Patent Publication Number: US-10770784-B2

Title: Antenna radome with absorbers

Description:
This application claims the benefit of the filing date of U.S. Provisional Application No. 62/086,494 filed on Dec. 2, 2014, the teachings of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     Field 
     The current disclosure relates to antennas and particularly, although not exclusively, to radomes for antennas. 
     Description of the Related Art 
     Microwave dish antennas, used for transmission of electromagnetic-radiation signals, are typically outfitted with an antenna shield and a radome for outdoor operation. The antenna shield functions to attenuate side-lobe and back-lobe radiation from the antenna, which may be required to avoid interference with other antennas and/or for regulatory compliance. Side lobes and back lobes refer to undesirable portions of an antenna&#39;s radiation pattern directed away from the forward direction—as opposed to the main lobe, which is the desired portion of the radiation pattern and is directed in the intended forward direction. The radome, meanwhile, provides environmental protection for the antenna from potential hazards such as rain, snow, ice, dirt, wind, and animals. 
       FIG. 1  is a top view of a conventional antenna assembly  100  including mount  101  for mounting the antenna assembly  100  on a pole (not shown), reflector dish  102  attached to the mount  101 , cylindrical shield  103  mounted on the rim  104  of the dish  102 , and radome  105  mounted on the outer rim  106  of the shield  103 . The forward transmission direction for antenna assembly  100  is indicated by the arrow  107 . The dish reflector  102  is a parabolic reflector that reflects the radiation generated by a radiating element, horn, or other feed element (not shown) located at the focus of the parabolic dish  102 . 
     Cylindrical shield  103  comprises a metallic material on its exterior, exposed surface, and a microwave-absorbent material (not shown) on its interior surface facing the reflector  102  and its corresponding feed element. The combination of the absorbent material and the reflective metal works to minimize unwanted side-lobe and back-lobe radiation from the antenna assembly  100 . 
     Conventional radomes, such as radome  105 , may be made of a polymer fabric, or other suitable material, since conventional radomes are typically designed to be thin, lightweight, resistant to environmental degradation, and minimally interfering with microwave radiation. Radome  105  is stretched taut over the aperture of the shield  103  to, for example and among other reasons, minimize vibration of the antenna assembly  100  in windy conditions. 
     Note that some dish antennas are outfitted with only a radome and no shield, where the radome is mounted directly on the rim of the dish antenna, thereby covering the antenna aperture, but those antennas tend to have less-effective attenuation of side lobes and back lobes than shielded antennas. 
       FIG. 2  is a perspective view of a conventional antenna assembly  200  comprising a dish reflector  201  outfitted with a radome  202  and no shield. The forward direction of transmission is indicated by the arrow  204 . Two semi-circular clamps  203 , located about the rim of the dish  201 , hold the radome  202  in place. The clamps  203  may include a layer of radio-frequency-absorbing material in order to improve operational characteristics. Additional elements may further improve operational characteristics. 
     SUMMARY 
     One embodiment of the disclosure can be a radome for mounting on an aperture of a radio-frequency (RF) antenna. The radome comprises a bulk material and a set of one or more absorbers (i) comprising an RF-absorbent material different from the bulk material and (ii) at least partially embedded in the bulk material. The set of one or more absorbers is adapted to attenuate side-lobe and back-lobe radiation from the antenna. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other aspects, features, and advantages of the invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings in which like reference numerals identify similar or identical elements. Note that elements in the figures are not drawn to scale. 
         FIG. 1  is a top view of a conventional antenna assembly including a mount, a reflector dish, a cylindrical shield, and a radome. 
         FIG. 2  is a perspective view of a conventional antenna assembly comprising a dish reflector outfitted with a radome and no shield. 
         FIG. 3A  is a back view of a radome in accordance with one embodiment of the disclosure. 
         FIG. 3B  is a cross-sectional top view of the radome of  FIG. 3A . 
         FIG. 3C  is an enlargement of the detail area of  FIG. 3B ,  FIG. 3E  is an enlargement of the detail area of  FIG. 3B  in accordance with an embodiment of the disclosure, and  FIG. 3F  is an enlargement of the detail area of  FIG. 3B  in accordance with an embodiment of the disclosure. 
         FIG. 3D  is a perspective view of the radome of  FIG. 3A . 
     
    
    
     DETAILED DESCRIPTION 
     Detailed illustrative embodiments of the present invention are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments of the present invention. Embodiments of the present invention may be embodied in many alternative forms and should not be construed as limited to only the embodiments set forth herein. Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the 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 further will be understood that the terms “comprises,” “comprising,” “has,” “having,” “includes,” and/or “including” specify the presence of stated features, steps, or components, but do not preclude the presence or addition of one or more other features, steps, or components. It also should be noted that, in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. 
