Luneburg lens for passive radar sensing

Abstract

A passive radar system for point-to-point directional communications comprising at least one Luneburg lens antenna.

Description

International Patent Application Atty. Docket No. 3000060-023977LUNEBURG LENS FOR PASSIVE RADAR SENSING CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application is an international patent application which claims priority to U.S. Provisional Application No. 63 / 724,100 filed on November 22, 2024, the disclosure of which is incorporated herein in its entirety.FIELD OF THE INVENTION

[0002] This disclosure relates to passive multi-static radar systems configured to scan using unwitting sources to identify uncooperative targets.BACKGROUND OF THE INVENTION

[0003] Satellite communications (SATCOM) and terrestrial microwave communications systems such as microwave line-of-sight, cellular, and tactical networking typically require the use of transmitter / receivers connected to directional antennas that aim the energy of a signal in either a general or specific direction towards another directional antenna connected to a transmitter / receiver. A common type of antenna used in both SATCOM and terrestrial communications is a parabolic reflector with a waveguide feed located at the focal point of the parabola. These antennas are effective in networks where both the antenna and the distant end antenna are stationary, such as in the case of a Geosynchronous Earth Orbit (GEO) satellite, or a microwave point-to-point link between two buildings or a building and a tower.

[0004] New satellite constellations that operate in Non-Geostationary Satellite Orbit (NGSO), specifically in Medium Earth Orbit (MEO) and Low Earth Orbit (LEO), as well as the increasingly ubiquitous implementation of terrestrial communications systems that require line- of-sight and non-line-of-sight beam-steering base stations with multiple beams of energy being radiated simultaneously are challenging the paradigm of single-beam, mechanically articulated parabolic reflector antennas. Several solutions involving Electronically Steerable Array (ESA) antennas and, more specifically, Active ESA (AESA) antennas have been developed to address these new challenges. The value these terminals bring to the marketplace is their inherent ability to direct one or several energy beams in different directions without any moving parts, allowing installers to place an antenna in one position and have it connect to distant end antennas that are in motion, such as NGSO, LEO, and MEO communication satellites, and antennas attached toInternational Patent ApplicationAtty. Docket No. 3000060-023977 moving vehicles such as Unmanned Aerial Vehicles (UAVs) and manned aircraft. Furthermore, these antennas can be placed on a moving vehicle such as an airplane, naval vessel, or ground vehicle such as a train, automobile, and drone, and concurrently track a distant end antenna regardless of whether that antenna is also moving or not.

[0005] However, AESA antennas are expensive due to the complexity of the circuitry being used and the vast volume of elements that must be employed to replicate the gain and directivity of a parabolic reflector. AESAs also require a tremendous amount of power as they have a large number of transmit-receive (TR) modules (one at every element) all operating simultaneously when compared to parabolic antennas which require only one TR module at its single feed point.

[0006] There exists a need in the art for improved radar systems. The present invention achieves technical advantages by using a Luneburg (Liineburg) Lens in the passive radar system described herein.SUMMARY OF VARIOUS EMBODIMENTS OF THE INVENTION

[0007] In an embodiment, a passive radar system comprising: a Luneburg lens antenna system, wherein at least one feed is electrically coupled to at least one Luneburg lens antenna; a switching network connecting the at least one feed to at least one receiver; wherein the system is configured to support one or more independent directional beams, configured to receive signals from unwitting transmitters, wherein the passive radar system is configured to capture both a direct signal from a transmitter, optionally an intentional transmitter and / or an unwitting transmitter, and a reflected signal from a target and further comprising software configured to correlate the direct signal and the reflected signal to detect the target, and, optionally, collect identifying information.

[0008] In an embodiment, the system further comprises a power source.

[0009] In an embodiment, the identifying information comprises speed, location, heading, or a combination thereof, of the target.

[0010] In an embodiment, the transmitter originates from the target, satellite, communications station, multiple frequencies, telemetry, vehicle, or a combination thereof.

[0011] In an embodiment, the system is configured to allow the intersection of the adjacent scanned beams to be designed to be approximately ldB-3dB below the peak gain value.International Patent ApplicationAtty. Docket No. 3000060-023977

[0012] In an embodiment, the Luneburg lens has a wideband frequency coverage allowing for operation in multiple frequency bands simultaneously.

[0013] In an embodiment, the Luneburg lens is configured for multiple simultaneous beams.

[0014] In an embodiment, the Luneburg lens is configured to provide coverage of the upper hemisphere relative to the antenna, optionally up to + / - 90 degrees from boresight at zenith.

