Patent Application
20240134027
Assignee:
Appl. No.:
CPC: G01S 13/00 (2006.01); G01S 13/02 (2006.01); G01S 13/03 (2006.01); G01S 13/72 (2006.01).
Field of Classification Search: G01S 7/02 (2006.01); G01S 7/023 (2006.01); G01S 7/03 (2006.01); G01S 7/354 (2006.01); G01S 7/040 (2006.01); G01S 7/4865 (2006.01); G01S 7/493 (2006.01); G01S 7/536 (2006.01); G01S 13/00 (2006.01); G01S 13/02 (2006.01); G01S 13/03 (2006.01); G01S 13/08 (2006.01); G01S 13/325 (2006.01); G01S 13/931 (2006.01); G01S 15/08 (2006.01); G01S 17/08 (2006.01); G01S 17/32 (2006.01).
Passive radars are based on the reception of a group of signals transmitted by outside non-cooperative sources. These signals may be of different kind, e.g., frequency-modulated (FM) radio, Digital Video Broadcasting (DVB-T), Global System for Mobile Communications (GSM), Global Navigation Satellite System (GNSS). The passive radar system receives these signals in two ways: first is the signal directly from a transmitter (direct or reference signal), second is the signal reflected from an object of interest (reflected or scattered from target signal) (
Passive radar utilizing space-born digital electromagnetic illuminators described in U.S. Pat. No. 7,619,554 B2 patent, Dan Abraham Shklarsky, November 2009, (PRIOR ART FIG. 1). In this passive radar system, a space-borne transmitter broadcasts wide-band digitally modulated signals over a region and illuminates the region. A receiver antenna is oriented to receive radiation from at least one portion of the region. The portion is an area viewed by the receiver antenna. A reference antenna is oriented toward the transmitter, the reference antenna receives a portion of the wide-band digitally modulated signal. A coherent processing time duration is selected based on a radar cross-section of a target within the viewed area, a bandwidth of the wide-band digitally modulated signal, and the viewing angle of the receiver antenna. The received signal from the receiver antenna is coherently processed with a reference signal from the reference antenna, over a time interval greater than the coherent processing time duration. But using of a few separate antennas required lot of space and pointing accuracy, which is sometime not possible.
A method of determining the location of a physical object using a passive radar receiver described in US 2022/0268908 A1 patent, Robert Clark Daniels, 08/2022 presented in PRIOR ART FIG. 2. A method of determining the location of a physical object using a passive radar receiver includes determining if a transmitter beam sweeping period (TBSP) is known and executing a TBSP-based receiver beam sweeping if the TBSP is known. If the TBSP is not known, determining if the TBSP can be measured, and executing the TBSP-based beam sweeping if the TBSP can be measured. The method includes executing a random receiver beam sweeping if the TBSP is not known and cannot be measured. The method includes determining a relative time of arrival of radio signals between the line of sight (LoS) path and the target path and determining the propagation times on the LoS path and on the target path. The method includes determining the location of the physical object using the propagation times.
In paper of Alp Sayin, Mikhail Cherniakov, Michail Antoniou “Passive radar using Starlink [1] the LEO satellites signals for radar passive detection examined. A study on passive radar detection capabilities using SpaceX broadband internet satellite constellation has been done. The passive radar system was found to be feasible when compared to an already proven system, GNSS, with a similar structure. For returns from a single satellite cell with over a 250 MHz bandwidth and the size of both the reference antenna (for direct signal reception) and the radar antenna (for echo reception) assumed to be 1 m2, at X-band, the beamwidth of such an antenna would be about 1.3 degrees. This antenna may be a phased array, or a multi-beam staring array for a chosen target area.
