Landing navigation based on radar altimeter and multi-echo RF beacon

Abstract

A method includes providing a radar sensor onboard a vehicle, and providing one or more active radar beacons around a landing point. Each beacon generates one or more man-made echoes in a certain mode, the one or more man-made echoes in the certain mode being different from the echoes in the certain mode generated by other beacons in the beacon. The method further includes directing the vehicle toward the landing point by transmitting a radar signal from the radar sensor to an area around the landing point; receiving return signals from the area around the landing point, including ground reflected signals and transmit signals from each beacon; and determining whether an artificial echo is detected in the received return signal. When artificial echoes are detected, beacon parameters are loaded from an airborne active beacon database; identifying a pattern in the artificial echo and associating it with a corresponding beacon from the database; and estimating a slope distance to each of the beacons through the pattern.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of and priority to U.S. Provisional Application No. 63 / 510,973, filed on June 29, 2023, the disclosure of which is incorporated herein by reference. Background Art

[0003] Navigation is one of the key components for autonomous aircraft operations. Moreover, for vertical take-off and landing (VTOL) aircraft, the landing phase is the most important phase of VTOL autonomous flight, especially in terms of navigation accuracy and integrity. The navigation solution for this landing phase assumes a mix of various sensors and systems to establish an overall solution that meets stringent navigation requirements. Examples of such sensors and systems include inertial sensors, inertial navigation systems (INS), global navigation satellite system (GNSS) sensors, barometers, and radar altimeters, which are used to determine the horizontal and vertical position of the aircraft.

[0004] The problem for systems on such aircraft is meeting navigation requirements in GNSS-denied conditions. Unfortunately, conventional radar altimeters, such as those used during the landing phase, only provide vertical position information. While multilateration of point-like ground reflective objects can extend radar altimeter capabilities, there are certain drawbacks.

[0005] For example, it has been considered to support VTOL operations using passive radar reflectors. However, the placement of passive radar reflectors is not a simple task. Even if the radar has the ability to provide accurate angular information (e.g., using monopulse or multiple-input multiple-output (MIMO) technology), due to side lobes or wide antenna beam widths, it is still necessary to distinguish between targets at the same distance (within the same sensor range bin). In addition, clear identification of each reflector is necessary for providing a reliable navigation solution with information of sufficient integrity. In addition, it is necessary to install the reflector both near the center of the helipad or vertical take-off and landing site (vertiport) (due to the radar beam width) and above the ground (at different distances outside the ground). This makes installation extremely time-consuming and complicated. Summary of the invention

[0006] A method includes providing a radar sensor unit onboard a vehicle, and providing one or more active radar beacons around a landing site. Each active radar beacon generates one or more artificial echoes of a certain pattern, and the one or more artificial echoes of a certain pattern are different from the one or more artificial echoes of a certain pattern generated by other active radar beacons in the one or more active radar beacons. The method also includes guiding the vehicle toward the landing site by a process including the following: transmitting a radar signal from the radar sensor unit to an area around the landing site; receiving a return signal from the area around the landing site in the radar sensor unit, the return signal including a ground reflection signal and a transmission signal from the one or more active radar beacons; and determining whether an artificial echo is detected in the received return signal. When an artificial echo is detected, the process also includes loading parameters of the one or more active radar beacons for the landing point from an onboard active beacon database; identifying one or more patterns in the detected artificial echo; associating the identified one or more patterns with corresponding one or more active radar beacons in the active radar beacons from the active beacon database; and estimating a slant range to each of the one or more active radar beacons by the identified patterns in the detected artificial echo. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Features of the present invention will become apparent to those skilled in the art through the following description with reference to the accompanying drawings. Understanding that the drawings depict only typical embodiments and are not therefore to be considered limiting of the scope of the invention, the invention will be described with additional specificity and detail through the use of the accompanying drawings, in which:

[0008] Figure 1 VTOL operation utilizing a passive radar reflector is shown according to one example;

[0009] Figure 2 VTOL operations utilizing active radar beacons according to one specific implementation are shown;

[0010] Figure 3 VTOL operations using an active radar beacon utilizing multiple artificial reflections according to another specific implementation are shown;

[0011] Figure 4 is a flow chart of an onboard process using a radar system utilizing an active radar beacon according to one specific implementation;

[0012] Figure 5 is a block diagram of an airborne radar system configured to use an active radar beacon according to one embodiment;

[0013] Figure 6 is a block diagram of an active radar beacon according to one embodiment;

[0014] Figure 7 is a schematic diagram of an active radar beacon that may be used for a frequency modulated continuous wave (FMCW) radar according to one embodiment;

[0015] Figure 8 is a graphical representation of exemplary FMCW signals received from a passive target and an active radar beacon;

[0016] Fig. 9 is a plot of example radar Fast Fourier Transform (FFT) data including ground clutter and two artificial echoes;

[0017] FIG. 10A to FIG. 10D is a schematic diagram of an active radar beacon according to various example embodiments;

[0018] Fig.11 is a schematic diagram of an active radar beacon according to another example embodiment; and

[0019] Fig.12 is a schematic diagram of an exemplary vehicle navigation method using at least one multi-point positioning beacon. DETAILED DESCRIPTION

[0020] In the following specific embodiments, the embodiments are fully described to enable those skilled in the art to practice the present invention. It should be understood that other embodiments may be utilized without departing from the scope of the present invention. Therefore, the following detailed description should not be considered to have a limiting meaning.