     In one embodiment, absorbers are integrated into a non-absorbent radome that can be mounted directly on a reflector antenna dish and which can attenuate side-lobe and back-lobe radiation without the use of a shield. 
       FIG. 3A  is a back view of a radome  300  in accordance with one embodiment of the disclosure.  FIG. 3B  is a cross-sectional top view of the radome  300  of  FIG. 3A  along line A-A.  FIG. 3C  is an enlargement of detail area  301  of  FIG. 3B .  FIG. 3D  is a perspective view of radome  300  of  FIG. 3A . Note that the radome  300  may be used in place of the radome  202  in the antenna assembly  200  of  FIG. 2 , where the radome  300  may be mounted directly on the dish  201 —with or without the semi-circular clamps  203 . 
     Radome  300  is substantially disc-shaped and designed for mounting on a corresponding dish antenna (not shown), such as, for example, conventional dish  102  of  FIG. 1  or conventional dish  201  of  FIG. 2 , where a perimeter  302  of the radome  300  would mount on or in the corresponding rim of the dish—such as, for example, rim  104  of dish  102 . The forward direction of transmission for the corresponding antenna is represented by the arrow  303  of  FIG. 3B . The radome  300  has an interior surface  304 , which is also called the signal surface since it is the side facing the corresponding reflector antenna. The interior surface  304  is flat. Note, however, that in alternative embodiments, the interior surface  304  may be curved, ridged, or otherwise non-flat. 
     Radome  300  has an exterior surface  305  which faces away from the corresponding reflector antenna—in other words, opposite to the interior surface  304 . Note that the perimeter  302  is a surface that connects the interior surface  304  to the exterior surface  305 . The exterior surface  305  is slightly convex. Note, however, that in alternative embodiments, exterior surface  305  may be flat or curved differently from the embodiment shown. Specifically, the curvature may be concave, ridged, grooved, or the curvature may be otherwise non-convex. The radome  300  has a notch  306  at the interface of the exterior surface  305  and the circumferential perimeter  302  in order to fit the radome  300  securely and/or properly to the rim of the corresponding antenna and/or a corresponding circular clamp (not shown), such as the clamp  203  of  FIG. 2 . In alternative embodiments, other notches, grooves, or recesses may be located on or near the circumferential perimeter  302 . 
     The bulk  307  of the radome  300  may comprise a lightweight material, such as, for example, expanded polystyrene or extruded polystyrene foam, that is minimally absorbent of—in other words, largely transparent to—microwave radiation. As seen in  FIG. 3E , exterior surface  305  may include a protective coating  315  comprising a harder and/or moisture-resistant material, such as, for example, epoxy or other polymer film, in order to provide superior physical protection to the radome  300  and the corresponding antenna. Note that the bulk material  307  and the protective material  315  should be formulated and shaped so as to minimize negative impact on the transmission efficacy of the corresponding antenna. In other words, the bulk material  307  and the protective coating  315  should be substantially transparent to RF signals over the relevant frequency range. Note that one should, nevertheless, preferably account for any reflection and absorption of radiation by the radome  300  across the intended transmission frequencies for the antenna assembly incorporating the radome  300  and the corresponding antenna. 
     Radome  300  comprises absorbers  308 ( 1 ) and  308 ( 2 ). The absorbers  308  comprise a radio-frequency(RF)-absorbing material such as, for example, a carbon-loaded foam. One example of a carbon-loaded foam is Eccosorb HR foam from Emerson &amp; Cuming Microwave Products N.V. of Geel, Belgium. Eccosorb HR foam—which is based on a reticulated (open-cell) polyurethane foam material impregnated with carbon black dispersions with controlled conductivity—is electrically conductive, and operates in the 5-70 GHz frequency range. Each absorber  308  may also include a metallic foil (not shown) on its exterior side  309  for improved absorption. Absorbers  308  may alternatively comprise flexible elastomers, rigid epoxy, and/or plastics. 
     The absorbers  308  are arranged near the perimeter  302 —or outer rim—of the radome  300 . Specifically, the absorbers  308  are located between a halfway point  312  from the center  311  and the perimeter  302 . Note, however, that, in alternative embodiments, the absorbers  308  may extend out to the perimeter  302  of the radome  300  or may extend inward past the halfway point  312 . The absorbers  308  are symmetrically arranged along and about the principle plane—also called the azimuth axis—of the radome  300 , where the principle plane corresponds to the line A-A in  FIG. 3A . In other words, the absorbers  308  are symmetric about the principle plane and about the center  311  of the radome  300 . Note, however, that in alternative embodiments, the absorbers  308  may be differently arranged about the center  311  and/or the principle axis. Note, also, that, in alternative embodiments, the radome  300  may comprise a different number of absorbers  308 . 
