Arbitrary time delay doppler echo simulation device and simulation method thereof

Abstract

The application belongs to the field of echo simulation equipment. The application provides an arbitrary time delay Doppler echo simulation device, which comprises an external transmitter, a radio frequency signal input module, a signal input module, a digital control circuit, an intermediate frequency signal generation module, a local oscillator signal generation module, a mixing module and an echo modulation module. The source code digital signal comprises simulation target parameters. The waveform parameters comprise a waveform modulation mode. When simulating a near field echo, a source code synchronization signal and a source code digital signal of the external transmitter are received synchronously, and a Doppler frequency shift control signal is generated according to the source code synchronization signal and the source code digital signal. When simulating a far field echo, the simulation target parameters are received by an industrial computer, and a Doppler frequency shift control signal is generated according to the simulation target parameters. After mixing with the local oscillator signal, frequency selection filtering, waveform modulation, amplification and attenuation, the simulated radio frequency echo is obtained. Thus, the simulation of an arbitrary time delay Doppler echo is realized.

Description

Technical Field

[0001] This invention pertains to analog echo devices, specifically to an arbitrary time-delay Doppler echo simulation device and its simulation method. Background Technology

[0002] A simulated echo device is used to simulate actual echo signals in radar or other sensing systems. This device can generate echo signals similar to those received in a real environment in a laboratory or testing setting, playing a crucial role in the design, debugging, testing, training, and maintenance of radar systems. In practical applications, simulated echo devices can be used in areas such as airborne SAR echo signal simulation, broadband radar echo signal simulation, and extended target echo simulation for digital array radar. By using simulated echo devices, the development and testing costs of radar systems can be effectively reduced, development efficiency improved, and strong support provided for the development of radar technology.

[0003] The main problems that simulated echo equipment needs to solve are simulating moving targets and simulating the target distance. The frequency of the signal reflected by a moving target exhibits the Doppler effect. Simulating a moving target simply requires superimposing the Doppler signal onto the radio frequency signal, which is usually achieved in two ways.

[0004] One method involves mixing the radio frequency (RF) signal and the Doppler signal using an IQ mixer to superimpose the Doppler frequency onto the RF signal, such as... Figure 1 As shown, this method outputs multiple spectral components, including the RF carrier leakage signal (f0), the lower sideband signal (f0 minus the Doppler frequency), the upper sideband signal (f0 plus the Doppler frequency), the Nth power of f0 plus the Doppler frequency, and the Nth power of f0 minus the Doppler frequency. However, only the upper sideband signal (f0 plus the Doppler frequency) is actually needed. Therefore, the other signals are all non-useful signals. Since these signals are very close in frequency, they cannot be suppressed by filters, ultimately affecting the quality of the echo signal.

[0005] Another way is to achieve this digitally, such as... Figure 2 As shown, the FPGA controls the DDS (Direct Digital Synthesizer) to generate a Doppler modulated intermediate frequency signal within the set range and rate of change according to the set Doppler modulation frequency range. This signal is then mixed and filtered with the local oscillator signal to obtain the desired radio frequency echo signal. The advantage of this method compared to the IQ mixing method is that it produces a radio frequency signal without any other components, has a single output spectrum, and does not affect the quality of the echo signal. The disadvantage is that it adds a frequency conversion channel, and the output Doppler modulation frequency is a set of discontinuous discrete frequency points.

[0006] The farther the target is, the longer the echo takes to arrive. Therefore, simulating the target distance means adjusting the delay time of the echo signal. There are generally two methods: one is to use an adjustable delay line for direct delay, such as... Figure 3 As shown. The advantage of this method is its small minimum delay time, which can simulate near-field echoes. The disadvantage is that the maximum delay time is also small, and it cannot simulate far-field echoes. For example, the specifications of the relatively advanced adjustable delay line product on the market, the NC12126C-218PD type 6 digitally controlled delay line, show that its maximum delay is only 700ps in the range of 2 to 18GHz, which is far from meeting the requirements for simulating far-field echoes.

[0007] Another method is to use an FPGA to control a DDS to generate an adjustable-delay intermediate frequency (IF) signal, which is then up-converted with the local oscillator signal to a radio frequency (RF) signal to simulate the echo. The advantage of this method is that the timing of the IF signal generation by the DDS can be controlled by the FPGA, allowing for the simulation of any far-field signal. The disadvantage is that due to the inherent system delay, typically 300ns to 500ns, it cannot simulate near-field echoes. Summary of the Invention

[0008] This invention addresses the limitation of existing echo simulation devices in simultaneously meeting the requirements of far-field and near-field echoes. It provides an arbitrary time-delay Doppler echo simulation device, comprising an RF signal input module, a signal input module, a digital control circuit, an intermediate frequency signal generation module, a local oscillator signal generation module, a mixing module, and an echo modulation module.

[0009] The radio frequency signal input module is used to detect and determine the start time of radio frequency signal transmission; the radio frequency signal is generated by an external transmitter reading the source code digital signal and configuring the signal when it receives the source code synchronization signal; the source code digital signal includes simulated target parameters, including target moving speed, target moving direction, target distance, echo attenuation, and waveform parameters; the waveform parameters include waveform modulation method.

[0010] When the distance to the simulated target is less than a preset distance threshold, it is considered a near-field simulation. When simulating near-field echoes:

[0011] The signal input module is used to synchronously receive the source code synchronization signal and source code digital signal from the external transmitter and transmit them to the digital control circuit.

[0012] The digital control circuit is used to generate Doppler frequency shift control signals and echo delay control signals based on the source code synchronization signal and the source code digital signal; and to control the intermediate frequency signal generation module to generate intermediate frequency signals based on the Doppler frequency shift control signals and echo delay control signals.

