A Virtual Verification and Simulation Method for Microwave Landing Systems Based on Ray Tracing

Abstract

This invention discloses a virtual verification simulation method for microwave landing systems based on ray tracing, relating to the field of aviation navigation. The method includes the following steps: S1, constructing a three-dimensional environment database; S2, loading beam scanning parameters; S3, setting the flight trajectory and discretizing the trajectory; S4, traversing each discretized position and simulating the signal reception process within a complete round-trip scanning cycle; S5, calculating the center point time interval; S6, calculating the azimuth angle of the aircraft; S7, calculating the error with the actual geometric angle; extracting the trajectory tracking error and control motion noise; S8, traversing all sampling position points and outputting the results of trajectory tracking error and control motion noise changing with the flight process. The proposed method can more realistically reflect the signal distortion caused by obstacles, providing a reliable basis for the compliance verification of the airspace protection zone, thereby effectively supporting airport planning and facility layout optimization.

Description

Technical Field

[0001] This invention relates to the field of aviation navigation technology, and in particular to a virtual verification and simulation method for microwave landing systems based on ray tracing. This method is suitable for high-fidelity digital modeling, simulation analysis, and virtual verification of the signal coverage characteristics, guidance accuracy, and system performance of microwave landing systems (MLS) under complex electromagnetic environments and terrain conditions. Background Technology

[0002] Microwave landing systems, as a key component of modern aviation precision approach and landing guidance systems, demonstrate significant technical value in complex weather conditions and high-density airspace operation scenarios due to their high precision, large capacity, and strong anti-interference capabilities. This system transmits time-referenced scanning beams from ground stations, combined with onboard receiving equipment that precisely measures the round-trip pulse time interval, enabling real-time calculation of the aircraft's azimuth and elevation angles relative to the runway centerline. This provides highly reliable trajectory guidance information for pilots or automatic landing systems. Given its crucial role in ensuring flight safety and improving airport operational efficiency, the verification and calibration of microwave landing system performance has become an indispensable part of the avionics system development and airworthiness certification process.

[0003] To reduce the cost of actual testing and improve the flexibility of verification, virtual verification methods based on computer simulation have gradually become the mainstream technical approach in recent years. For example, Chinese invention patent CN110456655A discloses a microwave landing simulation test system, which realizes dynamic simulation and visualization output of the working status of microwave landing system by constructing a comprehensive simulation framework that includes airport environment, flight trajectory and meteorological conditions, combined with avionics parameter mapping and navigation function calculation modules.

[0004] This approach, to a certain extent, meets the requirements for system-level functional verification and timeliness testing, particularly demonstrating good performance in parameter configuration consistency verification and basic navigation logic verification. However, such methods typically employ idealized free-space assumptions in signal propagation modeling, simplifying the path from the ground station to the receiver as a straight-line propagation. This fails to consider physical effects such as terrain undulations, building obstructions, and the resulting multipath reflections and diffraction in the actual environment. Since the angle measurement accuracy of microwave landing systems is highly dependent on the integrity and timing characteristics of the received pulse envelope, this simplification leads to simulations failing to accurately reproduce signal distortions caused by real obstacles. This results in key performance indicators such as track tracking errors deviating significantly from reality, thereby losing the ability to effectively evaluate the actual performance of the system.

[0005] Therefore, it is necessary to improve upon the shortcomings of existing technologies in order to solve the above problems. Summary of the Invention

[0006] This invention overcomes the shortcomings of the prior art and provides a virtual verification and simulation method for microwave landing systems based on ray tracing.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: Firstly, the present invention provides a virtual verification simulation method for a microwave landing system based on ray tracing, comprising the following steps:

[0008] S1. Construct a three-dimensional environment database containing the terrain and buildings of the target airport area. The three-dimensional environment database contains the geometric models of the terrain and buildings and their electromagnetic material properties.