[0015] In an embodiment, the individual elements of the antenna function as individual feeds for individual beams aimed in separate directions through the lens.

[0016] In an embodiment, the antenna is configured to passively receive signals at full gain.

[0017] In an embodiment, the antenna can receive a plurality of signals of beams simultaneously, optionally all signals of beams simultaneously.

[0018] In an embodiment, the antenna is configured to allow for detection and capture of signals within a hemispheric field of view.

[0019] In an embodiment, the antenna is configured for collecting signals pinpointed by source orientation relative to the antenna through back-end processing.

[0020] In an embodiment, the Luneburg lens antenna system is configured to receive a direct signal and a reflected signal from a target.

[0021] In an embodiment, the Luneburg lens antenna system is configured to receive a direct signal from an unwitting transmitter independent of the target and a reflected signal from the target.

[0022] In an embodiment, the Luneburg antenna is a multibeam antenna capable of efficiently capturing and tracking targets and references from multiple directions with high gain.

[0023] In an embodiment, the direct signal is a signal(s) of opportunity from a transmitting tower.

[0024] In an embodiment, the system utilizes signals from unwitting transmitters.

[0025] In an embodiment, the system is configured to covertly detect and track targets without emitting its own signals.

[0026] In an embodiment, the system comprises multiple Luneburg lens antenna systems, optionally configured to cover multiple frequency bands.

[0027] In an embodiment, the system is configured to receive signals from direct broadcast satellite (DBS) television transmitters in geosynchronous earth orbit (GEO).International Patent ApplicationAtty. Docket No. 3000060-023977

[0028] In an embodiment, the system is configured to receive signals from an unwitting transmitter, optionally wherein the unwitting transmitter is a low earth orbit (LEO) satellite, GEO, MEO, Non-geosynchronous satellites, Non-Geostationary Satellite Orbit (NGSO), specifically in Medium Earth Orbit (MEO) and Low Earth Orbit (LEO), terrestrial based transmitter, airborne transmitters, transmitters in orbit, vehicles, air, sea, and land based vehicles, or a combination thereof.

[0029] In an embodiment, the satellites are considered non-cooperative and their signals are not demodulated.

[0030] In an embodiment, the system utilizes both GEO and LEO satellite signals of opportunity.

[0031] In an embodiment, the multibeam sensor is configured to receive signals from multiple satellites simultaneously.

[0032] In an embodiment, the system is configured to leverage high bandwidth signals for improved range resolution and long duration signals for increased detection range.

[0033] In an embodiment, the system further comprises geosynchronous systems, optionally Direct Broadcast Satellite signals.

[0034] In an embodiment, each feed is linked to its own individual receiver.

[0035] In an embodiment, the system is configured to focus electromagnetic waves emanating from any direction.

[0036] In an embodiment, each feed has an unobstructed view to the opposite side of the lens.

[0037] In an embodiment, the system is configured to scan away from boresight at zenith with minimal scan loss.

[0038] In an embodiment, the Luneburg lens has a focal point located on the surface of the lens.

[0039] In an embodiment, the Luneburg lens has a focal point located outside the surface of the lens, optionally a gap consisting of air or other material.

[0040] In an embodiment, the focal point is located on an imaginary sphere surrounding the lens.

[0041] In an embodiment, the system comprises a plurality of lenses configured to provide unobstructed views for each feed to the opposite side of the lens.

[0042] In an embodiment, the system is configured to provide at least two simultaneous beams per terminal.International Patent ApplicationAtty. Docket No. 3000060-023977

[0043] In an embodiment, the system comprises a network of distributed sensors that provide data as inputs to algorithms for determining positions of emitting sources.

[0044] In an embodiment, the system comprises multiple Luneburg lens antenna systems, each one configured to provide unobstructed views for each feed to the opposite side of the lens.

[0045] In an embodiment, the system is configured to provide at least two simultaneous beams per terminal.

[0046] In an embodiment, the system is configured to provide uninterrupted scan coverage up to the horizon.

[0047] In an embodiment, a passive radar system of comprising: a plurality of Luneburg lens antenna, wherein at least one feed is electrically coupled to the Luneburg lens antenna; a switching network connecting the at least one feed to at least one receivers; wherein the system is configured to support one or more independent directional beams, configured to receive signals from unwitting transmitters.

[0048] In an embodiment, a vehicle can comprise the passive radar system described herein.

