Patent Grant
10770785
Example embodiments generally relate to plasma antenna technology and, more particularly, relate to the provision of a plasma radome for use with an antenna to flexibly control the functioning of the antenna.
High speed data communications and the devices that enable such communications have become ubiquitous in modern society. These devices make many users capable of maintaining nearly continuous connectivity to the Internet and other communication networks. Although these high speed data connections are available through telephone lines, cable modems or other such devices that have a physical wired connection, wireless connections have revolutionized our ability to stay connected without sacrificing mobility.
Traditionally, antennas have been defined as metallic devices for radiating or receiving radio waves. The paradigm for antenna design has traditionally been focused on antenna geometry, physical dimensions, material selection, electrical coupling configurations, multi-array design, and/or electromagnetic waveform characteristics such as transmission wavelength, transmission efficiency, transmission waveform reflection, etc. As such, technology has advanced to provide many unique antenna designs for a wide range of applications.
More recently, some attention has been paid to the highly reconfigurable nature of plasma for use in and with antennas. In particular, plasma has the ability to turn on and off quickly, and can be extremely flexible in terms of rapid reconfiguration. Accordingly, for example, a plasma element can be configured to rapidly change characteristics that may impact the ability of the plasma element to transmit, receive, filter, reflect and/or refract radiation. Given the significant increases in flexibility and configurability that can be achieved using plasma, recent attention has been paid to improve antenna designs that employ plasma elements in one way or another.
Some example embodiments may therefore be provided in order to enable the provision of an antenna element whose radiating characteristics may be controlled in a very flexible way by the addition of a plasma radome proximate to the antenna element. The plasma radome may have a unique shape to prevent leakage around the plasma elements therein, but may also allow for flexible and intelligent control of the ionization of the plasma elements to allow the radiation pattern of the antenna element to be strategically controlled. Example embodiments may therefore provide for the use of a plasma radome in connection with an antenna element in a way that produces a highly flexible and configurable communication structure that can be implemented in a desired manner on the basis of requirements for specific missions or applications. With such a system, aircraft or other communication platforms can take full advantage of the unique attributes of plasma elements to improve flexibility and performance.
In one example embodiment, an antenna assembly is provided. The antenna assembly may include an antenna element, a radome structure disposed proximate to the antenna element and including a plurality of plasma elements, a driver circuit operably coupled to the plasma elements to selectively ionize individual ones of the plasma elements, and a controller. The controller may be operably coupled to the driver circuit to provide control of plasma density of the individual ones of the plasma elements. The plasma elements may include respective enclosures. At least some of the enclosures may have all peripheral edge surfaces substantially fully contacted by corresponding peripheral edge surfaces of adjacent enclosures at at least one section along a longitudinal length thereof.
In another example embodiment, a radome structure for an antenna assembly is provided. The radome structure may include a plurality of plasma elements operably coupled to a driver circuit. The driver circuit may be configured to selectively ionize individual ones of the plasma elements responsive to operation of a controller operably coupled to the driver circuit to provide control of a plasma density of the individual ones of the plasma elements. The plasma elements may include respective enclosures. At least some of the enclosures have all peripheral edge surfaces substantially fully contacted by corresponding peripheral edge surfaces of adjacent enclosures at at least one section along a longitudinal length thereof.
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
Some example embodiments now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all example embodiments are shown. Indeed, the examples described and pictured herein should not be construed as being limiting as to the scope, applicability or configuration of the present disclosure. Rather, these example embodiments are provided so that this disclosure will satisfy applicable legal requirements such as reference numerals refer to like elements throughout. Furthermore, as used herein, the term “or” is to be interpreted as a logical operator that results in true whenever one or more of its operands are true. As used herein, the terms “data,” “content,” “information” and similar terms may be used interchangeably to refer to data capable of being transmitted, received and/or stored in accordance with example embodiments. As used herein, the phrase “operable coupling” and variants thereof should be understood to relate to direct or indirect connection that, in either case, enables functional interconnection of components that are operably coupled to each other. Thus, use of any such terms should not be taken to limit the spirit and scope of example embodiments.
Plasma elements of an example embodiment may generally be formed of plasma containers having selected shapes and selected spatial distributions. The plasma containers may have variable plasma density therein, and plasma frequencies may be established in ranges from zero to arbitrary plasma frequencies based on controlling plasma density.
