a specific instance of a class (a member of a collection), and reference numbers with variable subscript indexes (e.g., 10_i) may be used to refer to a non-specific instance of a class (a member of a collection). DETAILED DESCRIPTION

[0038] An example of an apparatus 10 for radio telecommunications is illustrated in the figure.

[0039] The device 10 includes a main reflector 12 and a feed device 20. The device is configured to operate as a high gain, high radiation pattern performance, dual band radio frequency antenna. The high gain comes from the narrow spatial beam associated with the main reflector 12. The device 10 can be used to transmit radio frequency waves and / or receive radio frequency waves.

[0040] The feeding device 20 includes a multi-band waveguide feed 30 and a sub-reflector 40 configured as a feed for the main reflector 12. The sub-reflector 40 couples the multi-band waveguide feed 30 and the main reflector 12.

[0041] The multi-band waveguide feed 30 includes a first waveguide feed 32 for a first frequency band and a second waveguide feed 34 for a second frequency band separate from the first frequency band. The first frequency band and the second frequency band are non-overlapping and separate.

[0042] The first waveguide feed 32 and the second waveguide feed 34 are symmetrical about a common axis (the sighting axis 17 of the device 10 ) and have a first aperture 31 and a second aperture 33 , respectively.

[0043] The first frequency band is a lower frequency band than the second frequency band. The first aperture 31 is larger than the second aperture 33 .

[0044] During transmission, the first waveguide feed 32 provides a first radio signal 13 in a first lower frequency band to the sub-reflector 40, which reflects the first radio signal 13 to the main reflector 12, which then generates a first directional beam including the first radio signal 13 centered on the sighting axis 17. The second waveguide feed 34 provides a second radio signal 15 in a second higher frequency band to the sub-reflector 40, which reflects the second radio signal 15 to the main reflector 12, which then generates a second directional beam including the second radio signal 15 centered on the sighting axis 17.

[0045] During reception, a received first directional beam (comprising a first radio signal 13 in a first lower frequency band) is reflected by the main reflector 12 toward the sub-reflector 40, which reflects the first radio signal 13 into the first waveguide feed 32. A received second directional beam (comprising a second radio signal 15 in a second lower frequency band) is reflected by the main reflector 12 toward the sub-reflector 40, which reflects the second radio signal 15 into the second waveguide feed 34.

[0046] The sub-reflector 40 includes a generally concave hyperbolic reflective surface 42 . Figure 3A An example of a hyperbolic reflective surface 42 is illustrated in FIG. Figure 3A is a cross-section of a portion of the sub-reflector 40. In at least some examples, the hyperbolic reflective surface 42 is a two-lobed hyperbolic surface, such as Figure 3B In at least some examples, the hyperbolic reflective surface 42 has a shape that can be formed by rotating the hyperbola 46 about the aiming axis 17 (the rotational symmetry axis of the main reflector 12), as shown in FIG. Figure 3C As shown in the figure.

[0047] Figure 2 The entire dual band feed 20 operating on the annular focus reflector 12 is illustrated. Figure 3A The higher frequency portion or region of the sub-reflector that controls the phase center of the feed is illustrated.

[0048] In at least some examples, the generally concave hyperbolic reflective surface 42 has a shape optimized to provide a phase center located at the focal point of the primary reflector 12 via reflection for frequencies in the second (higher) frequency band.

[0049] exist Figure 2In the example illustrated in , the main reflector 12 includes a generally concave parabolic reflective surface 42 having an annular focus. The generally concave hyperbolic reflective surface 42 has a shape optimized to provide, via reflection, a phase center trajectory 16 along the annular focus 14 of the main reflector 12. The annular focus 14 of the parabolic reflector 12 is offset and not on the sighting axis 17 for both the first frequency band and the second frequency band.

[0050] The main reflector 12 is a parabolic reflector; a toroidal focus reflector. The difference between a toroidal focus and a toroidal focus reflector is that the parabolic focus in the first case is located at a point on the parabolic sighting axis 17. The offset of the focus from the sighting axis 17 in the x direction is 0. In the toroidal focus reflector 12, the focus has an offset from the sighting axis 17 and is not 0, but + / -x in the xy plane. o The parabolic reflector shape is formed by rotating a parabola centered on the sighting axis 17 about the sighting axis 17. The annular focus parabolic reflector shape is formed by rotating a double parabola shape about the sighting axis 17. The double parabola shape is formed by two identical parabolas that have no offset in the y direction and an offset in the x direction, with the intersection of the parabolas centered on the sighting axis 17. One of the parabolas has a focus at +x o , and the other parabola has a focus at -x o The rotation of these foci about the sighting axis 17 produces a trajectory 16 having a radius x o The sighting axis 17 is centered on the sighting axis 17.