S. Harman in his paper “A comparison of staring radars with scanning radars for UAV detection” [2]. Staring radars have multiple static receiver beams that do not scan and are constantly sensing. The fundamental difference between staring and scanning radars is that for a staring radar the transmit beam is stationary and fully filled with potentially multiple static receiver beams. The number of receiver beams within the transmit floodlight determines the gain on receive and the ability to localize in angle. The key opportunity that staring radars offer is the ability to give exceptional information and utility e.g., optimal detection, tracking and target ID capability in an optimal time (
To reach maximal accuracy of direction finding Lipsky S. E. [3] proposed an antenna array of a plurality of fixed, narrow beamwidth antennas, geographically oriented to provide omnidirectional coverage, a set of antennas is selected. It presents an explanation of the monopulse method for microwave direction finding with two pairs of directional antennas, positioned by Azimuth and Elevation boresight. The general theory of the monopulse method considers that the angle sensing function falls into one of three categories: amplitude, phase, or a combination developed by combining their sum and difference (Σ−Δ).
The phase angle difference, as measured in each antenna, compared against the arriving signal phase front, is denoted as ψ. The difference in signal path length is defined by the equation, S=D sin φ, which depends on the antenna aperture displacement (spatial angular shift) D. Letting φ be the phase lag caused by the difference in the time of arrival between two signals gives:
If A and B are RF voltages measured at the reference boresight and incident antennas, respectively, then
where M is a common constant defined by signal power. This shows that the angle of arrival φ is contained in the RF argument or phase difference of the two beams for all signals off the boresight axis. Direction finding by way of amplitude comparison methods can provide a root mean square (RMS) accuracy smaller than 2° in 100 ns after a direct wave arrives. High accuracy phase measurements provide high accuracy and fast direction finding (
Combination of staring antenna array with high directional accuracy monopulse method proposed in paper P. Molchanov, A. Gorwara, “Fly Eye Radar Concept” [4].
Present invention related to systems using the reflection or reradiation of radio waves, e.g., radar systems, which including analogous systems using reflection. More particular to bistatic or multi-static radar systems with non-cooperative transmitting source. As transmitting source proposed application of LEO and VLEO satellite signals, which can provide more power than GNSS constellations and available at some remote areas.
In the patent “Passive coherent location system and method”, U.S. Pat. No. 6,522,295 B2 Baugh et al., Feb. 18, 2003, proposed passive radar system for enhancing object State awareness. The system includes a receiver subsystem that receives reference signals from an uncontrolled transmitter and scattered transmissions originating from the uncontrolled transmitter and scattered by an object. The system also includes a front-end processing subsystem that determines a radial velocity of the object based on the received transmissions. The system also includes a back-end processing subsystem that determines object state estimates based on the determined radial velocity.
System needs to use selected a subset of uncontrolled transmitters. The step may comprise Selecting a Subset of uncontrolled transmitters from a plurality of uncontrolled transmitters based on a Set of predetermined criteria. Subset of uncontrollable transmitters not always possible at some area of radar application.
Stephen Anthony Harman in his patent from Jul. 13, 2021, U.S. Pat. No. 11,061,114 B2 “Radar system for the detection of drones” and patent U.S. Pat. No. 9,097,793 B2 “System for the detection of incoming munitions” proposed a radar system for the detection of drones, including a transmitter, a receiver and a processor, wherein the processor is arranged to process demodulated return signals in a first process using a Doppler frequency filter, and to store locations of any detections therefrom, and to process the demodulated signals in a second process to look for signal returns indicative of a preliminary target having a rotational element at a location, and should a detection be found in the second process, to then attempt to match a location of the preliminary target with returns from the first process, and to provide a confirmed detection if a location of a detection from the first process matches with the location of a detection from the second process.
System provides good accuracy of multiple targets detection with non-scanning antenna beam that illuminates the entire search space, but it is not passive and transmitting signals can be detected. Computing of received signals take some time exceeded time for hypersonic missile hit on tactical distance.
In patent WO 2011/033320 A2, March 2011, by Oswald Gordon, which presented in PRIOR ART
Every antenna element in phase array needs to be omnidirectional as minimum in area of beam control. It means, all antenna elements will receive any jamming signal directed from all angles of view. Adaptive algorithm will be possible only, if jamming signal not large enough to saturate all antenna elements simultaneously.
Proposed phase controllable array of antenna elements, wherein first processing stage connected to a few antenna elements. Signals not digitizing on each antenna and not processing from each antenna. Simultaneous digitizing and processing of signals from each antenna element will provide faster processing time for radar.