[0049] In an embodiment, the vehicle is a surface vehicle, an airborne vehicle, or a submersible vehicle, optionally an unmanned marine vehicle (UMV).

[0050] In an embodiment, the vehicle is autonomous.

[0051] In an embodiment, a method for passive radar detecting comprising: configuring the passive radar system described herein to focus electromagnetic waves emanating from a plurality of directions; utilizing a plurality of feeds electrically coupled to the passive radar system to receive the focused electromagnetic waves; transmitting the focused electromagnetic waves through a plurality of feeds through a switching network to at least one receiver; sending at least one independent directional beams via the passive radar system; correlating the received signals to enable identification characteristics of at least one uncooperative target, optionally transmitting the identifying information.

[0052] In an embodiment, the system is configured to receive a direct signal from multiple transmitting towers.

[0053] In an embodiment, the system is configured to receive multiple reflected signals per target.

[0054] In an embodiment, two or more antennas are used in a system, and the exact location of any signal source is determined.International Patent ApplicationAtty. Docket No. 3000060-023977

[0055] In an embodiment, the antenna is used to locate two or more known signal sources to determine the exact position and orientation of the antenna.

[0056] In an embodiment, the antenna is used in an Alternate Positioning, Navigation, and Timing (APNT) scenarios.

[0057] In an embodiment, the passive radar captures both the direct signal and a reflected signal from the target, correlating them to identify and detect it.

[0058] In an embodiment, the system transmits the identifying information.

[0059] In an embodiment, the identifying information is speed, location, heading, or a combination thereof.

[0060] In an embodiment, the system operates when the emitting source locations are unknown.

[0061] In an embodiment, the passive radar system utilizes signals from terrestrial transmitters.

[0062] In an embodiment, the system is configured to receive signals within the frequency range of 87.5 to 108.0 MHz.

[0063] In an embodiment, the system is configured to receive signals over the UHF spectrum of 470 to 806 MHz.

[0064] In an embodiment, the system is configured to receive signals from cellular phone network frequency bands.

[0065] In an embodiment, the system is configured to receive signals from direct broadcast satellite (DBS) television transmitters in geosynchronous earth orbit (GEO), low earth orbit (LEO) satellites, GEO, MEO, Non-geosynchronous satellites, Non-Geostationary Satellite Orbit (NGSO), specifically in Medium Earth Orbit (MEO) and Low Earth Orbit (LEO), or a combination thereof.

[0066] In an embodiment, the system is configured to receive signals from low earth orbit (LEO) satellite constellations.

[0067] In an embodiment, the satellites are considered non-cooperative and their signals are not demodulated.

[0068] In an embodiment, both GEO and LEO satellite signals of opportunity are utilized.

[0069] In an embodiment, the Luneburg lens antenna system is configured to receive signals from multiple satellites simultaneously.

[0070] In an embodiment, the system focuses electromagnetic waves emanating from any direction.International Patent Application Atty. Docket No. 3000060-023977

[0071] In an embodiment, the system scans away from boresight at zenith with minimal scan loss.BRIEF DESCRIPTION OF THE DRAWINGS

[0072] FIG. 1 depicts an example of a passive bistatic radar system receiving a signal of opportunity from a radio station 101 and a reflected signal from a target 102 with a multi-beam antenna 100.

[0073] FIG. 2 depicts an example of a passive distributed radar system with multiple passive terminals 200 receiving signals of opportunity from several radio station 201 and reflections from multiple targets.

[0074] FIG. 3 depicts a passive distributed radar system with multiple passive terminals 300 receiving signals of opportunity from several satellite emitters 301 and reflections from multiple targets 302.

[0075] FIG. 4 depicts a Luneburg lens multibeam antenna which can provide many simultaneous beams with excellent wide scan performance.

[0076] FIG. 5 depicts an example of a multi-beam phased array antenna with an analog beamforming architecture.DETAILED DESCRIPTION OF PREFERRED EMBODIMENTSDefinitions

[0077] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. It should be appreciated that the term “substantially” is synonymous with terms such as “nearly”, “very nearly”, “about”, “approximately”, “around”, “bordering on”, “close to”, “essentially”, “in the neighborhood of’, “in the vicinity of’, etc., and such terms may be used interchangeably as appearing in the specification and claims. It should be appreciated that the term “proximate” is synonymous with terms such as “nearby”, “close”, “adjacent”, “neighboring”, “immediate”, “adjoining”, etc., and such terms may be used interchangeably as appearing in the specification and claims.