[0009] S2. Load the beam scanning parameters of the ground station group of the microwave landing system;

[0010] S3. Set the approach trajectory of the aircraft and discretize the trajectory into multiple sampling position points, each position point containing spatial coordinates and corresponding time information;

[0011] S4. For each discretized sampling location point, simulate the signal reception process within a complete round-trip scanning cycle: Set the start time, end time, and sampling interval of the round-trip cycle, discretize the round-trip cycle time, calculate the current beam pointing for each sampling moment within the round-trip cycle, and calculate the multipath propagation effect from the ground station to the location point in the three-dimensional environment database through the ray tracing model, synthesize the received signal strength of the aircraft at the current moment, and form the received pulse envelope of the sampling location point by the signal strength of all sampling moments within the round-trip cycle.

[0012] S5. Analyze the received pulse envelope, identify and extract the time interval between the center points of the pulse regions corresponding to the round-trip scan;

[0013] S6. Calculate the azimuth angle of the aircraft based on the time interval and the angle measurement principle of the microwave landing system;

[0014] S7. Compare the calculated angle with the actual geometric angle to obtain the original angle error; process the error sequence through a low-pass filter and a band-pass filter respectively to extract the trajectory tracking error and control motion noise;

[0015] S8. Traverse all sampling locations and output the results of track tracking error and control motion noise changes with the flight process to evaluate the performance of the microwave landing system in the target airport area environment.

[0016] In a preferred embodiment of the present invention, the step of constructing the three-dimensional environment database in step S1 includes: generating a digital elevation model and a three-dimensional vector model of buildings based on high-precision geographic data, and discretizing all models using triangular meshes under a preset geographic coordinate system, wherein the spatial resolution of the triangular meshes is not lower than a preset threshold; at the same time, assigning dielectric constant and conductivity parameters to the surfaces of the terrain and buildings.

[0017] In a preferred embodiment of the present invention, in step S2, the beam scanning parameters include beam scanning range, scanning rate, pulse repetition frequency, pulse width, antenna gain pattern, and transmit power.

[0018] In a preferred embodiment of the present invention, in step S3, the approach trajectory of the aircraft is generated by a six-degree-of-freedom dynamic model. The dynamic model receives flight control commands and couples aerodynamic parameters with external wind field disturbances to output high-fidelity flight status data in real time. The sampling position points are derived from the flight status data.

[0019] In a preferred embodiment of the present invention, in step S4, the step of calculating the multipath propagation path by the ray tracing model includes the following steps:

[0020] S41. Using the center of the ground station as the radiation source, emit a dense beam of radiation;

[0021] S42. For each ray, perform path tracing in the three-dimensional environment database. The path tracing includes performing line-of-sight determination, specular reflection calculation, and edge diffraction calculation based on the uniform diffraction theory.

[0022] S43. Collect all effective ray paths reaching the spatial location point and their corresponding propagation delay and signal attenuation information.

[0023] In a preferred embodiment of the present invention, a group of dense rays is emitted into three-dimensional space at certain angular intervals, with the ground station as the center.

[0024] In a preferred embodiment of the present invention, in step S4, after synthesizing the received pulse envelope, the method further includes simulating the receiver front-end characteristics of the synthesized signal, wherein the simulation includes at least bandpass filtering, signal amplification, and envelope detection processing.

[0025] In a preferred embodiment of the present invention, in step S5, the extraction of the center point time interval includes the following steps:

[0026] S51. Identify two pulse peak regions corresponding to forward scanning and backward scanning respectively in the received pulse envelope;

[0027] S52. For each pulse peak region, calculate the time point corresponding to the centroid of its signal envelope, and use it as the time to the pulse center point and the time to the pulse center point, respectively; where, the center point time... t go for:

[0028] ;in, a and b To find the upper and lower limits of the summation, k For summation index variables, t k Sampling time, This is the output signal of the detector at the observation time.

[0029] In a preferred embodiment of the present invention, in step S7, the cutoff frequency of the low-pass filter is 0.5 rad / s, used to extract track tracking error; the passband frequency range of the band-pass filter is 0.3-10 rad / s, used to extract control motion noise.

[0030] In a preferred embodiment of the present invention, in step S8, evaluating performance includes: comparing the values ​​of the track tracking error and the control motion noise with preset airworthiness standard limits, and marking the flight process stage or space region corresponding to exceeding the limits.

