Research On Key Technologies Of The Receiver And Transmiter Of S-band Nonlinear Junction Detector

The nonlinear junction detector is mainly used to detect the harmonic signals scattered by the metal junction and the PN junction.The nonlinear junction detector has excellent antiinterference performance and can detect the stealth target,which has great application value in military and civil aspects.But how to design the detector to detect the target object accurately involves many key technologies.This thesis focuses on the nonlinear correction of the power amplifier at the transmitting end and the pulse compression technology at the receiving end.The former can suppress the harmonic leakage at the emitting end,so as to reduce the interference to the harmonic of the target radiation in the detection process.The latter can improve the detection ability of small and weak targets and range resolution rate at the receiving end.Finally,the thesis introduces the technique of constant false alarm in the detection of target,which is used to determine whether the target object is detected or not.This thesis will study the key technologies of the transmitter and receiver of the nonlinear junction detector from the following aspects.(1)Aiming at the problem of harmonic leakage caused by the nonlinear characteristics of the power amplifier at the transmitter,some interference is caused to the target harmonics received.Applies the digital predistortion in the system of linear frequency modulation pulse harmonic detector system,that applies in traditional mobile communication.Set up in Simulink based on the structure of the indirect learning adaptive digital predistortion simulation platform.According to the date from the amplifier module,the power amplifier module of data,the design of inverse nonlinear function of the structure of the front module and power amplifier modules cascade,then based on LMS algorithm is set up after the module to update the predistortion model parameters.Finally,it is proved that the input and output data are close to linearization by drawing a graph.The power ratio of adjacent channel was calculated,and the pre-distortion module was added to improve 23.64 d B,which verified the effective suppression of the model for out-of-band spectrum leakage.It is proved that the method is effective in improving the nonlinear characteristics of the transmitter.(2)Pulse compression is a common signal processing method at the receiving end,but the high side lobe after pulse compression and the main lobe broadening caused by the use of window function.It may drown the weak target in the side lobe of the strong target.To this end,this thesis designs an adaptive pulse compression algorithm,which adopts LFM signal,estimates a matching filter coefficient for each distance unit based on MMSE algorithm,and calculates it with the received signal.Write Matlab program to complete the simulation analysis.Compared with the original pulse compression method.It is proved that the adaptive pulse compression algorithm is effective in multi-target recognition and sidelobe suppression.(3)After pulse compression at the receiving end,threshold detection is also used to determine whether the target object is detected.In this paper,the interference power of the reference window before and after the reference window is calculated by using the constant false alarm rate of smallest of cell averagingis,and the smaller of the two estimated values is selected to calculate the threshold value.This method can effectively improve the detection capability of multiple targets in the same reference window.Write Matlab program,the pulse compression compression of the data after the detection.Finally,several target objects are extracted effectively.