A Low-Profile Beamforming Patch Array With a Cosecant Fourth Power Pattern for Millimeter-Wave Synthetic Aperture Radar Applications

Abstract

In this article, a novel beamforming patch array with a cosecant fourth power pattern is proposed for millimeter-wave synthetic aperture radar (SAR) applications. It enables radar receiving identical power in the field of view, provided that the radar cross section levels of targets within the illuminated area are similar. Different from “one-way” communication application, the SAR is a “two-way” system such that the received power is inversely proportional to $R^{4}$ , not $R^{2}$ , where $R$ is the distance between target and radar. Thus, conventional cosecant squared patterns are not suitable for SAR. Here, the concept and link properties of the proposed cosecant fourth power pattern are introduced, while its synthesis process is facilitated by a mixed optimization method, including nonlinear fitting and active pattern methods. As demonstrated, an array prototype, which consists of 12 series-fed patch subarrays and a substrate integrated waveguide network for power distributing and phase shifting, is designed and fabricated. Particularly, the power-distributing section only consists of symmetrical T-junctions with equal power division, thus making the antenna more tolerant to fabrication error. Good cosecant fourth pattern performance is achieved from 23.8 to 25.0 GHz. The presented array also owns the advantage of low profile ( $\sim 0.09\lambda _{0}$ ), compact, reliable, and low cost.