[0031] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0032] (1) This invention provides a virtual verification simulation method for microwave landing systems based on ray tracing. It adopts a three-dimensional environment database based on real geographic information and introduces a physically consistent ray tracing model. It can dynamically simulate the propagation process of electromagnetic waves in complex airport environments containing terrain undulations and building obstructions. By tracing the path of each ray and synthesizing the signal, it can accurately reconstruct the pulse envelope of the receiving end, making the extraction of the time interval between the center points of the round-trip scanning pulses more accurate. It can effectively improve the authenticity of the angle measurement error calculation. Compared with the existing free space simplified propagation model, the proposed method can more realistically reflect the signal distortion caused by obstacles, providing a reliable basis for the compliance verification of the airspace protection zone, thereby effectively supporting the optimization of airport planning and facility layout.

[0033] (2) In this invention, by performing sampling ray tracing and synthesizing the received signal at each discrete flight position point, the center point time of the round-trip scanning pulse can be accurately extracted, and its temporal changes affected by multipath propagation can be analyzed, so as to achieve high-precision measurement of the pulse interval. In this way, the pulse deformation and time offset in the actual environment can be captured more accurately, so that the calculated azimuth error is closer to the real situation, thereby improving the credibility of the virtual verification result.

[0034] (3) The present invention uses a pure software simulation method to realize the virtual verification of the microwave landing system. There is no need to build a real test site and deploy physical equipment. By simulating the system workflow in the software environment, the early research and development and testing costs can be greatly reduced and the verification cycle can be shortened. The proposed method supports the rapid simulation of various complex scenarios in the software environment, thereby improving the comprehensiveness and flexibility of system testing and providing a means to identify potential signal problems in advance for the site selection of new or expanded airports. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a graph showing the relationship between the aircraft's position at different azimuth angles and the scanning beam time difference;

[0037] Figure 2 This is a flowchart illustrating a preferred embodiment of the virtual verification and simulation method for a microwave landing system based on ray tracing. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0040] This invention provides a virtual verification and simulation method for microwave landing systems based on ray tracing. Its core lies in constructing an end-to-end, physically consistent, and reproducible closed-loop simulation framework to achieve high-fidelity evaluation of the angle measurement performance of microwave landing systems (MLS) in complex airport environments. The following will provide a complete, sufficient, and unambiguous disclosure of the technical solution of this invention, combined with specific engineering parameters, algorithm flow, and implementation details.

[0041] It should be noted that the virtual verification scheme of the MLS system is based on the working principle of the MLS receiver. Specifically, the microwave landing system uses the time-referenced beam scanning angle measurement principle for angle measurement. When the azimuth beam scans from left to right relative to the runway centerline at a fixed rate and encounters the aircraft, the aircraft receives a "forward" pulse; then, when it scans from right to left and encounters the aircraft again, the aircraft receives a "return" pulse. Thus, for each "forward" and "return" scan, the aircraft receives a pair of "forward" and "return" pulses. The duration between these pairs of pulses is... t The relationship between the aircraft's azimuth and its position relative to the runway centerline is expressed as follows:

[0042] ;

[0043] in, V It is the beam scanning rate; T 0 It's an airplane. i The time interval between the forward and backward scan pulses received when the distance is 0º (on the extended centerline of the runway) is a definite known value for a fixed scan range. Therefore, as long as we know... t Then the azimuth angle can be calculated. i In other words, when the aircraft flies into the effective area of ​​the MLS, it will receive a pair of "forward" and "backward" scanning pulses, and the interval between these pulses will be measured. t This allows us to obtain the aircraft's azimuth angle relative to the runway centerline, which is the basic principle of time-based beam scanning angle measurement. For example... Figure 1 As shown, the intervals of the scanning pulse pairs corresponding to the aircraft being located at different azimuth angles.

[0044] Furthermore, the results obtained by the above method are only theoretical values; the actual measurement accuracy of MLS is constrained by various factors. The presence of most of these factors causes distortion in the scanning beam envelope, thereby affecting the round-trip time. t This affects the angle measurement error. Its accuracy requirements are expressed as path following error (PFE) and control motion noise (CMN).