[0021] Methods and systems for landing navigation based on radar sensors and multi-echo radio frequency (RF) beacons are described herein.

[0022] The present method and system may use active radar RF beacons together with radar sensors such as radar altimeters for landing operations of various aircraft. Examples of such aircraft include VTOL vehicles, such as helicopters, unmanned aerial vehicles (UAVs), urban air mobility (UAM) vehicles, etc. In addition, the present method and system may be applicable to other types of aircraft and various approach / landing paths. In some examples, other radar sensors that measure distance may also be used instead of radar altimeters that may be onboard. These examples include, but are not limited to, scanning radars, mechanically scanning radars, electronically scanning radars, radars using MIMO processing, etc. In addition, the present method is applicable to various radar installations, such as downward-looking radar sensors, forward-looking radar sensors, side-looking radar sensors, etc.

[0023] The use of a certain pattern of artificial ranges (or echoes) created by active transponders on the ground enables an onboard navigation system to determine not only vertical position but also horizontal position, and use conventional radar altimeter hardware with improved software functionality to support navigation integrity. The present method provides an additional alternative source of horizontal and vertical position that can improve the performance of current navigation solutions, or replace, for example, GNSS information sources in a navigation system.

[0024] Artificial echoes may be generated by active radar beacons to support beacon identification. The distance to the artificial echo includes the distance to the active radar beacon (which is changing) and an artificially established range offset (which is constant). The artificial range offset (which is different from the true range) remains constant during the vehicle's descent, thus making the beacon easier to identify.

[0025] The present method allows for the establishment of a unique beacon pattern (e.g., a pattern may be unique to a neighboring vertiport). In one embodiment, one or more active radar beacons may be implemented as signal repeaters around the landing site. The artificial distance represents a repeating signal that may or may not be modified.

[0026] The present system may include two subsystems, a ground subsystem and an airborne subsystem. The ground subsystem includes an active RF beacon with a known position and can operate in a radar altimeter band. The active RF beacon is configured to generate a unique multi-echo pattern for each active beacon. The airborne subsystem may use a radar altimeter (e.g., a single antenna radar altimeter (SARA)) with extended embedded software that can detect additional echoes at a distance farther from the active RF beacon. The airborne software can identify the pattern in the detected echo and associate the echo with the pattern of the active RF beacon stored in the airborne database for the specific beacon position. The airborne software estimates the slant range to the active beacon by the detected multi-echo pattern. Then, the software estimates its own three-dimensional (3D) position by locating the estimated slant range multipoint to the active RF beacon and their known positions and using other sensors on the vehicle to measure.

[0027] The method can estimate the 3D position of the aircraft in various reference frames for use in generating a navigation solution for the vehicle. Examples of reference frames include the North East Earth (NED) frame, the local landing zone frame, the vertical take-off and landing field frame, etc.

[0028] The radar sensor onboard the self / platform may be a common radar altimeter or any radar sensor capable of the following functionality. Additional processing may be implemented to obtain more detections (beyond the traditional distance to the ground), match these detections with active RF beacons, and calculate the self 3D position. The additional processing may be a software modification or extension of a standard radar altimeter (e.g., SARA). In other words, the additional functionality may be fully integrated into the processor of the radar altimeter. The processing of the raw radar altimeter data may also be done by an onboard computing platform external to the radar altimeter. As such, the additional functionality may be implemented in an onboard external computing platform for processing data from the radar altimeter. Alternatively, the additional functionality may be divided between the radar altimeter and the onboard external computing platform.

[0029] The present approach has the advantage of providing support for all-weather operations compared to alternatives such as those based on electro-optical / infrared (EO / IR) systems. The present approach also provides for the extension of radar altimeter capabilities to full 3D position solutions in conjunction with RF beacons on the ground (e.g., on a landing pad or vertiport). The present approach also allows support for multiple landing pads located at the same vertiport.

[0030] Furthermore, the system can be implemented without the need for additional onboard sensors and supports navigation integrity. A greater number of active RF beacons, receiver autonomous integrity monitoring (RAIM), solution separation or other integrity techniques can be used to ensure navigation integrity.

[0031] The present method is generally applicable to both continuous wave (CW) (including FMCW) and pulse radars. In addition, one or more passive targets or reflectors may be employed along with active RF beacons. Furthermore, active RF beacons may rebroadcast received signals without requiring additional adjustments other than amplification (thus establishing a strong zero ground reference "target").

[0032] In some implementations, the ground subsystem may be configured for activation only when a signal from a radar altimeter is detected.Beacon antennas with narrow beamwidths may be used by active RF beacons to limit areas where these beacons may interfere with or increase the noise level of radar altimeter measurements.

[0033] Furthermore, the method is generally applicable to different radars (except radar altimeters) operating in different frequency bands.

[0034] Additional details of various embodiments are described below and with reference to the accompanying drawings.

