Patent Grant
12341250
Antenna apparatuses are used in a variety of different technical fields, including communications, radar, etc. Within these different technical fields, antenna apparatuses are employed in several different applications. For example, a radar system that includes an antenna apparatus can be coupled to an aerial vehicle (e.g., an airplane, a drone, etc.), a ground vehicle (automobile, bus, freight-carrying truck), spacecraft, or watercraft. The output of the radar system can be employed in connection with determining the location and/or closing velocity of an external object, or even the location of the vehicle with respect to known external features. In another example, an antenna apparatus can be employed in connection with transmitting communications to a receiver and/or receiving communications from a transmitter.
Regardless of the technical field or application associated with an antenna apparatus, the antenna apparatus must meet a wide variety of electrical, mechanical, thermal, radiation, and (sometimes) aerodynamic specifications. Example electrical specifications include specifications for gain, beamwidth, and sidelobe level performance, where each of these specifications are to be met while meeting other constraints, which can relate to the use of specific materials (to survive extreme thermal and time-varying environmental conditions), size and weight requirements for the antenna apparatus, and so forth. With respect to antenna apparatuses of systems that are operated in harsh environments, existing antenna apparatuses can meet the electrical specifications but fail to meet requirements associated with materials, form factor, and resiliency that are necessary for the antenna apparatus to operate effectively and consistently in the harsh environments.
The following is a brief summary of subject matter that is described in greater detail herein. This summary is not intended to be limiting as to the scope of the claims.
Described herein are technologies related to an antenna apparatus. The antenna apparatus includes an array of reflector elements, where reflector elements in the array include curved (parabolic) reflector surfaces that are delimited by planar surfaces. The reflector elements in the array can optionally be arranged radially or in parallel with one another and have a same or similar size and shape.
With more particularity, a reflector element in the array is formed from a pair of metallic parallel (planar) plates and a curved reflector surface positioned at a periphery of the parallel plates and between the parallel plates. This arrangement forms a nonresonant waveguide cavity, where the nonresonant waveguide cavity is partially bounded by the curved reflector surface and is further bounded by the parallel metallic planar plates arranged on either side of the reflector surface along a width of the reflector surface. The width of the reflector surface is relatively small, such that the reflector element appears planar. The waveguide cavity is nonresonant, serving to guide the electromagnetic wave and provide space for wavefront collimation to occur. The reflector element further includes an aperture that opposes the reflector surface in the reflector element, where electromagnetic signals exit the reflector element by way of the aperture. The nonresonant waveguide cavity is partially populated with a dielectric window at the aperture, where the dielectric window is included in the reflector element to enhance robustness of the antenna element in hazardous environmental conditions. The nonresonant waveguide cavity can also be partially populated with air or vacuum (which are approximately lossless with respect to electromagnetic signals traveling through the nonresonant waveguide cavity). The aperture can be curved or straight, with a design depending upon an application of the antenna apparatus.
In an example, the reflector element is an offset reflector element. The reflector element includes a waveguide feed, where the waveguide feed is positioned such that an electromagnetic signal enters the nonresonant waveguide cavity in parallel with the planar surfaces that delimit the reflector surface. Positioning of the waveguide feed in the plane of the reflector element (such that the feed is in plane with the predominant extent of the reflector element) rather than out of the plane of the reflector element allows for the reflector elements in the array to be positioned very close to one another (thereby suppressing grating lobes of the antenna radiation pattern associated with the antenna array).
The antenna array is conformal and includes several reflector elements (that are identical or similar in size and shape) arranged in parallel with one another. For example, the antenna apparatus can include two reflector elements, four reflector elements, eight reflector elements, 16 reflector elements, or 32 reflector elements. Additionally, an antenna waveguide feed architecture described herein supports non-equal energy splits that enable amplitude tapering (such as for sidelobe control) or non-binary reflector element counts. The antenna apparatus described herein exhibits various advantages over conventional antenna apparatuses, including improved pattern gain and radiation efficiency relative to conventional antenna apparatuses, a lower geometric cross-section compared to conventional antenna apparatuses, and better dispersion characteristics relative to conventional antenna apparatuses, amongst others.
The antenna apparatus also optionally includes a feed network that supports the conformal antenna array referenced above. In an example, the feed network is a splitter network capable of half wavelength spacing between waveguide split ports for antenna arrays. The feed network described herein can include both “T” and “Y” splitters, where waveguide segments between splitters may span distances required by the split port pitch as the splitter network gets larger and not have an impedance matching function. Alternatively, overall impedance bandwidth of the waveguide splitter can be increased by employing known impedance matching techniques between splitters. The last splitter in the feed network is a “Y” splitter where the branch paths of the splitter are parallel to each other so that the feed network can be compact compared to “T” networks where the waveguides emanate from a common point in opposite directions.
