In the presence of the interference from a main-lobe direction, the monopulse measurements always get erroneous angle estimates. By polarization filtering, the interference can be suppressed. However, an error from the cross-polarization of the target and the unpolarized component of the interference is introduced in the monopulse processing. To effectively extract the angle of the extended target accurately after polarization filtering, duplex polarization filtering and polarization filtering extractor based on a covariance matrix are developed. In addition, it can be found that the variance of the angle estimates varies when the polarizations of the target and the interference fluctuate, which degrades the performance of the tracking filter. For this problem, an adaptive fixed-gain filter for stabilizing the variance of the target angle estimates is proposed.

In this letter, the problem of monopulse angle estimation error under mainlobe interference for dual- polarization array is investigated. The adaptive monopulse angle estimation considering cross polarization with array beam scanning is analyzed. To reduce the angle estimation error, an adaptive polarization-constrained monopulse approach based on combined constrained cross polarization and main polarization is proposed. The cross polarization of antenna and target signal is not regarded as a source of estimation error which needs to be suppressed in previous literature. Instead, it contributes to the angle estimation here. The proposed method could obtain accurate monopulse angle estimation while suppressing mainlobe interference. Simulation results verify the performance of the proposed method.

When a monopulse radar is subjected to main-lobe barrage interference, the target and the interference source are both located within the 3 dB beamwidth of the radar; the target returns are subsumed by the interference, which results in incorrect detection, erroneous angle measurements, and tracking error. Based on a hybrid polarimetric monopulse radar with six channels, a new approach is presented for estimating the target angle from a single snapshot in the presence of main-lobe barrage interference. By means of polarization filtering and polarization synthesis of signals from multiple channels with two orthogonal polarizations, a new pair of sum and difference signals is formed that represents the angle difference between the target and the interference source. After standard monopulse processing of these new signals and additional compensation, the estimate of the target angle is derived with low computational complexity.

A retrodirective cross-eye jamming mitigation method is proposed in this letter. Because the cross-eye jamming signals are transmitted by the active jammer antennas, and the target returns are reflected by a moving target with complex scattering structures, the polarization fluctuation of the target returns is more significant than that of the jamming signals. By weighting the sum channel and the difference channel of a polarized monopulse radar to cancel the target returns spatially, the energy ratio between the target returns and the jamming signals in the weighted outputs decreases, which means that the polarization fluctuation of the outputs decreases as well. When the weighting vector is searched, the polarization fluctuation of the weighted outputs reaches the minimum. Then the current weighting vector can be linearly transformed into a target angle estimate. The proposed method has low computation complexity and good antijamming performance, especially under a high jamming-to-signal ratio.

The phase-only beamforming (POB) technique manipulates the weighted phases of array antenna elements to create a desired radiation pattern, thereby reducing the hardware and power costs associated with large phased arrays. However, two significant challenges currently hinder the practical implementation of POB. First, the beam gain generated by POB can be severely distorted when a main lobe interference is present. Second, the POB method struggles to suppress interferences whose positions change within the spatial domain. To address these challenges, this letter proposes a novel POB method for dual-polarization array radar. This method incorporates polarization constraints on a Riemannian manifold under the condition of null broadening. By doing so, it generates robust nulls that can effectively suppress moving interferences in the main lobe and side lobes while preserving the beam gain. Numerical simulations demonstrate that this method exhibits excellent anti-interference performance.

Polarimetric phased array radar (PPAR) has the capability to suppress mainlobe and sidelobe interferences by fully utilizing multiple polarization channels. However, adaptive beamforming technique for PPAR, which generates nulls in the space-polarization domain, causes the received signals from multiple polarization channels to be weighted into one. This results in an inherent loss of target polarization, preventing the measurement of target polarization scattering matrix (PSM). In this paper, a robust adaptive beamforming (RAB) approach for PPAR is proposed to estimate the PSM while suppressing the mainlobe and sidelobe interferences. In our solution, dual-beams characterized by a pair of optimal orthogonal polarizations are adaptively formed to reconstruct the polarization channels. Furthermore, multiple uncertainty sets are devised, including a spatial uncertainty set and a pair of polarization-associated uncertainty sets, which respectively improve performance in beam polarization stability and mainlobe interference suppression. This problem is then formulated as a non-convex quadratically constrained quadratic programming (QCQP), which is transformed into a difference of convex (DC) programming problem. Subsequently, it is efficiently solved via a sequential convex programming (SCP) algorithm, incorporating an initial point selection strategy. We further conduct a thorough performance analysis focusing on three critical aspects. As a result, the dual-beams can suppress mainlobe and sidelobe interferences in the space-polarization domain while estimating the target PSM accurately. Simulation results demonstrate the validity of the proposed method.