[0013] The local oscillator signal generation module is used to generate a local oscillator signal;

[0014] The mixing module is used to mix the local oscillator signal with the intermediate frequency signal to obtain an analog echo signal;

[0015] The echo modulation module is used to perform frequency selective filtering on the analog echo signal and then modulate it according to the waveform modulation method to obtain an analog radio frequency echo.

[0016] When the distance to the simulated target is greater than or equal to a preset distance threshold, it is considered a far-field simulation. When simulating far-field echoes:

[0017] The signal input module is used to receive analog target parameters and transmit them to the digital control circuit;

[0018] The digital control circuit is used to generate Doppler frequency shift control signals and echo delay control signals based on the simulated target parameters; and to control the intermediate frequency signal generation module to generate intermediate frequency signals based on the Doppler frequency shift control signals and echo delay control signals.

[0019] The local oscillator signal generation module is used to generate a local oscillator signal;

[0020] The mixing module is used to mix the local oscillator signal with the intermediate frequency signal to obtain an analog echo signal;

[0021] The echo modulation module is used to perform frequency selective filtering on the analog echo signal and then modulate it according to the waveform modulation method to obtain an analog radio frequency echo.

[0022] In some embodiments, the radio frequency signal input module includes a pulse detection module and a comparison module;

[0023] The pulse detection module is used to detect whether an RF signal is input, and when an RF signal is input, it outputs a detection envelope.

[0024] The comparison module is used to compare the detector envelope and output an RF pulse signal to the digital control circuit to indicate that the RF signal has arrived.

[0025] In some embodiments, when simulating near-field echo, the waveform modulation method is random code phase modulation;

[0026] When simulating far-field echoes, the waveform modulation method is linear frequency modulation or pulse modulation.

[0027] In some embodiments, the echo modulation module includes a frequency selective filter, a 0 / π phase modulation switch, a gate switch, an amplifier, and a digitally controlled attenuator, which are connected in sequence.

[0028] During random code phase modulation, after the frequency selective filter performs frequency selective filtering on the analog echo signal, the digital control circuit controls the 0 / π phase modulation switch to modulate the phase according to the random code sequence, controls the gate switch to be normally open, and after the analog echo signal is amplified by the amplifier, the digital control circuit controls the digitally controlled attenuator to attenuate it to obtain the analog radio frequency echo.

[0029] During linear frequency modulation, after the frequency selective filter performs frequency selective filtering on the analog echo signal, the digital control circuit controls the 0 / π phase modulation switch to be in the 0 phase and controls the gate switch to be normally open. After the analog echo signal is amplified by the amplifier, the digital control circuit controls the digitally controlled attenuator to attenuate it, thereby obtaining the analog radio frequency echo.

[0030] During pulse modulation, after the frequency-selective filter performs frequency-selective filtering on the analog echo signal, the digital control circuit controls the 0 / π phase modulation switch to be in the 0 phase, and controls the gate switch to open when the pulse sequence arrives. After the analog echo signal is amplified by the amplifier, the digital control circuit controls the digitally controlled attenuator to attenuate it, thereby obtaining the analog radio frequency echo.

[0031] In some embodiments, the frequency selective filter includes an input terminal, a first one-to-multiple-channel switch, a filter, a second one-to-multiple-channel switch, and an output terminal, wherein there is at least one filter;

[0032] The mixer module is connected to the input terminal, which is connected to one end of the one-to-many switch. The other end of the one-to-many switch is connected to the input terminal of the filter. The output terminal of the filter is connected to one end of the one-to-many switch. The other end of the one-to-many switch is connected to the output terminal.

[0033] In some embodiments, an echo output detection module is also included for feeding back the echo detection signal;

[0034] The digital control circuit compares the time difference between the rising edge of the echo detector signal and the rising edge of the source code synchronization signal or the radio frequency pulse signal to obtain the actual delay time of the simulated radio frequency echo; the actual delay time is calibrated with the delay parameter to make the delay of the simulated radio frequency echo precise and controllable; the delay parameter is obtained by calculating the target distance.

[0035] This invention also provides a method for simulating arbitrary time-delay Doppler echoes, comprising the following steps:

[0036] When the distance to the simulated target is less than a preset distance threshold, it is considered a near-field simulation. When simulating near-field echoes:

[0037] Receives radio frequency signals generated by an external transmitter;

[0038] The system synchronously acquires external transmitter control signals, which include source code synchronization signals and source code digital signals. The source code digital signals include simulated target parameters, including target moving speed, target moving direction, target distance, echo attenuation, and waveform parameters. The waveform parameters include waveform modulation methods.

[0039] Based on the source code synchronization signal and the source code digital signal, a Doppler frequency shift control signal and an echo delay control signal are generated; and based on the Doppler frequency shift control signal and the echo delay control signal, the DDS is controlled to delay and generate an intermediate frequency signal with the Doppler effect.

[0040] The local oscillator signal is generated, and then mixed with the intermediate frequency signal to obtain the analog echo signal.

[0041] After frequency-selective filtering of the analog echo signal, it is modulated according to the waveform modulation method to obtain the analog radio frequency echo;

[0042] When the distance to the simulated target is greater than or equal to a preset distance threshold, it is considered a far-field simulation. When simulating far-field echoes:

[0043] Receives radio frequency signals generated by an external transmitter;

[0044] The system receives simulated target parameters, generates Doppler frequency shift control signals and echo delay control signals based on the simulated target parameters, and controls the DDS to delay and generate an intermediate frequency signal with Doppler effect after the radio frequency signal arrives.

[0045] The local oscillator signal is generated, and then mixed with the intermediate frequency signal to obtain the analog echo signal.

[0046] After frequency-selective filtering of the analog echo signal, it is modulated according to the waveform modulation method to obtain the analog radio frequency echo.