[0078] “Coordinated transmitter,” as used herein, refers broadly to a transmitter that intentionally provides signals that can be utilized by a radar system, optionally a passive radarInternational Patent ApplicationAtty. Docket No. 3000060-023977 system. The coordinated transmitter can also send additional information about a target and transmitting source to the radar system, optionally a passive radar system.

[0079] “Passive radar,” as used herein, refers broadly to a system that does not use any transmitter from its antenna, therefore cannot identify where the receiver is located. Passive radar are not detectable, e.g., “invisible” to other radar systems.

[0080] “Signals of opportunity,” as used herein, refers broadly to signals that can originate from any transmitting source. The transmitting source can be an unwitting transmitter. The transmitting source can be a low earth orbit (LEO) satellite, geostationary (GEO) satellite, medium Earth orbit (MEO) satellite, non-geosynchronous satellites, Non-Geostationary Satellite Orbit (NGSO), specifically in Medium Earth Orbit (MEO) and Low Earth Orbit (LEO), terrestrial based transmitter, airborne transmitters, transmitters in orbit, vehicles, air, sea, and land based vehicles, or a combination thereof.

[0081] “Unwitting transmission sources,” as used herein, refers broadly to any transmission source (transmitter) not associated with a particular receiving antenna. Furthermore, “unwitting” describes the fact that the transmitter is unaware that the passive radar receiver is making use of its broadcast signals.Passive Radar System

[0082] This disclosure provides for a high-performance multibeam sensor and establish a framework for its use in a distributed passive radar system. The passive radar system described herein comprises a Luneburg Lens antenna technology allows continuous full -hemispheric monitoring of spectrum with inherent directionality which offers distinct capability as a passive signals collector. The passive nature of the solution allows the capture of non-cooperative signals of interest in a stealthy manner without radiating energy that would otherwise expose the system to countermeasures. This passive receiver capability lends itself well as a solution to four problem sets:• Bi / Multi-static Passive Radar• Signals Intelligence (SIGINT)• Direction Finding (DF)• Alternative Position Navigation and Timing (APNT)

[0083] The Luneburg Lens technology described herein can be used for point-to-point directional communications. By configuring the antenna to passively receive signals at full gainInternational Patent ApplicationAtty. Docket No. 3000060-023977 in a single frequency or multiple frequencies on many, up to all, beams simultaneously, the present disclosure enables detection, capture and full directional awareness of all signals of interest in the hemispheric field of view. With applied back-end processing, this collection of signals is pinpointed by source in orientation relative to the antenna, and when two or more antennas are combined in a system, exact location of any signal source is determined, or in the case of APNT, when a single antenna is used to locate two or more known signal sources, the exact position and orientation of the antenna is determined. The lens, systems, and methods described herein overcome these and other obstacles in the field to provide a low-cost, wide- angle, multi-beam, multi-frequency beamforming lens antenna.

[0084] Most modem radar systems, such as those inside the nosecone of commercial and military aircraft for weather, collision avoidance, and general target detection, utilize the same antenna for transmitting and receiving. Also, Doppler weather radar stations, which are sometimes visible along major highways as a single dome on a tower have the transmitter and receiver in the same location. These radar systems with collocated receiver and transmitter are referred to as monostatic. A bistatic radar system has the transmitter and receiver separated in space usually by significant distances. Bistatic radar systems which are passive do not require a dedicated transmitter in the system as instead these utilize signals of opportunity from unwitting sources already in the environment. Signals of opportunity may originate from any transmitting source. The transmitting source can be an unwitting transmitter. The transmitting source can be a low earth orbit (LEO) satellite, GEO, MEO, Non-geosynchronous satellites, Non-Geostationary Satellite Orbit (NGSO), specifically in Medium Earth Orbit (MEO) and Low Earth Orbit (LEO), terrestrial based transmitter, Airborne transmitters, Transmitters in orbit, vehicles, air, sea, and land-based vehicles, or a combination thereof. A coordinated transmitter can be a transmitter that intentionally provides signals that can be utilized by a radar system, optionally a passive radar system. The coordinated transmitter can also send additional information about a target and transmitting source to the radar system, optionally a passive radar system.

[0085] The sources in a bistatic passive radar system are called unwitting since from the perspective of the transmitters, the use of their signals for radar purposes is unintentional and inadvertent. These passive radar sources are unaware that their signals are being used for these purposes and are noncooperative with the passive radar receivers. The passive radar receiving antenna captures both the direct signal and a reflected signal from the target, correlating them toInternational Patent ApplicationAtty. Docket No. 3000060-023977 identify and detect it. One advantage of passive radar is its ability to covertly detect and track targets without emitting its own signals, making it less susceptible to detection and malicious interference.

