Point and surface target altimeter echo simulator

Abstract

The invention provides a point and surface target altimeter echo simulator. Comprising a real-time simulation unit and a target echo radio frequency generation unit. The real-time simulation unit is composed of a main control computer and a real-time simulation machine and is responsible for man-machine interaction, system setting, flight path real-time display, terrain matching, map data real-time calculation and echo data real-time calculation. The target echo radio frequency generation unit comprises a down-conversion assembly, an up-conversion assembly, an intermediate frequency processing assembly and a short delay assembly. Convolution operation, echo signal attenuation control and delay control, target echo radio frequency signal generation and short-distance echo signal simulation of target echoes are realized. According to the invention, frequency modulation continuous wave and pulse system altimeter echo continuous simulation is completed, altimeter echo signals of a point target and a terrain surface target are simulated, after data such as flight position information of an aircraft are received, the echo signals are transmitted to an altimeter in real time, and the requirements of a semi-physical simulation test of the altimeter are met.

Description

Technical Field

[0001] The invention relates to a point and surface target altimeter echo simulator, in particular to a point and surface target altimeter echo simulator with strong real-time performance. Background Art

[0002] The altimeter is an important functional unit for detecting the flight altitude of an aircraft during flight. The health status of the altimeter is directly related to the overall working performance of the aircraft, so the assessment of the altimeter's function and performance is extremely important. In order to meet the needs of semi-physical simulation tests of altimeters, it is necessary to design an altimeter echo simulator that is suitable for continuous simulation of frequency modulated continuous waves and pulse altimeter echoes. Summary of the invention

[0003] The purpose of the present invention is to provide a point and surface target altimeter echo simulator. It completes the continuous simulation of frequency modulated continuous wave and pulse system altimeter echo, simulates the altimeter echo signal of point target and terrain surface target, and transmits the echo signal to the altimeter in real time after receiving the flight position information of the aircraft and other data, so as to meet the needs of the semi-physical simulation test of the altimeter.

[0004] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: it includes a real-time simulation unit and a target echo radio frequency generation unit.

[0005] The real-time simulation unit comprises a main control computer and a real-time simulation machine;

[0006] The human-computer interaction software of the main control computer includes working mode and system parameter configuration;

[0007] The real-time simulator includes a computer mainboard, a real-time computing card and an optical fiber reflection memory card; the computer mainboard is loaded with a real-time operating system for real-time reading of aircraft coordinate information stored in the optical fiber reflection memory card; the real-time computing card is based on a large-scale FPGA hardware circuit design to achieve fast map capture, real-time calculation of one-dimensional range image data, and target scattering function calculation; the optical fiber reflection memory card is used to receive real-time coordinate information of the aircraft in real time;

[0008] In point target mode, the computer mainboard calculates the current aircraft equivalent altitude and echo attenuation parameters in real time according to the current aircraft coordinate information, and sends the calculation results to the real-time calculation card, which sends the calculation results to the target echo RF generation unit, and finally the target RF generation unit generates the point target echo; in area target mode, the computer mainboard sends the current aircraft coordinate information to the real-time calculation card, which intercepts the map data of the corresponding range in real time according to the coordinate information, completes the real-time calculation of the one-dimensional range image data and the target scattering function through FPGA, and finally sends it to the target echo RF generation unit;

[0009] The target echo RF generation unit includes a down-conversion component, an up-conversion component, a DRFM component, and a short delay part; the down-conversion component receives the RF signal from the altimeter, mixes it with the local oscillator signal from the up-conversion component, and down-converts the input RF signal to an intermediate frequency signal; the intermediate frequency signal is divided into two paths and sent to the small step short delay component and the DRFM component respectively. At the same time, the down-conversion component provides two clock sources required by the system, one for the DRFM component and the other for the up-conversion component; in addition, it will also receive the local oscillator signal from the up-conversion component, and divide the local oscillator signal into two paths, one for this module to down-convert the RF input signal to the intermediate frequency, and the other for returning to the up-conversion component to up-convert the intermediate frequency signal to the RF output signal;

[0010] The DRFM component mainly completes the acquisition of intermediate frequency signals, digital signal processing, time domain convolution operation, signal playback and RF system control;

[0011] The short delay part includes a small-step short delay component, a large-step short delay component, a balanced amplifier component and a digitally controlled attenuator; the small-step short delay component and the large-step short delay component are connected in series with a real cable;

[0012] The up-conversion component receives the intermediate frequency signal from the DRFM and the large-step short-delay component, and up-converts it to achieve constant amplitude control of the RF signal.

