High-Resolution Microwave Photonic Radar Detection Method with Self-Interference Cancellation Function

Abstract

The detection method of a high-resolution microwave photon radar with self-interference cancellation function belongs to the field of microwave photon technology. The system used in this method includes a laser, a dual-parallel dual-polarization Mach-Zehnder modulator, a dual-drive Mach-Zehnder modulator, an arbitrary waveform generator, an optical coupler, a first photodetector, an electric power amplifier, a transmitting antenna, a receiving antenna, a low-noise amplifier, a second photodetector, a low-pass filter, and a signal acquisition and processing module. The present invention overcomes the disadvantages of traditional electronic radars and realizes the integration of a large-bandwidth and high-resolution functional microwave photon system.

Description

Technical Field

[0001] The present invention belongs to the field of microwave photon technology. More specifically, it is a microwave photon radar ranging system, which is a device that simultaneously realizes ranging and self-interference cancellation of radio frequency signals. Background Art

[0002] The invention of radar is one of the greatest achievements of mankind in the 20th century. It is an electronic device that uses electromagnetic waves to detect targets. It emits electromagnetic waves at the transmitting end to cover the target and receives its echo at the receiving end, thereby obtaining information such as the distance, speed, azimuth, altitude, and shape of the target.

[0003] The progress of technology has promoted the enhancement of the military strength of various countries and increased people's demands for production and life. This requires the radar system to develop in the directions of low cost, small volume, high precision, high resolution, high real-time performance, anti-interference, multi-function, and reconfigurability. However, due to the limitation of the "electronic bottleneck", traditional electrical radars are difficult to make breakthroughs in high frequency and large bandwidth. Photon technology has the advantages of light weight, low transmission loss, ultra-wide bandwidth, high speed, anti-electromagnetic interference, reconfigurability and reusability, and complements the advantages and disadvantages of microwave technology. Therefore, the advantages of photon technology are becoming the key technology to break through the high-frequency and wide-band bottleneck limitations of radars.

[0004] Among various types of radars, the continuous wave radar is a continuous transceiver radar. Its average power and maximum power are the same. It has technical characteristics such as a low intercept probability, strong anti-clutter performance, and no speed blind area. The continuous wave radar has the characteristics of simple structure, small volume, and good integration, and is widely used in fields such as reconnaissance radars, intercept radars, and low, slow, and small targets. However, in the process of development, the continuous wave radar has also encountered certain difficulties. Because the system needs to transmit and receive simultaneously, and the distance between the transmitting antenna and the receiving antenna is not high enough, the transmitted signal will enter the receiving antenna, interfering with the received echo signal, resulting in the weak echo signal being submerged, thus generating a self-interference problem. Due to the existence of the self-interference problem, the extraction of the signal fails, the sensitivity of the receiver decreases, and the nonlinear effect of the signal occurs, thus greatly reducing the performance of the receiver. However, few people focus on microwave photon ranging radars, and there is little relevant research at home and abroad on how to eliminate self-interference. Since the self-interference signal and the echo signal are of the same frequency, it is difficult to filter out the self-interference signal using an electrical filter. Therefore, the self-interference cancellation technology is the key to microwave continuous waves.

[0005] In existing radar systems, the self-interference problem cannot be directly filtered out, and the existing interference signals will disrupt the processing of echo signals. Although a series of multifunctional microwave photon detection systems have been developed at home and abroad, no one has proposed a solution to the self-interference problem existing in the ranging process of a short-distance high-precision transceiver integrated radar, so as to realize a ranging microwave photon detection system with accurate positioning. Summary of the Invention

[0006] For the above reasons, the main objective of the present invention is to propose a dual function of radar ranging and RF self-interference cancellation technology using microwave photon technology. Using microwave radar can effectively solve the deficiencies of traditional electronic radar in terms of bandwidth, volume, weight, electromagnetic interference, etc. At the same time, combined with ranging and RF self-interference technology, the self-interference problem of the radar is solved.