Although the antenna apparatus may be fed using a fixed feed network, as described herein, it is also possible to couple one or more antenna elements with separate transmit modules which enable independent control of signals across the antenna apparatus. These transmit modules may be replaced by receive modules or transmit/receive modules.
The above summary presents a simplified summary in order to provide a basic understanding of some aspects of the systems and/or methods discussed herein. This summary is not an extensive overview of the systems and/or methods discussed herein. It is not intended to identify key/critical elements or to delineate the scope of such systems and/or methods. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.
Various technologies pertaining to an antenna apparatus that is well-suited for use in harsh environments (as part of a radar system, a communications system, or the like) are now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects. It may be evident, however, that such aspect(s) may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing one or more aspects. Further, it is to be understood that functionality that is described as being carried out by certain system components may be performed by multiple components. Similarly, for instance, a component may be configured to perform functionality that is described as being carried out by multiple components.
Moreover, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise, or clear from the context, the phrase “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, the phrase “X employs A or B” is satisfied by any of the following instances: X employs A; X employs B; or X employs both A and B. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from the context to be directed to a singular form.
Note that the antenna element, antenna array, and feed networks described herein are reciprocal devices. Although an antenna may be described as having a signal incident upon the feed structure and radiated from the antenna or antenna array, it is also possible to have an electromagnetic field incident upon the antenna or antenna array and the received signal be propagated to the feed structure.
Various technologies pertaining to an antenna apparatus are described herein. The antenna apparatus includes an array of reflector elements, where each reflector element has a curved (parabolic) reflector surface. The curved reflector surface has a width that is delimited by planar surfaces that extend orthogonally from the reflector surface on both sides of the reflector surface and along a length of the reflector surface. The width of the reflector surface is relatively small, such that the reflector element appears to be planar. The array of reflector elements includes several reflector elements arranged in parallel, where the array of reflector elements is conformal. The antenna apparatus also optionally includes a feed network that simultaneously directs electromagnetic signals into waveguide cavities of the reflector elements in the array of reflector elements. The architectures of the antenna array and the feed network allow for the antenna apparatus to meet electrical specifications (such as gain, beamwidth, and sidelobe level performance specifications) while also meeting specifications associated with an environment in which the antenna apparatus is to be deployed (specifications as to materials, size, weight requirements, etc.).
With reference now to
The antenna apparatus 100 additionally includes a ground plane 108 that is coupled to the reflector elements 102-106 near the aperture surfaces of the reflector elements 102-106. While not illustrated in
The reflector elements 102-106 include feeds 110-114. The feeds 110-114 are positioned on the support surfaces and relative to the reflector surfaces of the reflector elements 102-106 such that the reflector elements 102-106 are offset reflectors. Electromagnetic signals are directed into the waveguide cavities of the reflector elements 102-106 and towards the reflector surfaces of the reflector elements by way of the feeds 110-114, respectively. The feeds 110-114 are positioned on the structural surfaces of the reflector elements 102-106, respectively, such that electromagnetic signals are injected into the waveguide cavities of the reflector elements 102-106 in parallel with the planar surfaces, which are orthogonal to the reflector surfaces and the support surfaces. The placement of the feeds 110-114 on the support surfaces (rather than on the planar surfaces) allows for the reflector elements 102-106 to be positioned close to one another and in parallel with one another, as space is not needed between adjacent reflector elements in the array to accommodate feeds that would otherwise be positioned between reflector elements.
The antenna apparatus 100 additionally optionally includes a feed network 116 that is coupled to the reflector elements 102-106 by way of the feeds 110-114. The feed network 116 can be a splitter that receives an electromagnetic signal and splits the electromagnetic signal amongst the feeds 110-114. The feed network 116 is relatively compact, as the reflector elements 102-106 are placed in parallel with one another and in close proximity to one another. Furthermore, in an example, the feed network 116 can be a one-dimensional feed network.
In operation, an electromagnetic signal is provided to the feed network 116, which splits the electromagnetic signal and directs resultant electromagnetic signals to the feeds 110-114 of the reflector elements 102-106. The reflective surfaces of the reflector elements 102-106 reflect the electromagnetic signals through the apertures of the reflective elements 102-106, and the antenna apparatus 100 emits an electromagnetic signal based upon the reflected signals.