[0051] The phase centre trace 16 is the trace where signals in the second (higher) frequency band have the same phase when transmitted by the second waveguide feed 34 .

[0052] The optimization algorithm may minimize the difference 18 between the phase center position 16 and the ring focus position 14, where the phase center position 16 is the phase center of the higher frequency band.

[0053] The hyperbolic surface values ​​(d, a, and b) may be calculated using an optimization algorithm with the constraint that the phase center be as close as possible to the known value of the ring focus location 14 of the parabolic reflector 12 at the second higher frequency band.

[0054] This produces a hyperbolic surface (x, y) defined by the parameters (d, a, and b) 42

[0055]

[0056] The antenna phase center position 16 is closely related to the geometry of the two-blade hyperboloid. The semi-major axis (a), semi-minor axis (b), and diameter (d) are constants of the two-blade hyperboloid geometry. λ is the wavelength of the higher frequency. (x,y) defines the surface of the hyperboloid. The diameter d of the hyperboloid extends perpendicular to the boresight axis, as Figure 2 and Figure 3B As shown in the figure.

[0057] The phase center of the optimized hyperbolic reflecting surface 22 is adjusted to the toroidal focus of the parabolic reflector 12 for the second higher frequency band. Most of the parabolic reflector 12 will be accurately illuminated / fed by the in-phase field. The antenna gain and radiation pattern will be greatly optimized.

[0058] Figure 4 An external view of an example of a feedthrough 20 is illustrated. Figure 5 Picture shows Figure 4 2. A cross-sectional view of the feedthrough 20 is shown in FIG. The feedthrough 20 comprises a multi-band waveguide feed 30 and a sub-reflector 40 located behind a dielectric body 60.

[0059] The front (forward) portion 22 of the feeding device is farther from the main reflector 12, while the rear (rear) portion 26 of the feeding device 20 is closer to the main reflector 12. The central portion 24 of the feeding device 20 is located between the front portion 22 and the rear (rear) portion 26, and is interconnected with the front portion 22 and the rear (rear) portion 26.

[0060] The outer surface 23 of the front portion 22 and the outer surface 27 of the rear portion 26 are electrically conductive. These electrically conductive portions may be formed, for example, of aluminum or a metallized dielectric or the like.

[0061] The outer surface 25 of the central portion 24 comprises a dielectric material. The dielectric material has a relatively high relative permittivity, for example a relative permittivity greater than 2.

[0062] The feedthrough 20 has a generally cylindrical volume. It deviates from the cylindrical shape due to a number of steps or notches 14 on the outer surface.

[0063] The feed arrangement 20 comprises a multi-band waveguide feed 30 and a sub-reflector 40. The sub-reflector 40 comprises outer surfaces 23, 25, 27 with different annular recesses 14. The outer surfaces 23, 25, 27 and the annular recess 14 have a rotational symmetry about the aiming axis 17 of the main reflector 12. Figure 6 The recess 14 is shown in more detail.

[0064] The secondary reflector 40 includes an outer conductive surface 23, which is located farther from the main reflector 12 than the generally concave hyperbolic reflective surface 42, and has one or more different first annular recesses 14_1, which have rotational symmetry about the aiming axis 17 of the main reflector 12. Each ring 14_1 is centered on the aiming axis. In this example (but not necessarily in every example), the depth of the recess increases as the distance from the parabolic reflector 12 decreases.

[0065] The sub-reflector 40 comprises an outer dielectric surface 25 which is located closer to the main reflector 12 than one or more distinct first annular recesses 14_1 and has one or more distinct second annular recesses 14_2 having a rotational symmetry about the sighting axis 17 of the main reflector 12 .

[0066] In this example, the different first annular notch 14_1 is a deep notch with a depth (length li) greater than the width (thickness ti), while the different second annular notch 14_2 is a shallow notch with a depth less than the width. However, the depth can be greater than the width, and vice versa, the width can be greater than the depth. The same is true for the notch 14_2.