[0035] The nomenclature used herein and in the accompanying drawings is defined as follows:

[0036] R1, R2, R3 passive target / radar reflector;

[0037] h R1 、h R2 、h R3 The installation height of reflectors R1 to R3 (height above the ground / helipad / vertiport);

[0038] h Self / platform height above ground / helipad / vertiport;

[0039] r1, r2, r3 are the slant distances between the airborne radar and the reflectors R1, R2, R3; if the reflector is an active beacon, the slant distance is between the actual antenna positions of the airborne radar and the active beacon;

[0040] R A1 , R A2 , R A3 Active radar beacons (location of transmitter (TX) and receiver (RX) antennas);

[0041] R A1-AP1 Active radar beacon R A1 Established artificial position (artificial range echo) #1;

[0042] R A1-AP2 Active radar beacon R A1 Established artificial position (artificial range echo) #2;

[0043] Δr 3-AP1 Active radar beacon R A3 Created artificial slant range offset #1 (first);

[0044] Δr 3-AP2 Active radar beacon R A3 Created artificial slope range offset #2 (second).

[0045] Figure 1 An example VTOL operation 100 for a vehicle 102 (e.g., a helicopter, UAV, UAM vehicle, etc.) using passive radar reflectors R1, R2, R3 positioned at a landing site 110 is shown. As shown, the vehicle 102 is at an altitude h above the landing site 110 and has respective slant ranges r1, r2, r3 to the passive radar reflectors R1, R2, R3. The passive radar reflectors R1, R2, R3 have respective mounting altitudes h above the landing site 110. R1 、h R2 、h R3 .

[0046] Figure 2 An example of using an active radar beacon R located at a landing point 210 according to one embodiment of the present method is shown. A1 , R A2, R A3 VTOL operation 200 for a vehicle 202 (eg, a helicopter, UAV, UAM vehicle, etc.). As shown, the vehicle 202 is at an altitude h above a landing site 210 and has a direct line of sight to an active radar beacon R A1 , R A2 and R A3 The corresponding slant ranges r1, r2 and r3 of the active radar beacon R A1 Establish a corresponding artificial slant range offset Δr 1-AP1 Artificial position (artificial range echo) R A1-AP1 . Active radar beacon R A2 Establish a corresponding artificial slant range offset Δr 2-AP1 The artificial position R A2-AP1 . Active radar beacon R A3 Establish a corresponding artificial slant range offset Δr 3-AP1 The artificial position R A3-AP1 .

[0047] When only passive reflectors are used (such as Figure 1 As shown), Figure 2 The active radar beacon shown can overcome the distance separation problem by offsetting the actual distance between the radar and the beacon (e.g., the artificial slant range may be different for each beacon). In addition, the physical size of the active radar beacon can be embedded at the landing site surface during installation and thereby prevent any obstacles from being established within the landing area.

[0048] Figure 3 Another embodiment of the present method is shown using an active radar beacon R located at a landing point 310. A1 , R A2 , R A3 VTOL operation 300 for a vehicle 302 (eg, a helicopter, UAV, UAM vehicle, etc.). As shown, the vehicle 302 is at an altitude h above a landing site 310 and has a direct line of sight to an active radar beacon R A1 , R A2 and R A3 The corresponding slant ranges r1, r2 and r3 of the active radar beacon R A1 Create multiple artificial positions (artificial range echoes) R with corresponding artificial slant range offsets A1-AP1 , R A1-AP2 , R A1-AP3 For example, the artificial position R A1-AP1 With artificial slope range offset Δr 1-AP1 , and the artificial position R A1-AP3 With artificial slope range offset Δr 1-AP3 . Active radar beacon R A2Create an artificial slant range offset Δr 2-AP1 The artificial position R A2-AP1 . Active radar beacon R A3 Establish a corresponding artificial slant range offset Δr 3-AP1 and Δr 3-AP2 Multiple artificial locations R A3-AP1 , R A3-AP2 .

[0049] Figure 3 A scenario is shown where each active radar beacon produces a different set of artificial slant ranges. The artificial slant ranges may be different for each beacon, and the set of slant ranges may be different for each installation / landing zone. This information establishes a pattern and can be used to identify individual active beacons and landing zones.

[0050] Figure 4 4 is a flow chart of an onboard process 400 for using a radar system utilizing one or more active radar beacons according to one specific implementation. The process 400 begins by measuring radar data (block 410) from received return signals (including ground reflection signals and transmitted signals from one or more active radar beacons), such as to form an FFT data distribution. The process 400 also performs ground detection (block 412) using ordinary altimeter logic. The process 400 then performs additional detection for any additional echoes at additional distances generated by the active radar beacons (block 414), and makes a determination as to whether additional echoes are detected (block 416). If not, the process 400 repeats starting at block 410.

[0051] If additional echoes are detected at box 416, the process 400 loads parameters for one or more active radar beacons for the current location / landing zone from the onboard database (box 418). The process 400 identifies patterns in the detected echoes and associates these patterns with patterns of active radar beacons stored in the onboard database (DB) (box 420). For example, the detected additional echoes may form a multi-echo pattern that is identified and associated with patterns of active radar beacons stored in the onboard database for that particular location. The process 400 then estimates the slant range to the active radar beacon (box 422). For example, the slant range to each active radar beacon may be estimated by one or more detected echoes. Finally, the process 400 performs its own 3D position estimation by multi-point positioning of the estimated slant range to the active radar beacons and their known positions (box 424). The position may be estimated in various reference frames, such as the NED frame, the local landing zone frame, the vertical take-off and landing field frame, etc.

