Low-Profile Dual-Polarized Monopulse Antenna Excited by a Single-Layer Substrate Integrated Waveguide-Enabled Comparator

A low-profile and compact 2-D dual-polarized monopulse antenna excited by a single-layer substrate integrated waveguide (SIW) enabled comparator is reported. As the beamforming feed network, the SIW-based comparator consists of four hybrid rings that provide excitations with proper amplitudes and phases to four cavity-backed slot antennas (CBSA). Thanks to the compactly cascaded design of the four hybrid rings, the monopulse array can provide two sum beams and two 2-D difference beams with different polarizations when each input port is individually excited. To prove the concept, a prototype is designed, fabricated and measured at the K band. The measured results exhibit the developed antenna is operating at 22.4 GHz for all four ports. The realized gain values of the dual-polarized sum beams are 11.19 dBi for vertical polarization and 11.52 dBi for horizontal polarization, respectively, and the values of the difference beam in the xoz-plane and yoz-plane are 9.81 and 9.65 dBi, respectively. The null depth of the difference beam is -24.65 dB. Noticeably, the profile of the final prototype is only 0.13 lambda(0),which makes it an ideal candidate for wireless applications that require low-profile 2-D monopulse antennas.