[0067] The notch 14_1 is located in the conductive material of the front portion 22 of the sub-reflector 20. The notch 14_2 is located in the dielectric material of the central portion 24 of the sub-reflector 20.

[0068] The dimensions of the notches 14_1 , 14_2 are optimized to minimize the linear electric field at the first (lower) frequency band.

[0069] This provides increased inter-band isolation (IBI) from the second (higher) frequency band to the first (lower) frequency band.

[0070] By adjusting the diffraction field and surface current along the edge of the sub-reflector 40, the phase-out vector becomes an in-phase component field, thereby increasing the antenna gain on the first (lower) frequency band. The radiation phase-out vector generated by the second (higher) frequency band reduces the maximum value of the antenna gain in the first (lower) frequency band and is suppressed. This avoids reflections / standing waves.

[0071] refer to Figure 6 The conductive front portion 22 of the sub-reflector 40 has N impedance steps (notches 14_1) which are formed by a depth (length l i ) and width (thickness t i ) is defined. The notch 14_1 extends inwardly perpendicular to the sighting axis 17. The depth (length l i ). The width (thickness t i ).

[0072] The dielectric middle portion 24 of the sub-reflector 40 has a series of steps (notches 14_2). The step length 14_2 of the dielectric body 60 adjacent to the conductive front portion 22 is l s The step length 13_2 is used as a short circuit. The dielectric body 60 has a platform formed between the notches 14_2. The platform has a length l d The width defined by the thickness t d1 The platform ends with two rectangular steps with a depth / thickness t at the notch 14_2 d2 .

[0073] The geometric value of the size parameter can be calculated using the following formula

[0074]

[0075] Among them l i =l1+l2+l3 ... and m and n, the tuning constants can be varied to 0.89≤m≤1.05 and 0.92≤n≤1.08. λ is the wavelength of the first lower frequency band.

[0076] The notch 14 eliminates the need for expensive and complex waveguide filters and mitigates the second (higher) frequency band signals from the second waveguide feed 34 from entering the first waveguide feed 32 .

[0077] Reference again Figure 5 , the generally concave hyperbolic reflective surface 42 forms part of a front surface 52 of an air-filled dielectric channel 50 that widens in a radial direction (R) from the aiming axis 17 of the main reflector 12 to an opening 54. The opening 54 of the channel 50 is short-circuited by a dielectric material 60. In this example (but not necessarily in all examples), the relative dielectric constant of the dielectric material is greater than 1.5 or greater than 2. The dielectric material 60 has a variable thickness (see Figure 6 ).

[0078] The second waveguide feed 34 is a higher frequency feed, while the first waveguide feed 32 is a lower frequency feed. The opposing second waveguide feed 34 is generally cylindrical and is an inner waveguide feed positioned within and coaxial with the outer first waveguide feed 32.

[0079] The first waveguide feed 32 comprises a constricted neck adjacent to the first aperture 31. This reduces interference from reflected waves in the second (higher) frequency band.

[0080] In the illustrated example, the first waveguide feed 32 supports a lower frequency coaxial TE11 mode for both polarizations, and the second waveguide feed 34 supports a higher frequency circular TE11 mode for both polarizations. In the illustrated example, the first waveguide feed 32 is dimensioned to transmit radio waves at a frequency less than 25 GHz, and the second waveguide feed 34 is dimensioned to transmit radio waves at a frequency greater than 30 GHz. The first (lower) frequency band may be, for example, a microwave frequency band, such as one of 14.2 GHz-15.35 GHz, 17.7 GHz-19.7 GHz, and 21.2 GHz–23.6 GHZ. The second (higher) frequency band may be, for example, a millimeter wave frequency band, such as 71 GHz to 86 GHz.

[0081] The radome 100 of the device 10 may be selected to match the second (higher) frequency band requirements. Figure 1 An example of a radome is illustrated in FIG. The thickness of the radome 100 can be obtained after millimeter wave RF matching and final tuning, which corresponds to , where k is a constant calculated by optimization in the range of 0.81≤k≤1.17, and λ is the free space wavelength.

[0082] For example, the apparatus 10 may be used to transmit and / or receive in a dual-frequency backhaul system for transmitting network information.

[0083] For example, the apparatus 10 may be used for transmission and / or reception in a dual-frequency backhaul system using band and carrier aggregation (BCA) that aggregates a first frequency band and a second frequency band.

[0084] For example, the apparatus 10 may be used for transmission and / or reception in a dual-frequency backhaul system of a New Radio (NR) 3rd Generation Partnership (3GPP) system.

