Design of a high-isolation quad-port microstrip triplexer featuring a modified resonator structure for next-generation IoT devices

Abstract This paper presents a quad-port triplexer structure designed for next-generation wireless portable devices. The proposed triplexer consists of three bandpass filters isolated from one another. Filters 1 and 2 are designed using identical coupled line structures with varying physical properties, while filter 3 is developed with a novel coupled line structure. The modified coupled line enables a compact triplexer design, enhances isolation and bandwidth, and reduces the insertion loss. A comprehensive analysis of the proposed triplexer is conducted, and the S-parameter response demonstrates that the triplexer operates at 2. 91, 4. 43, and 1. 20 GHz, with fractional bandwidths of 30. 2 \%, 22 \%, and 33. 3 \%, respectively. The in-band return loss is better than 12. 3 dB across the entire passband. Additionally, the triplexer features three transmission poles for the first two passbands and two for the third. The in-band insertion loss is less than 0. 63 dB for all three passbands. The measured performance of the fabricated triplexer closely corresponds to the simulated results, validating its effectiveness in achieving the desired specifications. This makes the triplexer highly suitable for 5G networks and IoT-based wireless communication devices that demand multiband, high-performance filtering.