[0047] In some embodiments, the method includes detecting whether an radio frequency (RF) signal is input; when an RF signal is input, outputting a detection envelope; comparing the detection envelope and outputting an RF pulse signal, wherein the rising edge of the RF pulse signal indicates that the RF signal has arrived.

[0048] In some embodiments, characterized in that,

[0049] When simulating near-field echoes, the waveform modulation method is random code phase modulation;

[0050] When simulating far-field echoes, the waveform modulation method is linear frequency modulation or pulse modulation.

[0051] In some embodiments, the method further includes: acquiring an echo detection signal; comparing the time difference between the rising edge of the echo detection signal and the rising edge of the source code synchronization signal or the radio frequency pulse signal to obtain the actual delay time of the simulated radio frequency echo; calibrating the actual delay time with the delay parameter so that the delay of the simulated radio frequency echo is accurately controllable; the delay parameter is obtained by calculating the target distance.

[0052] The beneficial effects of this invention are as follows: When simulating near-field echoes, the generation time and modulation method of the simulated echo signal are controlled by the source code synchronization signal and the source code digital signal, thereby achieving near-field echo simulation. When simulating far-field echoes, the generation time and modulation method of the simulated echo are controlled by the RF synchronization input detection signal provided by the RF detection circuit and the simulation target parameters, thereby achieving far-field echo simulation. This enables the simulation of Doppler echoes with arbitrary time delays. Simultaneously, this invention divides the wideband into several narrowbands, providing corresponding RF filtering paths for echo signals of different frequency bands, thereby achieving wideband echo simulation. Furthermore, this invention detects the output echo signal and calibrates the delay by comparing the time difference between the synchronization signal and the echo detection signal in a closed loop, thereby achieving precise control of the echo delay. Attached Figure Description

[0053] Figure 1 The structural diagram of the direct mixing Doppler modulation method model in the background technology of this invention.

[0054] Figure 2 The structure diagram of the digital Doppler modulation method model in the background technology of this invention.

[0055] Figure 3 A schematic diagram of the direct delay method using delay lines in the background technology of this invention.

[0056] Figure 4 1. Echo simulation circuit diagram in the embodiment of the present invention.

[0057] Figure 5 A structural diagram of the arbitrary time-delay Doppler echo simulation device in this embodiment of the invention.

[0058] Figure 6 Circuit diagram of the arbitrary time-delay Doppler echo simulation device in the embodiments of the present invention.

[0059] Figure 7 A schematic diagram of the total delay in an embodiment of the present invention.

[0060] Figure 8 Analysis diagram of near-range simulated echo signal in an embodiment of the present invention.

[0061] Figure 9 Analysis diagram of long-distance simulated echo signal in an embodiment of the present invention.

[0062] Figure 10Schematic diagrams of a sine wave with an initial phase of 0 and a sine wave with an initial phase of π in embodiments of the present invention.

[0063] Figure 11 The waveform represented by the binary number 10011 in this embodiment of the invention.

[0064] Figure 12 A schematic diagram illustrating the effect of the random code sequence on echo information in an embodiment of the present invention.

[0065] Figure 13 A diagram of the frequency-selective filter structure in an embodiment of the present invention.

[0066] Figure 14 A schematic diagram of segmented filtering for different frequency bands in an embodiment of the present invention.

[0067] Figure 15 A schematic diagram of radio frequency signal transmission and reception in an embodiment of the present invention. Detailed Implementation

[0068] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0069] The Doppler effect reflects the frequency shift characteristics of a moving object. When the object's direction of movement is the same as the direction of its emitted or reflected signal, the signal frequency exhibits a blue shift, meaning the frequency increases. The faster the object moves, the greater the frequency increase. Conversely, when the object's direction of movement is opposite to the direction of its emitted or reflected signal, the signal frequency exhibits a red shift, meaning the frequency decreases. The faster the object moves, the faster the frequency decreases. Simulating a Doppler echo involves superimposing the frequency change onto the reflected echo to obtain the change in the target's speed.

[0070] The formula for calculating Doppler frequency is: Where c is the speed of light, v is the moving speed of the signal source (target), f0 is the echo frequency when the target is stationary, and f is the echo frequency when the target is moving. Since the speed of light is much greater than the moving speed of the target, the difference in echo frequencies between the stationary and moving targets is Δf = f0 - f. This difference is very small relative to the echo frequency f0 when the target is stationary, generally not exceeding a few megahertz. Because mixing generates spurious signals ±nΔf + f0 (n is a positive integer, and n ≠ 1), which are too close to the Doppler frequency f = Δf + f0, it is difficult to filter them out using an RF filter. Therefore, the direct mixing method is not applicable.

[0071] This example provides a digital Doppler method, in which the DDS generates a Doppler intermediate frequency (IF) signal that is itself superimposed with Δf, and then mixes this IF signal onto the radio frequency (RF) signal. Since the IF signal itself has a frequency of several hundred megahertz, the spurious signals of the RF signal (Doppler frequency-modulated signal) obtained by mixing are far from the main signal and can be effectively filtered out.

[0072] In one embodiment, the echo simulation device is specifically as follows: Figure 4 As shown.

[0073] The input RF signal is detected and compared to obtain an echo enable signal. On the rising edge of this signal, the FPGA controls the DDS to generate an adjustable-delay intermediate frequency (IF) signal. This IF signal is then up-converted with the local oscillator signal to simulate the RF echo. The advantage of this method is that the FPGA can control the timing of the IF signal generation by the DDS, allowing for the simulation of any far-field signal. The disadvantage is that due to the inherent delay of the detection and comparison circuit and the mixing and filtering circuit, typically 300ns to 500ns, it cannot simulate near-field echoes.