[0045] Furthermore, in actual work, the specific measurement method for PFE and CMN errors is as follows: instruct the pilot to fly according to the predetermined course, while recording the guidance indication data output from the angle data output filter of the airborne equipment, and subtracting it from the absolute reference position of the aircraft measured by the laser tracking system or the precision radar tracking system, and then outputting their respective error values ​​using the PFE filter and CMN filter respectively.

[0046] Understandably, according to the principle of MLS angle measurement, angle measurement requires testing the time interval between the round-trip pulses, that is, measuring the time interval between the center points of this pair of pulses. Accurately finding the center point is key to obtaining the precise angle of MLS. The goal of envelope processing is to find the center point and then calculate the time interval between the center points of the round-trip pulses. The envelope of the received pulse is related to the actual propagation scenario, such as... Figure 2 As shown, the PFE and CMN angle errors in the actual propagation scenario are calculated as follows:

[0047] During the simulation initialization phase, high-precision geographic data of the target airport area is acquired. This data includes a 5m resolution digital elevation model (DEM) and three-dimensional vector models of man-made structures such as buildings, control towers, and hangars.

[0048] In this 3D environment database, each entity is discretized using triangular meshes, with the maximum side length of each mesh not exceeding 0.5 m. The normal vectors are standardized and stored in the vertex attributes. Terrain and building surface material information, including dielectric constants, are entered synchronously. e r With conductivity s Typical values ​​are taken for concrete, asphalt, and metal structures, which are used for subsequent electromagnetic interaction calculations.

[0049] Furthermore, the transmission parameters for azimuth and elevation beam scanning of the ground station group of the microwave landing system are loaded, including but not limited to: beam scanning start angle, end angle, and scanning rate. V The pulse repetition frequency, pulse width, main lobe half-power beamwidth, transmit power, and antenna gain pattern are specified. The azimuth scanning beam completes a forward scan from left to right in the horizontal plane at a constant angular velocity, followed by a return scan from right to left, constituting a complete round-trip scanning cycle. The duration of this cycle is specified. T total satisfy ,in This is the time interval between the "forward" and "backward" scan pulses received by the aircraft when θ=0° (on the extended centerline of the runway). It is a known value for a fixed scan range, for example, 4800 μs when the scan range is ±40°.

[0050] For example, taking the MLS Type A system specified in ICAO Annex 10 Volume I as an example, the MLS ground station angle guidance system (azimuth station and elevation station) operates on the same frequency, transmitting signals in a time-division multiple access manner. The operating frequency band is 5031.0~5090.7 MHz, divided into 200 channels with a channel spacing of 300 kHz and a pulse repetition frequency of... PRF=10 kHz, single pulse width t p =1 μs, main lobe half-power beamwidth HPBW =2°, antenna gain G =25 dBi. The beam performs a round-trip scan in the horizontal plane: from i Starting at -40°, scan to the right at a constant angular velocity V=20000 ° / s until θ=+40°, time taken After a certain pause (synchronization and protection time), the reverse scan returns to θ=-40°, which takes time. The elevation beam parameters are similar, but the scanning range is 0°-20°. In this embodiment, the focusing azimuth channel and the elevation channel processing logic are the same.

[0051] Furthermore, the approach trajectory of the aircraft is defined; the approach trajectory is a continuously differentiable three-dimensional spatial curve, with its starting point located outside the boundary of the microwave landing system's effective area and its ending point located at a designated altitude above the runway threshold; this trajectory is defined by the International Civil Aviation Organization (ICAO) standard approach procedure or a specific test mission, and is discretized in time series form. N Each sampling point contains precise geographic coordinates, namely longitude, latitude, altitude, and corresponding time. Time step Δ t The sampling time is no more than 1 ms, which is used to meet the sampling requirements for the dynamic response of high-speed scanning beams.

[0052] For example, the ICAO standard CAT III precision approach procedure LOC-MLS RWY 27L was used as the test trajectory. The starting point was located 20 km from the runway threshold at an altitude of 300 m, and the ending point was 15 m above the runway threshold. This trajectory was output by the Flight Management System (FMS) and discretized in time series form. N = 20000 sampling points, time step Δ t = 1 ms, which satisfies the Nyquist sampling theorem requirement for a scan rate of 80° / s, which corresponds to a maximum frequency component of approximately 22 Hz.