Some of the physics of plasma transparency and reflection are explained as follows. The plasma frequency is proportional to the density of unbound electrons in the plasma or the amount of ionization in the plasma. The plasma frequency sometimes referred to a cutoff frequency is defined as:
where ηe is the density of unbound electrons, e is the charge on the electron, and me is the mass of an electron. If the incident RF frequency ω on the plasma is greater than the plasma frequency ωp (i.e., when ω>ωp), the electromagnetic radiation passes through the plasma and the plasma is transparent. If the opposite is true, and the incident RF frequency ω on the plasma is less than the plasma frequency ωp (i.e., when ω<ωp), the plasma acts essentially as a metal, and transmits and receives electromagnetic radiation.
Accordingly, by controlling plasma frequency, it is possible to control the behavior of the plasma antenna element for various applications. The electronically steerable and focusing plasma reflector antenna of the present inventor has the following attributes: the plasma layer can reflect microwaves and a plane surface of plasma can steer and focus a microwave beam on a time scale of milliseconds.
The definition of cutoff as used here is when the displacement current and the electron current cancel when electromagnetic waves impinge on a plasma surface. The electromagnetic waves are cutoff from penetrating the plasma. The basic observation is that a layer of plasma beyond microwave cutoff reflects microwaves with a phase shift that depends on plasma density. Exactly at cutoff, the displacement current and the electron current cancel. Therefore there is an anti-node at the plasma surface, and the electric field reflects in phase. As the plasma density increases from cutoff the reflected field increasingly reflects out of phase. Hence the reflected electromagnetic wave is phase shifted depending on the plasma density. This is similar to the effects of phased array antennas with electronic steering except that the phase shifting and hence steering and focusing comes from varying the density of the plasma from one tube to the next and phase shifters used in phased array technology is not involved.
This allows using a layer of plasma tubes to reflect microwaves. By varying the plasma density in each tube, the phase of the reflected signal from each tube can be altered so the reflected signal can be steered and focused in analogy to what occurs in a phased array antenna. The steering and focusing of the mirror can occur on a time scale of milliseconds. This structure, or others, may be employed in plasma antenna elements of example embodiments. Moreover, regardless of the particular structure employed, example embodiments may enable the plasma antenna element to be operated according to the general principles described above, but require less power to achieve desired plasma densities, and also intelligently select plasma densities in some cases. In an example embodiment, the control of plasma density may be accomplished by controlling the pulse width of the driving current used to ionize the plasma.
Based on the description above, it should be appreciated that plasma structures can be designed and configured to act as a radiating element, a reflecting surface, or a dielectric layer. Moreover, through the control of plasma density, a single plasma structure or element can function as a combination of those elements over a desired frequency band. Given these characteristics, a plasma element can be configured to have unique properties when combined with other structures as well. For example, some example embodiments described herein may provide a unique application of plasma elements arranged in a layered pattern over a radiating structure in order to enhance or control the radiation pattern of the radiating structure. The layered pattern may form a radome relative to the radiating structure (which could be any type of radiating structure).
Of note, conventionally, plasma elements have often been defined as cylindrically shaped tubes inside which plasma is ionized. These cylindrically shaped tubes, when placed adjacent to each other, typically experienced some amount of leakage around the sides of the tubes via the air gaps created between the tubes. For optimal efficiency relative to control of the output of the radiating structure, this leakage should be minimized. Accordingly, some example embodiments further provide a structure that optimizes efficiency by nearly eliminating leakage paths proximate to the plasma elements. Each of the plasma elements may then be controlled to achieve a desired electrical response (e.g., from conductor to dielectric insulator) such that the resulting structure allows for the creation of a unique distribution of electrical response that cannot be achieved in a typical, monolithic radome structure.