[0013] The advantages of the present invention are: it can adapt to various input signal forms, such as frequency modulated continuous wave, pulse, pseudo random code (BPSK); complete frequency modulated continuous wave and pulse system altimeter echo continuous simulation, simulate the altimeter echo signal of point target and terrain surface target, and can realize ultra-short distance echo simulation with the shortest distance of 2m. After receiving the flight position information and other data of the aircraft, the point target or surface target echo signal is simulated in real time and transmitted to the altimeter, meeting the needs of the semi-physical simulation test of the altimeter. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a composition diagram of the present invention.

[0015] Figure 2 Schematic diagram of the scattering point calculation principle

[0016] Figure 3 The real-time simulation system structure diagram of the present invention is

[0017] Figure 4 is a one-dimensional distance image

[0018] Figure 5 The principle of delayed multiplication and addition time domain convolution calculation DETAILED DESCRIPTION

[0019] The present invention is further described in detail below in conjunction with embodiments.

[0020] The invention is composed of a real-time simulation unit and a target echo radio frequency generating unit.

[0021] 1. Real-time simulation unit

[0022] The real-time simulation unit consists of a main control computer, a real-time simulation machine and KVM (Keyboard Video Mouse keyboard, video or mouse function unit), which is responsible for human-computer interaction, system settings, real-time display of flight trajectories, terrain matching, real-time calculation of map data, and real-time calculation of echo data.

[0023] The main control computer is the carrier of the system's human-computer interaction software, which is used to display the human-computer interaction interface, configure system parameters, save map data, save real-time simulation data, etc.

[0024] The real-time simulator includes a computer motherboard, a real-time computing card, and a fiber-optic reflection memory card. The fiber-optic reflection memory card is used to receive the real-time position information of the aircraft in real time. The computer motherboard is loaded with a real-time operating system, which is used to read the aircraft coordinate information stored in the fiber-optic reflection memory card in real time; in point target mode, the computer motherboard calculates the current aircraft equivalent altitude and echo attenuation parameters in real time based on the current aircraft coordinate information, and sends the calculation results to the real-time computing card, which sends the calculation results to the target radio frequency generation unit, and finally the target radio frequency generation unit generates a point target echo; in surface target mode, the computer motherboard sends the current aircraft coordinate information to the real-time computing card, and the real-time computing card performs the next step of real-time calculation. The real-time computing card is based on a large-scale FPGA hardware circuit design, and is mainly used to realize fast map capture, real-time calculation of one-dimensional range image data, target scattering function calculation, etc. In point target mode, the real-time computing card is used to transmit point target echo information; in surface target mode, the real-time computing card receives the aircraft coordinate information from the computer motherboard, and captures the map data of the corresponding range in real time according to the coordinate information, and completes the real-time calculation of one-dimensional range image data and target scattering function calculation through FPGA, and finally sends it to the target echo RF generation unit through the network port for subsequent processing.

[0025] The real-time simulator must support both point target and surface target working modes. It communicates with the simulation center through the optical fiber reflection memory card (PCI board) to receive flight trajectory data and control instructions. It communicates with the back-end DRFM (digital radio frequency memory) module through the network port (UDP) or optical fiber interface to send calculated data and control instructions.

[0026] Before the simulation starts, the human-computer interaction interface of the host computer sets the working mode, which is divided into point target mode and surface target mode. After the host computer sets the working mode and equipment parameters, the simulation is started.

[0027] 1. Point target mode

[0028] The real-time simulator receives the flight trajectory data (data update cycle 1ms) and control instructions sent by the simulation center in real time, and sends them directly to the FPGA of the DRFM (digital radio frequency memory) module through the network port (UDP) or optical fiber interface, and at the same time sends the flight trajectory data to the main control computer through the optical fiber network port.

[0029] 2. Face target mode

[0030] (1) Program-controlled instruction processing

[0031] The real-time simulation machine sends the control instructions sent by the simulation center directly to the DRFM module through the network port (UDP) or optical fiber interface.

[0032] (2) Flight trajectory processing

[0033] Before the simulation starts, the current simulation map scene is selected through the human-computer interaction interface of the main control computer. Then the real-time simulator moves the selected map data stored in the hard disk of the main control computer to the memory (4GB DDR3) on the real-time computing card board. After the simulation starts, the real-time simulator intercepts the map area (i.e., the irradiation area) corresponding to the current position according to the flight trajectory data updated every 1ms in the optical fiber reflection memory card (the maximum antenna height is 3000m, the beam normal is vertically downward, the beam width is ±45 degrees, the maximum irradiation area is 6000m×6000m, the map resolution is 5m, and the elevation information is 16bit. Therefore, the map data is at most 1200*1200=1440000 points). The real-time simulator calculates the radial distance between the antenna and 1440000 points in the irradiation area in real time, without considering the occlusion problem, such as Figure 2 As shown in the schematic diagram of the scattering point calculation principle, the radial distance calculation formula between the flight trajectory point and the map point is:

[0034]

[0035] Where R k is the distance between the antenna and the kth point on the map, (x0, y0, z0) are the coordinates of the trajectory point, (x k ,y k 、z k ) is the coordinate of the kth point on the map, x k ,y k The data sequence number of the map is multiplied by the resolution of 5m. k For the given 16-bit elevation data, k is 1, 2, ... N, and the maximum value of N is 1440000.

