This paper presents a design of a compact, lowloss and high passband ratio substrate integrated waveguide (SIW) triplexer based on the Complementary Split Ring Resonator (CSRR) structure. The proposed triplexer operates at three passbands of 6 GHz, 8 GHz and 10 GHz that correspond to the passband ratios of 1.33 and 1.67. By appropriately designing square CSRRs on the surface of the SIW, the low-loss and compact passband resonators below the cut-off frequency of the SIW at each operation frequency can be realized. The proposed triplexer is designed on the costeffective RO4003C substrate. The simulated results show insertion losses are 0.9 dB, 1.02 dB and 1.04 dB at 6 GHz, 8 GHz and 10 GHz bands, respectively. The triplexer occupies just an area of 32.5 ×23.5 mm². The triplexer is designed using Keysight ADS and CST Microwave Studio simulators.

*This research is partly funded by VIET ELECTRONIC TECHNOLOGY SOLUTIONS CO., LTD.