| In the simultaneous same-frequency full-duplex technology,due to the short separation distance between the transmitting antenna and the receiving antenna,part of the transmitted signal will directly leak to the receiving end.The leakage signal always with high power makes the target echo signal submerged and indiscernible.The threshold sensitivity of the receiving end is also reduced.In a single-antenna system,where the transmitting antenna and the receiving antenna share one,the problem of transmitted signal leakage is more serious due to the poor transceiver isolation.In order to improve the transceiver quality,it is particularly critical to eliminate the self-interference of the system.Currently the best solution is active radio frequency(RF)cancellation technology.The traditional electronic RF cancellation technology is limited by the working frequency and working bandwidth of the device,which makes it unable to meet the future needs of high-frequency broadband transceivers.With the development of microwave photonics technology,photonic RF cancellation technology has also emerged.Photonic RF cancellation technology has the advantages of large working bandwidth and high tuning accuracy.Compared with electronic RF cancellation technology,it greatly improves the isolation and cancellation depth of the system.In this thesis,microwave photonic RF cancellation technology is conducted.The full text includes the following four aspects:1.The lack of isolation in the current simultaneous same-frequency full-duplex technology and the radar field is analyzed.The existing common RF cancellation methods are listed.Compared with the RF cancellation technology in the electronics,the advantages and development prospects of the photonic RF cancellation technology system are obtained.2.Through the theoretical analysis of the RF cancellation technology,the core condition of the RF cancellation technology is obtained that the interference signal and the reference signal have equal amplitudes and opposite phase.In the numerical analysis with MATLAB,the influence of amplitude and phase error on the cancellation depth is obtained.The principles of electro-optic modulators commonly used in microwave optical subsystems and the functions of modulators in radio frequency cancellation technology are also introduced,which provides a theoretical basis for subsequent work.3.A photonic RF cancellation system based on a single dual-parallel Mach-Zehnder modulator(DPMZM)is proposed.Numerical analysis of the proposed system is carried out by MATLAB simulation software.First of all,under the perfect cancellation condition,the cancellation effect of single-frequency signal and wideband signal is verified.The changes of the cancellation depth under different signal center frequencies,input powers and different bandwidths are also analyzed.Then,taking into account the limitations in practical applications,the cancellation depth under unideal condition is simulated which provides a reference for the experiment.4.A photon RF cancellation experimental system based on a single DPMZM is carried out and experimentally verified.Combined with numerical simulation,the cancellation depth of single frequency signal and wideband signal under different center frequency,input power and modulation bandwidth is studied. |