[0036] According to the radar equation:

[0037]

[0038] R k is the spacing calculated previously, and other parameters are set in the system human-computer interaction interface: P t is the transmission power, G is the antenna gain, λ is the wavelength, and σ is the scattering cross-sectional area. The known parameters can be calculated in advance, and the real-time calculation formula only needs to be multiplied by a coefficient. rk is the echo amplitude of a single scattering unit on the map, k is 1, 2, …N, and the maximum value of N is 1440000.

[0039] Next, R k k is 1, 2, ... N, and the maximum value of N is 1440000 for rounding. k The value range is 1m, 2m, ...5196m.

[0040] Next, the same R k Value of P rk Accumulate and get P rm , the value range of m is 1, 2, …M, and the maximum value of M is 5196.

[0041] P rm After saturation processing, M (the maximum value of M is 5196) amplitude coefficients are sent to the DRFM module through the network port (UDP) or the optical fiber interface.

[0042] The entire process from when the fiber optic reflectance memory card receives the update data to when the calculated data is sent to the DRFM module does not exceed 0.6ms.

[0043] The real-time simulation system structure diagram is as follows: Figure 3 As shown, the hardware of the real-time simulation machine includes an industrial computer, a real-time computing card, a display, a keyboard, and connection accessories.

[0044] The software includes the industrial computer mainboard operating system software (linux), DSP data forwarding and map range calculation software, FPGA map real-time calculation software on the real-time calculation card, and various data interface software.

[0045] 2. Target echo RF generation unit

[0046] The target echo RF generating unit is mainly composed of a down-conversion component, an up-conversion component, an intermediate frequency processing component DRFM component, and a short delay component. The short delay component is composed of a small-step short delay component, a large-step short delay component, a balanced amplification component and a digitally controlled attenuator.

[0047] The main functions completed are: receiving the RF signal sent by the altimeter, generating the target echo RF signal, receiving the target scattering function data from the real-time simulator, realizing the convolution operation of the target echo, echo signal attenuation control and delay control, target echo RF signal generation and short-distance echo signal simulation, and realizing RF system control.

[0048] Among them, the down-conversion component receives the RF input signal of f0~(f0+0.4)GHz from the altimeter, mixes it with the local oscillator signal from the up-conversion component, and down-converts the input RF signal to an intermediate frequency signal of 900±200MHz. The intermediate frequency signal is divided into two paths and sent to the small step short delay component and the DRFM component respectively. At the same time, the down-conversion component provides two 100MHz clock sources required by the system, one for the DRFM component and the other for the up-conversion component. In addition, the local oscillator signal from the up-conversion component is also received, and the local oscillator signal is split into two paths, one for this module to down-convert the RF input signal to the intermediate frequency, and the other returns to the up-conversion component to up-convert the intermediate frequency signal to the RF output signal.

[0049] The DRFM component can simulate the echo of point and surface targets within the range of 15-3000m. The intermediate frequency input and output are both 900±200MHz, and the module is provided with a 100MHz clock by the down-conversion component. The DRFM component mainly completes the functions of intermediate frequency signal acquisition, digital signal processing, time domain convolution operation, signal playback and RF system control.

[0050] The 2-15m short delay part is realized by a combination of a small-step short delay component, a large-step short delay component and a balanced amplifier component. The small-step short delay component and the large-step short delay component are realized by a real cable combination. The small-step short delay component has a step of 0.1m, and the large-step short delay component has a step of 1m. The two modules are connected in series to realize the 2-15m point target simulation. The two components realize their own delay functions through the switch array inside.

[0051] The up-conversion component receives the intermediate frequency signal from the DRFM and large-step short-delay components, and up-converts it to f0~(f0+0.4)GHz, and realizes the amplitude control of the RF signal. At the same time, the up-conversion component is internally designed with a phase-locked source circuit, which receives the 100MHz clock signal from the down-conversion component, generates a local oscillator signal, and provides it to the down-conversion component and the up-conversion component for frequency conversion of the RF input and RF output signals.

