Planar Structure-Shared Antenna Using Microstrip Patch and Substrate Integrated Waveguide Cavity-Backed Monopulse Slot Array

In this paper, a planar structure-shared antenna is designed with compact size and high channel isolation. And the substrate integrated waveguide (SIW) cavity-backed monopulse slot array (CBMSA) is used to replace the microstrip patch, which operate in X- and L-band, respectively. Characteristic mode analysis is applied to insightfully design new microstrip patch antenna with the feed structures of SIW CBMSA. This structure-shared configuration features high channel isolation with about 90 dB at the low frequency and 35 dB at the high frequency, which is because: 1) The radiation mode of SIW slot is much higher than the fundamental mode of new microstrip patch; 2) the coaxial lines of feed structures penetrate through the substrate of the microstrip patch, directly connected to the SIW CBMSA; 3) an isolator layer is added on the top. The SIW CBSMA is realized with boresight gain of sum beam pattern being 13.3 dBi and the null depth of difference beam pattern being 25.3 dB (Z-axis gain is -12 dBi).