Compact high-isolation self-diplexing antenna based on SIW for C-band applications

This paper presents a novel compact high-isolation cavity-backed inverted U-shaped slot antenna using substrate-integrated waveguide (SIW) for C-band applications. The SIW cavity is loaded by an inverted U-shaped slot that produces two fictitious aperture for radiation at two distinct frequency bands and to exhibit self-diplexing antenna (SDA) characteristics. Two orthogonal microstrip feed lines are applied for excitation of fundamental mode ( $TE_{110} $TE110) and two degenerated modes ( $TE_{120} $TE120 and $TE_{210} $TE210). The perturbation of these modes due to slot loading allows to achieve size miniaturization. Compared with conventional SIW cavity without slot, the proposed SDA allows a size reduction of 56%. High isolation is achieved due to the transmission zeros produced by these modes and orthogonal feed lines. This isolation is further improved (>40.5 and >32.8 dB) due to off-centered input ports that creates very weak cross-coupling path between them. The resonating frequencies of the proposed SDA can be designed individually. Finally, an SDA working at 4.29 and 7.52 GHz is fabricated for validation of simulated performances. The measured gains of the fabricated SDA are 5.38 and 5.82 dBi at the resonating frequencies of 4.29 and 7.52 GHz, respectively. A good consistency is found between measured and simulated results.