[0074] To simultaneously simulate near-field and far-field echoes, another embodiment is introduced based on the above real-time example, such as... Figure 5 As shown, the system includes an RF signal input module, a signal input module, a digital control circuit, an intermediate frequency (IF) signal generation module, a local oscillator (LO) signal generation module, a mixer module, and an echo modulation module. The RF signal input module and the signal input module are connected to the digital control circuit, which in turn is connected to the IF signal generation module, the LO signal generation module, and the echo modulation module. The IF signal generation module and the LO signal generation module are connected via the mixer module, which is in turn connected to the echo modulation module.

[0075] In one embodiment, an arbitrary time-delay Doppler echo simulation device, such as Figure 6 As shown, the radio frequency (RF) signal input module is used to detect and determine the start time of RF signal transmission. It includes a pulse detection circuit and a comparator. The pulse detection circuit detects whether an RF signal is input; when an RF signal is input, it outputs a detection envelope. The comparator compares the detection envelope and outputs an RF pulse signal to the digital control circuit, indicating that the RF signal has arrived. The RF signal is generated by an external transmitter. When the external transmitter receives the source code synchronization signal, it reads the source code digital signal, performs signal configuration, and generates the RF signal. The source code digital signal includes simulated target parameters, including target movement speed, target movement direction, target distance, echo attenuation, and waveform parameters. The waveform parameters include the waveform modulation method. The external transmitter transmitting the RF signal based on the simulated target parameters is a relatively mature technical solution in the prior art and will not be elaborated further here.

[0076] In this example, the intermediate frequency (IF) signal generation module is a DDS (Digital Signal Generation System). The echo modulation module includes a frequency-selective filter, a 0 / π phase modulation switch, a gate switch, an amplifier, and a digitally controlled attenuator. The frequency-selective filter, 0 / π phase modulation switch, gate switch, amplifier, and digitally controlled attenuator are connected sequentially. The operation of this device is described in detail below.

[0077] This example uses a distance of 200 meters as the boundary between the near and far fields. However, it should be understood that the boundary between the near and far fields is not fixed in actual operation. The near and far fields can be defined according to actual needs, and the delay of the echo simulation device itself can be adjusted accordingly.

[0078] Short-range detection typically employs a pseudo-random code phase modulation mode, using continuous waves to determine the target's location through phase changes in the echo. However, long-range detection using continuous waves consumes excessive energy, and due to the great distance, phase modulation alone is insufficient to determine the target's location. In such cases, pulse modulation or linear frequency modulation modes are required to determine the target's location.

[0079] The inherent delay is the delay of the analog echo device itself, including the DDS configuration time and the delay time of the RF link (including the mixer module and the analog echo module) hardware. The DDS delay time, on the other hand, refers to the delay control time of the digital control circuit. (This example uses an FPGA as the digital control circuit, hereinafter referred to as FPGA). The delay time relationship is as follows: Figure 7 As shown. When the inherent delay of the arbitrary time-delay Doppler echo simulation device is greater than or equal to the echo delay requirement, the near-range echo simulation method is used. In this case, the total delay is not equal to the echo delay time (total delay > echo delay). When the inherent delay of the echo simulation device is less than the echo delay requirement, the far-range echo simulation method is used. In this case, the total delay equals the echo delay. The difference between near-range (≤200m) and far-range (>200m) echo delay is as follows: Figure 8 and Figure 9 As shown.

[0080] When simulating near-field echoes:

[0081] Because the near-field echo delay is shorter than the inherent delay of the simulation device, the echo simulation device cannot simulate near-field echoes if it only begins processing after receiving the RF signal. Therefore, for near-field (≤200m) signals, we added two digital control signals: a source code synchronization signal and a source code digital signal. These two signals are used by an external transmitter to generate the input RF signal. When the external transmitter receives the source code synchronization signal, it reads the source code digital signal, configures the signal, and generates the RF signal. The purpose of providing this signal to the arbitrary delay Doppler echo simulation device is to enable the echo simulation device to control the FPGA to perform the corresponding delay before the RF signal arrives. This ensures that the echo simulation device can accurately determine the start time, i.e., the rising edge of the source code synchronization signal, thereby accurately simulating the delay time of the near-field echo signal.

[0082] Specifically, in near-field simulation, the signal input module is used to synchronously receive the source code synchronization signal and source code digital signal from the external transmitter and transmit them to the FPGA. The FPGA generates Doppler frequency shift control signal and echo delay control signal based on the source code synchronization signal and source code digital signal; and controls the DDS to generate the intermediate frequency signal for near-field simulation based on the Doppler frequency shift control signal and echo delay control signal.

[0083] The local oscillator (LO) signal is a stable radio frequency signal generated in radio frequency equipment such as wireless communication, radar, and spectrum analyzers. The quality of the LO signal has a significant impact on the performance of the entire communication system. An ideal LO signal should be frequency stable, have low phase noise, and constant amplitude. Frequency stability and phase noise are two key parameters for evaluating the performance of the LO signal. The better the frequency stability, the higher the frequency resolution of the system; the lower the phase noise, the higher the signal-to-noise ratio (SNR) of the system, and the better the signal quality.

[0084] To improve the performance of the local oscillator signal, this example employs phase-locked loop (PLL) technology to lock the oscillator's frequency and phase, thereby obtaining a local oscillator signal with high stability and low phase noise. PLL technology can effectively reduce the oscillator's phase noise, improve signal purity, and enhance the overall system performance. Based on the RF frequency requirements, the PLL generates a local oscillator signal of the corresponding frequency, which is then mixed with the intermediate frequency (IF) signal generated by the DDS (Digital Frequency Controller) to produce the required analog echo signal. After filtering by a frequency-selective filter, further echo modulation is performed.