In this example, the patch antenna 110 may be expected, when operated, to generate a somewhat omnidirectional radiation pattern 120. The radiation pattern 120 may be different for corresponding different radiating structures and may depend upon the specific characteristics of the radiating structures themselves. However, regardless of the specific radiating structure employed, it can be appreciated that the radiation pattern 120 is often desirably uninhibited by the radome employed to protect the radiating structure. As such, conventional radomes are often designed to be structurally rugged, but transparent to RF energy. Thus, a desirable conventional radome might be expected to have no impact (or at least minimal impact) on the radiation pattern 120 generated by the patch antenna 110 shown in
In accordance with an example embodiment, a radome structure may be provided over the patch antenna 110 to selectively enable control or modification of the radiation pattern 120. In particular, the radome structure may be configurable in real time to control the characteristics of the radiation pattern in any desirable way based on the plasma density of individual elements of the radome structure. The radome structure may be provided proximate to or enclose the radiating structure (e.g., the patch antenna 110) and may therefore allow modification of the radiation pattern by changing the plasma density in selected ones of the individual elements of the radome structure. In some cases, the radome structure may be defined by layers of plasma elements that form a planar structure or sheet. For coverage of a microstrip antenna like the patch antenna 110, the radome structure may simply be a sheet of material formed to cover the patch antenna 110 and lie in a plane substantially parallel to the surface of the aircraft skin 100. However, for other structures such as protruding antenna elements, the radome structure could be defined by multiple sheets attached to each other to form an enclosure around the radiating structure.
The radome structure 200 is formed by placing a plurality of plasma elements 220 that are each defined by an enclosure 222 and ionizable gas retained inside the enclosure 222. As shown in
As can be appreciated from
However, it should also be appreciated that the advantages provided by the honeycomb structure can be approximated with enclosures having other geometries as well so long as the geometries permit assembly of the radome structure 200 in a way that prevents leakage between adjacent enclosures. In particular, any structure that results, when such enclosures are assembled to form the radome structure 200, in all enclosures that are surrounded by adjacent enclosures on all sides to have substantially full contact with every one of its adjacent enclosures about its entire periphery along longitudinal sides thereof. Thus, edge enclosures may be different since at least one side may not have an adjacent enclosure. However, for interior enclosures, all peripheral edges thereof are substantially fully contacted by corresponding surfaces of adjacent enclosures along at least a majority of the length of the longitudinal sides thereof. As such, square shapes, rectangular shapes, triangular shapes, or other such shapes may alternatively be employed in some example embodiments.
In some embodiments a first control surface 230 may be disposed at a first longitudinal end of each of the plasma elements 220. Meanwhile, a second control surface 232 may be disposed at a second longitudinal end (i.e., the opposing end relative to the first longitudinal end) of the plasma elements 220. The first and second control surfaces 230 and 232 may be defined by a series of individually addressable or selectable electrodes. The electrodes may be individually selectable in pairs at opposing ends of particular ones of the plasma elements 220 to allow individual plasma elements 220 to be ionized to control plasma density inside the corresponding enclosures 222. The individual plasma elements 220 may therefore have their respective plasma densities strategically controlled to control the behavior of the plasma therein relative to passing, blocking or acting as a lens relative to the radiation pattern generated by the patch antenna 210. Moreover, groups of the individual plasma elements 220 may be controlled to define specific patterns that allow steering of beams from the patch antenna 210 as described herein.
In this regard, for example, if all of the elements are not ionized (i.e., in an off state), then the radiation pattern 400 of
As can be appreciated from
In some example embodiments, it may be desirable to have some of the enclosures that are provided in the honeycomb structure be filled with material other than plasma. For example, non-plasma elements 500 may be distributed into a radome structure 200′ in any desirable pattern as shown in
The examples shown in
As can be appreciated from the examples described above, the radome structures achievable by employing example embodiments can be operably coupled to an antenna assembly to modify the radiation pattern of the antenna assembly. As such, the radome structures described herein can be used with a device or system in which a component (e.g., a controller) is provided to control operation of a plurality of plasma elements housed within an enclosure that is shaped to have substantially all peripheral edges thereof in contact with corresponding edge surfaces of an adjacent enclosure to prevent leakage between enclosures. The controller can control the plasma elements of the radome structure and the resultant antenna element may be operated to function as a radiating antenna, a receiving antenna, a reflector or a lens to manipulate radio frequency (RF) signals associated with wireless communication or other applications. The arrangements of the antenna element or elements of some example embodiments may allow the controller to configure the plasma elements to support communication over one or multiple frequencies sequentially, simultaneously and/or selectively. Accordingly, plasma element advantages including low thermal noise, invisibility to radar when switched off or to a lower frequency than the radar, resistance to electronic warfare, plus the versatility provided by dynamic tuning and reconfigurability for frequency, direction, bandwidth, gain, and beamwidth in both static and dynamic modes of operation, may be provided to a platform (e.g., an aircraft) hosting the plasma elements forming the radome structure and the antenna elements included therewith.