[0052] Slant ranges to active radar beacons with their known positions can be used as navigation measurements in the vehicle navigation system and can be used in conjunction with other navigation measurements from other vehicle sensors. In some examples, the angular orientation of the vehicle over the area around the landing zone can be determined based on received return signals from navigation sensors onboard the vehicle. It should be noted that for beacon identification and slant range estimation, at least one artificial echo is required per active beacon.

[0053] The vehicle may partially or completely determine its 3D angular orientation using two or more sensors that receive return signals from beacons. In some examples, the vehicle may estimate its 3D angular orientation using one or more sensors that receive return signals from beacons coupled to an inertial measurement unit. In other examples, the vehicle may estimate its 3D angular orientation using one or more sensors that receive return signals from beacons with angle determination capabilities.

[0054] Airborne radar systems and active radar beacons

[0055] Figure 5 5 is a block diagram of an airborne radar system 500 configured for use with an active radar beacon according to one embodiment. The system 500 includes a radar sensor unit 510 onboard a vehicle 502, such as a VTOL vehicle. The radar sensor unit 510 generally includes at least one antenna 512, a transmitter 514 operatively coupled to the antenna 512, and a receiver 516 operatively coupled to the antenna 512. The antenna 512 may be configured to transmit radar signals or receive return signals, such as an antenna array, etc. In addition, the antenna 512 may be implemented with beam steering capabilities or with a fixed beam direction. In some embodiments, the receiver 516 and the transmitter 514 may each use their own dedicated antenna instead of the antenna 512.

[0056] The radar sensor unit 510 also includes at least one processor unit 520 (e.g., a digital signal processor (DSP), a general purpose processor (GPP), etc.), which includes a radar signal processing and control module 521 that operates to perform radar signal / data processing and radar control. The radar signal processing and control module 521 hosts a signal processing module 522, which is configured to receive a signal from the receiver 516 and process the received signal. The signal processing may include filtering, thresholding, forming a radar image, identification and tracking of targets, etc. The signal processing module 522 can be configured to output raw radar data, radar detection signals, tracking, or any other radar output data. The radar signal processing and control module 521 also hosts a radar configuration and control module 524, which operates to send control signals to the transmitter 514, the receiver 516, or both to control radar scanning and configuration. The radar signal processing and control module 521 may also host other control units ( Figure 5 ), to provide overall radar functionality (eg, radar waveform definition and control, etc.). The radar sensor unit 510 may be configured to operate in different frequency bands (eg, C, X, K, Ku, Ka).

[0057] Onboard application modules 530 are in operative communication with signal processing module 522. In one embodiment, application modules 530 may be hosted on radar sensor unit 510, such as in radar signal processing and control module 521. In another embodiment, application modules 530 may be hosted on a computing platform 532 external to radar sensor unit 510 and onboard vehicle 502. Alternatively, application modules 530 may be distributed across both radar sensor unit 510 and external computing platform 532. Application modules 530 may include radar altimeter applications, Doppler navigation applications, terrain-aided navigation applications, or other similar applications.

[0058] Onboard active beacon database 540 may be hosted on radar sensor unit 510, such as in radar signal processing and control module 521, or may be hosted on a computing platform / storage external to radar sensor unit 510 onboard vehicle 502. Alternatively, active beacon database 540 may be distributed across both radar sensor unit 510 and external computing platform / storage. Active beacon database 540 is configured to store patterns for active radar beacons at specific locations.

[0059] Application module 530 may access information from active beacon database 540 and radar output data (e.g., raw data, altitude, detections, tracks, etc.) from signal processing module 522. Application module 530 may also access platform navigation data 550 from one or more other sensors, which may include the position and attitude of the vehicle or, in some embodiments, information about a landing area for an approach.

[0060] Application module 530 includes program instructions for performing onboard processing using signals from active radar beacons, such as described above with reference to Figure 4 For example, application module 530 may include program instructions for: detection of significant echoes (e.g., detection of distances between radar sensor unit 510 and various beacons (both active and passive)); processing of active beacon database 540 (e.g., extracting data from database 540 using platform navigation data 550); identification of detected echoes (e.g., matching active radar beacons with radar detections); and calculation of own 3D position estimates.

[0061] During operation, application module 530 processes radar data provided by signal processing module 522 using information from active beacon database 540 and platform navigation data 550 (if available).

[0062] Output signals from the application module 530 may be sent to a data receiver / consumer 560, such as a display, indicator light, etc. In some embodiments, the radar sensor unit 510 may use additional processing to determine the direction to the active radar beacon. The direction information may be provided as additional information for vehicle navigation. Additionally, the radar sensor unit 510 may use additional processing to determine the Doppler velocity to the active radar beacon. The Doppler velocity may also be provided as additional information for vehicle navigation.