[0085] In near-field detection, the primary radar detection mode is random code phase modulation ranging. Since the autocorrelation function of a random sequence reaches its maximum value only at a certain point, the timing of autocorrelation between the transmitted and echo random sequences is determined by cross-correlation calculations. This allows for the calculation of the echo time and the target's distance. This modulation mode offers extremely high accuracy and strong anti-interference capability for measuring the distance and angle of near-field targets. Another modulation method involves 0 and π phase modulation of the continuous wave signal. Each phase modulation generates a narrow pulse, which is then used to form a pseudo-random sequence for transmission. This method is only suitable for low-speed near-field targets.

[0086] In near-field simulation, the waveform modulation method is random code modulation, so the waveform parameters contain random code sequence information. After being converted into a waveform modulation signal by the FPGA, the 0 and π phase modulation switches are controlled sequentially to generate a random code sequence, thereby achieving phase modulation of the simulated echo signal. At this time, the gate switch is normally open.

[0087] The working principle of the 0 and π phase modulation switch is as follows:

[0088] like Figure 10 As shown, a sine wave with an initial phase of 0 is defined as 0, and a sine wave with an initial phase of π is defined as 1. Therefore, the binary number 10011 can be represented as follows: Figure 11 The waveform shown is as follows. When a continuous sine wave signal is input into a 0 and π modulation switch, the output signal does not shift phase when the control signal is 0, and the output signal shifts phase by π when the control signal is 1. This modulation is called pseudo-random code modulation (it is called pseudo-random code because it is not a truly random signal).

[0089] For the effect of random code sequences on echo information, see [link / reference]. Figure 12 The echo signal sequence is indistinguishable from the transmitted signal in terms of data, carrying the same data phase. The only differences are in frequency and phase; the frequency change comes from the Doppler effect, and the initial phase change comes from the echo delay.

[0090] Since the intermediate frequency signal generated by DDS has relatively low power (approximately 0 dBm), and after mixing and frequency filtering, the power will be even lower, typically <-10 dBm, it cannot simulate large near-field signals. Therefore, an amplification module is needed to amplify the signal.

[0091] The numerically controlled attenuation module is used to control the amplitude of the simulated echo; the amplitude of the echo signal will inevitably differ at different distances. The FPGA adjusts the attenuation amount of the numerically controlled attenuation module based on the numerically controlled attenuation signal to obtain echoes of different amplitudes: higher amplitude for simulating nearby echo signals and lower amplitude for simulating distant echo signals. The numerically controlled attenuation signal is determined by the FPGA based on the echo attenuation amount, ultimately resulting in a simulated radio frequency echo.

[0092] As can be seen in the near-field simulation: the DDS generates a continuous intermediate frequency sine wave, which is mixed with the local oscillator signal to generate an RF signal of nIF±LO (n is an integer), which is then filtered by a frequency selection filter to obtain the RF signal of IF+LO, which is then generated by a 0 / π phase modulation switch to generate a random code sequence, which is then generated by a normally open (always conducting) gate switch, which is then amplified and attenuated to obtain the near-field simulated RF echo.

[0093] At this point, the delay of the echo simulation device consists only of the FPGA delay and the inherent delay of the RF link, which theoretically can be as low as approximately 30ns. The DDS intermediate frequency signal, however, is generated only after the source code synchronization signal and the source code digital signal appear, and the DDS delay is typically around 200ns. Therefore, the arrival time of the external RF signal at the echo delay module can theoretically be later than the time the echo signal is generated. Thus, this method can simulate any echo signal within a range of 200m.

[0094] When simulating far-field echoes:

[0095] When the simulated distance is greater than 200m, the radar's detection mode changes to linear frequency modulation mode or pulse modulation mode. These two modulation methods are mainly used to detect moving targets in the far field.

[0096] When simulating this far-field test RF signal, the signal input module no longer inputs the source code synchronization signal and the source code digital signal. After the RF signal is input, the detector can detect the input signal pulse, as detailed in the far-distance echo simulation timing diagram.

[0097] Radio frequency (RF) signals are discontinuous waves. When there is no signal input, the detector's output voltage is 0V. When an RF signal is output, the detector outputs the detection envelope of the RF signal. After comparison by a comparator, the detection envelope outputs an RF pulse signal. When the FPGA detects the rising edge of the RF pulse signal, it indicates the arrival of the RF signal. At this time, the signal input module no longer receives the source digital signal from the external transmitter, but instead sends analog target parameters to the FPGA via the industrial control computer and network port. The FPGA configures the DDS according to the analog target parameters, thereby generating an intermediate frequency (IF) echo signal. The waveform modulation method is either pulse modulation or linear modulation. It is important to know that the analog target parameters sent by the industrial control computer and network port contain the same information as the source digital signal; the only difference is the data format and the transmission speed.

[0098] The FPGA generates Doppler frequency shift control signals and echo delay control signals based on the simulated target parameters; and controls the DDS to generate far-field simulated intermediate frequency signals based on the Doppler frequency shift control signals and echo delay control signals.

[0099] Based on the RF frequency requirements, the phase-locked loop generates a local oscillator signal of the corresponding frequency, which is then mixed with the intermediate frequency signal generated by the DDS to produce the analog echo signal required for far-field simulation. A frequency-selective filter then performs frequency-selective filtering on this analog echo signal.

[0100] If the analog echo signal is frequency modulated using linear frequency modulation mode, the 0 / π phase modulation switch is always in the 0 phase, the gate switch is normally open (always conducting), and the analog echo signal is then amplified and attenuated to obtain the analog radio frequency echo.

[0101] If the pulse frequency modulation mode is used to modulate the analog echo signal, the 0 / π phase modulation switch is always in the 0 phase, the gate switch is opened when the pulse sequence arrives and closed at other times, and the analog echo signal is then amplified and attenuated to obtain the analog radio frequency echo.

