A novel 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 like, which creates three patches facing three different ports and radiates at three different frequencies (4.14 GHz, 6.1 GHz, 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 trade-off 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.

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 ( $T{E}_{110}$) and two degenerated modes ( $T{E}_{120}$ and $T{E}_{210}$). 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.

In this communication a compact planar-fed substrate integrated waveguide (SIW)-based self-multiplexing (SM) antenna for hexa-band operation is proposed for the first time. Six different patches with planar $50~\Omega $ feed lines are designed and attached to the top side of the rectangular SIW cavity. The antenna operates at six different frequencies (5.33, 5.76, 6.31, 6.86, 7.34, and 7.8 GHz) simultaneously. The antenna attains 4.5, 4.94, 4.9, 5.12, 6.12, and 6.6 dBi peak gain at respective resonant frequencies. Port relocation, stepped patches, and additional vias are exploited to maintain isolation (>23 dB) between any two ports. The front-to-back ratios (FTBRs) are between 10 and 20 dB and Co-pol to Cross-pol ratios are between 10 and 29 dB. The design supports single-variable independent frequency tuning for all six patches and eligible for wide range of applications. The proposed design is fabricated and results are validated through measurement. The antenna is suitable for planar microwave devices.