[0063] Figure 66 is a block diagram of an active radar beacon 610 for use at a landing site according to one embodiment. The active radar beacon 610 includes a receiving (RX) antenna 612 configured to receive a radar signal from an airborne radar system, and a transmitting (TX) antenna 620 configured to send a modified signal back to the airborne radar system. The received radar signal can be amplified and filtered (if necessary) at a first power level adjustment and filtering module 614. The RX signal modification module 616 is configured to perform signal adjustment, which may include signal amplification, signal delay, frequency shift, etc. In addition, the RX signal modification module 616 may also include parallel processing (e.g., signal delay by a parallel delay line). The modified signal from the RX signal modification module 616 can be further amplified and filtered (if necessary) at a second power level adjustment and filtering module 618. The modified signal is then transmitted back to the airborne radar system via the TX antenna 620. Alternatively, the active radar beacon 610 can use a single antenna for receiving and transmitting signals.

[0064] Optionally, active radar beacon 610 may include detection circuitry 630 (e.g., a simple power detector or a more complex conversion to baseband) operative to receive received radar signals and an active beacon control module 634 operatively coupled to detection circuitry 630. Both detection circuitry 630 and active beacon control module 634 may be used to enable active radar beacon 610 to provide a signal only when an incoming radar signal is received (e.g., active radar beacon 610 does not transmit in the absence of an active incoming radar signal) to control the power and / or other parameters of the signal transmitted by active radar beacon 610. Furthermore, additional RF components (e.g., circulators, isolators, attenuators, etc.) may be used as desired for a given active beacon implementation.

[0065] Figure 7 7 is a schematic diagram of a system 700 for using an airborne FMCW radar 710 with an active radar beacon 720 according to an example embodiment. The FMCW radar 710 includes a TX antenna 712 and an RX antenna 714. The active radar beacon 720 includes the RX antenna 722 coupled to a first input of a mixer 724. A signal generator 726 is coupled to a second input of the mixer 724. A TX antenna 728 is coupled to an output of the mixer 724.

[0066] During operation, a signal transmitted from the TX antenna 712 of the FMCW radar 710 is received by the RX antenna 722 of the active radar beacon 720. The received signal is modified by the mixer 724 and transmitted by the TX antenna 728 to the RX antenna 714 of the FMCW radar 710. In this example, the received signal (f RX ) based on the signal (f LO) and is frequency shifted. This frequency shift affects the transmission signal (f TX In an alternative embodiment, either or both of the FMCW radar 710 and the active radar beacon 720 may have a single antenna, rather than Figure 7 . In addition, additional RF components (eg, circulators, isolators, attenuators, etc.) may be used as desired for a given implementation.

[0067] Figure 8 is a graphical representation 800 of exemplary FMCW signals received from a passive target and an active radar beacon. In the case of a passive target, the signal propagation delay T1 (between the radar and the passive target) causes a frequency shift (Δf ) between the transmitted and received signals. P In the case of an active radar beacon, a frequency shift (Δf A =Δf2+Δf LO The total time delay includes the propagation delay T2 (between the radar and the active radar beacon; resulting in a frequency shift Δf2) and the additional delay T caused by the active radar beacon (e.g., due to the cable between the TX antenna, mixer, and RX antenna). AB (corresponding to the frequency shift Δf LO ).

[0068] Fig. 9 is a graph of example radar FFT data from a radar altimeter, including a ground clutter peak 910 (at 30 m) and two artificially created echoes (targets) 912 and 914 (AT1 and AT2) at 43 m and 59 m, respectively. These two artificial echoes were created using a positive slant range offset, and therefore, the signal indicates that the target appears to be lower than the ground (i.e., the target distance is longer than the actual distance to the ground).

[0069] Example of an active radar beacon

[0070] Active beacon implementations can be accomplished in a variety of different ways. For example, an active beacon may use separate receive and transmit antennas; a single antenna; signal retransmission only (including signal amplification); retransmission of a delayed (and amplified) signal; and transmission of a modified received signal (e.g., signal modification may be implemented in the RF domain, intermediate (IF) domain, or in baseband).

[0071] FIG. 10A to FIG. 10D is a schematic diagram of an active radar beacon according to various example embodiments.

[0072] Fig. 10A An active radar beacon 1010 is shown that is configured to transmit an amplified receive signal, such as through an amplifier 1012 coupled between an RX antenna and a TX antenna. Fig. 10B An active radar beacon 1020 is shown that is configured to transmit an amplified and delayed receive signal. For example, the active radar beacon 1020 may be implemented using an amplifier 1022 coupled between an RX antenna and an RF cable having a length selected for the delay of a delay line 1024 coupled to a TX antenna.

[0073] Fig. 10C An active radar beacon 1030 is shown that is configured to transmit an amplified and multiply delayed received signal using a delay line. For example, the active radar beacon 1030 can be implemented using an amplifier 1032 coupled between an RX antenna and a pair of delay lines 1034, 1036 that are coupled to an output summer 1038 coupled to a TX antenna.

[0074] Fig. 10D An active radar beacon 1040 is shown configured to transmit a received radar signal having a modified frequency using a signal generator 1042 coupled to a mixer 1044 coupled between the RX antenna and the TX antenna. If desired, the active radar beacon 1030 may be implemented using an amplifier coupled between the RX antenna and the TX antenna.