[0102] Generation of linear frequency modulation echo: DDS generates intermediate frequency linear frequency modulation signal - mixes with local oscillator signal to generate nIF±LO (n is an integer) RF signal - IF+LO RF signal is selected by frequency selection filter - 0 / π phase modulation switch is always in 0 phase - gate switch is normally open (always conducting) - amplification - attenuation - to obtain far field simulated RF echo.

[0103] Generation of pulse-modulated echo: DDS generates intermediate frequency pulse signal - mixes with local oscillator signal to generate RF pulse signal of nIF±LO (n is an integer) - IF+LO RF signal is selected by frequency selective filter - 0 / π phase modulation switch is always in 0 phase - gate switch is opened when pulse sequence arrives, and closed at other times - amplification - attenuation - to obtain far-field simulated RF echo.

[0104] The far-field echo delay consists of the DDS configuration time, the DDS delay time, and the inherent delay of the RF link. In this example, the FPGA clock is 100MHz, and the DDS configuration interface is a parallel interface, so the configuration time is 10ns (1 / 100MHz). The DDS operating clock is 2.4GHz, approximately 0.416ns (1 / 2.4GHz). The DDS waveform is generated after 296 clock cycles, so the DDS delay time is 296 × 0.416ns = 123.1ns. The inherent delay of the RF channel is approximately 30ns. Therefore, the minimum echo delay is 10ns + 123.1ns + 30ns = 163.1ns, which is much smaller than the echo delay time of 2d / c (d is the target distance, c is the speed of light) = 2 × 200m ÷ 300000000m / s = 1333.3ns at a distance of 200m. Therefore, this method can simulate target echoes at distances greater than 200m.

[0105] Because the echo simulation device needs to generate broadband echo signals, ranging from hundreds of MHz to tens of GHz, the spectrum needs to be divided into several segments. Each segment uses a different local oscillator signal and filter, and the frequency bands are arranged in parallel. These segments are then switched and selected by a switch to splice them into a complete broadband echo signal. A phase-locked loop generates a local oscillator signal of the corresponding frequency, which is then mixed with the intermediate frequency signal generated by the DDS to obtain the simulated echo signal. To achieve broadband echo simulation, this example performs frequency-selective filtering on the simulated echo signal. (The frequency-selective filtering operation for the simulated echo signal is the same in both far-field and near-field simulated echoes, and will not be described separately in this example.) Since the local oscillator module itself can generate signal sources at different frequencies, the broadband simulation function can be achieved simply by switching the corresponding filter using a switch. This device of switching the filter is the frequency-selective filter, which filters different frequency bands in segments to eliminate spurious signals generated during mixing.

[0106] The frequency-selective filter in this example is, for example... Figure 13 As shown, it includes an input terminal, a one-to-many switch, a filter, a two-to-many switch, and an output terminal, wherein there is at least one filter; the mixer module is connected to the input terminal, the input terminal is connected to one end of the one-to-many switch, the other end of the one-to-many switch is connected to the input terminal of the filter, the output terminal of the filter is connected to one end of the two-to-many switch, and the other end of the two-to-many switch is connected to the output terminal.

[0107] The number of filters needs to be determined based on the signal segmentation. For example, a switching filter circuit that divides a 1GHz to 8GHz frequency band into 4 segments would be used. Figure 14 As shown. If divided into 8 segments, then 8 filters are needed, and the switches are two identical 1-to-8 switches.

[0108] In one embodiment, to ensure precise and controllable echo signal delay, this example also introduces an echo output detector module for feeding back the echo detection signal, thus forming a closed loop in the entire echo simulation process. Further, this example's echo output detector module includes a resistor, a coupler, a detector module, and an amplifier. One end of the resistor is grounded, the other end is connected to one end of the coupler, the other end of the coupler is connected to the detector module, and the output of the detector module is amplified by the amplifier to obtain the echo detection signal, which is then input to the FPGA. The FPGA obtains the actual delay time of the echo signal by comparing the time difference between the rising edge of the synchronization signal (source code synchronization signal or RF pulse signal) and the rising edge of the echo detection signal. This is then compared with the system's required delay time to perform delay calibration, thereby ensuring precise and controllable echo signal delay.

[0109] In some embodiments, an echo simulation method for the above-described arbitrary time-delay Doppler echo simulation device is also provided, comprising the following steps:

[0110] When the distance to the simulated target is less than a preset distance threshold, it is considered a near-field simulation. When simulating near-field echoes:

[0111] Receives radio frequency signals generated by an external transmitter;

[0112] The system synchronously acquires external transmitter control signals, which include source code synchronization signals and source code digital signals. The source code digital signals include simulated target parameters, including target moving speed, target moving direction, target distance, echo attenuation, and waveform parameters. The waveform parameters include waveform modulation methods.

[0113] Based on the source code synchronization signal and the source code digital signal, a Doppler frequency shift control signal and an echo delay control signal are generated; and based on the Doppler frequency shift control signal and the echo delay control signal, the DDS is controlled to delay and generate an intermediate frequency signal with the Doppler effect.

[0114] The local oscillator signal is generated, and then mixed with the intermediate frequency signal to obtain the analog echo signal.

[0115] After frequency-selective filtering of the analog echo signal, it is modulated according to the waveform modulation method to obtain the analog radio frequency echo;

[0116] When the distance to the simulated target is greater than or equal to a preset distance threshold, it is considered a far-field simulation. When simulating far-field echoes:

[0117] Receives radio frequency signals generated by an external transmitter;

[0118] The system receives simulated target parameters, generates Doppler frequency shift control signals and echo delay control signals based on the simulated target parameters, and controls the DDS to delay and generate an intermediate frequency signal with Doppler effect after the radio frequency signal arrives.

