Research On Some Key Technologies In Synthetic Wideband Signals Processing And Wideband Array Radar

The high-range resolution profile (HRRP) represents a target's radial backscattering intensity, which can reflect potentially discriminative information about the target's geometry and structure. As compared to a two-dimensional or three-dimensional radar image, the HRRP is easier to generate due to the lower computational cost. As a result, the high-range resolution radar has become a leading candidate to provide all weather target recognition and battle sense.In order to acquire high-range resolution profile, radar must have the ability to process the wideband signals. There are only immature theories available of the wideband radar in the generation of wideband radar signal, target motion compensation, adaptive processing and so on. Based on the previous work, this dissertation is focused on the synthetic range profile (SRP), the temporal and space adaptive processing of the wideband radar system using synthetic wideband waveforms. Some new methods are presented, and all of which are evaluated on simulated data.In general, this dissertation is composed of the following parts:1. The research on the synthetic wideband waveform processingBased on the analysis of the characteristics of multiple synthetic wideband waveforms, a general structure model of obtaining synthetic range profile (SRP), together with a new error criterion of the SRP and a new analytical method, is established on the analysis of the characteristics of multiple synthetic wideband waveforms. At the same time, for the different synthetic wideband waveforms, their improved realization structures are proposed.2. The research on the temporal processing of the synthetic wideband waveformA general structure model of the synthetic wideband waveform's temporal processing is established. A wideband imaging architecture based on synthetic wideband waveform and conventional Doppler filter bank structure using FFT is developed and followed by a detailed analysis of its performance. Both the theoretical analysis and simulation results show that owing to Doppler dispersion effect, the target's SRP, with an increase in velocity, produces distortion, including range shift and shape deformation. At the same time, two related theoretical formulas are deduced for the calculation of the range shift value and evaluation of the amplitude deformation extent of a moving target's SRP formed by the proposed imaging architecture, and thereby the maximum critical velocity is derived. When target velocity is less than the maximum critical velocity, a moving target's SRP with acceptable amplitude distortion can be obtained.A new synthetic wideband filter bank based on the velocity bin structure is proposed, and the critical conditions of obtaining a SRP with acceptable distortion are achieved. Furthermore, the theoretical analysis results show that in order to obtain the SRP with acceptable distortion, target radial velocity must be less than the minimum subband maximum unambiguous radial velocity. Meantime, based on this proposed synthetic wideband filter bank architecture, a new method for resolving velocity ambiguity is proposed.A new synthetic wideband filter bank based on the variable PRF among subbands is proposed. By setting parameters reasonably, this new synthetic wideband filter bank architecture not only can provide a moving target's SRP with acceptable distortion at any target velocity, but also can be implemented through a fast Fourier transform (FFT) for computational efficiency.3. The research on the space adaptive processing of the synthetic wideband signalsA general structure model of the synthetic wideband signal's space adaptive processing is established. A wideband imaging architecture based on synthetic wideband signal and conventional adaptive processing using estimated interference-plus-noise covariance matrix is developed with a detailed analysis of its performance. The theoretical analysis and simulation results show that owing to the independent estimation of the covariance matrix in each subband, the target's SRP produces random range sidelobes across entire range domain, which are mainly caused owing to the noise's variance estimation varying at random from subband to subband. Two methods are proposed to relieve and eliminate the random range sidelobes. One is diagonal loading method and the other is orthogonal subspace projection method.A segment adaptive processing is proposed in order to simplify the subband adaptive processing architecture and at the same time, its performances are analyized in theory. A variable space sampling rate adaptive processing method is proposed to lower the computation complexity and its implemented method is deduced in theory.4. An efficient relative delay measurement method for digital wideband array radar with LFM waveformA relative delay measurement method for digital wideband array radar using linear frequency modulation (LFM) waveform is put forward along with a deep investigation of its basic aspects. Based on Dechirping processing technique and applying digital decimation method, the proposed measurement system can work at low processing rates, thus effectively reducing the computation and lowering hardware complexity. Moreover, by means of reasonable parameter setting and unique design construction, relative delay values among multiple digital transmit/receive (T/R) modules can be measured at one single measurement process. Their measurement accuracy is deduced in a theoretical way, while some significant factors are evaluated thereafter. It is shown that measurement error, resulting from the module thermal noise and the interaction of multiple co-existing LFM pulses respectively, consists of noise error and systematic error. Based on these analysis results, parameters of the measurement system can be optimized and its performances are predicted.