[0075] It should be noted that the specific implementation of the active radar beacon needs to conform to the radar type. For example, modifying the active radar beacon 1040 such as Fig. 10D The signal frequencies shown in will only work for FMCW radars (see Figure 7 ). However, introducing Fig. 10B The signal delays shown in will work for all radar types using various signal modulations.

[0076] More sophisticated active radar beacons may be implemented to receive and analyze radar signals. Fig.111 is a schematic diagram of an active radar beacon 1110 according to such a specific implementation. The active radar beacon 1110 is configured to analyze radar signals and transmit artificial response signals. For example, using mixers and various digital signal processing (DSP) components, the artificial response signal transmitted back to the airborne radar system can be controlled to establish not only artificial distance, but also artificial speed. For example, the active radar beacon 1110 can be implemented using a pair of input mixers 1112, 1114 connected between the RX antenna and the DSP component 1116 (e.g., analog-to-digital converter (ADC), microcontroller unit (MCU), digital-to-analog converter (DAC)). The output of the DSP component 1116 is connected to a signal generation component 1118 (e.g., voltage controlled oscillator (VCO), direct digital synthesis (DDS)). The output of the signal generation component 1118 is connected to the mixers 1112, 1114 in the feedback loop, and is connected to the output adder 1120 connected to the TX antenna.

[0077] Navigation using multi-lateration beacons

[0078] The following example method shows how to perform vehicle navigation using multilateration positioning (i.e., pseudorange multilateration) by processing slant ranges from multilateration beacons. The example method can estimate the aircraft 3D position in various reference frames for use in generating a navigation solution for the vehicle.

[0079] Fig.12 is a schematic diagram illustrating a vehicle navigation technique 1200 in which an example method may be employed. Aircraft 1210 communicates with at least one multilateration beacon 1220 located at a landing zone 1230. Multilateration beacon 1220 establishes artificial positions 1222 and 1224 with corresponding artificial slant range offsets. The example method and vehicle navigation technique 1200 employs various formulas and includes the following parameters:

[0080] F Lz ≡ Reference frame, landing area;

[0081] m≡measurement;

[0082] N≡number of beacons;

[0083] J nK ≡The number of artificial positions for beacon n;

[0084]

[0085] ‖*‖≡norm;

[0086]

[0087] In an example method, the slant range formula for each beacon n, such as multilateration beacon 1220, is as follows:

[0088]

[0089] In the example method, the general linearized distance formula used for each distance measurement is as follows:

[0090]

[0091] In the example method, the geometry matrix H for each beacon n is n as follows:

[0092]

[0093]

[0094] The example method may be used to compute a vehicle navigation solution, such as for an aircraft 1210, by following the steps below. In a first step, the method receives a measurement m from each beacon n, such as a multilateration beacon 1220, at a current time period. In a second step, the method provides a measurement m at a landing zone, such as a landing zone 1230. )'s reference frame. Initial Position Guess The source of can be the onboard navigation system, a previous measurement period, or a user selection. In the third step, an initial position guess is used The method calculates the estimated distance from the aircraft 1210 to each beacon n using the following formula:

[0095]

[0096] In the fourth step, the method calculates the estimated geometry matrix for each beacon n using the following formula

[0097]

[0098] Next, in the fifth step, the method calculates the error between the measured distance and the estimated distance for each beacon n using the following formula:

[0099]

[0100] In the sixth step, the method uses each beacon to calculate the position error δR using the following formula v :

[0101]

[0102] Thereafter, in the seventh step, the method is compared with F Lz Update the vehicle position estimate as follows:

[0103]

[0104] Finally, in the eighth step, the method converts the position error δR v is compared with the user-selected threshold ε. If ‖δR v ‖≤ε, the iteration of the method is completed, and the navigation solution is a navigation solution with covariance Cov(δR v )of If ‖δR v ‖>ε, the iteration is not completed and the iteration returns to the third step of the method, where Used for location guessing.

[0105] The processing unit and / or other computing device used in the methods and systems described herein may be implemented using software, firmware, hardware, or a suitable combination thereof. The processing unit and / or other computing device may be supplemented or incorporated into a specially designed application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). In some specific implementations, the processor unit and / or other computing device may communicate with other computing devices outside the system, such as computing devices associated with the management system or computing devices associated with other subsystems controlled by the management system, through an additional transceiver. The processing unit and / or other computing device may also include or run with software programs, firmware, or other computer-readable instructions to perform various processing tasks, calculations, and control functions used in the methods and systems described herein.

[0106] The methods described herein can be implemented by computer executable instructions (such as program modules or components) executed by at least one processor or processing unit. Typically, program modules include routines, programs, objects, data components, data structures, algorithms, etc. that perform specific tasks or implement specific abstract data types.

[0107] Instructions for performing various process tasks, calculations, and generation of other data used in the operation of the methods described herein may be implemented in software, firmware, or other computer-readable instructions. These instructions are typically stored on a suitable computer program product that includes a computer-readable medium for storing computer-readable instructions or data structures. Such computer-readable media may be available media that can be accessed by a general or special-purpose computer or processor or any programmable logic device.