[0086] In reference to FIG. 1, a passive bistatic radar system is depicted. In this configuration, an antenna terminal designed to receive signals from various directions picks up a direct signal of opportunity from a transmitting tower 101. Concurrently, the tower's signal bounces off a target 102 and is reflected to the receiving antenna 100. Central to this system as shown is the multibeam receiving antenna 100, recognized for efficiently capturing and tracking targets and references from multiple directions with high gain. Other implementations could use multiple low-gain antennas at a receiving site.

[0087] In reference to FIG. 2, a distributed passive radar system can comprise multiple receiving terminals distributed over a given coverage area. Each antenna terminal 200 receives a direct signal from the three depicted transmitting towers 201 and three reflected signals per target 202 for a total of six reflected signals. The rays indicate the originating signal tower 201 with the dashed lines indicating the direct radiation reference signals. The distributed passive radar system offers several advantages. The distributed passive multistatic radar system provides additional degrees of freedom to determine angle of arrival and location of targets more accurately. Second, in cases where the emitting source locations are unknown, networking the distributed sensors can provide the necessary data as inputs to algorithms to determine their positions.

[0088] The range at which signals from various terrestrial transmitters can be received depends upon the frequency, transmitter power, receiver sensitivities, and antenna size and locations. FM radio station broadcasts, operating within the frequency range of 87.5 to 108.0 MHz, generally have a local reach of about 50 to 100 miles. High-Definition Television (HDTV) stations in the United States typically broadcast over the UHF (Ultra High Frequency) spectrum of 470 to 806 MHz. Users with simple wall-mounted indoor antennas can receive HDTV signals from 45 miles away while larger Yagi or log-periodic antennas mounted outdoors may be able to pull in these signals from ranges of 70 to 100 miles. Exact cellular phone network frequency bands depend upon the specific carrier. However, these signals occupy spectrum in the vicinity of 700, 800, 1700, 1800, and 1900MHz. While the typical user of a mobile phone communicates with a tower which is several miles away, most tower transmitters can close a link at 45 miles. Oftentimes, theInternational Patent ApplicationAtty. Docket No. 3000060-023977 tower will reduce transmit power so as not to interfere with other towers in adjacent cells. Direct broadcast satellite (DBS) television transmitters in geosynchronous earth orbit (GEO) transmit to home ground receivers from distances of 36,000km. New low earth orbit (LEO) satellite constellations such as Starlink and OneWeb communicate from distances on the order of 500 - 1000 km.

[0089] The coverage area for the passive radar system is not strictly confined to the exact coverage area of the designed communications system. Larger antennas with more directive beams could be employed to extend the range of the passive radar receiver. While the passive radar range is influenced by numerous factors, including target size, receiver sensitivity, and receive antenna size, it is also closely tied to the distances of the noncooperative transmitters of interest. The passive radar system described herein provides a multi-beam terminal capable of receiving and correlating signals from multiple sources and targets.

[0090] In reference to FIG. 3, a passive array system is depicted in which passive multibeam antennas receive both direct and reflected radio frequency (RF) signals from satellites. The satellites are considered non-cooperative in that they are not expected to be commanded to locate to certain areas, their signals will not be demodulated, and they have no knowledge of the receivers. Both GEO and LEO satellite signals of opportunity are useful non-cooperative sources in a passive bistatic radar system. Radar applications with high bandwidth signals have better range resolution and long duration signals provide enhanced detection range. The communication signals of the LEO satellites offer both wide bandwidths and long duration making them attractive for use as signals of opportunity in passive radar. The inventors created a multi-beam terminal capable of receiving and correlating signals from multiple satellites including geosynchronous systems such as DirecTV satellite signals. The passive radar system described herein leverages high bandwidth, long duration signals for enhanced detection range.