There are various advantages associated with the antenna apparatus 100 over conventional antenna apparatuses. The planar topology of the reflector elements 102-106 and the feeds 110-114 allow for the reflector elements 102-106 to be arrayed with relatively close spacing (less than half of a wavelength of radiation emitted by the reflector elements) for grating lobe suppression over a scan. Furthermore, placement of the feeds 110-114 on the support surfaces of the reflector elements 102-106 (rather than upon the planar surfaces of the reflector elements 102-106) allows for ready integration with the feed network 116, which, as noted above, may be one-dimensional. More specifically, arrayed aperture illumination is obtained with a one-dimensional feed, given the aspect ratio of the apertures, thereby reducing complexity of the feed network 116. In addition, the offset reflector feed configuration in the parallel plate waveguide topology eliminates feed blockage, thereby enabling larger bandwidths and lower sidelobe levels when compared to non-offset feed approaches. Moreover, the reflector surface can be parabolic or have another curved shape to control antenna pattern sidelobe performance. Other advantages will be discussed below.
Referring now to
A dielectric window 210 partially populates the nonresonant waveguide cavity and defines the boundary of the aperture 204 of the reflector element 200. The nonresonant waveguide cavity can also be partially populated with air, vacuum, or an alternative material with a low dielectric constant (e.g., aerogel). The reflector element 200 further includes a feed 212 that extends from the support surface 206, where the feed 212 can be a single ridge waveguide feed incorporating a single ridge 214. Compared to a standard rectangular waveguide, the ridge waveguide has a lower cutoff frequency allowing the geometric cross-section to be reduced. The cutoff frequencies of the higher order modes are also increased, allowing the reflector element 200 to be operated with better dispersion characteristics. An inductive iris 215 is used to impedance match the feed 212 to the nonresonant waveguide cavity.
An end launched coaxial-to-waveguide transition 216 is used to excite the ridge waveguide feed 212. The end launched coaxial-to-waveguide transition 216 is centered in the waveguide and the top of the coaxial probe is shorted to the waveguide wall forming a loop—the loop magnetically couples energy into the fundamental waveguide mode. A section of standard, non-ridged waveguide impedance matches the end launched coaxial-to-waveguide transition 216 to the ridge waveguide feed 212.
To minimize direct aperture illumination, the focal length of the reflector surface 202 is typically between 0.75 and 1.5 guided wavelengths. The dielectric window 210 can be used at the aperture 204 to maintain aerodynamic requirements. The aperture 204 can be curved to conform to a conical or cylindrical platform (as shown in
The depth of the dielectric window 210 along with a capacitive diaphragm 218 across the bottom of the dielectric window 210 forms a single section impedance matching network that minimizes aperture reflections. The aperture impedance is first transformed by the dielectric window 210, which forms a transmission line with a length equal to the depth of the dielectric forming the dielectric window 210. The impedance is then further transformed by the capacitive diaphragm 218 which provides a capacitive admittance. The depth of the dielectric window 210 and the capacitive diaphragm 218 can be tuned to impedance match the aperture. Increased bandwidth can be obtained by moving the capacitive diaphragm 218 closer to the aperture 204. In some embodiments, however, it may be desirable to sacrifice bandwidth to keep the capacitive diaphragm 218 away from the aperture 204, which simplifies manufacturability and improves survivability of the dielectric window 210 in a harsh environment.
Now turning to
As depicted in
Referring now to
The reflector elements 402-416 include respective dielectric windows 418-432 that partially populate the waveguide cavities of the reflector elements 402-416 and extend from the waveguide cavities of the reflector elements 402-416 to define the apertures of the reflector elements 402-416. Note that due to the flexibility of the invention, the radius of curvature of the dielectric windows 418-432, and corresponding apertures, are not constrained. For example, within the array of reflector elements 400, the radius of curvature may be different for each of the dielectric windows 418-432, thereby permitting a conical conformal surface. Further, it can be noted that although the coaxial-to-waveguide transition 216, is shown in
While
Note that although subsequent figures describe feed networks for a linear antenna array, it is possible to feed the reflector elements individually, such as with transmit/receive modules that allow electronic scanning from such antenna arrays.