[0119] The local oscillator signal is generated, and then mixed with the intermediate frequency signal to obtain the analog echo signal.

[0120] After frequency-selective filtering of the analog echo signal, it is modulated according to the waveform modulation method to obtain the analog radio frequency echo.

[0121] In some embodiments, the presence or absence of an input radio frequency (RF) signal is detected. When an RF signal is input, a detection envelope is output. The detection envelope is compared to output an RF pulse signal, and the rising edge of the RF pulse signal indicates that the RF signal has arrived.

[0122] In some embodiments, when simulating near-field echo, the waveform modulation method is random code phase modulation. During random code phase modulation, after the frequency-selective filter performs frequency-selective filtering on the analog echo signal, the digital control circuit controls the 0 / π phase modulation switch to modulate the phase according to the random code sequence, controls the gate switch to be normally open, and after the analog echo signal is amplified by the amplifier, the digital control circuit controls the digitally controlled attenuator to attenuate it to obtain the analog radio frequency echo.

[0123] When simulating far-field echoes, the waveform modulation method is either linear frequency modulation (LFM) or pulse modulation. In LFM, after the frequency-selective filter selectively filters the analog echo signal, the digital control circuit controls the 0 / π phase modulation switch to be at phase 0, and the control gate switch is normally open. The analog echo signal is amplified by the amplifier, and then the digital control circuit controls the digitally controlled attenuator to attenuate it, obtaining an analog radio frequency echo. In pulse modulation, after the frequency-selective filter selectively filters the analog echo signal, the digital control circuit controls the 0 / π phase modulation switch to be at phase 0, and the control gate switch is opened when the pulse sequence arrives. The analog echo signal is amplified by the amplifier, and then the digital control circuit controls the digitally controlled attenuator to attenuate it, obtaining an analog radio frequency echo.

[0124] In some embodiments, the method further includes: acquiring an echo detection signal; comparing the time difference between the rising edge of the echo detection signal and the rising edge of the source code synchronization signal or the radio frequency pulse signal to obtain the actual delay time of the simulated radio frequency echo; calibrating the actual delay time with the delay parameter so that the delay of the simulated radio frequency echo is accurately controllable; the delay parameter is obtained by calculating the target distance.

[0125] In the above embodiment, the frequency of the intermediate frequency signal is Where f s Here, is the reference frequency of the DDS, and FTW is the frequency control word, taking values ​​from 1 to 2^n-1, where n is the number of divideable bits in the DDS. In the above embodiment, the DDS has 32 divideable bits, and the reference frequency is 2.4 GHz. Therefore, the minimum frequency step is 2.4 GHz ÷ 2^32 ≈ 0.56 Hz. It can be seen that the arbitrary time-delay Doppler echo simulation device and simulation method of the present invention can simulate Doppler modulation and echo delay, ensuring that the Doppler frequency change step is <0.56 Hz and the echo delay time satisfies 0 to ∞.

[0126] Meanwhile, the simulation distance of the echo simulation channel in this invention can reach 2m to 40km. The FPGA reference clock is 100MHz, so one clock cycle is 1 / 100MHz = 10ns. Since the radio frequency signal travels at the speed of light, and the speed of light in air is approximately 3 × 10⁸ m / s, the distance the radio frequency signal travels in one FPGA clock cycle is 10ns × 3 × 10⁸ m / s = 3m. Figure 15As shown, since the distance to the target object is only half the distance of the radio frequency signal, the minimum step of the measurable target distance can reach 1.5m within one clock cycle.

[0127] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0128] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. An arbitrary time-delay Doppler echo simulation device, characterized in that, It includes an RF signal input module, a signal input module, a digital control circuit, an intermediate frequency signal generation module, a local oscillator signal generation module, a mixer module, and an echo modulation module; The radio frequency signal input module is used to detect and determine the start time of radio frequency signal transmission; The radio frequency signal is generated by an external transmitter reading the source code digital signal and configuring the signal upon receiving the source code synchronization signal. The source code digital signal includes simulated target parameters, which include target moving speed, target moving direction, target distance, echo attenuation, and waveform parameters. The waveform parameters include the waveform modulation method. When the distance to the simulated target is less than a preset distance threshold, it is considered a near-field simulation. When simulating near-field echoes: The signal input module is used to synchronously receive the source code synchronization signal and source code digital signal from the external transmitter and transmit them to the digital control circuit. The digital control circuit is used to generate Doppler frequency shift control signals and echo delay control signals based on the source code synchronization signal and the source code digital signal; and to control the intermediate frequency signal generation module to generate intermediate frequency signals based on the Doppler frequency shift control signals and echo delay control signals. The local oscillator signal generation module is used to generate a local oscillator signal; The mixing module is used to mix the local oscillator signal with the intermediate frequency signal to obtain an analog echo signal; The echo modulation module is used to perform frequency selective filtering on the analog echo signal and then modulate the analog echo signal according to the waveform modulation method to obtain an analog radio frequency echo. When the distance to the simulated target is greater than or equal to a preset distance threshold, it is considered a far-field simulation. When simulating far-field echoes: The signal input module is used to receive analog target parameters and transmit them to the digital control circuit; The digital control circuit is used to generate Doppler frequency shift control signals and echo delay control signals based on the simulated target parameters; and to control the intermediate frequency signal generation module to generate intermediate frequency signals based on the Doppler frequency shift control signals and echo delay control signals. The local oscillator signal generation module is used to generate a local oscillator signal; The mixing module is used to mix the local oscillator signal with the intermediate frequency signal to obtain an analog echo signal; The echo modulation module is used to perform frequency selective filtering on the analog echo signal and then modulate the analog echo signal according to the waveform modulation method to obtain an analog radio frequency echo.