[0091] In reference to FIG. 4, plane waves impinging on the lens surface in equal phase fronts focus to antenna feed points on the opposite side of a Luneburg lens. For example, a Luneburg lens is a sphere with a dielectric constant of 2 in the center which tapers to a value of 1 at the perimeter. The Luneburg lens is capable of supporting tens to hundreds of independent directional beams. In one architecture, multiple clusters of feeds are linked through a switch network that is connected to multiple receivers, ensuring coverage within the multiple specified regions. Alternatively, linking each feed to its own individual receiver is a possibility; however,International Patent ApplicationAtty. Docket No. 3000060-023977 this could entail the need for several thousand receivers, potentially exceeding budgetary constraints. The Luneburg lens design depicted in FIG 4 scans to 60° from boresight at zenith, with very little scan loss as there is little to no blockage of the aperture area from feeds on the opposite side of the lens. This is in stark contrast to the phased array example of FIG 5 which would have at best 3dB of scan loss at 60° look angles and likely higher values of scan loss due to scan impedance mismatch. Analog beamforming phased arrays are currently limited to four simultaneous receive beams, with two beams being more common, as state-of-the art chips and printed circuit board layouts cannot accommodate more electronics. Element level digital beamforming receive arrays can theoretically produce many more antenna beams, but the associated analog-to-digital converters and associated electronics drive up cost and power consumption. And the digital phased arrays still have the same scan loss limitations as previously mentioned for their analog counterparts. The phased array is low profile compared to the spherical Luneburg lens which may be an advantage in certain applications such as for airborne platforms. However, if profile is not a constraint, the Luneburg lens has significant advantages of the large number of beams and better extreme angle scan performance.

[0092] The Luneburg lens is capable of combining multiple unwitting signals to identify the location of one or more targets. Unlike legacy systems that rely on low-gain, single-output omnidirectional antennas, the Luneburg lens can collect multiple direct and reflected signals from numerous unwitting transmitters with high gain. The system can also be configured to transmit location, speed, and other identifying data about uncooperative targets to a centralized processing center via wired or wireless channels, if desired.

[0093] By employing multiple lens antennas, the passive radar system described here improves accuracy in determining the angle of arrival and location of targets compared to a single bistatic radar system. As with all passive radar systems, this multi-static configuration is less susceptible to detection and malicious interference than active radar because it does not transmit any signals. Instead, it relies entirely on receiving signals from unwitting transmitters, making it more difficult to detect and jam.Luneburg Lens for Beamforming & Beam-steering

[0094] Due to the inherent property of essentially infinite focal points, a Luneburg Lens is an attractive option for an antenna because it can focus on radio waves emanating from any direction.International Patent Application Atty. Docket No. 3000060-023977

[0095] While the present invention is described with respect to what is presently considered to be the preferred embodiments, it is understood that the invention is not limited to the disclosed embodiments. The present invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

[0096] Furthermore, it is understood that this invention is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to limit the scope of the present invention, which is limited only by the appended claims.

[0097] Although the invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it should be understood that certain changes and modifications may be practiced within the scope of the appended claims. Modifications of the above-described modes for carrying out the invention that would be understood in view of the foregoing disclosure or made apparent with routine practice or implementation of the invention to persons of skill in electrical engineering, telecommunications, computer science, and / or related fields are intended to be within the scope of the following claims.

[0098] All publications (e.g., Non-Patent Literature), patents, patent application publications, and patent applications mentioned in this specification are indicative of the level of skill of those skilled in the art to which this invention pertains. All such publications e.g., Non-Patent Literature), patents, patent application publications, and patent applications are herein incorporated by reference to the same extent as if each individual publication, patent, patent application publication, or patent application was specifically and individually indicated to be incorporated by reference.

Claims

International Patent Application Atty. Docket No. 3000060-023977CLAIMSWe claim:

1. A passive radar system comprising: a Luneburg lens antenna system, wherein at least one feed is electrically coupled to at least one Luneburg lens antenna; a switching network connecting the at least one feed to at least one receiver; wherein the system is configured to support one or more independent directional beams, configured to receive signals from unwitting transmitters, wherein the passive radar system is configured to capture both a direct signal from a transmitter, optionally an intentional transmitter and / or an unwitting transmitter, and a reflected signal from a target and further comprising software configured to correlate the direct signal and the reflected signal to detect the target, and, optionally, collect identifying information.

2. The passive radar system of claim 1, wherein the system further comprises a power source.

3. The passive radar system of claim 1 or 2, wherein the identifying information comprises speed, location, heading, or a combination thereof, of the target.

4. The passive radar system of any one of claims 1-3, wherein the transmitter originates from the target, satellite, communications station, multiple frequencies, telemetry, vehicle, or a combination thereof.

5. The passive radar system of any one of claims 1-4, wherein the system is configured to allow the intersection of the adjacent scanned beams to be designed to be approximately ldB-3dB below the peak gain value.

6. The passive radar system of any one of claims 1-5, wherein the Luneburg lens has a wideband frequency coverage allowing for operation in multiple frequency bands simultaneously.