[0053] Each sampling point P i Including longitude l i ,latitude f i Altitude h i and UTC timestamp t n After coordinate transformation, the ECEF coordinates are obtained. x i , y i, z i Actual geometric azimuth i true,i We obtain this through vector operations: Let the unit vector in the direction of the runway centerline be... u runway The position vector of the spacecraft relative to the phase center of the ground station is ri ,but ,in k It is a vertically upward unit vector.

[0054] Furthermore, at the current location point P i The simulation of signal reception within a complete round-trip scan cycle is performed, and the logic flow is as follows: the round-trip scan cycle is divided into a certain sampling interval. Discretization, for each discrete sampling point, is performed based on the sampling point index and sampling interval. Calculate the current beam pointing of the ground azimuth station ,in The starting angle for scanning is given. Based on the beam direction and combined with station and antenna parameters, a ray tracing model is used to calculate the overall signal strength at the current location. The signal strength at all sampling times forms the signal envelope of the round-trip scanning cycle at the current location, which is used to subsequently calculate the angle of the current location relative to the runway.

[0055] Furthermore, at each sampling time t k With the ground station phase center O Using a radiation source, a set of rays is emitted around the surrounding area at certain horizontal and vertical angle intervals. For each ray, the following steps are performed sequentially:

[0056] 1) Line-of-Sight (LoS) determination: Calculate the intersection points of the ray with all triangular faces, and take the closest intersection point;

[0057] 2) If the Loss of Sorrow (LOS) exists and there are no obstacles, then record the direct path.

[0058] 3) If occluded, check if the edge of the occluded object is obstructed; if yes, initiate UTD diffraction calculation; if no, calculate the reflection path using the Fresnel reflection principle, with a maximum of 3 reflections; the ray tracing engine is based on a hybrid model of geometric optics (GO) and physical optics (PO), and the reflection field strength is calculated using Fresnel equations:

[0059] The formulas for the reflection coefficients of vertical and horizontal polarization are as follows:

[0060] ;

[0061] ;

[0062] in, i i Angle of incidence i t The transmission angle; For the intrinsic impedance of air, the complex impedance of the dielectric is... The expression is , The permeability of free space, The vacuum permittivity, The relative permittivity of the medium, For dielectric conductivity, Angular frequency, The unit is imaginary. The diffracted field strength is corrected using the UTD term:

[0063] ;

[0064] in, Strong diffraction field; For a strong incident field; The diffraction factor; L The length of the diffraction path; k =2π f 0 / c For wave number, f 0 represents the operating frequency. c It is the speed of light.

[0065] Furthermore, regarding the current position of the aircraft P i Collect all valid ray paths reaching that point. Each path j Carry: Path length L j Delayed transmission t j = L j / c (c = 2.99792458 × 10) 8 m / s), amplitude attenuation A j Phase shift f j = kL j + f refl / diff Combined electric field strength E ( t k The sum of all path complex signals is:

[0066] ;

[0067] in,J To reach the current location P i The total number of effective ray paths; A j For the first j Amplitude attenuation along the path; carrier angular frequency oh 0 = 2π f 0.

[0068] It should be noted that the received power envelope S ( t k ) = | E ( t k )| 2 Obtained via square-law detection. To simulate the characteristics of a real receiver front-end, a receiver simulation module is then introduced: first, it passes through a sixth-order Butterworth bandpass filter with a center frequency of 5061 MHz and a bandwidth of 30 MHz; then it passes through a low-noise amplifier (gain 40 dB, equivalent noise temperature). T e = 169 K, corresponding to noise figure NF = 2 dB); finally processed by a first-order RC envelope detector, time constant t rc = 100 ns, its output is:

[0069] ;

[0070] in, This is the output signal of the detector at the observation time; A time-based explanation of RC circuits; The time-varying input to the detector The signal of change; For the variable used in integration operations.

[0071] The signal was downsampled to 100 ps resolution and stored to form a complete round-trip scan receive envelope sequence.

