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.

This paper is focused on resolving the problem of suppressing mainbeam deceptive jammers in the element-pulse coding (EPC) radar. At the modeling stage, the element-pulse phase coding matrix (EPPCM) is employed at the transmit side, introducing extra coding degrees-of-freedom (DOFs) for the discrimination of the true target and mainbeam jammers. By utilizing the extra coding DOFs, nonadaptive and adaptive suppression method for mainbeam jammers are developed. Firstly, in order to suppress the jammers non-adaptively, the EPPCM is designed based on the coding steering vector orthogonalization (CSVO) method, which requires the identical angle of the true and false targets. Then, the adaptive suppression method is proposed for the general cases, where the angle deviation between the true and false targets occurs. To this end, the unitary EPPCM is designed to achieve the coding DOFs at the transmit side. Moreover, we take the towed radar active decoy (TRAD) jammer as an example and the sample selection scheme for the estimation of jammer-plus-noise covariance matrix is proposed. At the analysis stage, experimental and numerical results in terms of output signal-to-jammer-plus-noise ratio (SJNR) demonstrate the effectiveness of the devised methods for suppressing mainbeam deceptive jammers.

It is reported that the traditional frequency diverse array (FDA)-multiple-input multiple-output (MIMO) radar has the capability of suppressing deceptive jamming delayed more than one pulse. However, mitigating the fast repeater deception jamming that distributed in the same range bin as the true target is intractable. To address this problem, the novel FDA-MIMO framework with a dual-frequency increment (DFI) scheme is presented, where the whole transmit array is split into two subarrays with different frequency shifts. The subarray with smaller frequency increment is motivated to resolve range ambiguity. In contrast, the subarray with larger frequency increment is designed for combating fast-repeated jammer by increasing the range resolution. Moreover, maximum likelihood estimator (MLE) is applied to obtain joint range-angle estimation of target, where the adaptive beamforming weight vector is optimized under minimizing variance distortionless response (MVDR) criterion. The transmit spatial smooth (TSS) method is incorporated to eliminate the component corresponding to the target, overcoming target cancellation issue. Extensive simulations are conducted to verify the superiority of the presented algorithm in mitigating fast repeater deception jamming.

In this paper, mainlobe deceptive jammer mitigation for multiple targets is investigated using a subaperture-frequency diverse array (FDA)-multiple-input multiple-output (MIMO) radar. At the modelling stage, the transmit array is divided into multiple overlapped subapertures consisting of fully-overlapped secondary subarrays, where a small frequency increment is introduced among different subapertures, while a phase coding modulation is adopted among different secondary subarrays. In this respect, all targets and jammers can be separated in a three-dimensional (3-D) space-time cube, including the transmit spatial domain, the slow-time pulse domain, and the receive spatial domain. In this case, the problem of jammer mitigation is formulated, and a two-stage beamforming method is proposed, where the jammers with delayed pulses are firstly suppressed, and the jammers, which are located within the same transmit pulse, are further mitigated. Specifically, an alternating procedure is developed by transforming the suppression problem into several one-dimensional sub-problems. In order to further improve the jammer mitigation performance, the subaperture transmit weights are also designed by maximizing the worst-case output signal-to-jammer-plus-noise ratio (SJNR) resorting to an iterative successive convex approximation (ISCA) algorithm. Numerical results corroborate the effectiveness of the developed methods in mitigating mainlobe deceptive jammers for the case of multiple true targets.

In this article, we explore the security transmission issues of Multiple Input Single Output (MISO) integrated sensing and communication (ISAC) system, focusing on the communication security transmission in radar-embedded communication systems. This system simultaneously detects and tracks target when transmitting communication information to downlink users. However, in the presence of hostile eavesdropping devices, the communication transmission security of ISAC system cannot be guaranteed. We have considered two common deployment scenarios: deployment of eavesdropper within the main lobe (DEML) and deployment of eavesdropper within the side lobes (DESL). In DEML scenario, the sensing target is considered as eavesdropper, we introduce cooperative jamming (CJ) device to disrupt the eavesdropper and ensure the transmission security. Through a combination of traversal search and a series of semidefinite relaxation methods, we optimize the covariance matrices of the transmission signal and CJ signal, ensuring both sensing and communication performance requirements while enhancing the overall system secrecy rate. In DESL scenario, we mainly focus on the situation where the eavesdropper is located on the transmission channel between the ISAC system and the user, the intelligent reflecting surfaces (IRS) is proposed to enhance the ISAC system communication security. We employ a combined approach of alternating optimization and fractional programming to jointly solve for the covariance matrix of the transmission signal and the reflection phase shift matrix, optimizing the system's secrecy rate. The numerical results validate the effectiveness of the proposed algorithms under both deployment scenarios and compare the advantages and disadvantages of the two methods. The results demonstrate that the designs of both CJ and IRS under the two deployment scenarios significantly enhance the system's secure communication rate, and the IRS scheme can provide higher performance gains, which is attributed to the IRS's rational utilization of energy losses in other directions.