Patent Application
20210376480
The present invention relates to dual reflector antennas utilizing deep dish or shallow dish parabolic reflectors and, more particularly, to dual reflector antennas having improved control of signal radiation pattern characteristics.
Dual reflector antennas employing self-supported feeds direct a received signal, which is incident on the main reflector, onto a sub-reflector mounted adjacent to the focal region of the main reflector, which in turn directs the signal into a waveguide transmission line typically via a feed horn or aperture to the first stage of a receiver. When the dual reflector antenna is used to transmit a signal, the signals travel from the last stage of the transmitter system, via the waveguide, to the feed aperture, sub-reflector, and main reflector to free space.
The electrical performance of a reflector antenna is typically characterized by its gain, radiation pattern, cross-polarization and return loss performance. Efficient gain, radiation pattern and cross-polarization characteristics may be important for efficient microwave link planning and coordination, while a good return loss may be important for efficient radio operation. The above characteristics are determined by a feed system designed in conjunction with the main reflector profile.
Deep dish reflectors are reflector dishes wherein the ratio of the reflector focal length (F) to reflector diameter (D) (i.e., F/D≤ratio) is made less than or equal to 0.25, whereas shallow dish reflectors have an F/D≤ratio of greater than 0.25. Such deep dish designs can achieve improved radiation pattern characteristics without the need for a separate shield assembly when used with a carefully designed feed system which provides controlled dish illumination, particularly toward the edge of the dish. In contrast, shallow dish reflectors may utilize shield assemblies to achieve improved radiation characteristics. Examples of shield assemblies are disclosed in commonly owned U.S. Pat. No. 8,581,795 to Simms et al. and U.S. Pat. No. 9,019,164 to Brandau et al., the disclosures of which are hereby incorporated herein by reference.
An example of a dielectric cone feed sub-reflector configured for use with a dual reflector antenna is disclosed in commonly owned U.S. Pat. No. 6,919,855 to Hills (“the '855 patent”), the disclosure of which is hereby incorporated herein by reference. As disclosed by the '855 patent, a dual reflector antenna may utilize a generally conical dielectric block cone feed with a sub-reflector surface and a leading cone surface having a plurality of downward angled non-periodic perturbations concentric about a longitudinal axis of the dielectric block. The cone feed and sub-reflector dimensions are made to be relatively small to reduce blockage of the signal path from the reflector dish to free space. Although a significant improvement over prior designs, such configurations have signal patterns in which the sub-reflector edge and distal edge of the feed boom radiate a portion of the signal broadly across the reflector dish surface, including areas proximate the reflector dish periphery and/or a shadow area of the sub-reflector where secondary reflections with the feed boom and/or sub-reflector may be generated, degrading electrical performance. Furthermore, the plurality of angled features and/or steps in the dielectric block typically require relatively complex manufacturing procedures which increase the overall manufacturing cost.
Therefore it is the object of the invention to provide apparatus that overcome limitations in the prior art, and in so doing present solutions that allow feed designs to provide enhanced reflector antenna characteristics, which meet stringent electrical specifications over the entire operating band used for typical wireless communication links (e.g., microwave).
Parabolic reflector antennas according to embodiments of the present invention advantageously support low side lobe radiation patterns for ETSI class 4 performance, by utilizing: (i) metal choke plates adjacent a distal end of a dielectric cone within a sub-reflector assembly, (ii) “lossy” material feed boom waveguide sleeves and/or (iii) extended length cylindrical shields lined with radiation absorbing materials. In some of embodiments of the invention, relatively shallow and large diameter parabolic reflectors having an F/D≤ratio of greater than about 0.25 may be provided with one or more of the identified (i)-(iii) enhancements, where “F” denotes reflector focal length and “D” denotes reflector diameter.
In some of these embodiments, a parabolic reflector antenna can be provided with: a dish reflector and a feed boom waveguide having a promixal end coupled to the dish reflector and a sub-reflector assembly coupled to a distal end of the feed boom waveguide. The sub-reflector assembly can include a dielectric block coupled to a distal end of the feed boom waveguide and a sub-reflector on a distal end of the dielectric block. A metal choke plate can also be provided, which may be coupled to the distal end of the dielectric block. This metal choke plate may have a maximum diameter equal to or greater than an outer diameter of the sub-reflector. In addition, the metal choke plate may have at least one annular-shaped groove therein, which is spaced longitudinally relative to the distal end of the dielectric block. The metal choke plate and the sub-reflector may be formed of different materials.