[0052] Therefore, according to different functions to be implemented, the target echo RF generation unit is divided into 7 standard components, as shown in Table 1.

[0053] Table 1 Functional description of standard components

[0054]

[0055] The method of simulating the echo signal of the terrain surface target is as follows:

[0056] The altimeter echo signal needs to intercept the corresponding digital map according to the ±45° radar beam angle based on the target position (longitude and latitude) and altitude information received in real time during the simulation. The digital map has been imported into the simulator before the simulation. The area of ​​the intercepted map is divided by the digital map resolution to obtain the number of grids corresponding to the irradiated area and the elevation information of the digital map corresponding to the grid. The elevation information and scattering coefficient of the grid are convolved point by point with the collected altimeter transmission signal in the time domain. The intermediate frequency signal after the operation is up-converted and transmitted to form the altimeter echo signal.

[0057] From the above analysis, we can know that there are several key factors that affect the generation of echo signals: the interception of digital maps and the calculation and distribution method of map information, the fitting calculation method of the collected altimeter signal with map information and scattering characteristics, the selection of scattering model, the minimum inherent delay time generated by the echo signal matching the terrain, and the influence of the flight attitude of the aircraft.

[0058] The influence of the aircraft's flight attitude on the radar beam angle can be ignored, because the radar beam angle range of ±45° can already cover the range of the ground radiation beam angle changes when the aircraft is in any flight attitude. Therefore, the influence of the aircraft's flight attitude on the echo signal can be ignored.

[0059] The calculation of the altimeter echo for simulated terrain matching is divided into the following 6 steps:

[0060] (1) Call the coverage map area based on the altimeter track position and beam angle;

[0061] (2) Calculate the delay value and target scattering coefficient of each scattering point in the beam coverage scene;

[0062] (3) Obtaining the one-dimensional target scattering impact response coefficient;

[0063] (4) Receive altimeter echo;

[0064] (5) Convolution calculation with the received altimeter transmission signal;

[0065] (6) Get the echo and transmit it.

[0066] In the above step (1), the method for generating the target scattering point amplitude is as follows: Figure 2 The schematic diagram of the scattering point calculation principle shown in the figure shows that the digital map resolution is 5m×5m and the maximum scattering point array is 1200×1200 points.

[0067] First, the delay value is calculated. The radial distance between the target scattering point and the altimeter is calculated as follows:

[0068]

[0069] The scattering coefficient is temporarily set to a constant of 1 and does not need to be calculated. Then the amplitude parameters of each scattering target point are calculated according to the radar equation.

[0070] In the above step (2), the calculation method of the target scattering function mapping is as follows

[0071] Calculate the delay value and scattering coefficient of each scattering target point to obtain the one-dimensional target scattering coefficient. Figure 4 shown.

[0072] The maximum height is 3000m, so it is necessary to process the surface target scattering coefficients of 1200×1200 points, and superimpose all the scattering coefficients within the same 1m distance interval to obtain a one-dimensional range image echo impulse response coefficient of up to 3000 points.

[0073] In the above step (5), the method for calculating the height echo convolution is as follows:

[0074] For the one-dimensional target scattering function, the closest distance is H0 = 10m, the farthest distance is H0 = 3000m, the impact coefficient interval is 1m, the corresponding sampling rate is 150MHz, and 3000m corresponds to 3000-point coefficients.

[0075] The instantaneous bandwidth of the simulator is 300MHz, so the intermediate frequency sampling rate is designed to be fs=1200MHz, the pulse width of the transmitted signal is 500ns, and the number of transmitted signal points is 600.

[0076] Therefore, each point coefficient corresponds to 1200 / 150=8 points of DRFM ADC acquisition signal, that is, every 8 sampling points are multiplied by the same amplitude coefficient, that is, 75 multipliers are required at the same delay time.

[0077] The number of transmitted signal points is small, and the number of target impact function signal points is large, so the time domain convolution method is adopted (the frequency domain convolution multiplication method is not adopted).

[0078] The echo point calculation requires delayed tap multiplication and addition operations, and multiple multipliers are calculated in parallel. The principle is as follows Figure 5 shown.

[0079] The many features and advantages of these embodiments are apparent from this detailed description, and thus the appended claims are intended to cover all such features and advantages of these embodiments that fall within their true spirit and scope. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not intended that the embodiments of the invention be limited to the exact construction and operation illustrated and described, but rather all suitable modifications and equivalents falling within the scope thereof are intended to be covered.

[0080] Parts of the present invention that are not described in detail are well known to those skilled in the art.