Some example embodiments may employ characteristics of stealth, interference resistance and rapid reconfigurability in order to provide an adaptable and highly capable mobile communication platform. Moreover, example embodiments provide for the intelligent control of the plasma density of the plasma elements in any desirable pattern to achieve various results in terms of beam formation and steering. In some cases, the controller onboard the platform may respond to external stimuli (e.g., user input or environmental conditions) or follow internal programming to make inferences and/or probabilistic determinations about how to steer beams, select array lengths, employ channels/frequencies for communication with various communications equipment. Load balancing, antenna beam steering, interference mitigation, network security and/or denial of service functions may therefore be enhanced by the operation of some embodiments.
In an example embodiment, the processing circuitry 710 may include one or more instances of a processor 712 and memory 714 that may be in communication with or otherwise control a device interface 720 and, in some cases, a user interface 730. As such, the processing circuitry 710 may be embodied as a circuit chip (e.g., an integrated circuit chip) configured (e.g., with hardware, software or a combination of hardware and software) to perform operations described herein. However, in some embodiments, the processing circuitry 710 may be embodied as a portion of an on-board computer. In some embodiments, the processing circuitry 710 may communicate with various components, entities, sensors and/or the like, which may include, for example, the driver circuit 710 and/or a plasma density sensor (e.g., an interferometer) that is configured to measure plasma density in the plasma elements 220.
The user interface 730 (if implemented) may be in communication with the processing circuitry 710 to receive an indication of a user input at the user interface 730 and/or to provide an audible, visual, mechanical or other output to the user. As such, the user interface 730 may include, for example, a display, one or more levers, switches, indicator lights, touchscreens, buttons or keys (e.g., function buttons), and/or other input/output mechanisms. The user interface 730 may be used to select channels, frequencies, modes of operation, programs, instruction sets, or other information or instructions associated with operation of the driver circuit 740 and/or the plasma elements 220.
The device interface 720 may include one or more interface mechanisms for enabling communication with other devices (e.g., modules, entities, sensors and/or other components). In some cases, the device interface 720 may be any means such as a device or circuitry embodied in either hardware, or a combination of hardware and software that is configured to receive and/or transmit data from/to modules, entities, sensors and/or other components that are in communication with the processing circuitry 710.
The processor 712 may be embodied in a number of different ways. For example, the processor 712 may be embodied as various processing means such as one or more of a microprocessor or other processing element, a coprocessor, a controller or various other computing or processing devices including integrated circuits such as, for example, an ASIC (application specific integrated circuit), an FPGA (field programmable gate array), or the like. In an example embodiment, the processor 712 may be configured to execute instructions stored in the memory 714 or otherwise accessible to the processor 712. As such, whether configured by hardware or by a combination of hardware and software, the processor 712 may represent an entity (e.g., physically embodied in circuitry—in the form of processing circuitry 710) capable of performing operations according to embodiments of the present invention while configured accordingly. Thus, for example, when the processor 712 is embodied as an ASIC, FPGA or the like, the processor 712 may be specifically configured hardware for conducting the operations described herein. Alternatively, as another example, when the processor 712 is embodied as an executor of software instructions, the instructions may specifically configure the processor 712 to perform the operations described herein.
In an example embodiment, the processor 712 (or the processing circuitry 710) may be embodied as, include or otherwise control the operation of the controller 700 based on inputs received by the processing circuitry 710. As such, in some embodiments, the processor 712 (or the processing circuitry 710) may be said to cause each of the operations described in connection with the controller 700 in relation to adjustments to be made to plasma density patterns in the radome structure 200 responsive to execution of instructions or algorithms configuring the processor 712 (or processing circuitry 710) accordingly. In particular, the instructions may include instructions for altering the configuration and/or operation of one or more instances of the plasma elements 220 as described herein. The control instructions may mitigate interference, conduct load balancing, implement antenna beam steering, select an operating frequency/channel, select a mode of operation, increase efficiency or otherwise improve performance of an antenna assembly through the control of the plasma element 220 as described herein.
In an exemplary embodiment, the memory 714 may include one or more non-transitory memory devices such as, for example, volatile and/or non-volatile memory that may be either fixed or removable. The memory 714 may be configured to store information, data, applications, instructions or the like for enabling the processing circuitry 710 to carry out various functions in accordance with exemplary embodiments of the present invention. For example, the memory 714 could be configured to buffer input data for processing by the processor 712. Additionally or alternatively, the memory 714 could be configured to store instructions for execution by the processor 712. As yet another alternative, the memory 714 may include one or more databases that may store a variety of data sets responsive to input sensors and components. Among the contents of the memory 714, applications and/or instructions may be stored for execution by the processor 712 in order to carry out the functionality associated with each respective application/instruction. In some cases, the applications may include instructions for providing inputs to control operation of the controller 700 as described herein.
