Research On The Application Of MIMO Techniques In Over-the-Horizon Radar

Skywave over-the-horizon radar (OTHR) can track target more than3000Km away and over millions of square kilometers of open ocean. Due to this reason, OTHR plays an important role in modern air defense system and has a wide range of applications in both military and civil fields. However, due to the existence of many environment perturbations in high-frequency band, OTHR have many problems in range resolution, target detection, interference suppression and so on. The solution of these problems plays a key role in improving OTHR performance.Recently, the concept of multiple-input multiple-output (MIMO) radar has been proposed and has drawn attention from many researchers. The MIMO radar is a multiple antenna radar system which can transmit waveform from each transmitting antenna element. At the receive side, the individual transmit antenna element transmissions can be separately processed with a matched filter following reception to form transmit beams. MIMO radar has significant potentials in target detection, interference suppression, resolution enhancement and so on. Fully using these advantages can improve OTHR performance in target detection, parameter estimation, target tracking and so on.This paper focuses on the existing problems in OTHR system, and the MIMO techniques are applied in OTHR system to improve OTHR performance. The summary of our main research work is as follows:(1) After brief introduction of the basic theory in radar system, the MIMO OTHR model is given combining OTHR architecture and MIMO configuration, at the same time, the main features of which is described. Based on MIMO OTHR signal model, the signal processing of MIMO OTHR is presented in detail.(2) Orthogonal waveform set with satisfactory property of auto-correlation and low level of cross-correlation is crucial for MIMO architecture application. The design of orthogonal frequency division linear frequency modulation (OFD-LFM) signal is analyzed based on ambiguity function, then the design rule of OFD-LFM signal is presented.(3) Poor range resolution is a main problem in OTHR caused by the narrowband. After the brief introduction of the concept of range resolution, the output signal of MIMO OTHR is analyzed from the perspective of the Fourier transform, and then the spectrum relationship between the output signals of transmit beamform at the receiver and the input signals is given. Based of this spectrum relationship, the advantage of the OFD-LFM signal in range resolution enhancement is discussed, and computer simulation results are given.(4) In terms of interference suppression, firstly, the characteristics of the mainlobe interference are analyzed. Then, the limitations of the conventional approaches in mainlobe suppression are analyzed in detail. Finally, the principle of mainlobe interference using MIMO techniques is given, and the effectiveness of this approach is proved based on the simulation results.