Compact Quarter-Mode SIW Self-triplexing Antenna for C-band and X-band Applications

An ultracompact substrate integrated waveguide (SIW)-based triplexing antenna operating at three independent frequencies of 4, 7.8, and 10.68 GHz is proposed in this study. It is consisting of two miniaturized Square-shaped quarter-mode SIW (SQMSIW) resonators and one triangular one (TQMSIW). Their miniaturization was accomplished by inserting rectangular slots at the closed ends of each resonator, resulting in an increased shunt capacitance. As a result, the resonance frequencies were shifted to the lower end of their fundamental frequencies. The proposed design has a dimension of just 0.08 $\lambda _g^2$. Furthermore, the lowest attainable isolation level was as low as 27.5 dB. At the design frequencies, the highest realized peak gains were 4.9, 5.43, and 5.3 dBi at 4, 7.8, and 10.68 GHz, respectively. The final design has been fabricated, and the simulation findings agree well with the measured ones. In terms of independent frequency tuning functions, the proposed design demonstrated its versatility. This was accomplished simply by varying the length of the capacitive slots, making it a viable choice for compact multi-band wireless communication systems.