As shown in
Accordingly, for example, the controller 700 may define a target plasma density for the individual ones of the plasma elements 220 and the driver circuit 740 may be operated to provide current pulses to the plasma elements 220 to ionize the gas therein to the corresponding target plasma density. Any change in target plasma density triggered by user input or by programmed operation of the controller 700 may then cause a corresponding change in operation of the driver circuit 740 to achieve the new target plasma density.
Example embodiments may operate over a range of frequencies that may be required for various different applications. However, it should be noted specifically that example embodiments can also work well at frequencies above 800 MHz due to the ability of the driver circuit 740 to generate fast, high current pulses. As can be appreciated from the descriptions above, one or more of the plasma elements 220 may be configured to support wireless communication between external communication equipment and a platform employing the one or more antenna assembly having the radome structure 200 and corresponding plasma elements 220. The provision of the plasma elements 220 for communications support may provide for configurable communications capabilities while minimizing the penetrations through the fuselage of an aircraft and may also minimize the drag associated with providing communications antennas for the aircraft. However, numerous other platforms may also benefit from employing example embodiments of the plasma elements 220 employed as described herein.
Plasma frequency is related to plasma density, and thus, the controller 700 can also or alternatively be configured to control the frequency of any array employing plasma elements simply by controlling the plasma density as described herein. In any case, the controller 700 may also be configured to control the plasma elements and/or their respective antenna assemblies to perform time and/or frequency multiplexing so that many RF subsystems (e.g., multiple different radios associated with the radio circuitry) may share the same antenna resources. In situations where the frequencies are relatively widely separated, the same aperture may be used to transmit and receive signals in an efficient manner. In some embodiments, higher frequency plasma antenna arrays may be arranged to transmit and receive through lower frequency plasma antenna arrays. Thus, for example, the antenna arrays (assuming they also employ plasma elements of some sort) may be nested in some embodiments such that higher frequency plasma antenna arrays are placed inside lower frequency plasma antenna arrays.
In some embodiments, multiple reconfigurable or preconfigured antenna elements may be provided to enable communications over a wide range of frequencies covering nearly the entire spectrum, or at least being capable of providing such coverage based on relatively minimal changes to controllable and selectable characteristics of the radome structure 200 and the components associated therewith by the controller 700. Some ranges or specific frequencies may be emphasized for certain commercial reasons (e.g., 790 MHz to 6 GHz, 2.4 GHz, 5.8 GHz, 14 GHz, 26 GHz, 58 GHz, etc.). However, in all cases, the controller 700 may be configured to provide at least some control over the frequencies, channels, multiplexing strategies, beam forming, or other technically enabling programs that are employed. Because plasma elements can be ‘tuned’ rapidly, fast switching could also accomplish the same goal of using the same physical plasma element to communicate at high speed with multiple devices in a time-division duplexed fashion.
As mentioned above, beam forming capabilities may be enhanced or provided by the controller 700 exercising control over the plasma elements 220. In this regard, for example, when the plasma elements 220 include layers, the layers may be individually operated to define patterns to allow narrow beam formation and steering. Thus, the controller 700 may control the radome structure 200 to generate reflective properties or employ beam collimation so that beam steering may be accomplished. In such an example, the controller 700 may be configured to control the plasma elements 200 to focus or steer radiation patterns passing through the radome structure 200 to allow shaping and steering of beams without the use of a phased array antenna.
Regardless of whether the plasma elements 220 are used to facilitate operation of an antenna assembly to radiate, receive, focus beams, steer beams, reflect beams or otherwise conduct some form of beamforming function, the controller 700 may be used to control the operation of the plasma elements 220 to achieve the desired functionality, but further enable the plasma elements to be operated efficiently and intelligently in cooperation with the antenna element that the radome structure 200 covers.
In some embodiments, the controller that performs the method above (or a similar controller) may be a portion of an antenna assembly or system. The system or assembly may include an antenna element, a radome structure disposed proximate to the antenna element and including a plurality of plasma elements, a driver circuit operably coupled to the plasma elements to selectively ionize individual ones of the plasma elements, and a controller. The controller may be operably coupled to the driver circuit to provide control of plasma density of the individual ones of the plasma elements. The plasma elements may include respective enclosures. At least some of the enclosures may have at least two (or in some cases all) peripheral edge surfaces substantially fully contacted by corresponding peripheral edge surfaces of adjacent enclosures at at least one section along a longitudinal length thereof.