[0108] Suitable computer-readable storage media may include, for example, nonvolatile memory devices, including semiconductor memory devices, such as random access memory (RAM), read-only memory (ROM), electrically erasable programmable ROM (EEPROM), or flash memory devices; magnetic disks, such as internal hard disks or removable disks; optical disk storage devices, such as compact disks (CDs), digital versatile disks (DVDs), Blu-ray disks; or any other medium that can be used to carry or store desired program code in the form of computer-executable instructions or data structures.

[0109] Example Implementation

[0110] Embodiment 1 includes a method, the method comprising: providing a radar sensor unit onboard a vehicle; providing one or more active radar beacons around a landing site, wherein each active radar beacon generates one or more artificial echoes of a certain pattern, and the one or more artificial echoes of a certain pattern are different from the one or more artificial echoes of a certain pattern generated by other active radar beacons in the one or more active radar beacons; and guiding the vehicle toward the landing site by a process comprising: transmitting a radar signal from the radar sensor unit to an area around the landing site; receiving a return signal from the area around the landing site in the radar sensor unit, the return signal The signal includes a ground reflection signal and a transmission signal from the one or more active radar beacons; determining whether an artificial echo is detected in the received return signal; when an artificial echo is detected, loading parameters of the one or more active radar beacons for the landing point from an onboard active beacon database; identifying one or more patterns in the detected artificial echo; associating the identified one or more patterns with corresponding one or more active radar beacons from the active beacon database; and estimating a slant range to each of the one or more active radar beacons through the identified pattern in the detected artificial echo.

[0111] Embodiment 2 includes the method of embodiment 1, further comprising providing the slant range to each of the one or more active radar beacons to an onboard navigation system for further processing.

[0112] Embodiment 3 includes the method according to embodiment 2, which further includes: using the slant range to each of the one or more active radar beacons and other navigation measurements from one or more other sensors onboard the vehicle to estimate the three-dimensional (3D) position of the vehicle.

[0113] Embodiment 4 includes the method of any one of Embodiments 1 to 3, wherein: the active radar beacon is implemented as a signal repeater; and the artificial echo represents a modified repetitive signal.

[0114] Embodiment 5 includes the method according to any one of embodiments 1 to 4, further comprising: determining the altitude of the vehicle above the area around the landing point based on the received return signal.

[0115] Embodiment 6 includes a method according to any one of embodiments 1 to 5, further comprising: determining the angular orientation of the vehicle over the area around the landing point based on received return signals from one or more other sensors onboard the vehicle.

[0116] Embodiment 7 includes a method according to any one of embodiments 1 to 6, wherein the vehicle includes a vertical take-off and landing (VTOL) aircraft, a helicopter, an unmanned aerial vehicle (UAV), or an urban air mobility (UAM) vehicle.

[0117] Embodiment 8 includes the method of any one of Embodiments 1 to 7, wherein the radar sensor unit includes a radar altimeter.

[0118] Embodiment 9 includes the method according to any one of embodiments 1 to 8, further comprising: determining the direction to the one or more active radar beacons by the radar sensor unit and further processing as additional information for navigation.

[0119] Embodiment 10 includes the method according to any one of embodiments 1 to 9, further comprising: determining Doppler velocity to the active radar beacon by the radar sensor unit and further processing as additional information for navigation.

[0120] Embodiment 11 includes a system comprising: a radar sensor unit onboard a vehicle, the radar sensor unit comprising: at least one antenna; a transmitter operatively coupled to the at least one antenna, the transmitter configured to transmit a radar signal through the at least one antenna to an area around a landing site including one or more active radar beacons; a receiver operatively coupled to the at least one antenna, the receiver configured to receive a return signal from the area around the landing site, the return signal including a ground reflection signal and a transmission signal from the one or more active radar beacons; and at least one processor unit, the at least one processor unit comprising a radar signal processing and control module operative to perform radar signal / data processing and radar control, wherein the radar signal processing and control module comprises: a signal processing module configured to receive and process the received return signal from the receiver; and a radar configuration and control module operative to send a control signal to the transmitter and the receiver to control radar scanning and configuration; and an onboard application module in operative communication with the signal processing module; and an onboard active beacon database in operative communication with the application module, the active beacon database being configured to store signal patterns for active radar beacons at specific locations; wherein the onboard application module includes program instructions for executing a process that helps guide the vehicle toward the landing point, the process comprising: determining whether an artificial echo is detected in the received return signal; when an artificial echo is detected, loading parameters of the one or more active radar beacons for the landing point from the active beacon database; identifying one or more patterns in the detected artificial echo; associating the identified one or more patterns with corresponding one or more active radar beacons from the active beacon database; estimating a slant range to each of the one or more active radar beacons by the identified pattern in the detected artificial echo; and providing the slant range to each of the one or more active radar beacons to the onboard vehicle navigation system for further processing.

[0121] Embodiment 12 comprises the system of embodiment 11, wherein the application module operates to access the position and attitude of the vehicle.

[0122] Embodiment 13 includes the system of any one of Embodiments 11-12, wherein the application module is hosted by the radar sensor unit or hosted by an onboard computing platform external to the radar sensor unit.

[0123] Embodiment 14 includes the system of any one of Embodiments 11-12, wherein the application module is distributed across both the radar sensor unit and an onboard computing platform external to the radar sensor unit.