Rectangular metal waveguides, such as may be used for the connecting waveguides 706, have two basic dimensions that are normal to the direction of propagation of energy through waveguide. There is a broad wall and a narrow wall. For the fundamental mode of propagation (TE10 in a standard waveguide), the electric fields are oriented normal to the broad walls (parallel to the narrow walls). There are standard waveguide sizes, and the narrow wall is commonly half as tall as the broad wall. For a common rectangular waveguide, the length of the broad wall primarily sets the cutoff frequency of the waveguide.
For a single-ridge (or double-ridge) waveguide, the broad wall dimension can be made smaller by the capacitive loading effect of the ridge (or ridges) within the waveguide. As the capacitive gap between the ridge and the opposite wall of the waveguide (or the opposite ridge in the case of dual-ridge waveguide) decreases, the capacitive loading of the waveguide increases and the cutoff frequency decreases. Decreasing this to a very small gap increases the manufacturing sensitivities. By using a single-ridge waveguide, overall cross-sectional area of the inside of the waveguide can be decreased to 25% of its standard area and high manufacturability can be maintained. This decrease in cross-sectional area is equivalent to dielectric loading of a waveguide with a dielectric having a relative permittivity of 4.
With waveguides, there are two basic types of splitter networks—E-plane splitters and H-plane splitters. When the waveguide is operated in its fundamental mode, the “E” and “H” refer to whether the split happens parallel to the direction of the electric field (H-plane splitter) or perpendicular to the direction of the electric field (E-plane splitter). For an H-plane splitter, the electric field vector at the ports is generally oriented in the same direction for all three ports. One of the basic characteristics of an E-plane splitter is that the phase at the two split ports is often 180-degrees out of phase (if the electrical lengths of the split-port paths are equal). For a nominal E-plane splitter, the electric field vector of the common and split ports will not be oriented in the same plane. Alternatively, the energy at the split ports of an H-plane splitter is in phase if the lengths of the split port paths are equal and the energy is split 50% to each branch. The splitters used in the feed network 116 can be E-plane splitters.
For E-plane splitters, there are two splitter network topologies, which are referred to herein as T splitters and Y splitters (704 and 702 in
In the feed network 116, the last splitter is a Y splitter so that the feed network can be compact compared to networks where the waveguides emanate from a common point in opposite directions. The E-plane splitters have opposite phases at each split ports. However, by shaping the T-junction into a Y configuration, the field polarization is rotated in space, such that the field polarization is spatially the same at each antenna port, thereby correcting the out of phase fields from each E-plane split. By feeding the antenna ports in phase, the energy combines constructively in free space.
When non-equal power splits can be supported (and not simply equal splits), a few additional characteristics that can be supported by feed network 116 include the following: 1) non-binary split networks can be supported (e.g., a 12-way splitter); and 2) amplitude tapering can be supported (e.g., unequal power distribution at the split ports supporting a Taylor taper or another amplitude taper supporting sidelobe reduction of an antenna pattern).
A few different methods of assembly are possible using this splitter feed network topology. The different pieces need to be aligned. This can be done with holes machined in each piece and pins that fit in the holes. This can also be done by precision machining the outer walls of the pieces and using flats to align the pieces. The pieces can have compression between the different layers, which can be accomplished by clamping the pieces together (such as with bolts and nuts). Further, this can be done using an adhesive such as a conductive epoxy or solder. Such an epoxy can be applied as a preform, using a stamping process, using a stencil, or otherwise.
Although the images and the text describe fabricating these pieces using standard machining with end mills, other alternatives exist. The through holes can be cut using waterjet. Both the through holes and routing of channels in the parts can be fabricated using electrical discharge machining (EDM), including plunge EDM for the channels that do not go through the part. With a process that can create parts with smaller corner radii than a common end mill, this can simplify the design process and be useful for higher frequency designs (such as for millimeter-wave frequencies).
Referring solely to
Now turning to
What has been described above includes examples of one or more embodiments. It is, of course, not possible to describe every conceivable modification and alteration of the above devices or methodologies for purposes of describing the aforementioned aspects, but one of ordinary skill in the art can recognize that many further modifications and permutations of various aspects are possible. Accordingly, the described aspects are intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims. Furthermore, to the extent that the term “includes” is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term “comprising” as “comprising” is interpreted when employed as a transitional word in a claim.
This invention was made with Government support under Contract No. DE-NA0003525 awarded by the United States Department of Energy/National Nuclear Security Administration. The Government has certain rights in the invention.
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| Number | Date | Country |
|---|---|---|
| 112952356 | Jun 2021 | CN |
| Entry |
|---|
| Translation of CN-112952356-A (Year: 2021). |
