Research On Radar Signal Parameter Measurement Technology Based On Microwave Photonics

Information is a fundamental feature of modern warfare,and the signals received by radar on the battlefield contain valuable information in information warfare.Accurately obtaining this information can gain the initiative in warfare.Therefore,radar signal detection technology has significant strategic significance.Among the numerous parameters of radar signals,Doppler Frequency Shift(DFS)is a key parameter in radar measurement systems,which originates from the relative motion between the measured object and the radar,and carries the velocity information of the measured object.Angle Of Arrival(AOA)is also an important parameter used for precise location detection of the measured object.Measuring both DFS and AOA can accurately track the speed and direction of the target object.Traditional electric domain parameter measurement systems have inherent electronic device speed bottlenecks,limited measurement range,and poor performance in complex and variable measurement environments.In recent years,photonic-assisted microwave signal measurement technology has received widespread attention due to its inherent advantages such as strong electromagnetic interference resistance,low insertion loss,small size,and light weight.This paper firstly reviews the research background and current domestic and international research status of radar signal parameter measurement based on microwave photonics.After in-depth analysis of the devices and principles related to microwave photonics measurement,three schemes for simultaneously measuring DFS and AOA based on microwave photonics are proposed.The feasibility of each scheme has been verified through theoretical derivation and simulation.The main research work of this paper is summarized as follows:(1)A simultaneous measurement scheme for DFS and AOA based on Dpol-DDMZM is proposed.In this scheme,the echo signal and the local oscillator signal are modulated onto the optical wave by Dpol-DDMZM.As both sub-DDMZMs are set to suppress the carrier,most of the carrier is suppressed.The signal output from the modulator is filtered by a tunable optical filter(TOF)to remove the negative first-order sideband.After polarization beam splitter(PBS)demultiplexing,the two signals are input to the balanced photodetector(BPD).By detecting the frequency and phase of the output photocurrent,the DFS and AOA of the target can be calculated,and the radial velocity and azimuth information of the object can be obtained.As the carrier is suppressed,the energy of the useless sidebands is greatly reduced,reducing the interference to the useful signal and improving the measurement accuracy.In simulation,when the RF signal is at 10,30,and 50 GHz,and the frequency difference between the echo signal and the local oscillator signal is less than 500 kHz,the measurement error of DFS is less than 0.05 Hz,and the measurement error of AOA is less than 1° within the measurement range of 0° to 90°.(2)A simultaneous DFS and AOA measurement scheme without ambiguity based on DDMZM is proposed.In this scheme,a DC bias voltage is applied to introduce a phase difference into the upper and lower branches of the modulator.The output signal of the DDMZM is filtered by a comb-like filter,and the+1st and-1st order sidebands are extracted.Finally,the frequency and phase relationship of the beat frequency signal after the two paths are measured can be used to calculate the DFS and then obtain the radial velocity of the target.The no-directional-ambiguity AOA is obtained by measuring the power of the two paths and comparing it with the theoretical curve after mapping.The advantage of this scheme lies in dynamically adjusting the slope of the measurement curve by switching the DDMZM operating point,solving the problem of low AOA measurement accuracy in the critical range.Moreover,the unambiguity AOA measurement is achieved by constructing two measurement curves with phase differences.In simulation,when the RF signal is at 10 GHz and the frequency difference between the echo signal and the local oscillator signal is within 500 kHz,the measurement error of DFS is less than 0.05 Hz,and the AOA error is less than 0.8° in the measurement range of-90° to 90°.(3)A DFS and AOA measurement scheme based on Dpol-DDMZM without filtering is proposed.In this scheme,a reference signal,which is 2 MHz higher than the local oscillator signal,is injected into the lower ports of two sub-Mach-Zehnder modulators,while the two echo signals are input to the upper ports of the modulators.The phase difference and hence the AOA can be obtained by comparing the ratio of the instantaneous power of the two photocurrents with the theoretical amplitude comparison function(ACF).The magnitude and direction of the DFS can be inferred from the peak frequency of the photocurrent.The advantage of this scheme is that it eliminates the complex process of measuring the voltage amplitude of the measurement echo signal and the error caused by laser power fluctuations by constructing the ACF using the power of the two channels.The simulation results show that when the RF signal is at 10 GHz and the frequency difference between the echo signal and the local oscillator signal is within 500 kHz,the DFS error is less than 0.05 Hz,and the AOA error is less than 0.6° within the measurement range of 0° to 90°.