[0124] Embodiment 15 includes the system according to any one of embodiments 11 to 14, wherein the application module includes a radar altimeter application, a Doppler navigation application, or a terrain-aided navigation application.

[0125] Embodiment 16 includes the system of any one of Embodiments 11 to 15, wherein the active beacon database is hosted by the radar sensor unit or hosted by an onboard computing platform / storage external to the radar sensor unit.

[0126] Embodiment 17 includes the system of any one of Embodiments 11 to 15, wherein the active beacon database is distributed across both the radar sensor unit and an onboard computing platform / storage external to the radar sensor unit.

[0127] Embodiment 18 comprises a system according to any one of Embodiments 11 to 17, wherein the vehicle comprises a vertical take-off and landing (VTOL) aircraft, a helicopter, an unmanned aerial vehicle (UAV), or an urban air mobility (UAM) vehicle.

[0128] Embodiment 19 includes a system according to any one of Embodiments 11 to 18, the system also including one or more active radar beacons, the one or more active radar beacons including: a receiving antenna, the receiving antenna being configured to receive the radar signal from the radar sensor unit onboard the vehicle; a signal modification module operatively communicating with the receiving antenna, the signal modification module being configured to perform signal adjustment of the radar signal from the receiving antenna to produce a modified signal; and a transmitting antenna operatively communicating with the signal modification module, the transmitting antenna being configured to transmit the modified signal to the radar sensor unit.

[0129] Embodiment 20 includes a system according to embodiment 19, which further includes: a first power level adjustment and filtering module, which is operatively connected between the receiving antenna and the signal modification module; a second power level adjustment and filtering module, which is operatively connected between the signal modification module and the transmitting antenna; a detection circuit, which operates to receive the radar signal from the first power level adjustment and filtering module; and an active beacon control module, which is operatively connected to the detection circuit, the signal modification module and the second power level adjustment and filtering module; wherein the detection circuit and the active beacon control module operate to activate the active radar beacon when an incoming radar signal is received.

[0130] The present invention may be embodied in other specific forms without departing from its basic characteristics. The embodiments described are to be considered in all respects as merely illustrative and non-restrictive. Therefore, the scope of the present invention is indicated by the appended claims rather than the foregoing description. All changes within the meaning and scope of the equivalence of the claims will be encompassed within their scope.

Claims

1. A method, comprising: Providing vehicle-mounted radar sensor units; providing one or more active radar beacons around the landing site, wherein each active radar beacon generates a pattern of one or more artificial echoes that is different from the pattern of one or more artificial echoes generated by other active radar beacons of the one or more active radar beacons; and Guiding the vehicle toward the landing point by a process comprising: transmitting a radar signal from the radar sensor unit to an area surrounding the landing site; receiving, in the radar sensor unit, return signals from the area around the landing site, the return signals comprising ground reflection signals and transmission signals from the one or more active radar beacons; determining whether an artificial echo is detected in the received return signal; loading parameters of the one or more active radar beacons for the landing point from an onboard active beacon database when an artificial echo is detected; identifying one or more patterns in the detected artificial echoes; associating the identified one or more patterns with corresponding one or more of the active radar beacons from the active beacon database; as well as The slant range to each of the one or more active radar beacons is estimated from the identified pattern in the detected artificial echo.

2. The method according to claim 1, further comprising: providing the slant range to each of the one or more active radar beacons to an onboard navigation system for further processing; as well as A three-dimensional (3D) position of the vehicle is estimated using the slant range to each of the one or more active radar beacons and other navigation measurements from one or more other sensors onboard the vehicle.

3. A system, comprising: A radar sensor unit onboard a vehicle, the radar sensor unit comprising: at least one antenna; a transmitter operatively coupled to the at least one antenna, the transmitter configured to transmit radar signals through the at least one antenna to an area surrounding a landing site including one or more active radar beacons; a receiver operatively coupled to the at least one antenna, the receiver configured to receive return signals from the area surrounding the landing site, the return signals comprising ground reflected signals and transmitted signals from the one or more active radar beacons; and at least one processor unit, the at least one processor unit comprising a radar signal processing and control module operative to perform radar signal / data processing and radar control, wherein the radar signal processing and control module comprises: a signal processing module configured to receive and process the received return signal from the receiver; and a radar configuration and control module operative to send control signals to the transmitter and the receiver to control radar scanning and configuration; an onboard application module in operative communication with the signal processing module; and an onboard active beacon database in operative communication with the application module, the active beacon database configured to store signal patterns for active radar beacons at specific locations; wherein the onboard application module includes program instructions for executing a process that facilitates guiding the vehicle toward the landing site, the process comprising: determining whether an artificial echo is detected in the received return signal; loading parameters of the one or more active radar beacons for the landing point from the active beacon database when an artificial echo is detected; identifying one or more patterns in the detected artificial echoes; associating the identified one or more patterns with corresponding one or more of the active radar beacons from the active beacon database; estimating a slant range to each of the one or more active radar beacons by using the identified pattern in the detected artificial echo; and providing the slant range to each of the one or more active radar beacons to an onboard vehicle navigation system for further processing.

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