In some embodiments, the assembly described above may include additional and/or optional components and/or the components described above may be modified or augmented. Some examples of modifications, optional changes and augmentations are described below. It should be appreciated that the modifications, optional changes and augmentations may each be added alone, or they may be added cumulatively in any desirable combination. In an example embodiment, the at least some of the enclosures may have a hexagonal cross sectional shape. In an example embodiment, opposing longitudinal ends of the plasma elements may be operably coupled to first and second control surfaces, respectively. Additionally, the driver circuit may be operably coupled to the first and second control surfaces to selectively ionize the individual ones of the plasma elements. In some examples, selectively ionizing the individual ones of the plasma elements may further define a corresponding plasma density within the individual ones of the plasma elements. In an example embodiment, the radome structure may include at least some elements that are non-plasma elements. In some cases, the non-plasma elements may be defined by enclosures filled with dielectric or metallic materials. In an example embodiment, the radome structure may include a first layer of plasma elements in which respective plasma elements each lie substantially parallel to each other, and a second layer of plasma elements in which corresponding plasma elements each lie substantially parallel to each other and substantially orthogonal to the respective plasma elements of the first layer of plasma elements. In some examples, the controller may be configured to define a first group of plasma elements having a first plasma density and a second group of plasma elements having a second plasma density different than the first plasma density within the first layer, and the controller may be configured to define a third group of plasma elements having a third plasma density and a fourth group of plasma elements having a fourth plasma density different than the third plasma density in the second layer to control a radiation pattern leaving the radome structure. In some embodiments, the controller may be configured to define a first group of plasma elements having a first plasma density and a second group of plasma elements having a second plasma density different than the first plasma density to control a radiation pattern leaving the radome structure. In an example embodiment, the controller may be configured to adjust plasma density in selected ones of the plasma elements to define and steer a beam passing through the radome structure. Additionally or alternatively, the controller may be configured to adjust plasma density in selected ones of the plasma elements to define and steer multiple beams passing through the radome structure simultaneously. In an example embodiment, the antenna element may be a conformal antenna configuration or micropatch antenna and the antenna element may be disposed at a surface of an aircraft or other large structure such as a ground station.
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although the foregoing descriptions and the associated drawings describe exemplary embodiments in the context of certain exemplary combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative embodiments without departing from the scope of the appended claims. In this regard, for example, different combinations of elements and/or functions than those explicitly described above are also contemplated as may be set forth in some of the appended claims. In cases where advantages, benefits or solutions to problems are described herein, it should be appreciated that such advantages, benefits and/or solutions may be applicable to some example embodiments, but not necessarily all example embodiments. Thus, any advantages, benefits or solutions described herein should not be thought of as being critical, required or essential to all embodiments or to that which is claimed herein. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
| Number | Name | Date | Kind |
|---|---|---|---|
| 2085406 | Zworykin | Jun 1937 | A |
| 7772774 | Pavliscak et al. | Aug 2010 | B1 |
| 7999747 | Wedding | Aug 2011 | B1 |
| 20030218575 | Walker | Nov 2003 | A1 |
| 20060220980 | Metz | Oct 2006 | A1 |
| 20090109115 | Dittrich | Apr 2009 | A1 |
| 20110025565 | Anderson | Feb 2011 | A1 |
| 20150214610 | Kim et al. | Jul 2015 | A1 |
| 20170264015 | Stratis | Sep 2017 | A1 |
| Number | Date | Country |
|---|---|---|
| 0230969 | Aug 1987 | EP |
| 2014192651 | Oct 2014 | JP |
| 2016032164 | Mar 2016 | JP |
| Entry |
|---|
| Fuchs, et al., “Design Optimization of Multishell Luneburg Lenses,” IEEE Transactions on Antennas and Propagation, IEEE Service Center vol. 55, No. 2, Feb. 1, 2007, all enclosed pages cited. |
| International Search Report and Written Opinion of PCT/US2018/024504 dated Jun. 15, 2018, all enclosed pages cited. |
| Number | Date | Country | |
|---|---|---|---|
| 20180294561 A1 | Oct 2018 | US |