     Absorbers  308  are substantially quadrant-like or wedge-like in shape, with the apex  313  of the absorber  308  pointing towards the center  311 . Note, however, that in alternative embodiments, the absorbers  308  may have different shapes. In these alternative embodiments, the absorbers should be shaped and sized to sufficiently attenuate side-lobe and/or back-lobe radiation without excessively attenuating the antenna gain. In some embodiments, the area of the antenna aperture (and, consequently, of the radome) that is covered by absorbers  308  is 4-8% of the total area of the aperture. In some embodiments, a particularly useful balance between desired side-lobe and back-lobe attenuation and antenna-gain reduction may be achieved by using a coverage area of 5-7% of the total aperture/radome area. 
     The absorbers  308  are located inside correspondingly shaped recesses in radome  300 . The absorbers  308  may be secured in place using only friction or may be attached to the bulk material  307  using an adhesive (not shown) or mechanical fasteners (not shown). The interior surface  310  of each absorber  308  may be substantially flush with the interior surface  304  of the radome  300 . Note, however, that in alternative embodiments, one example of which is shown in  FIG. 3F , the interior surface  310  of one or more absorbers  308  may extend beyond or lie inside of the radome&#39;s interior surface  304 . In some alternative embodiments, the absorbers  308  may be embedded within the bulk material  307  of the radome  300 . 
     The absorbers  308  may have a substantially uniform thickness as seen in the cross-sectional view of  FIG. 3B . Note, however, that in alternative embodiments, the absorbers  308  have a variable thickness. The recesses for absorbers  308  are shown as partial recesses on the interior surface  304 . Note, however, that in some alternative embodiments, the recesses—and, optionally, the absorbers  308 —may extend out to the exterior surface  305  of the radome  300  so that the absorbers  308  may be flush with the exterior surface  305 —or may even extend beyond the exterior surface  305 . Note that, in the various above-described embodiments, the absorbers  308  may be considered to be at least partially embedded in the bulk material  307 . 
     As noted above, unwanted side lobes and back lobes, which may degrade antenna performance, are caused by electromagnetic energy transmitted in a direction different from the forward transmission direction and in particular over the periphery of the dish. The absorbers  308 , placed at the periphery of the dish, comprise carbon-loaded material with RF-absorbent and electrically conductive properties, and those properties cause gradual reduction (attenuation) of the energy penetrating the absorbers, thereby reducing the energy transmitted over the periphery of the dish and forming the side lobes and back lobes. 
     Embodiments of the disclosure have been described where the radome  300  is circular and adapted for mounting on a dish antenna having a corresponding circular aperture. Note, however, that the invention is not so limited and that, in alternative embodiments, the radome may have a non-circular shape and be adapted for mounting on an antenna with a corresponding non-circular aperture. Such apertures may be, for example, oval or rectangular. 
     In certain embodiments of the disclosure, an antenna assembly comprises a reflector antenna whose aperture is covered by a radome. The radome has a principle plane corresponding to the azimuth axis of the antenna. The radome comprises a bulk material and one or more absorbers comprising an RF-absorbent material different from the bulk material. The absorbers may be arranged along the principle plane and near the perimeter of the radome. The absorbers may cover from 4%-8% of the total aperture area of the antenna. 
     Other embodiments of the disclosure may be the radomes for such antenna assemblies, where each radome comprises at least one absorber. 
     It will be understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of this invention may be made by those skilled in the art without departing from the scope of the invention as expressed in the following claims. 
     Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.” 
     Unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word “about” or “approximately” preceded the value of the value or range. As used in this application, unless otherwise explicitly indicated, the term “connected” is intended to cover both direct and indirect connections between elements. 
     For purposes of this description, the terms “couple,” “coupling,” “coupled,” “connect,” “connecting,” or “connected” refer to any manner known in the art or later developed in which energy is allowed to be transferred between two or more elements, and the interposition of one or more additional elements is contemplated, although not required. The terms “directly coupled,” “directly connected,” etc., imply that the connected elements are either contiguous or connected via a conductor for the transferred energy. 
     The use of figure numbers and/or figure reference labels in the claims is intended to identify one or more possible embodiments of the claimed subject matter in order to facilitate the interpretation of the claims. Such use is not to be construed as limiting the scope of those claims to the embodiments shown in the corresponding figures. 
     The embodiments covered by the claims in this application are limited to embodiments that (1) are enabled by this specification and (2) correspond to statutory subject matter. Non-enabled embodiments and embodiments that correspond to non-statutory subject matter are explicitly disclaimed even if they fall within the scope of the claims. 
     Although the steps in the following method claims are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those steps, those steps are not necessarily intended to be limited to being implemented in that particular sequence.