[0007] The specific technical solution of the present invention is as follows:

[0008] A dual-function system method for ranging and radio frequency self-interference cancellation based on microwave photon technology. The specific implementation link of the method includes a laser, a dual-parallel dual-polarization Mach-Zehnder modulator DP-DPMZM, a dual-drive Mach-Zehnder modulator DDMZM, an arbitrary waveform generator, an optical coupler OC, a first photodetector, an electric power amplifier, a transmitting antenna, a receiving antenna, a low-noise amplifier, a second photodetector, a low-pass filter, and a signal acquisition and processing module. Among them, DD-MZM includes an upper-arm sub-PM and a lower-arm sub-PM. The method includes the following steps:

[0009] Step 1: Generate a detection signal with a large instantaneous bandwidth, specifically as follows:

[0010] The optical signal generated by the laser is injected into the DP-DPMZM as an optical carrier. After the baseband linear frequency modulation signal passes through a 90° hybrid coupler, it is loaded onto the two radio frequency ports of the upper-path modulator of the DP-DPMZM, and the DC bias points of MZM1, MZM2, and the upper-path main modulator are all set at the maximum transmission point to obtain 0th order and ±4th order signals. The radio frequency ports of the lower-path modulator of the DP-DPMZM are short-circuited, that is, MZM3 and MZM4 are used as intensity modulators to adjust the amplitude of the optical carrier, so that the amplitude power of the lower-path optical carrier is equal to that of the upper-path optical carrier. Adjust the cascaded polarization controller (PC) to introduce a 180° phase difference between the optical signals in two perpendicular polarization states. When passing through a 45° polarizer, ±4th order signals are obtained as Figure 2 shown by the spectrum at point b in

[0011] Next, use a 50:50 coupler OC to divide the output signal of the MZM into two paths. One path is injected into the first photodetector for photoelectric conversion to obtain an eight-fold frequency linear frequency modulation signal as Figure 2as shown by the spectrum at point c in

[0012] Finally, the signal is first injected into a broadband power amplifier for amplification, and then transmitted into free space using a transmitting antenna as a radar detection signal.

[0013] Step 2: Range detection and self-interference signal suppression

[0014] Use a 50:50 coupler OC to input the other path of the output signal of the MZM into a dual-drive Mach-Zehnder modulator DD-MZM, and adjust the bias voltage of the DD-MZM to the minimum bias voltage; the DD-MZM has two drive signals. The first drive signal is the microwave signal received through the receiving antenna and received by a low-noise amplifier, while the second drive signal is the modulated transmission signal. After the output of the DD-MZM passes through a second photodetector and low-pass filtering, it is collected by a signal acquisition and processing module to obtain a low-frequency signal. Next, by solving this signal, the range information of the target can be obtained.

[0015] In the transmitting end of the present invention, a dual-parallel Mach-Zehnder modulator DP-DPMZM is used to perform octupling on the intermediate-frequency linear frequency modulation signal generated by an arbitrary waveform generator, generating a linear frequency modulation (LFM) signal with a large instantaneous bandwidth and transmitting it into free space as a detection signal. The transmitted signal after delay phase modulation and the received echo signal are used as the dual-drive Mach-Zehnder modulator DD-MZM. Finally, by adjusting the DC bias voltage of the dual-drive Mach-Zehnder modulator (DDMZM), the signals modulated by up and down PM are counteracted, and the range information of the target is obtained through the low-frequency signal after self-interference cancellation.

[0016] Advantages of the present invention:

[0017] The present invention is a dual-functional system for ranging and cancellation based on microwave photon technology. It is a method that combines microwave cancellation method and microwave optical radar detection technology. The distance to the target is detected by a single radar and its radio frequency self-interference is eliminated. This method can generate an eight-fold frequency signal, and the established detection link has a smaller size and lighter weight, which is convenient for use in military and civilian fields. Moreover, the self-interference problem of a transceiver integrated radar, especially a short-range high-precision transceiver integrated radar, is effectively solved. Description of the Drawings

[0018] Figure 1 It is a schematic diagram of the link structure of a dual-functional system for radar ranging and radio frequency self-interference cancellation technology based on microwave photon technology modulation.

