A planar substrate integrated waveguide (SIW) based cavity‐backed self‐triplexing slot antenna is proposed for X‐Ku band applications. The antenna comprises of the SIW cavity, radiating slots, and feeding networks. The radiating slots; that are etched on the upper metallic plane of the SIW, are backed up by the three radiated quarter cavities (QCs). The radiating slots in the respective QCs are of different lengths, excited by three separated orthogonal feed lines to resonate at three different frequencies as 11.01, 12.15, and 13.1 GHz. By fine‐tuning the antenna parameters, an intrinsic input port isolation of better than 26 dB is realized which helps in achieving the self‐triplexing property. The behaviors of individual cavity modes at three resonant frequencies are explained with the help of Z‐parameter. The proposed antenna layout is easy to integrate with the planar circuit. The proposed antenna is fabricated and measured results display a close concern with the simulated results. Moreover, a unidirectional radiation pattern and gain of 5.1, 5.54, and 6.12 dBi at resonant frequencies are realized.

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This paper demonstrates a novel kind of cavity-backed self-quadplexing slot antenna for S- and C-band applications. The proposed antenna consists of four distinct U-shaped slots of different lengths and produces quad frequency bands for wireless communication systems. These slots are excited through separate and orthogonally placed 50 Ω micro-strip feed lines and generate four distinct operating bands at 3.2, 4.1, 5.8, and 7.2 GHz. Due to the perturbation of the different U-shaped slots over a substrate-integrated waveguide cavity with defined positions, the high intrinsic port isolation value is better than 30.5 dB. Thus, the proposed unique antenna structure combines the four independent operating bands with minimum mutual coupling and negligible interference among the input ports, showing the antenna's self-quadplexing feature. The proposed antenna also has frequency tunability with unidirectional radiation patterns and gains of 5.8, 5.4, 4.01, and 3.47 dBi at corresponding operated frequencies. The cross polarization is below 17.3 dB and the front-to-back ratio is higher than 21.5 dB at all operating quad bands. Good agreement was obtained between the simulated |S| parameter and equivalent circuit model results.

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In this paper, a low profile substrate integrated waveguide (SIW) based self-quadplexing antenna with high isolation is demonstrated for multiband wireless applications. Here the SIW based resonator cavity is integrated with an "X"-shaped resonator and formed the four quarter mode cavities having the individual microstrip feed lines. Each quarter mode cavity consists of "V"-shaped slots of different lengths; are in front to feed line and produce the four distinct resonant frequencies at 7.8 GHz, 8.5 GHz, 10.2 GHz, and 10.6 GHz, respectively. The working principle depends upon the perturbation of higher-order modes in a particular quarter mode cavity. The minimum intrinsic isolation of below than -26dB is attained between any of the two input ports by adequately modifying the antenna dimensions. Hence, a single antenna consists of four individual signals without interfering with each other, which determines the self-quadplexing property of the antenna. The proposed antenna is realized for maximum efficiency and minimum value of frequency ratio. The measured gain of the proposed antenna is 4.5 dBi, 5.28 dBi, 7.1 dBi, and 7.4 dBi at the four resonant frequencies, respectively.

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