Channel Equalization In Wideband Digital Array Radar Technology Research

Wideband Digital Array Radar (WDAR) is a fully digitized array antenna radar in which wideband signal waveform is transmitted and digital beam forming (DBF) technology is used in receiving and transmitting. Compared with conventional phased array radar, it can offer significant advantages. Such as low side lobes, high dynamic range (DR), rapid multi-beams steering, etc. But the change in the characteristic of analog devices and circuits in the element channels will cause the frequency-dependent amplitude and phase difference of receiver channels and transmitter channels in WDAR. The differences among the frequency responses of the channels are called channel mismatch. Channel mismatch will affect the superior performance of the WDAR seriously.In this thesis, the impact of the mismatch on WDAR's performance is analyzed. Adaptive channel equalization in order to compensate for the channel mismatch is investigated.First of all, the impact of channel mismatch on DBF and pulse compress is analyzed. The simulation based on FIR mismatch model is given. It shows that impact of mismatch on low-sidelobe beams is serious. Therefore, the real project requires precise control of the radar receiver's frequency response across the entire signal waveform bandwidth.Two channel equalization algorithms, named frequency-domain based and time-domain-based algorithms are investigated for compensating the channel mismatch. Channel equalization time-domain-based algorithm is based on Weiner filter theory and Least Squares theory. Basic algorithm of the time domain equalization is presented. And simulation based on IIR mismatch model is given. Frequency-domain based channel equalization algorithm is investigated mainly which is based on least squares fitting method. A modified method is presented which is weight least squares fitting method, and the diagonal elements are the reference channel magnitude response. Good equalization performances are achieved by using the improved method. Impacts of many factors on equalization performance are analyzed. Such as the mismatch extent of frequency response of the receive channel, SNR, the length of equalizer L, Bandwidth-Time delay product, FFT-points. All of these factors have references to real project.To satisfy the request of less computation and better performance in real projects, calibration is considered to replace equalization to some extent. The simulation is given. It showed that calibration may achieve high performance with some restriction of the mismatch extent of frequency response, SNR, Bandwidth-Time delay product, equalizer length L, FFT-points M, etc.Finally, the blue print of channel equalizer in WDAR is presented. The Flow of equalizer of both receiving and transmitting is described. For the coefficients of FIR filter in Matlab are complex number, but they can't be implemented in FPGA. So the structure of FIR filter is modified in which four real FIR filters substitute for one complex FIR filter. FIR filters consist of MAC mainly. It's wasteful and inefficient that FIR filters are simply constructed by multiplications and coefficient registers. So the Distributed Arithmetic which coverts the multiplications into some look-up operations is presented. In this thesis, an improved optimum representation of integer coefficient and a discrete coefficient method is introduced according to the FPGA structure. It can assure the decrease of hardware logic resource and the increase of compute performance.