[0019] Figure 2 (a) Figure 1 Schematic diagram of the spectrum at point a in

[0020] Figure 2 (b) Figure 1 Spectrum diagram of point b

[0021] Figure 2 (c) Figure 1 Spectrum diagram of point c Detailed implementation manners

[0022] For the current integrated transceiver radar, especially the integrated transceiver radar with short distance and high precision, due to its own interference, the detection effect is affected to a certain extent. At the same time, due to the large size and weight of the detection link constructed by the traditional detection method, it is not conducive to the use in military and civilian fields. The present invention proposes a dual-functional system based on microwave photon technology modulation for radar ranging and radio frequency self-interference cancellation technology, which uses the radar detection signal to detect the distance of the target at the same time, and finally realizes radar ranging and radio frequency self-interference cancellation.

[0023] The detection method of the dual-functional system based on microwave photon technology modulation for radar ranging and radio frequency self-interference cancellation technology of the present invention is as follows:

[0024] The optical signal generated by the laser is injected into the dual-parallel dual-parallel Mach-Zehnder modulator DP-DPMZM as the optical carrier. After the baseband linear frequency modulation signal passes through a 90° hybrid, it is loaded onto the two radio frequency ports of the upper path modulator of the DP-DPMZM. The DC bias points of MZM1, MZM2 and the upper path main modulator are all set at the maximum transmission point to obtain the 0th order and ±4th order signals. The radio frequency ports of the lower path modulator of the DP-DPMZM are short-circuited, that is, MZM3 and MZM4 are used as intensity modulators to adjust the amplitude of the optical carrier, so that the amplitude of the lower path optical carrier is equal to the amplitude power of the upper path optical carrier. The cascaded polarization controller (PC) is adjusted to introduce a 180° phase difference between the optical signals in two perpendicular polarization states. When passing through a 45° polarizer, ±4th order signals are obtained. The output signal of the DP-DPMZM is injected into a 50:50 coupler and divided into two paths. One path enters the first photodetector, and the beat frequency obtains an eight-fold frequency linear frequency modulation signal. The frequency-doubled linear frequency modulation signal is amplified by a broadband electrical amplifier and then transmitted into free space by the transmitting antenna as the radar detection signal. The other path is used as a reference signal and injected into the dual-drive Mach-Zehnder modulator DD-MZM as its carrier; the two drive signals of the DD-MZM are respectively the microwave signal received by the receiving antenna and the transmitted signal after modulation. The output of the DD-MZM is detected by photoelectricity and filtered by low-pass, and then collected by the signal acquisition and processing module, and a low-frequency signal related to the direction and distance of the non-cooperative target can be obtained; next, by solving this signal, the distance of the target can be obtained simultaneously.

[0025] For the convenience of public understanding, the present invention will be further described below in conjunction with the accompanying drawings and mathematical derivations:

[0026] Figure 1 FIG. is a schematic diagram of the link structure of the dual-functional system method for range measurement and radio frequency self-interference cancellation based on microwave photon technology of the present invention, including a laser, a dual-parallel dual-parallel Mach-Zehnder modulator DP-DPMZM, a dual-drive Mach-Zehnder modulator DDMZM, an arbitrary waveform generator, an optical coupler OC, a first photodetector, an electric power amplifier, a transmitting antenna, a receiving antenna, a low-noise amplifier, a second photodetector, a low-pass filter, and a signal acquisition and processing module.

