Improved HMSIW Cavity for Differential Antenna With High Common-Mode Rejection

In this letter, a differential antenna with high common-mode (CM) rejection is proposed, which consists of dual improved half-mode substrate-integrated waveguide (HMSIW) cavities and a square substrate-integrated waveguide (SIW) coupling-feeding cavity (CFC). First, a novel approach to enhance the differential-mode (DM) radiation performance by flipping the symmetrical TE201 cavity is presented. The two E-field components excited from reversed magnetic walls are superposed in phase. Then, a pair of improved HMSIW cavities with oppositely magnetic walls is adopted to suppress the CM and enhance the uniformity of the radiation pattern on E- and H-planes. The square TE202 CFC with four coupling holes is discussed for the DM excitation. Meanwhile, it is equivalent to a band-stop filter further to improve CM rejection under CM excitation. The four perturbation holes in the CFC for the adjacent E-field isolation are analyzed. Finally, the proposed antenna is fabricated. The measured and simulated results show good agreement. The high CM rejection (27.3 dB) is achieved through the two-step rejection of the radiator and CFC.