Study On Some Key Issues Of Microwave Array Synthetic Impulse And Aperture Radar

Synthetic Impulse and Aperture Radar(SIAR) technique have been successful applied in meterwave band and ground wave band. It has great advantages of encountering the threats such as stealth target, anti-radiation missile, composite electronic jamming and low-flying target penetration. To improve the radar’s range and angle resolution, a microwave synthetic impulse and aperture radar which uses a large gathering array to transmit FMCWs of multiple carrier-frequencies to ensure the energy emitted covers a rather large sector, and an array or omni-antenna to receive the echoes is researched. The system has the advantages of miniaturization, high resolution and high flexibility. It is also called Multi-Carrier-Frequency(MCF) Multiple-Input Multiple-Output(MIMO) radar. Focusing on the relevant theories of MIMO radar and the key techniques to implement microwave SIAR, this dissertation deals mainly with the following contents:1. A brief introduction is given to the radar system and its characteristics. What follows is the processing flow of multi-carrier-frequency FMCW and the waveform parameters selection, with an emphasis on the transmitting and receiving pattern synthesis process when the transmitting and receiving station are uniform plane arrays. Finally, the time and frequency synchronization of system are introduced.2. The gain and phase error model of SIAR is presented. Under the situation of separated tranmitting and receiver, the direct wave could be seen as a target echo because Signal to Noise Ratio(SNR) of it is very high. When the angle information of the direct wave is precisely known, two estimation methods, Subspace Fitting(SF) Method and Maximum Likelihood(ML) Method, are proposed to estimate the gain and phase error. Due to tha fact that the size of microwave SIAR array antenna is small, the array antenna can be rotated and the rotation angle can be precisely known in the actual projects. Then a new method based on array rotation is proposed, which can estimate the DOA of the direct wave and gain and phase errors simultaneously. The Cramer-Rao Bound(CRB) of gain and phase error estimation are derived. When the array antenna position error is existed, a revised array antenna rotation algorithm and Covariance Matrix Fitting(CMF) are proposed to estimate the error. Finally the simulation results are given to prove the effectivity of these methods.3.Based on the analysis of the direct wave interference, the interference suppression are proposed. The direct wave interference can be seen as an interference with specific Doppler and range-angle. So the interference suppression in the time, range-angle and Doppler domain respectively is proposed. These three methods for direct wave suppression are evaluated from the aspects of computation complexity and processing gain. Finally the simulation and real data results are given to prove the effectivity of these methods.4. Studys on different angle estimation methods for SIAR radar with different geometries. Because the computation complexity of angle estimation methods for SIAR radar is usually expensive, these methods focuse on reduction of computation complexity. For monostatic SIAR radar, a Reduced-Dimensional Re-Iterative SuperResolution(RD-RISR) algorithm is proposed. When the targets have correlation, such as in in multipath environments, the performance of SCM-based methods are degraded. The RD-RISR, which do not require an SCM or eigendecomposition, can estimate coherent targets. It can estimate the number, amplitude and angle information of targets with reducing the computation complexity simultaneously. For the bistatic SIAR radar, A beamspace Unitary ESPRIT algorithm that for estimating the joint direction of arrival(DOA) and the direction of departure(DOD) is proposed. In a radar application, the operation of reduced dimension is facilitated in beamspace when one has priori information on the general angular locations of the signal arrivals. On this condition, one can utilize the beamspace transform matrix to form beams involving the sector of interest, thereby yielding reduced computational complexity. And if there is no priori information, one may apply angle estimation algorithm via parallel processing each of number of sets of successive overlapped sectors, which will also reduce computational complexity. The conjugate centrosymmetrized DFT matrix is applied to transform the receive data into beamspace. Then the invariance property of the transmit beam and the receive beam is respectively exploited to calculate the DODs and the DOAs of targets which requires no pair matching and has better angle estimation performance. For the SIAR radar with distributed non-identical subarrays antennas, which with the baselines greater than a half-wavelength results in the grating lobes in the combined array beampattern and ambiguity in DOA estimation, a new method based on root rank reduction estimator(root-RARE)is proposed. A estimation of signal parameters via combined of the root-RARE and MUSIC is used to resolve the ambiguities. The Cramer-Rao bound(CRB) of direction is calculated. The relation of the baseline ambiguity threshold and the signal to noise ratio threshold is analyzed. Simulation results demonstrate the validity and effectiveness of the proposed algorithm.