Claims

1. A point or surface target altimeter echo simulator, characterized in that: It includes a real-time simulation unit and a target echo radio frequency generation unit; The real-time simulation unit comprises a main control computer and a real-time simulation machine; The human-computer interaction software of the main control computer includes working mode and system parameter configuration; The real-time simulator includes a computer mainboard, a real-time computing card and an optical fiber reflection memory card; the computer mainboard is loaded with a real-time operating system for real-time reading of aircraft coordinate information stored in the optical fiber reflection memory card; the real-time computing card is based on a large-scale FPGA hardware circuit design to achieve fast map capture, real-time calculation of one-dimensional range image data, and target scattering function calculation; the optical fiber reflection memory card is used to receive real-time coordinate information of the aircraft in real time; In point target mode, the computer mainboard calculates the current aircraft equivalent altitude and echo attenuation parameters in real time according to the current aircraft coordinate information, and sends the calculation results to the real-time calculation card, which sends the calculation results to the target echo RF generation unit, and finally the target RF generation unit generates the point target echo; in area target mode, the computer mainboard sends the current aircraft coordinate information to the real-time calculation card, which intercepts the map data of the corresponding range in real time according to the coordinate information, completes the real-time calculation of the one-dimensional range image data and the target scattering function through FPGA, and finally sends it to the target echo RF generation unit; The target echo RF generation unit comprises a down-conversion component, an up-conversion component, a DRFM component, and a short delay part; the down-conversion component receives the RF signal from the altimeter, mixes it with the local oscillator signal from the up-conversion component, and down-converts the input RF signal to an intermediate frequency signal; The intermediate frequency signal is divided into two paths and sent to the small step short delay component and the DRFM component respectively. At the same time, the down-conversion component provides two clock sources required by the system, one for the DRFM component and one for the up-conversion component; in addition, it will also receive the local oscillator signal from the up-conversion component and divide the local oscillator signal into two paths, one for this module to down-convert the RF input signal to the intermediate frequency, and the other for the up-conversion component to up-convert the intermediate frequency signal to the RF output signal; The DRFM component mainly completes the acquisition of intermediate frequency signals, digital signal processing, time domain convolution operation, signal playback and RF system control; The short delay part includes a small-step short delay component, a large-step short delay component, a balanced amplifier component and a digitally controlled attenuator; the small-step short delay component and the large-step short delay component are connected in series with a real cable; The up-conversion component receives the intermediate frequency signal from the DRFM and the large-step short-delay component, and up-converts it to achieve constant amplitude control of the RF signal.

2. A point or surface target altimeter echo simulator as claimed in claim 1, characterized in that: The flight trajectory processing process of the surface target mode is as follows: The radial distance calculation formula between the flight track point and the map point is: Where R k is the distance between the antenna and the kth point on the map, (x0, y0, z0) are the coordinates of the trajectory point, (x k ,y k 、z k ) is the coordinate of the kth point on the map, x k ,y k The data number of the map is multiplied by the resolution of 5m. k is the given elevation data, k is 1, 2, ... N, N is the map data point; According to the radar equation: R k is the spacing calculated previously, and other parameters are set in the system human-computer interaction interface: P t is the transmission power, G is the antenna gain, λ is the wavelength, σ is the scattering cross-sectional area, P rk is the echo amplitude of a single scattering unit on the map; Next, R k k is 1, 2, ... N, and rounding is performed. k Value of P rk Accumulate and get P rm , the value range of m is 1, 2, …M, and M is the maximum value. P rm After saturation processing, the M amplitude coefficients are sent to the DRFM module.

3. A point or surface target altimeter echo simulator as claimed in claim 2, characterized in that: The altimeter echo signal calculation is divided into the following 6 steps: 1) calling the coverage map area according to the altimeter track position and beam angle; 2) calculating the delay value and target scattering coefficient of each scattering point in the beam coverage scene to obtain a one-dimensional target scattering coefficient; 3) obtaining a one-dimensional target scattering impulse response coefficient; 4) Receive the altimeter echo; 5) Convolve it with the received altimeter transmission signal; 6) Get the echo and transmit it.

4. A point or surface target altimeter echo simulator as claimed in claim 1, characterized in that The human-computer interaction software of the main control computer includes a human-computer interaction interface, system parameter configuration, map data storage, and real-time simulation data storage.

5. A point or surface target altimeter echo simulator as claimed in claim 1, characterized in that The small-step short-delay component and the large-step short-delay component realize their respective delay functions through a switch array inside.

6. A point or surface target altimeter echo simulator as claimed in claim 1, characterized in that The local oscillation signal is realized by a phase-locked source circuit designed inside the up-conversion component.

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