[0027] Using Figure 1 The link structure shown above, the process of the dual-functional system method for range measurement and radio frequency self-interference cancellation based on microwave photon technology is as follows:

[0028] Step 1: Generate a detection signal with a large instantaneous bandwidth;

[0029] The optical signal generated by the continuous wave laser is expressed as E(t) = E 0 exp(jω 0 t), where E 0 and ω 0 respectively represent the amplitude and the central angular frequency of this optical signal, and j in the formula represents the imaginary unit. Use an arbitrary waveform generator to generate an electrical baseband linear frequency modulation signal, which can be expressed as:

[0030]

[0031] That is, its frequency is f(t) = f m + k·t, where f m is the central frequency of this signal, k is the frequency modulation slope, V LFM represents the amplitude of this baseband linear frequency modulation signal, T represents the duration of the signal. After passing the baseband linear frequency modulation signal through a 90° hybrid, it is loaded onto the two radio frequency ports of the upper modulator of the DP-DPMZM, and the DC bias points of MZM1, MZM2, and the upper main modulator are all set at the maximum transmission point. Then the output optical signal of this path can be expressed as

[0032]

[0033] Here, m is the modulation coefficient of the DP-DPMZM, that is, m = πV LFM / V π1 , where V π1 is the half-wave voltage of this modulator DP-DPMZM, and V LFM is the amplitude of the linear frequency modulation signal. J n(m) is the Bessel function of the first kind, where the value of n represents the order of the sideband. For example: J 0 (m) represents the carrier wave, and J 4 (m) represents the positive fourth-order sideband, and J -4 (m) represents the negative fourth-order sideband.

[0034] Short-circuit the RF port of the lower sub-modulator of the DP-DPMZM, so that MZM3 and MZM4 are used as intensity modulators to adjust the amplitude of the optical carrier wave, making the amplitude and power of the lower optical carrier wave equal to those of the upper optical carrier wave, as shown by the spectrum at point a in Figure 2 Adjust the cascaded polarization controller (PC) to introduce a 180° phase difference between the optical signals in two perpendicular polarization states. When passing through a 45° polarizer, the optical signal can be expressed as

[0035]

[0036] Since the optical carrier waves of the two paths have equal amplitudes and opposite phases, interference cancellation is achieved, that is, the generation of positive and negative fourth-order optical sideband signals with carrier suppression is realized. Input this optical signal into a photodetector, and the resulting photocurrent can be expressed as

[0037] i(t) ∝ cos(2π(8f m + 8k·t)·t) (4)

[0038] Therefore, this system can generate a linearly frequency-modulated microwave signal with 8 times the frequency and 8 times the bandwidth.

[0039] Finally, first inject this signal into a broadband power amplifier for amplification, and then use a transmitting antenna to transmit it into free space as a radar detection signal.

[0040] Step 2: Distance detection and self-interference signal suppression

[0041] Inject another optical signal output by the OC into the dual-drive Mach-Zehnder modulator DD-MZM at the receiving end as a reference signal; after this signal enters the DD-MZM, it is equally divided in power and enters the upper and lower sub-PMs.

[0042] The echo signal S(t) and the self-interference signal I(t) can be respectively expressed as

[0043] S(t) = S 1 cos(2π(8f m + 8k·t + 8k·Δτ)·t) (5)

[0044] I(t) = I 1 cos(2π(8f m + 8k·t + 8k·t 1 )·t) (6)

[0045] Where S 1 and I 1 represent the amplitudes of the received echo signal and the self-interference signal respectively, and Δτ and t 1 represent the delays experienced by the echo signal and the self-interference signal respectively. At the same time, a part of the transmitted signal is coupled out as the reference signal R(t), which can be expressed as

[0046] R(t) = R 1 cos(2π(8f m +8k·t + 8k·t 2 ))·t) (7)

[0047] Where R 1 represents the amplitude of the given reference signal, and t 2 represents the delay experienced by the reference signal. The received signal is loaded onto the upper RF input port of the dual-drive Mach-Zehnder modulator, and the reference signal is loaded onto the lower RF input port, and the DC bias voltage of the dual-drive Mach-Zehnder modulator is adjusted to the half-wave voltage. Then, the output optical signal of the upper sub-PM can be expressed as

[0048]

[0049] Here, m 1 is the modulation coefficient of the upper sub-PM for the echo signal S(t), that is, m 1 = πS 1 / V π2 , and here, m 2 is the modulation coefficient of the upper sub-PM for the self-interference signal I(t), that is, m 2 = πI 1 / V π2 , where V π2 is the half-wave voltage of the upper sub-PM of this modulator.