[0085] The device 10 can improve the antenna RF performance (return loss, gain, radiation pattern, inter-band isolation, etc.) on two frequency bands.

[0086] The apparatus 10 is configured to propagate (receive or transmit) two radio frequency (RF) signals 13, 15, one in a first low frequency band and the other in a second high frequency band. In at least some examples, orthogonal polarizations are used in both frequency bands.

[0087] If a structural feature has been described, it may be replaced by a component for performing one or more of the functions of the structural feature, whether this function or these functions are explicitly or implicitly described.

[0088] The above example can be used as an enabling component for:

[0089] Automotive systems; telecommunications systems; electronic systems, including consumer electronics; distributed computing systems; media systems for generating or presenting media content, including audio, video and audiovisual content and mixed, mediated, virtual, and / or augmented reality; personal systems, including personal health systems or personal fitness systems; navigation systems; user interfaces, also known as human-machine interfaces; networks, including cellular, non-cellular, and fiber-optic networks; ad hoc networks; the Internet; the Internet of Things; virtualized networks; and related software and services.

[0090] According to the examples of the present disclosure, the device can be provided in an electronic device, such as a mobile terminal. However, it should be understood that the mobile terminal only illustrates an electronic device that will benefit from the implementation examples of the present disclosure, and therefore should not be considered to limit the scope of the present disclosure to this. Although in some implementation examples, the device can be provided in a mobile terminal, other types of electronic devices, such as but not limited to: mobile communication devices, handheld portable electronic devices, wearable computing devices, portable digital assistants (PDAs), pagers, mobile computers, desktop computers, televisions, gaming devices, laptops, cameras, video recorders, GPS devices, and other types of electronic systems, can easily adopt the examples of the present disclosure. In addition, whether the device is intended to provide mobility, the device can easily adopt the examples of the present disclosure.

[0091] The term "comprising" is used in this document in an inclusive rather than exclusive sense. That is, any reference to X including Y indicates that X may include only one Y or may include multiple Ys. If "comprising" is intended to be used in an exclusive sense, it will be made clear in the context by referring to "including only one..." or using "consisting of..."

[0092] In this specification, the terms "connected", "coupled", and "in communication" and their derivatives mean operationally connected / coupled / in communication. It should be understood that any number or combination of intermediate components (including no intermediate components) may be present, i.e., to provide direct or indirect connection / coupling / in communication. Any such intermediate components may include hardware and / or software components.

[0093] As used herein, the term "determining" (and its grammatical variations) may include, but is not limited to: calculating, computing, processing, deriving, measuring, investigating, identifying, searching (e.g., searching in a table, database, or other data structure), ascertaining, etc. Furthermore, "determining" may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory), obtaining, etc. Furthermore, "determining" may include resolving, selecting, choosing, establishing, etc.

[0094] In this specification, reference is made to various examples. The description of features or functions associated with an example indicates that these features or functions are present in the example. Whether explicitly stated or not, the use of the term "example" or "for example" or "may" or "might" in the text indicates that these features or functions are at least present in the described example, regardless of whether they are described as examples, and they may but not necessarily be present in some or all other examples. Therefore, "example", "for example", "may" or "might" refers to a specific instance in an example class. The attributes of an instance may be attributes of only the instance, or attributes of the class, or attributes of a subclass of the class, which includes some but not all instances in the class. Therefore, it is implicitly disclosed that the features described with reference to one example rather than with reference to another example may be used in the other examples as part of an effective combination where possible, but do not necessarily have to be used in the other examples.

[0095] Although the examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims.

[0096] Features described in the preceding description may be used in combinations other than the combinations explicitly described above.

[0097] Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

[0098] Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not.

[0099] As used herein, the terms "a", "an", or "the" have an inclusive rather than exclusive meaning. That is, any reference to X that includes a / an / the Y indicates that X may include only one Y or may include multiple Ys, unless the context clearly indicates otherwise. If "a", "an", or "the" is to be used to indicate an exclusive meaning, it should be clearly stated in the context. In some cases, "at least one" or "one or more" may be used to emphasize the inclusive meaning, but the absence of the use of these terms should not be considered to imply an exclusive meaning.

[0100] The presence of a feature (or combination of features) in a claim refers to the feature or (combination of features) itself, and also to features that achieve substantially the same technical effect (equivalent features). Equivalent features include, for example, features that are variants, achieving substantially the same result in substantially the same way. Equivalent features include, for example, features that perform substantially the same function in substantially the same way to achieve substantially the same result.

