In this paper, we investigate the problem of target localization with a multiple-input multiple-output (MIMO) and frequency diverse array MIMO (FDA-MIMO) dual-mode radar system. The signal model for this newly introduced radar system is presented in detail. On this basis, a computationally efficient method for joint angle and range estimation is proposed by taking advantage of the subspace principle. First, the direction-of-arrival (DOA) of each target is determined by utilizing the fused signal data received via this dual-mode radar. In order to solve the coupling of target range and direction-of-departure (DOD) in FDA MIMO radar mode, we use the monostatic-like characteristics of the dual-mode radar to develop an effective decoupling method. More specifically, by employing the same eigenmatrix corresponding to MIMO and FDA-MIMO radar data, the coupling of DOD and range in the FDA-MIMO mode can be easily overcome, and the parameters can be successively estimated with automatic paring. Further, to make full use of the transmit array for DOD estimation, we propose to compensate the range information in the transmit array steering vector to achieve an improved estimate of target DOD. Extensive simulation results are performed to show that the proposed approach can provide superior DOD and range estimation accuracy while maintaining DOA estimation performance under the presented dual-mode radar system, and does not require the design of additional parameter pairing strategies with low computational cost, exhibiting excellent target localization behavior.

The main-beam range deceptive jamming forms active jamming by storing, modulating, and retransmitting radar signals into the radar receiver, which greatly reduces the efficiency of radar detection. In this work, we propose a method based on simulated annealing algorithm frequency diverse array multiple-input multiple-output (SA-FDA MIMO) radar to suppress main-beam range deceptive jamming. This method firstly uses simulated annealing algorithm to calculate nonlinear FDA frequency increments. Its beampattern has the characteristic of single peak decoupled, which is different from the traditional range-angle coupled FDA beampattern. Secondly, by receiving signal compensation, the non-linear frequency increments make false target echoes present discrete distribution in the power spectrum. Finally, the echoes adaptively filtered, main-beam range deceptive jamming suppression is achieved while the desired target signals are retained. The simulation results demonstrate that the proposed approach can effectively suppress main-beam range deceptive jamming. In comparison with MIMO and traditional linear frequency increment FDA radar, the performance of the proposed method has the superiority.

The problem of mainlobe deceptive jammer suppression with a novel stepped frequency (SF)-receive delay array (RDA) radar is addressed in this paper. In our system design, the linear frequency modulation (LFM) waveform with a SF across the antenna elements is transmitted in a uniform linear array, and the received echo is delayed with a time shift between adjacent antenna elements, introducing extra range-dependent degrees-of-freedom (DOFs) in both transmit and receive domains. Consider a typical form of mainlobe jammers, where multiple false targets are generated in the same transmit pulse or same range bin behind the true target after short time modulation. In this respect, the jammers are discriminated from the true target in the joint transmit-receive spatial frequency domain, and suppressed via a data-dependent beamformer based on the minimum variance distortionless response (MVDR) criterion. To further solve the problem of sample selection due to the pseudo-random distribution of the false targets, two kinds of robust beamformers based on the enhanced Capon power spectrum (ECPS) and the eigen-projection elimination (EPE), are developed to reconstruct the jammer-plus-noise covariance matrix and estimate the steering vector of the true target. The performance of the proposed methods in suppression of mainlobe deceptive jammers is evaluated via numerical simulations and compared with the existing systems and robust beamforming methods.

High speed, high maneuverability, and weak space-moving targets (SMTs) are major threats for space-borne radar (SBR) systems. First, the severe range migration (RM) and Doppler extension are induced by complex relative motion between the radar platform and non-cooperative moving targets, making moving target detection (MTD), and parameter estimation particularly difficult. Apart from this challenge, Doppler ambiguity and Doppler aliasing arise from the limited pulse repetition frequency (PRF) of a SBR system to ensure an adequate coverage rate, which may make the existing MTD algorithms deteriorate dramatically. To address these issues, we focus on the detection of high speed and high maneuverability targets based on the modified keystone transform matched filtering (MKTMF), whose Doppler frequency exceeds PRF as well as spans multiple PRFs. The proposed method is suitable for the weak MTD under a low signal-to-noise ratio (SNR) case since the nonlinear operation is not involved. Finally, some numerical results and real data results are provided to validate the superiority of the proposed method.

We recently proposed a direction-of-arrival (DOA) estimation method for the coexistence of uncorrelated and coherent signals, which is related to the uniform linear antenna arrays with mutual coupling (MC) in the presence of unknown nonuniform noise. This technique, however, relies on the assumption of mixed signals and is not suitable for scenarios with purely coherent signals. This paper extends the mixed signal scenario to the purely coherent signals one on one hand, and on the other hand, allows us to directly adopt the ESPPRIT algorithm to perform DOA estimation in MC environments. To be specific, with the help of the least squares (LS) criterion, the nonuniform noise is first eliminated, and the traditional middle subarray scheme can then be employed to be immune to the influence of MC. Unlike the former operation, following a different line of attack the latter can make full use of the whole array and provide a larger array antenna aperture. Furthermore, we derive a new strategy to directly determine the DOAs without taking MC into account and performing spectral search. This brings substantial benefits to the DOA estimation accuracy and computational cost. The superiority of the proposed approaches is verified by numerical examples.

Generally ground clutter has serious range dependence and range ambiguity in the forward-looking array airborne radar system under a high pulse repetition frequency (PRF) system. In this work, a range ambiguous clutter suppression method based on transmitting beam main lobe correction for the FDA MIMO radar is proposed. Firstly, this method uses the designed transmission pulse weights to compensate for the initial phases formed by the accumulation of frequency increments between pulses, so as to solve the problem that the main lobe high gain illuminated angle is inconsistent between the MIMO equivalent transmitting beampattern pulses synthesized at the receiving in the traditional FDA MIMO system. Secondly, by restoring and compensating received echoes, the influence of the main lobe correction weights of the transmitting signal is eliminated. Finally, through the characteristics of transmitter correction compensation to distinguish different range ambiguous clutters, the echoes from the range ambiguous areas can be discretely distributed in the power spectrum while preserving the signal echoes in the observation area. Thus range ambiguous clutter suppression is realized. The simulation results show that the proposed method can improve the clutter suppression performance compared with the MIMO and linear frequency increment FDA radar.