LAUSR

This paper proposes the design of a gain enhanced single circular patch radiator (SCPR) with a cavity-backed structure using multiple substrate integrated waveguide (SIW) feeders for monopulse systems. We derive the equations of a radiation pattern for the multi-feed SCPR and compare it with the full EM simulation results. Based on the theoretical results, the proposed SCPR with multiple feeds is designed by adding the cavity-backed structure to obtain high gain characteristics. In the feeding network, four SIW structures are designed and circularly arranged, which can reduce loss and mutual coupling. Each pair of the SIW feeders can provide sum ( $\Sigma$ ) and difference ( $\Delta$ ) patterns to achieve the monopulse direction finding (DF) properties in both elevation and azimuth directions. To verify the feasibility, the proposed antenna is fabricated, and the antenna characteristics are measured. The measured reflection coefficient is −14.5 dB at 5.8 GHz, and the maximum gains are 4.9 dBi and 4.8 dBi in zy-plane. To observe the monopulse DF, the estimated direction of arrival (DOA) results are examined in both elevation and azimuth directions. In the whole estimated angle range, the estimation error is lower than 0.49, and the average error is 0.26.