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Abstract-In order to eliminate the negative influence of the rotational phase component (RPC) of target prominent scattering centres on the performance of Doppler centroid tracking (DCT) method, a coherent phase compensation method is proposed. The coherence of echo pulses sampled directly in intermediate frequency (IF) is firstly analyzed and proved.Based on the coherence property, the proposed approach improves the translational phase component (TPC) estimation accuracy of DCT. Compared to the modified Doppler centroid tracking (MDCT) algorithm, the proposed method achieves better phase compensation performance with simpler operations. Both the theoretical analysis and experimental results based on the real ISAR data prove the effectiveness and efficiency of the presented strategy.

This paper investigates a subarray based algorithm for direction of arrival (DOA) estimation of wideband uniform linear array (ULA), under the presence of frequency-dependent mutual coupling effects. Based on the Toeplitz structure of mutual coupling matrices, the whole array is divided into the middle subarray and the auxiliary subarray. Then two-sided correlation transformation is applied to the correlation matrix of the middle subarray instead of the whole array. In this way, the mutual coupling effects can be eliminated. Finally, the multiple signal classification (MUSIC) method is utilized to derive the DOAs. For the condition when the blind angles exist, we refine DOA estimation by using a simple approach based on the frequency-dependent mutual coupling matrixes (MCMs). The proposed method can achieve high estimation accuracy without any calibration sources. It has a low computational complexity because iterative processing is not required. Simulation results validate the effectiveness and feasibility of the proposed algorithm.

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Wideband digital array radar (WDAR) has the potential of achieving high resolution and providing multi-function simultaneously, but it is limited in practical use due to the effects of frequency-dependent array model errors. A method to jointly calibrate gain-phase perturbations and mutual coupling effects in WDRA is presented. First, a sparse-based method is deployed to calculate the narrowband calibration matrices at a set of discrete frequencies. Moreover, using a group of finite-impulse response filters, a wideband calibration matrix is constructed, which is capable of compensating the imperfections of array at any frequency in the band. The proposed method is simple and feasible for actual applications, which can be applied to arbitrary array geometries. Simulations and experimental results with measured data demonstrate the validity and effectiveness of the proposed method.Introduction: Most signal processing methods for wideband digital array radar (WDAR) assume that the array manifold is ideal. However, gain-phase mismatches and mutual coupling effects are unavoidable in actual systems, leading to substantial performance degradation [1,2]. Several methods have been developed to address this problem [3,4]. In [3], the full-wave method and receiving mutual impedance method are employed to compensate for mutual coupling effects at different frequencies, but these methods are only suitable for narrowband signals. Furthermore, an improved wideband direction of arrival (DOA) estimation method has been proposed in [4]. The wideband signals are decomposed into multiple narrowband components, which are modified by the mutual coupling matrices (MCM) at the corresponding sub-bands. However, the method results in poor accuracy, because it can only cope with mutual coupling errors at some discrete frequencies.It is well known that the gain-phase and mutual coupling errors are frequency dependent. However, calculating these errors at different frequencies using computational electromagnetic solvers is time-consuming and essentially impractical once arrays are in operation. As a result, how to compensate the errors in wideband arrays is still an open issue. In this Letter, we propose an finite-impulse response (FIR)-filter-based method, which has the capability of calibrating the array model errors at all frequencies. Finally, the feasibility is verified with measured data obtained by an S-band WDAR test bed.

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