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In this letter, a shielded quarter-mode substrate integrated waveguide (S-QMSIW)-based self-diplexing antenna for closely spaced bands and high isolation is proposed. A ${\rm Y}$ -shaped slot is engraved on the top of the metal to enhance the extra capacitance of the QMSIW cavity resonator; thus, it helps to reduce its size as well as achieve dual-band characteristics. The S-QMSIW resonator is then excited by two orthogonal microstrip feed lines in the full-wave electromagnetic simulator (high-frequency structure simulator) to operate at two distinct frequencies (3.47 and 3.84 GHz). A transmission zero is generated at 3.56 GHz to provide port isolation better than 47 dB. In addition, a lumped circuit model is predicted to validate the antenna structure. To demonstrate the proposed concept, an S-QMSIW-based self-diplexing antenna is designed, fabricated, and tested. The recorded peak gains of the antenna are 4.8 and 5.7 dBi at 3.47 and 3.84 GHz, respectively. At each band, the antenna front-to-back ratio is greater than 20 dB. The circuit size of the proposed antenna is very compact (0.15 $\lambda _g^{2}$). [ABSTRACT FROM AUTHOR]

A novel and compact all planer-fed self-triplexing patch antenna is designed and demonstrated for triple-band operation simultaneously. The model is comprised of one substrate-integrated waveguide (SIW) cavity, three planar ports, and one modified I-shaped slot. The proposed antenna is designed in a simple three-step method to achieve improved self-triplexing property. In the first step, a rectangular slot is created and its position is altered to obtain initial isolation (>20 dB) between any two ports. Secondly, the same slot is modified to an I-shape, which creates three patches facing three different ports and radiates at three different frequencies (4.14, 6.1, and 8.32 GHz) with minimum isolations above 28.4 dB. In the third step, one input-port is off-centered to obtain port isolation tradeoff so that isolation between any two ports is better than 30.8 dB. Importantly, the proposed design also supports easy individual frequency tuning using single variable. For demonstration purpose, the antenna is fabricated and characterized. The proposed planar antenna is very simple, compact, and feasible for handheld microwave devices. [ABSTRACT FROM AUTHOR]