7. The passive radar system of any one of claims 1-6, wherein the Luneburg lens is configured for multiple simultaneous beams.International Patent Application Atty. Docket No. 3000060-0239778. The passive radar system of any one of claims 1-7, wherein the Luneburg lens is configured to provide coverage of the upper hemisphere relative to the antenna, optionally up to + / - 90 degrees from boresight at zenith.

9. The passive radar system of any one of claims 1-8, wherein the individual elements of the antenna function as individual feeds for individual beams aimed in separate directions through the lens.

10. The passive radar system of any one of claims 1-9, wherein the antenna is configured to passively receive signals at full gain.

11. The passive radar system of any one of claims 1-10, wherein the antenna can receive a plurality of signals of beams simultaneously, optionally all signals of beams simultaneously.

12. The passive radar system of any one of claims 1-11, wherein the antenna is configured to allow for detection and capture of signals within a hemispheric field of view.

13. The passive radar system of any one of claims 1-12, wherein the antenna is configured for collecting signals pinpointed by source orientation relative to the antenna through back-end processing.

14. The passive radar system of any one of claims 1-13, wherein the Luneburg lens antenna system is configured to receive a direct signal and a reflected signal from a target.

15. The passive radar system of any one of claims 1-14, wherein the Luneburg lens antenna system is configured to receive a direct signal from an unwitting transmitter independent of the target and a reflected signal from the target.

16. The passive radar system of any one of claims 1-15, wherein the Luneburg antenna is a multibeam antenna capable of efficiently capturing and tracking targets and references from multiple directions with high gain.

17. The passive radar system of any one of claims 1—16, wherein the direct signal is a signal(s) of opportunity from a transmitting tower.

18. The passive radar system of any one of claims 1-17, wherein the system utilizes signals from unwitting transmitters.

19. The passive radar system of any one of claims 1-18, wherein the system is configured to covertly detect and track targets without emitting its own signals.International Patent Application Atty. Docket No. 3000060-02397720. The passive radar system of any one of claims 1-19, wherein the system comprises multiple Luneburg lens antenna systems, optionally configured to cover multiple frequency bands.

21. The passive radar system of any one of claims 1-20, wherein the system is configured to receive signals from direct broadcast satellite (DBS) television transmitters in geosynchronous earth orbit (GEO).

22. The passive radar system of any one of claims 1-21, wherein the system is configured to receive signals from an unwitting transmitter, optionally wherein the unwitting transmitter is a low earth orbit (LEO) satellite, GEO, MEO, Non-geosynchronous satellites, Non-Geostationary Satellite Orbit (NGSO), specifically in Medium Earth Orbit (MEO) and Low Earth Orbit (LEO), terrestrial based transmitter, airborne transmitters, transmitters in orbit, vehicles, air, sea, and land based vehicles, or a combination thereof.

23. The passive radar system of any one of claims 1-22, wherein the satellites are considered non-cooperative and their signals are not demodulated.

24. The passive radar system of any one of claims 1-23, wherein the system utilizes both GEO and LEO satellite signals of opportunity.

25. The passive radar system of any one of claims 1-24, wherein the multibeam sensor is configured to receive signals from multiple satellites simultaneously.

26. The passive radar system of any one of claims 1-25, wherein the system is configured to leverage high bandwidth signals for improved range resolution and long duration signals for increased detection range.

27. The passive radar system of any one of claims 1-26, wherein the system further comprises geosynchronous systems, optionally Direct Broadcast Satellite signals.

28. The passive radar system of any one of claims 1-27, wherein each feed is linked to its own individual receiver.

29. The passive radar system of any one of claims 1-28, wherein the system is configured to focus electromagnetic waves emanating from any direction.

30. The passive radar system of any one of claims 1-29, wherein each feed has an unobstructed view to the opposite side of the lens.

31. The passive radar system of any one of claims 1-30, wherein the system is configured to scan away from boresight at zenith with minimal scan loss.International Patent Application Atty. Docket No. 3000060-02397732. The passive radar system of any one of claims 1-31, wherein the Luneburg lens has a focal point located on the surface of the lens.

33. The passive radar system of any one of claims 1-32, wherein the Luneburg lens has a focal point located outside the surface of the lens, optionally a gap consisting of air or other material.

34. The passive radar system of any one of claims 1-33, wherein the focal point is located on an imaginary sphere surrounding the lens.

35. The passive radar system of any one of claims 1-34, wherein the system comprises a plurality of lenses configured to provide unobstructed views for each feed to the opposite side of the lens.