[0072] Furthermore, on Perform pulse center point detection. Using a fixed threshold method combined with a first-order derivative zero-crossing point localization strategy, two significant pulse peak regions are first identified, corresponding to the "forward" and "backward" scan events, respectively. Within each peak region, the envelope centroid is calculated as the pulse center point time. Specifically, the "forward" pulse coverage time interval is set as […]. t a , t b ], then the center point time t go for:

[0073] ;

[0074] in, a and b To find the upper and lower limits of the summation; similarly, calculate the time of the "return" pulse center point. t back This yields the round-trip pulse time interval. t c = t back - t go .

[0075] Furthermore, based on the MLS angle measurement principle, the azimuth angle is calculated. i i :

[0076] ;

[0077] in, T 0 is the plane in i The time interval between the forward and backward scan pulses received at 0° (on the extended centerline of the runway) is a known value for a fixed scan range. This angle is then calculated. i relative to the actual geometric azimuth of the aircraft i true (Depend on P i The original angle error Δ is obtained by comparing the coordinates (calculated using the extended line of the runway centerline) with the coordinates. i i = i - i true .

[0078] Furthermore, the original angular error Δ of all discrete position points i i The error time series is constructed in chronological order; this series is then input into a PFE filter and a CMN filter that conform to the RTCA DO-198B standard, respectively.

[0079] PFE filter: Second-order Butterworth low-pass filter, transfer function ;in, ; For azimuth PFE, ; S It is a complex frequency variable.

[0080] It should be noted that the low-pass filter can extract the track tracking error. Its cutoff frequency is 0.08 Hz for direction, 0.24 Hz for elevation and range, and 0.32 Hz for leveling.

[0081] CMN filter: Fourth-order Butterworth bandpass filter with a passband of 0.3-10 rad / s, implemented by cascading a low-pass and a high-pass filter.

[0082] The filter is discretized using the bilinear transform method, with a sampling rate of f s = 1 kHz, the output is PFE ( t i )and CMN ( t i ).

[0083] Furthermore, traverse all P i Then, output curves showing the changes in PFE and CMN as a function of flight distance. Airworthiness limits are based on ICAO Doc 9379: PFE ≤ ±0.033°, CMN ≤ ±0.017°. Areas exceeding these limits are highlighted for airspace compliance assessment.

[0084] To further simplify and make the present invention achieve its objectives and effects, the present invention will be further illustrated in conjunction with the following specific embodiments and comparative examples, but the present invention is not limited to the scope of the embodiments described herein.

[0085] Example: An approach scenario for RWY 09R at an international airport, where a new 45-meter-high terminal building (120-meter-long, 80-meter-wide) is being constructed 500 meters east of the runway. The simulation uses the method of this invention, with a standard ILS-MLS hybrid approach trajectory, decreasing in altitude from 500 meters to 15 meters. A 3D environment database contains a model of the terminal building, with the material set to concrete. Ray tracing is enabled with triple reflections and UTD diffraction, and the receiver simulation module is activated.

[0086] Comparative example: All other conditions are exactly the same, the difference is that the Free-Space PathLoss (FSPL) model is used, ignoring all obstacles and only calculating the direct path.

[0087] The simulation results are shown in Table 1 below (three key points were selected: 5 km, 3 km, and 1 km from the runway entrance).

[0088] Table 1:

[0089]

[0090] As shown in Table 1, at a distance of 3 km, both PFE and CMN in this embodiment significantly exceeded the limits, while the comparative example remained within the limits. Path analysis revealed that this location directly faces the east facade of the terminal building, creating a strong specular reflection path, causing the "forward" pulse to advance and the "return" pulse to delay, resulting in a time interval... t Increasing the value shifts the solution angle to the left (negative value). The proposed method accurately captures the physical phenomenon, while the FSPL model completely fails to reflect it.

[0091] In summary, this invention constructs an engineerable virtual verification platform by deeply integrating high-fidelity ray tracing and MLS time-referenced angle measurement principles. Data from implementation examples demonstrate its ability to accurately reproduce obstacle interference effects. This method requires no physical equipment deployment to complete airworthiness performance assessments, providing a reliable tool for airport planning, system design, and safety certification.

