| Electromagnetic wave is an important tool for information transmission and information acquisition in this day and age.However,in nowadays extremely complex electromagnetic environment composed of various radiation sources and scattering sources,spectrum resources and signal security issues have attracted more and more attention,and signal parameter measurement technology has been widely used in numerous scenarios.While due to the limitation of electronic bottlenecks,there exist technical problems such as narrow operating frequency band,susceptibility to electromagnetic interference,high volume,weight and power consumption in the electrical domain signal parameter measurement systems.In recent years,with the rapid development of microwave photonic technology,signal parameter measurement systems based on microwave photonic technology rely on its unique advantages such as large instantaneous bandwidth,low transmission loss,and antielectromagnetic interference,as well as photonic integrated devices with small size,low power consumption,and high stability.It avoids the electronic bottleneck problem faced by the electrical domain systems,greatly improves the performance index of the signal parameter measurement systems,and provides a new solution for a new generation of signal parameter measurement systems.In this paper,relying on microwave photonic technology,the key technology of angle of arrival and doppler frequency shift measurement with large instantaneous bandwidth is studied.The specific work is as follows:A large instantaneous bandwidth angle of arrival measurement technology based on microwave photonic technology is studied,and an ambiguity-free angle of arrival measurement system based on dual parallel Mach-Zehnder modulators is proposed.The system inputs the signals received by the two antennas to the two sub-modulators of the dualparallel Mach-Zehnder modulator.By introducing a static phase shift between the upper and lower sub-modulators,and then filtering out the positive and negative of the modulated signal by an optical filter,two optical power interference channels are constructed to form two different power phase mapping curves.The system breaks the symmetrical structure of the original mapping curve,and realizes the unambiguous mapping of power and phase difference within the phase difference range of 0 to 360 degrees,that is,the angle of arrival measurement in the range of 0 to 180 degrees.The final experiment proves that the error of phase difference measurement is within 2.24 degrees.Compared with other schemes,the system has a simple structure and excellent performance,which doubles the measurement range of the angle of arrival with only one dual-parallel Mach-Zehnder modulator.Aiming at the problem that the input signal power is required to be fixed in the angle of arrival measurement receiver,a power-free angle of the arrival measurement system based on dual-polarization Mach-Zehnder modulators is studied and proposed.The system is based on a double-polarization positive Mach-Zehnder modulator,and uses microwave photonic polarization multiplexing technology to construct a system with constructive and destructive optical power interference channels.By comparing the power values measured by the two channels,the purpose of removing the input signal power parameter is achieved.The final experiment shows that the system achieves the angle of arrival measurement without power limitation of the input signal to a certain extent,and achieves the phase difference measurement accuracy within 5.5 degrees between 18 degrees to 162 degrees phase difference measurement.The space angle of arrival measurement technology is studied.The one-dimensional unambiguous angle of the arrival measurement system is extended to two dimensions by using the principle of space geometry and the idea of microwave photonic integration.The system uses the quadrature polarization modulation with an integrated modulator to construct a two-dimensional arrival angle measurement system on the X-axis and Y-axis polarization states respectively,and then separate them by a polarization beam splitter.The two modulated signals are processed separately,and then the spatial angle of arrival can be calculated.The two-dimensional unambiguous angle of the arrival measurement system can be extended to realize the ambiguity-free measurement of the angle of arrival in four quadrants in space,and the measurement range is expanded four times.The microwave photonic doppler frequency shift measurement technology with large instantaneous bandwidth is studied,and a cascaded modulation system based on microwave photonic technology is proposed.The system employs a structure in which dual-polarization modulators and phase modulators are cascaded.Using polarization multiplexing technology and the sensitivity of the phase modulator to polarization,the optical signals in the X and Y polarization states can be modulated separately.After the modulated signals are combined with a 45-degree polarization and filtered out of one sideband,the beat signal can be obtained by a low-speed photodetector.Finally,doppler frequency shift measurement and direction determination can be realized by measuring beating signal frequency.If the modulated signal is constructed by the cascaded modulation chain,the signal component at the optical carrier does not interfere with the normal operation of the system,which greatly reduces the requirements for the optical filter,enables the system to use low-frequency transmission signals,and increases the system bandwidth.Since the entire measurement process is only related to the signal frequency,the system is not affected by the signal phase,and is compatible with microwave photonic distributed systems such as long-distance transmission.The microwave photonic integration technology is studied,and an integrated system of microwave photon Doppler frequency shift and angle of arrival measurement is proposed.The system uses a four-port dual-parallel Mach-Zehnder modulator.The echo signals received by the two antennas are input to the three RF input ports of the modulator with equal power to construct an optical power interference with an amplitude ratio of 2 to 1.The system introduces a 30-degree phase shift between the upper and lower sub-modulators through the main bias voltage,breaking the symmetrical structure of the power phase mapping curve,and separating the upper and lower sidebands from the output signal of the modulator with an optical wavelength division multiplexer to form two channels.Output signals from each of them are then beat by a low-speed photodetector.Finally,the system realizes doppler frequency shift measurement by measuring the frequency of the two beating frequency signals;by comparing the phase relationship between the output signals of the two channels,the determination of the Doppler direction is realized;by measuring the power of the output signals of the two channels,the ambiguity-free phase difference mapping within 360-degree range is realized,and the 180-degree angle of arrival measurement is completed. |
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