36. The passive radar system of any one of claims 1-35, wherein the system is configured to provide at least two simultaneous beams per terminal.

37. The passive radar system of any one of claims 1-36, wherein the system comprises a network of distributed sensors that provide data as inputs to algorithms for determining positions of emitting sources.

38. The passive radar system of any one of claims 1-37, wherein the system comprises multiple Luneburg lens antenna systems, each one configured to provide unobstructed views for each feed to the opposite side of the lens.

39. The passive radar system of any one of claims 1-38, wherein the system is configured to provide at least two simultaneous beams per terminal.

40. The passive radar system of any one of claims 1-39, wherein the system is configured to provide uninterrupted scan coverage up to the horizon.

41. A passive radar system of comprising: a plurality of Luneburg lens antenna, wherein at least one feed is electrically coupled to the Luneburg lens antenna; a switching network connecting the at least one feed to at least one receivers; wherein the system is configured to support one or more independent directional beams, configured to receive signals from unwitting transmitters.

42. A vehicle comprising the passive radar system of any one of claims 1-41.

43. The vehicle of claim 42, wherein the vehicle is a surface vehicle, an airborne vehicle, or a submersible vehicle, optionally an unmanned marine vehicle (UMV).International Patent Application Atty. Docket No. 3000060-02397744. The vehicle of claim 42 or 43, wherein the vehicle is autonomous.

45. A method for passive radar detecting comprising: a. configuring the passive radar system of any one of claims 1-41 to focus electromagnetic waves emanating from a plurality of directions; b. utilizing a plurality of feeds electrically coupled to the passive radar system to receive the focused electromagnetic waves; c. transmitting the focused electromagnetic waves through a plurality of feeds through a switching network to at least one receiver; d. sending at least one independent directional beams via the passive radar system; e. correlating the received signals to enable identification characteristics of at least one uncooperative target, f. optionally transmitting the identifying information.

46. The method of claim 45, wherein the system is configured to receive a direct signal from multiple transmitting towers.

47. The method of claim 45 or 46, wherein the system is configured to receive multiple reflected signals per target.

48. The method of any one of claims 45-47, wherein two or more antennas are used in a system and the exact location of any signal source is determined.

49. The method of any one of claims 45-48, wherein the antenna is used to locate two or more known signal sources to determine the exact position and orientation of the antenna.

50. The method of any one of claims 45-49, wherein the antenna is used in an Alternate Positioning, Navigation, and Timing (APNT) scenario.

51. The method of any one of claims 45-50, wherein the passive radar captures both the direct signal and a reflected signal from the target, correlating them to identify and detect it.

52. The method of any one of claims 45-51, wherein the system transmits the identifying information.

53. The method of claim 52, wherein the identifying information is speed, location, heading, or a combination thereof.

54. The method of any one of claims 45-53, wherein the system operates when the emitting source locations are unknown.International Patent Application Atty. Docket No. 3000060-02397755. The method of any one of claims 45-54, wherein the passive radar system utilizes signals from terrestrial transmitters.

56. The method of any one of claims 45-55, wherein the system is configured to receive signals within the frequency range of 87.5 to 108.0 MHz.

57. The method of any one of claims 45-56, wherein the system is configured to receive signals over the UHF spectrum of 470 to 806 MHz.

58. The method of any one of claims 45-57, wherein the system is configured to receive signals from cellular phone network frequency bands.

59. The method of any one of claims 45-58, wherein the system is configured to receive signals from direct broadcast satellite (DBS) television transmitters in geosynchronous earth orbit (GEO), low earth orbit (LEO) satellites, GEO, MEO, Non-geosynchronous satellites, Non-Geostationary Satellite Orbit (NGSO), specifically in Medium Earth Orbit (MEO) and Low Earth Orbit (LEO), or a combination thereof.

60. The method of any one of claims 45-59, wherein the system is configured to receive signals from low earth orbit (LEO) satellite constellations.

61. The method of any one of claims 45-60, wherein the satellites are considered non- cooperative and their signals are not demodulated.

62. The method of any one of claims 45-61, wherein both GEO and LEO satellite signals of opportunity are utilized.

63. The method of any one of claims 45-62, wherein the Luneburg lens antenna system is configured to receive signals from multiple satellites simultaneously.

64. The method of any one of claims 45-63, wherein the system focuses electromagnetic waves emanating from any direction.

65. The method of any one of claims 45-64, wherein the system scans away from boresight at zenith with minimal scan loss.

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