In this letter, a W-band multipolarized monopulse Cassegrain antenna is proposed, in which a phased dual-polarized microstrip patch quad is employed to feed the hyperbolic subreflector. Due to the more even polarization distribution on the aperture of the quad, the high aperture efficiency of the Cassegrain antenna is achieved. Simulation results verify that the microstrip patch quad is qualified to work as the multipolarized monopulse feed source by adjusting phases and amplitudes among the four feed ports. The metallic structure of this W-band multipolarized monopulse Cassegrain antenna is fabricated by using high-precision milling machine to assure the design parameters. At 94 GHz, the integral gain is 39.6 dBi and the aperture efficiency is 51.9%. Measurement results demonstrate the proposed antenna has excellent polarization synthesis and polarized monopulse performances further.

A W-Band High-Aperture-Efficiency Multipolarized Monopulse Cassegrain Antenna Fed by Phased Microstrip Patch Quad

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.

Angle Estimation of Extended Targets in Main-Lobe Interference With Polarization Filtering

In this letter, the regular amplitude angle monopulse estimation method is proven not suitable for polarimetric radars because it sets up correlation between azimuth angle and elevation angle of the target and can result in low accuracy. To solve this problem, the polarimetric amplitude angle monopulse estimation method is proposed to obtain the correct angle. By changing the channel synthesis method when the radar receives the signals, the proposed method shows a higher accuracy than the regular method through formulation and the experiment results.

Amplitude Angle Monopulse Estimation for the Four-Channel Hybrid Polarimetric Radar System

In this paper, we present a polarization sensitive frequency diverse array (PSFDA), which benefits both from frequency diverse array (FDA) and polarization sensitive array (PSA), producing angle-range-polarization-dependent beamforming capability. To simultaneously improve the angle, range and polarization resolution, the l1-norm minimization-based sparse constraint and l∞-norm constraint for sidelobe region are further applied. Besides, the performance of the optimal output signal-to-interference-plus-noise ratio (SINR) is analyzed for such a high-dimensional arrays. Numerical results demonstrate that the proposed PSFDA provides both range and polarization resolution as well as target angle estimation. Moreover, the PSFDA virtually increases the array size by exploiting multiple electromagnetic fields at each physical point. In addition, the proposed beamforming method can effectively null interferences, without degrading the array gain for the signals of interest.

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Angle-range-polarization-dependent beamforming for polarization sensitive frequency diverse array

Filters with antenna arrays are widely used for interference suppression in the temporal domain, frequency domain, space domain and so on. Meanwhile, the interference mitigation performance of a single-domain-based filter depends on a noticeable difference between the target signal and interference in the corresponding domain. However, the interference cannot be efficiently suppressed by a single-domain-based filter when the difference in this individual domain is small. To solve this problem, a multi-domain collaborative oblique projection filter is proposed in this study. First, multi-domain spaces are theoretically derived to distinguish the target signal and the interference, and then a multi-domain oblique projection operator is provided to recover the original target and suppress the interference. Depending on the multi-domain spaces, the filter has excellent performance when the difference is insignificant in each individual domain, whereas the performances of the single-domain-based filter and cascade filter degrade significantly. Finally, a space–polarisation–frequency domain collaborative filter based on oblique projection is given as an illustration. Performance analysis and simulation results are provided to illustrate the superiority of the proposed filter for interference mitigation.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-spr.2016.0140

Multi‐domain collaborative filter for interference suppressing

Polarisation filtering is a valid approach for interference suppression in high-frequency surface wave radar (HFSWR) and other systems. Based on the fundamental principle of the oblique projection and polarised filtering, an oblique projection polarisation filter (OPPF), which can be constructed from the polarisation subspaces of the target signal and those of the interference or directly from experimental data, is proposed in this study. Generalised methods for constructing the OPPF operators (theoretical OPPF and improved OPPF) are provided and the impact on the performance caused by the estimation errors is also discussed. Numerical results from simulation and experimental data demonstrate that the proposed filter is an effective means of interference cancellation. It is proved that OPPF is an extension of the conventional polarised filter, whereas the improved OPPF is more suitable for the situation where the interference is unknown.

R. Guo

Papers

Oblique projection polarisation filtering for interference suppression in high-frequency surface wave radar