According to further embodiments of the invention, a radiation absorbing sleeve may be provided, which is wrapped around at least a majority of a length of the feed boom waveguide. This radiation absorbing sleeve may be formed of a material selected from a group consisting of foam, rubber, plastics and liquid-filled mediums, for example. In addition, the dielectric block may be formed to have a plurality of annular-shaped grooves therein that are spaced along a length of the dielectric block (as measured along a longitudinal axis of the dielectric block), whereas the metal choke plate may have a plurality of annular-shaped grooves, which are spaced radially outward relative to a longitudinal axis of the dielectric block. The metal choke plate may also have at least one annular-shaped groove that is spaced along the longitudinal axis of the dielectric block relative to the annular-shaped grooves in the dielectric block.
According to additional embodiments of the invention, the sub-reflector assembly is configured to redirect a feed signal transmitted along the feed boom waveguide into an RF transmission signal, which is directed from the sub-reflector to an interior concave surface of the parabolic dish reflector with a maximum signal intensity at an angle in a range between about 35 degrees and about 60 degrees for F/D≤ratios in a range from about 0.25 to about 0.4. This angle is measured between a longitudinal axis of the feed boom waveguide and a line extending from a focal point of the dish reflector and the interior concave surface of the dish reflector. According to preferred aspects of these embodiments of the invention, the sub-reflector assembly is further configured so that the RF transmission signal has a 3 dB “half-power” beamwidth in a range between about 25 degrees and about 35 degrees and a 10 dB beamwidth in a range between about 35 degrees and about 45 degrees, where the half-power beamwidth is the angle between the half-power (−3 dB) points of the main lobe, when referenced to the peak effective radiated power of the main lobe.
According to still further embodiments of the invention, the sub-reflector assembly can include a choke plate coupled to the distal end of the dielectric block, with the choke plate having a maximum diameter equal to or greater than an outer diameter of the sub-reflector. The choke plate may have at least one annular-shaped groove therein, which is spaced longitudinally relative to the distal end of the dielectric block. In particular, the dielectric block may have an annular-shaped groove therein at a first radius relative to a longitudinal axis of the feed boom waveguide and the choke plate may have an annular-shaped groove therein at a second radius relative to the longitudinal axis of the feed boom waveguide, which is greater than the first radius. The choke plate may also have a plurality of annular-shaped grooves therein, which are spaced radially (from each other) relative to the longitudinal axis of the dielectric block.
Additional embodiments of the invention may also include a parabolic reflector antenna containing a dish reflector and a feed boom waveguide having a promixal end coupled to an interior of the dish reflector. A cylindrically-shaped shield, which is coupled to a periphery of the dish reflector, is also provided. The shield has a distal peripheral edge (e.g., rim), which is sufficiently spaced from the periphery of the dish reflector so that a subtended angle between a longitudinal axis of the feed boom and a line extending from a focal point of the dish reflector to a point on the distal peripheral edge of the shield is about 50 degrees or less. According to preferred aspects of these embodiments of the invention, a radiation absorbing sleeve is also provided, which is wrapped around at least a majority of a length of the feed boom waveguide to thereby enhance the radiation patterns of the antenna. This radiation absorbing sleeve may include a material selected from a group consisting of foam, rubber, plastics and liquid-filled mediums. A sub-reflector assembly may also be provided, which includes: (i) a dielectric block coupled to a distal end of the feed boom waveguide, (ii) a sub-reflector on a distal end of the dielectric block; and (iii) a metal choke plate extending adjacent the sub-reflector. This metal choke plate, which may have a maximum diameter equal to or greater than an outer diameter of the sub-reflector, may contain at least one annular-shaped groove therein, which is spaced longitudinally relative to the distal end of the dielectric block. In particular, the dielectric block may have an annular-shaped groove therein at a first radius relative to a longitudinal axis of the feed boom waveguide and the metal choke plate may have an annular-shaped groove therein at a second radius relative to the longitudinal axis of the feed boom waveguide, which is greater than the first radius. The metal choke plate may also have a plurality of annular-shaped grooves therein, which are spaced radially relative to the longitudinal axis of the dielectric block. A radiation absorbing liner may also be provided on at least a portion of an interior surface of the cylindrically-shaped shield. This radiation absorbing liner may be provided as a foam absorbers, resonant rubber absorbers and “lossy” dielectric materials, etc.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, where like reference numbers in the drawing figures refer to the same feature or element and may not be described in detail for every drawing figure in which they appear and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention.
The present invention now will be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided 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 reference numerals refer to like elements throughout.
It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprising”, “including”, “having” and variants thereof, when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. In contrast, the term “consisting of” when used in this specification, specifies the stated features, steps, operations, elements, and/or components, and precludes additional features, steps, operations, elements and/or components.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
As will now be described herein, improvements in radiation pattern control and thus overall reflector antenna performance may be realized by reducing or minimizing the electrical effect of the feed boom end and sub-reflector overspill upon the radiation pattern of conventional dielectric cone sub-reflector assemblies, by providing reflector dish illumination that is spaced away from the vertex area of the reflector dish.