[0101] In this specification, reference is made to various examples using adjectives or adjective phrases to describe example features. Such descriptions of characteristics associated with examples indicate that the characteristics are identical to the described in some examples and substantially the same as the described in other examples.

[0102] The above description describes some examples of the present disclosure, however, those skilled in the art will be aware of possible alternative structures and method features that provide equivalent functionality to the specific examples of the above structures and features, and have been omitted from the above description for the sake of brevity and clarity. Nevertheless, the above description should be understood to implicitly include references to such alternative structures and method features that provide equivalent functionality, unless such alternative structures or method features are explicitly excluded in the above description of examples of the present disclosure.

[0103] While efforts have been made in the foregoing description to call attention to those features regarded as important, it should be understood that the applicant may seek protection by way of claims for any patentable feature or combination of features mentioned above and / or shown in the drawings, whether or not emphasis has been placed thereon.

Claims

1. A device comprising: Main reflector; as well as A feeding device, the feeding device comprising: a multi-band waveguide feed comprising a first waveguide feed for a first frequency band and a second waveguide feed for a second frequency band separate from the first frequency band, wherein the first waveguide feed and the second waveguide feed are coaxial and have a first aperture and a second aperture, respectively; as well as A sub-reflector is configured as a feed for the main reflector, the sub-reflector comprising at least one generally concave hyperbolic reflective surface.

2. The apparatus of claim 1, wherein the hyperbolic reflective surface has a shape that can be formed by rotating a hyperbola about a symmetric aiming axis of the main reflector.

3. An apparatus according to any one of the preceding claims, wherein the generally concave hyperbolic reflective surface has a shape optimized to provide a phase center located at the focus of the primary reflector.

4. An apparatus according to any of the preceding claims, wherein the main reflector comprises a generally concave parabolic reflective surface having a ring focus, wherein the generally concave hyperbolic reflective surface has a shape optimized to provide a phase center trajectory along the ring focus of the main reflector.

5. The device according to any of the preceding claims, wherein the sub-reflector comprises an outer surface with different annular recesses, wherein the outer surface and the annular recesses have a rotational symmetry around the aiming axis of the main reflector.

6. The apparatus of claim 5, wherein the sub-reflector comprises a first external conductive surface positioned farther from the main reflector than the generally concave hyperbolic reflective surface and having one or more distinct first annular recesses having rotational symmetry about an aiming axis of the main reflector.

7. A device according to claim 5 or 6, wherein the sub-reflector includes an external dielectric surface, which is positioned closer to the main reflector than the one or more different first annular recesses, and has one or more different second annular recesses, which have rotational symmetry around the aiming axis of the main reflector.

8. The device according to claims 6 and 7, wherein the first different annular recess is a deep recess having a depth greater than its width, and the second different annular recess is a shallow recess having a depth less than its width.

9. The apparatus of claim 5, 6, 7, or 8, wherein a size of the notch is optimized to maximize a linear electric field at the first frequency band, wherein the first frequency band is a lower frequency band than the second frequency band.

10. A device according to any of the preceding claims, wherein the generally concave hyperbolic reflective surface forms a front surface of an air-filled dielectric channel, wherein the air dielectric channel widens to an opening along a radial direction from the line of sight of the main reflector, wherein the opening of the channel is short-circuited by a dielectric material having a relative dielectric constant greater than 2. The device of claim 10 , wherein the dielectric material has a variable thickness.

12. The apparatus of any one of the preceding claims, wherein the second waveguide feed is a higher frequency feed and the first waveguide feed is a lower frequency feed, wherein the second waveguide feed is generally cylindrical and is an inner waveguide feed positioned within and coaxial with the outer first waveguide.

13. A device according to any one of the preceding claims, wherein the first waveguide comprises a constricted neck adjacent to the first aperture.

14. An apparatus according to any preceding claim, wherein the first waveguide feed supports a lower frequency coaxial TE11 mode for both polarizations and the second waveguide feed supports a higher frequency circular TE11 mode for both polarizations.

15. An apparatus according to any preceding claim, wherein the first waveguide feed is dimensioned to transmit radio waves at a frequency less than 25 GHz and the second waveguide feed is dimensioned to transmit radio waves at a frequency greater than 30 GHz.

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