2. The arbitrary time-delay Doppler echo simulation device according to claim 1, characterized in that, The radio frequency signal input module includes a pulse detection module and a comparison module; The pulse detection module is used to detect whether an RF signal is input, and when an RF signal is input, it outputs a detection envelope. The comparison module is used to compare the detector envelope and output an RF pulse signal to the digital control circuit to indicate that the RF signal has arrived.

3. The arbitrary time-delay Doppler echo simulation device according to claim 1 or 2, characterized in that, When simulating near-field echoes, the waveform modulation method is random code phase modulation; When simulating far-field echoes, the waveform modulation method is linear frequency modulation or pulse modulation.

4. The arbitrary time-delay Doppler echo simulation device according to claim 3, characterized in that, The echo modulation module includes a frequency selective filter, a 0 / π phase modulation switch, a gate switch, an amplifier, and a digitally controlled attenuator, which are connected in sequence. During random code phase modulation, after the frequency selective filter performs frequency selective filtering on the analog echo signal, the digital control circuit controls the 0 / π phase modulation switch to modulate the phase according to the random code sequence, controls the gate switch to be normally open, and after the analog echo signal is amplified by the amplifier, the digital control circuit controls the digitally controlled attenuator to attenuate it to obtain the analog radio frequency echo. During linear frequency modulation, after the frequency selective filter performs frequency selective filtering on the analog echo signal, the digital control circuit controls the 0 / π phase modulation switch to be in the 0 phase and controls the gate switch to be normally open. After the analog echo signal is amplified by the amplifier, the digital control circuit controls the digitally controlled attenuator to attenuate it, thereby obtaining the analog radio frequency echo. During pulse modulation, after the frequency-selective filter performs frequency-selective filtering on the analog echo signal, the digital control circuit controls the 0 / π phase modulation switch to be in the 0 phase, and controls the gate switch to open when the pulse sequence arrives. After the analog echo signal is amplified by the amplifier, the digital control circuit controls the digitally controlled attenuator to attenuate it, thereby obtaining the analog radio frequency echo.

5. The arbitrary time-delay Doppler echo simulation device according to claim 4, characterized in that, The frequency selective filter includes an input terminal, a one-to-many switch, a filter, a two-to-many switch, and an output terminal, wherein there is at least one filter; The mixer module is connected to the input terminal, which is connected to one end of the one-to-many switch. The other end of the one-to-many switch is connected to the input terminal of the filter. The output terminal of the filter is connected to one end of the one-to-many switch. The other end of the one-to-many switch is connected to the output terminal.

6. The arbitrary time-delay Doppler echo simulation device according to claim 5, characterized in that, It also includes an echo output detector module for feeding back the echo detection signal; The digital control circuit compares the time difference between the rising edge of the echo detector signal and the rising edge of the source code synchronization signal or the radio frequency pulse signal to obtain the actual delay time of the simulated radio frequency echo. The actual delay time is calibrated with the delay parameters to make the delay of the simulated radio frequency echo precise and controllable; the delay parameters are obtained by calculating the target distance.

7. An arbitrary time-delay Doppler echo simulation method, characterized in that, Includes the following steps: When the distance to the simulated target is less than a preset distance threshold, it is considered a near-field simulation. When simulating near-field echoes: Receives radio frequency signals generated by an external transmitter; The system synchronously acquires external transmitter control signals, which include source code synchronization signals and source code digital signals. The source code digital signals include simulated target parameters, including target moving speed, target moving direction, target distance, echo attenuation, and waveform parameters. The waveform parameters include waveform modulation methods. Based on the source code synchronization signal and the source code digital signal, a Doppler frequency shift control signal and an echo delay control signal are generated; and based on the Doppler frequency shift control signal and the echo delay control signal, the DDS is controlled to delay and generate an intermediate frequency signal with the Doppler effect. The local oscillator signal is generated, and then mixed with the intermediate frequency signal to obtain the analog echo signal. After frequency-selective filtering of the analog echo signal, it is modulated according to the waveform modulation method to obtain the analog radio frequency echo; When the distance to the simulated target is greater than or equal to a preset distance threshold, it is considered a far-field simulation. When simulating far-field echoes: Receives radio frequency signals generated by an external transmitter; The system receives simulated target parameters, generates Doppler frequency shift control signals and echo delay control signals based on the simulated target parameters, and controls the DDS to delay and generate an intermediate frequency signal with Doppler effect after the radio frequency signal arrives. The local oscillator signal is generated, and then mixed with the intermediate frequency signal to obtain the analog echo signal. After frequency-selective filtering of the analog echo signal, it is modulated according to the waveform modulation method to obtain the analog radio frequency echo.

8. The arbitrary time-delay Doppler echo simulation method according to claim 7, characterized in that, This includes detecting whether an RF signal is input, and outputting the detector envelope when an RF signal is input; The detector envelope is compared and an RF pulse signal is output. The rising edge of the RF pulse signal indicates that the RF signal has arrived.

9. The arbitrary time-delay Doppler echo simulation method according to claim 8, characterized in that, When simulating near-field echoes, the waveform modulation method is random code phase modulation; When simulating far-field echoes, the waveform modulation method is linear frequency modulation or pulse modulation.

10. The arbitrary time-delay Doppler echo simulation method according to claim 9, characterized in that, Also includes: Acquire the echo detection signal; compare the time difference between the rising edge of the echo detection signal and the rising edge of the source code synchronization signal or the RF pulse signal to obtain the actual delay time of the simulated RF echo; The actual delay time is calibrated with the delay parameters to make the delay of the simulated radio frequency echo precise and controllable; the delay parameters are obtained by calculating the target distance.

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