The Amplitude And Phase Calibration In Multi-channel High-frequency Receiver Of Ground Wave Radar

High-frequency(HF) Ground wave Radar is a kind of remote sensing equipment developed in the past thirty years in the world. It can monitor ocean surface successively and widely. It can also measure various kinds of dynamical oceanographic parameters, such as the wind, wave and flow. At the same time, it has many advantages, such as broad detection coverage, low cost, real-time and24-hour all-weather coverage etc. Additionally HF radar also has a lot of advantages in detecting and tracking low-speed moving targets.The development of science and technology requires radars to provide more advanced performance. This puts forward higher requirements for the important component of radars-the receives. They have the following characteristics:multi-channel reception, broadband high-resolution, high integration, high reliability and a very strong anti-interference ability. The multi-channel receiver’s amplitude and phase calibration are important aspects of the performance of the multi-channel receivers of high-frequency ground wave radar. These include the various amplitude and phase errors caused by components within a single channel, and various amplitude and phase errors among channels. Based on this, this thesis studies the amplitude and phase calibrations of multi-channel receivers of high-frequency ground wave radars. The main contents are as follows.Firstly, I describe the history, current research and applications of the development of HF ground wave radar and introduce the basic principles of HF ground wave radar receivers. Then I introduce the structural design of HF ground wave radar receivers under the linear frequency modulated interrupted continuous wave system. The principle of multi-channel receivers is also introduced. After that I analyze the structures of high frequency ground wave radar superheterodyne receivers and software multi-channel high-frequency ground wave radar receivers. This forms the basis for the later analysis of the amplitude and phase errors.Secondly, I do a detailed analysis of the amplitude and phase errors generated by the signal quadrature demodulation. And I study the impact of the amplitude and phase errors on the transfer function of the receiver system. On the basis of the above work, the impact of quadrature demodulation errors on the linear frequency modulated interrupted continuous wave (FMICW) radar receiver is analyzed in detail. For software HF radar multi-channel receivers, the same analysis is done for the quadrature demodulation errors of bandpass sampling and their impacts on the beamforming. Also the array-errors of multi-channels and the impact of array-errors of multi-channels on the performance of MUSIC algorithm are analyzed.Based on the above error analysis, a number of compensation programs are proposed accordingly. These include the compensation method in time domain and frequency domain for the single-frequency signal demodulation errors. Simulation results confirm the feasibility of the two compensation methods. Also, a number of ways to correct the quadrature demodulator errors of broadband signal are proposed, which include the least squares calibration method and the improved Gram-Schmidt orthogonalization correction method. The subsampling-based digital quadrature demodulation errors are also analyzed. A correction method is proposed and verified by simulations.Because of the wide applications of adaptive algorithm in channel corrections, the basic principles of the least mean square (LMS) algorithm, and the performance indicators of the LMS algorithm are introduced systematically. Based on the LMS algorithm, a least mean square algorithm with variable step size is studied and a modified least mean square algorithm with variable step size is proposed. After these improvements, a balance is achieved between the steady-state error and the speed of convergence. And the overall performance of the algorithm is improved. The simulation results show that the modified algorithm works effectively in calibrating the amplitude and phase of narrow-band signals for multi-channel receivers. And the improvement to the original algorithm is significant.According to the multi-channel receiver architecture of HF ground wave radars, the entire radar receiver system is divided into two parts: broadband and narrowband systems. It is called a broadband system before the oblique mixer and a narrowband system after the oblique mixer. According to this division, respectively, the compensation method for broadband and narrowband systematic errors is studied. A set of feasible solutions of hardware platform is proposed. Based on the VXI bus a set of correction modules is designed, which includes digital modules and analog modules. Through this set of correction modules one can calibrate the amplitude frequency characteristics and phase frequency characteristics of receive channels. Then the amplitude frequency characteristics and phase frequency characteristics of the multi-channel receivers are consistent among different channels, and are close to the ideal transmission characteristics of transmission networks. Furthermore these correction modules can work automatically with radar online every0.5to1hour without human interventions and multi-channel calibrations can be finished in one time.