Application of antennas with overlap antenna patterns will allow better direction finding accuracy by application monopulse method of signals processing and signals from reference antennas.
An objective of the present invention is development of passive radar system and method of detection of low-profile low altitude targets based on application of Low Earth Orbit (LEO) and Very Low Earth Orbit (VLEO) satellites signals. Staring array of directional antennas can cover entire sky and will provide continuous illumination (receiving reflected satellite signals) from multiple targets for fast detection, recognition and targets tracking and increasing detection range. Coupling of each directional antenna with separate receiver cannel will allow fast continuous process of information from all targets simultaneously. Monopulse processing of signals from reference sub-set of antennas with overlap antenna patterns can provide highest directing accuracy and better clutter/noise and media influence suppression. Directional antenna array does not need beam forming module. System will have small weight, size, may be portable or mounted on light vehicle or small drone because small size and weight.
Proposed passive radar system based on application of LEO and VLEO satellites signals for detection of low-profile low altitude targets. In first embodiment radar receiver comprising at least one array of antenna elements and at least one processing stage adapted to process signals received via each antenna element of said array wherein for fast targets signals processing said array of antenna elements arranged as staring array of directional antennas covering entire sky and provide simultaneous continuous illumination (receiving reflected satellite signals) of multiple targets. Each directional antenna coupled with separate processing stage providing fast continuous parallel process of information from all targets simultaneously. Antenna patterns of said directional antennas overlap in one or more directions for creating monopulse subarrays, where signals from reference antennas providing highest directing accuracy and better clutter/noise and media influence suppression. Each said processing stage comprising receiving chain with signal conditioning circuit including voltage or current limiters, anti-aliasing circuits and connected to Field-Programmable Gate Array (FPGA) and to actuator control. Each said monopulse subarray comprising of FPGA for simultaneous one or multi-axis processing of all signals in receiving chains as ratio of amplitudes and/or phase shift of signals for direction finding and one-iteration adapting for clutter suppressing or decrease transferring media influence to receiving chain parameters by phase shift in subarray of neighboring directional antennas with overlap antenna patterns. Each said monopulse subarray connected by digital interface arranged as universal serial bus (USB) or microwave and/or fiber optic waveguides directly to actuator control for fast control of alarm, display, communication or executive means. All said processing stages comprising receiving chains, monopulse processor and signal processor connected with synchronization means.
Detection of direct satellite signals and satellite signals reflected from targets providing by continuous (not scanning) staring array of directional antennas covering entire sky or area of observation and providing simultaneous continuous illumination (receiving reflected satellite signals) of multiple targets. Simultaneous (parallel) processing of direct satellite signals and satellite signals reflected from targets from each directional antenna by separate processing stage including a reference signal for target detection, which is correlated with the reflected signal. Digitizing of direct satellite signals and satellite signals reflected from targets directly in each directional antenna by separate processing stage comprising receiving chain with signal conditioning circuit including voltage or current limiters, anti-aliasing circuits, analog-to-digital converter and connected by digital interface to signal processor and feed network. Simultaneous (monopulse) processing of direct satellite signals and satellite signals reflected from targets received by said directional antennas with overlap antenna patterns in one or more directions for creating monopulse subarrays, where signals from reference antennas providing highest directing accuracy and better clutter/noise and media influence suppression. Simultaneous (monopulse) processing of all signals in receiving chains as ratio of amplitudes and/or phase shift of signals for direction finding and one-iteration adapting for clutter suppressing or decrease transferring media influence to receiving chain parameters by phase shift in subarray of neighboring directional antennas with overlap antenna patterns. Transferring processed signals to feed network by digital interface arranged as universal serial bus (USB) or microwave and/or fiber optic waveguides connected to signal processor. Synchronization of all said processing stages comprising receiving chains, monopulse processors and signal processor connected by digital interface.
PRIOR ART FIG. 1 shows known embodiment of the passive radar system using satellite signals with array of separate directional antennas.