[0092] The above description is based on the preferred embodiments of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of the invention is defined by the appended claims rather than the foregoing description, and all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0093] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A virtual verification and simulation method for a microwave landing system based on ray tracing, characterized in that, Includes the following steps: S1. Construct a three-dimensional environment database containing the terrain and buildings of the target airport area. The three-dimensional environment database contains the geometric models of the terrain and buildings and their electromagnetic material properties. S2. Load the beam scanning parameters of the ground station group of the microwave landing system; S3. Set the approach trajectory of the aircraft and discretize the trajectory into multiple sampling position points, each position point containing spatial coordinates and corresponding time information; S4. For each discretized sampling location point, simulate the signal reception process within a complete round-trip scanning cycle: Set the start time, end time, and sampling interval of the round-trip cycle, discretize the round-trip cycle time, calculate the current beam pointing for each sampling moment within the round-trip cycle, and calculate the multipath propagation effect from the ground station to the location point in the three-dimensional environment database through the ray tracing model, synthesize the received signal strength of the aircraft at the current moment, and form the received pulse envelope of the sampling location point by the signal strength of all sampling moments within the round-trip cycle. S5. Analyze the received pulse envelope, identify and extract the time interval between the center points of the pulse regions corresponding to the round-trip scan; S6. Calculate the azimuth angle of the aircraft based on the time interval and the angle measurement principle of the microwave landing system; S7. Compare the calculated angle with the actual geometric angle to obtain the original angle error; process the error sequence through a low-pass filter and a band-pass filter respectively to extract the trajectory tracking error and control motion noise; S8. Traverse all sampling locations and output the results of the trajectory tracking error and control motion noise as the flight process changes, and evaluate the performance of the microwave landing system in the target airport area environment. In step S1, the step of constructing the three-dimensional environment database includes: generating a digital elevation model and a three-dimensional vector model of buildings based on high-precision geographic data, and discretizing all models using triangular meshes under a preset geographic coordinate system, wherein the spatial resolution of the triangular meshes is not lower than a preset threshold; at the same time, assigning dielectric constant and conductivity parameters to the surfaces of the terrain and buildings. In step S3, the approach trajectory of the aircraft is generated by a six-degree-of-freedom dynamic model. The dynamic model receives flight control commands and couples aerodynamic parameters with external wind field disturbances to output high-fidelity flight status data in real time. The sampling position points are derived from the flight status data. In step S4, the step of calculating the multipath propagation path using the ray tracing model includes the following steps: S41. Using the center of the ground station as the radiation source, emit a dense beam of radiation; S42. For each ray, perform path tracing in the three-dimensional environment database. The path tracing includes performing line-of-sight determination, specular reflection calculation, and edge diffraction calculation based on the uniform diffraction theory. S43. Collect all valid ray paths reaching the sampling location point and their corresponding propagation delay and signal attenuation information; Centered on the ground station, a dense set of rays is emitted into three-dimensional space at certain angular intervals.

2. The virtual verification and simulation method for a microwave landing system based on ray tracing according to claim 1, characterized in that: In step S2, the beam scanning parameters include beam scanning range, scanning rate, pulse repetition frequency, pulse width, antenna gain pattern, and transmit power.

3. The virtual verification and simulation method for a microwave landing system based on ray tracing according to claim 1, characterized in that: In step S4, after synthesizing the received pulse envelope, the process further includes simulating the receiver front-end characteristics of the synthesized signal. The simulation includes at least bandpass filtering, signal amplification, and envelope detection processing.

4. The virtual verification and simulation method for a microwave landing system based on ray tracing according to claim 1, characterized in that: In step S7, the cutoff frequency of the low-pass filter is 0.5 rad / s, used to extract track tracking error; the passband frequency range of the band-pass filter is 0.3-10 rad / s, used to extract control motion noise.

5. The virtual verification and simulation method for a microwave landing system based on ray tracing according to claim 1, characterized in that: In step S8, evaluating performance includes comparing the values ​​of the track tracking error and the control motion noise with preset airworthiness standard limits, and marking the flight process phase or space region that exceeds the limits.

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