[0050] Since the DC bias voltage of the dual-drive Mach-Zehnder modulator is the half-wave voltage at this time, then the output optical signal of the lower sub-PM can be expressed as

[0051]

[0052] Here, m 3 is the modulation coefficient of the lower sub-PM for the reference signal R(t), that is, m 3 = πR 1 / V π3 , where V π3 is the half-wave voltage of the lower sub-PM of this modulator.

[0053] Therefore, the output of the dual-drive Mach-Zehnder modulator can be obtained and can be expressed as

[0054]

[0055] Then when the conditions

[0056]

[0057] That is, by adjusting the amplitude and delay of the given reference signal, the output of the dual-drive MZM can be obtained as

[0058]

[0059] Substitute

[0060]

[0061] into Equation (12), then we can get

[0062]

[0063] As Figure 2 shown by the spectrum at point c. After that, the output optical signal of the DDMZM is filtered by a filter to select the frequency and input into a low-speed photodetector for square-law detection. The frequency of the obtained microwave signal is

[0064] Δf = 8k·Δτ. (15)

[0065] Therefore, after optical mixing and de-chirping, a low-frequency microwave signal can be obtained, which not only reduces the high-speed requirements for signal processing such as the radar backend receiver, sampling, and analog-to-digital conversion, but also further calculates the delay Δτ of the echo signal according to the known chirp rate of the linear frequency modulation signal. Then, the distance of the target to be measured from the radar antenna can be calculated by the following formula

[0066]

[0067] where c represents the speed of light; B = kt is the bandwidth of the signal.

[0068] The present invention is a ranging and cancellation dual-functional system based on microwave photonics technology. It is a method that combines microwave cancellation method and microwave optical radar detection technology. Through a single radar detection signal, while realizing distance detection, it realizes self-interference cancellation of RF. It solves the self-interference problem of the transceiver integrated radar, especially the short-range high-precision transceiver integrated radar.

Claims

1. A high-resolution microwave photon radar detection system with self-interference cancellation function, characterized in that, the system includes: a laser (1) for inputting continuous detection light to a dual-parallel dual-polarization Mach-Zehnder modulator (2); a dual-parallel dual-polarization Mach-Zehnder modulator (2) for modulating the input light with a chirp signal and outputting ±4th-order modulated optical signals; a 90° hybrid (3) for providing a 90° phase difference for the chirp signal; a first photodetector (4) and a coupler, the coupler splitting the output signal of the dual-parallel dual-polarization Mach-Zehnder modulator (2) into two paths, one of which is injected into the first photodetector (4) for photoelectric conversion to obtain an octave frequency signal; a transmitting antenna (5) for transmitting the octave frequency signal; a receiving antenna (9) for receiving an echo signal and a self-interference signal; a dual-drive Mach-Zehnder modulator DD-MZM (6), the other optical signal output by the coupler being injected into the DD-MZM as a first reference signal; after the first reference signal enters the DD-MZM, it is equally divided in power and enters the upper and lower sub-phase modulators; the echo signal and the self-interference signal are input into the DD-MZM as a modulation signal of one path of the DD-MZM for modulation, and a part of the octave frequency signal is obtained as a second reference signal R(t) after time delay and phase adjustment, and the second reference signal R(t) is input into the other sub-phase modulator of the DD-MZM as a modulation signal, and the self-interference signal is eliminated by adjusting the amplitude and delay of the second reference signal; a filter (7), the dual-drive Mach-Zehnder modulator (6) using the filter (7) to select the required frequency signal; a second photodetector (8) for converting the optical signal obtained by the filter (7) into an electrical signal to obtain the time information of the echo.

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