PRIOR ART FIG. 2 shows known passive radar system based on application of signals of cell phones base station and sweeping phase array.
PRIOR ART FIG. 3 shows holographic phase array receiver structure.
Corresponding to preliminary investigation LEO or/and VLEO satellites transmitting signals, which can be used for passive targets detection [1]. Diagram of proposed passive radar system based on application of LEO and VLEO satellites signals for detection of low-profile low altitude targets presented in
Scanning phase array allows simultaneous detecting and tracking multiple targets by switching beam, which decreasing more time of each target illumination. Array of directional antennas allows simultaneous parallel processing of signals from all antennas same time.
Increasing of number of scanning beams proportional decreasing number of beam forming antenna elements and decreasing array gain, sensitivity and radar range. Gain and radar range constant for array of directional antennas.
As seen from diagram, smaller phase difference and same phase difference can be measured with much better accuracy by using antennas with overlap antenna patterns.
Operation
Proposed passive detection of low-profile low altitude targets based on application of Low Earth Orbit (LEO) and Very Low Earth Orbit (VLEO) satellites signals by the radar receiver comprising at least one array of antenna elements and at least one processing stage adapted to process signals received via each antenna element of said array. Detection of direct satellite signals and satellite signals reflected from targets providing by continuous (not scanning) staring array of directional antennas covering entire sky or area of observation providing by simultaneous continuous illumination (receiving reflected satellite signals) of multiple targets.
Next step is simultaneous (parallel) processing of direct satellite signals and satellite signals reflected from targets from each directional antenna by separate processing stage including a reference signal for target detection, which is correlated with the reflected signal. Direct satellite signals and satellite signals reflected from targets are digitizing directly in each directional antenna by separate processing stage comprising receiving chain with signal conditioning circuit including voltage or current limiters, anti-aliasing circuits, analog-to-digital converter and connected by digital interface to signal processor and feed network. Processing of direct satellite signals and satellite signals reflected from targets received by said directional antennas with overlap antenna patterns creating monopulse subarrays, providing simultaneously, by application of monopulse method. In this case signals from reference antennas providing highest directing accuracy and better clutter/noise and media influence suppression. All signals in receiving chains are processing simultaneous (monopulse method) as ratio of amplitudes and/or phase shift of signals for direction finding and one-iteration adapting for clutter suppressing or decrease transferring media influence to receiving chain parameters by phase shift in subarray of neighboring directional antennas with overlap antenna patterns. Processed signals are transferring to feed network by digital interface arranged as universal serial bus (USB) or microwave and/or fiber optic waveguides connected to signal processor. Synchronization of all said processing stages, monopulse processors and signal processor providing by synchronization means.
Cover of entire sky and continuous illumination (receiving reflected satellite signals) of multiple targets providing by staring array of directional antennas increasing radar sensitivity, detection range and recognition probability for low profile low altitude targets.
Coupling of each directional antenna with separate receiver channel allows receive information about multiple targets simultaneously and much faster.
Monopulse processing of signals from reference sub-set of antennas with overlap antenna patterns provides highest directing accuracy and better clutter/noise and media influence suppression.
Separate controlling of transmitting power and gain of receiver chains in each subdivided sectors by automatic gain control circuit provides possibility to use proposed radar system in urban and mountains areas. Automatic gain control circuits also allow to simultaneous detection of small range targets with high amplitude reflected targets and targets with small, reflected signals.
Application of multiple directional antennas provides larger signal gain compere to phase arrays, where signal gain decreasing proportional to number of beams.
Distribution of directional antennas decrease passive radar vulnerability because each directional antenna/subarray covering one subdivided sector and cannot be damaged by EMP positioned outside of sector area because of application of directional antennas. Reflected signals simultaneously receiving from all targets within each subdivided sector and can be processed same time.
Digitizing and synchronization of all receiving signals by microwave or/and optical means directly on directional antennas allows loos distribution of antennas without complicate phase adjustment matrixes.
Directional antenna array does not need beam forming module. System has small weight, size, may be portable or mounted on light vehicle or small drone because small size and weight.
