Highly Miniaturized Self-Diplexed U-Shaped Slot Antenna Based on Shielded QMSIW

This article presents an efficient yet simple design approach to highly miniaturized cavity-backed self-diplexing antenna (SDA) with high-isolation. The structure employs a shielded quarter-mode substrate integrated waveguide (QMSIW). Two U-shaped slots are engraved on the top conducting plane, which realize two frequency bands and significant size reduction. The slots are excited by two independent
$50\Omega $
orthogonal feed-lines to achieve high isolation while enabling radiation at 3.5 GHz and 5.4 GHz. The proposed design approach allows us to design the two frequency bands independently from each other. The SDA structure is verified using an equivalent circuit model, full-wave electromagnetic (EM) analysis, and experimental validation of the antenna prototype. Excellent consistency between simulated and measured responses has been demonstrated. According to the measurement, the SDA has peak gains of 5.26/5.60 dBi at 3.5/5.4 GHz, and the return loss better than 21.6 dB. The isolation between ports is greater than 40 dB, whereas excellent front-to-back-ratio and co-to-cross polarization are obtained for the proposed SDA. Furthermore, the total size of the SDA is only
$0.129~\lambda ^{2}$
, with
$\lambda $
being the guided wavelength at 3.5 GHz.