As shown in
A generally cylindrical dielectric radiator portion 25 situated between the waveguide transition portion 5 and a sub-reflector support portion 30 of the dielectric block 10 is also increased in size. The dielectric radiator portion 25 may be dimensioned, for example, with a minimum diameter of at least 3/5 of the sub-reflector diameter. The enlarged dielectric radiator portion 25 is operative to pull signal energy outward from the end of the waveguide 3, thus minimizing the diffraction at this area observed in conventional dielectric cone sub-reflector configurations, for example as shown in
A plurality of corrugations are provided along the outer diameter of the dielectric radiator portion as radial inward grooves 35. The radial inward grooves 35 may be provided perpendicular to a longitudinal axis of the dielectric block 10. In the present embodiment of
The waveguide transition portion 5 of the sub-reflector assembly 1 may be adapted to match a desired circular waveguide internal diameter so that the sub-reflector assembly 1 may be fitted into and retained by the feed boom waveguide 3 that supports the sub-reflector assembly 1 within the dish reflector 50 of the reflector antenna proximate a focal point of the dish reflector 50. The waveguide transition portion 5 may insert into the waveguide 3 until the end of the waveguide abuts a shoulder 55 of the waveguide transition portion 5.
The shoulder 55 may be dimensioned to space the dielectric radiator portion 25 away from the waveguide end and/or to further position the periphery of the distal end 20 (the farthest longitudinal distance of the sub-reflector signal surface from the waveguide end) at least 0.75 wavelengths of the desired operating frequency. The exemplary embodiment is dimensioned with a 14.48 mm longitudinal length, which at a desired operating frequency in the 22.4 GHz microwave band corresponds to 1.08 wavelengths. For comparison, the conventional dielectric cone of
As shown best by
When applied with an 0.167 F/D≤deep dish reflector 50, the sub-reflector assembly 1 provides surprising improvements in the signal pattern, particularly in the region between 10 and 45 degrees. For example, as shown in
In contrast,
The illumination of the concave inner surface of the dish reflector 50 by the exemplary controlled illumination cone radiator sub-reflector assembly 1 utilizing the enhanced dielectric radiator portion 25 results in dish reflector illumination wherein both the maximum signal intensity and the majority of dish reflector illumination, in general, are shifted outward along the dish reflector surface, away from the vertex area.
In addition, as shown by the dish reflector illumination amplitude charts of
For ease of demonstration,
One skilled in the art will appreciate that in the exemplary embodiments utilizing the dielectric radiator portion 25 the resulting illumination pattern forms an annular region of illumination intensity coaxial with the longitudinal axis of the waveguide, that is—in contrast with the prior art, there is minimal signal illumination (effectively a null) at the vertex area, one of the aspects of the invention which enables enlarged sub reflector diameters without introducing corresponding signal blockage.
The shifting of the dish reflector illumination outward from the vertex area is demonstrated in solutions for exemplary 0.168 and 0.25 F/D≤deep dish reflectors and sub-reflector assemblies in
One skilled in the art will appreciate that while additional shielding and/or radiation absorbing materials may be applied to assist with correction of the radiation pattern with respect to the vertex and/or sub-reflector spill-over regions, the reduction in these regions, along with the previously unobtainable 10 to 45 degree region radiation reduction has been obtained in the present example without any such additional structure. As this signal pattern improvement is made without absorbing the signal energy projected in unwanted directions by additional means, more of the signal energy is applied to the free space target, resulting in a 6% improved antenna efficiency measured by the inventor's software based models of the exemplary embodiment operating in the 22.4 GHz microwave band.
Where each of the shoulders 55, steps 60 and grooves 35 formed along the outer diameter of the unitary dielectric block are provided radially inward, manufacture of the dielectric block 10 may be simplified, reducing overall manufacturing costs. Dimensioning the periphery of the distal surface as normal to the longitudinal axis of the assembly provides a ready manufacturing reference surface 85, further simplifying the dielectric block 10 manufacture process, for example by machining and/or injection molding.
According to further embodiments of the invention, the unitary dielectric blocks 10 associated with the sub-reflector assemblies 1 of
Referring now to
Next, as shown by the sub-reflector assemblies 120c-120g of
Furthermore, as shown by
In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.
This application is a continuation-in-part (CIP) of U.S. application Ser. No. 16/640,161, filed Feb. 19, 2020, now U.S. patent Ser. No. ______, and a continuation-in-part (CIP) of U.S. application Ser. No. 16/649,294, filed Mar. 20, 2020, now U.S. patent Ser. No. ______, the disclosures of which are hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16640161 | Feb 2020 | US |
| Child | 17355517 | US | |
| Parent | 16649294 | Mar 2020 | US |
| Child | 16640161 | US |
