Design of a Stub-Loaded Coupled Line Diplexer for IoT-Based Applications

This letter presents the design of a microstrip-based diplexer for the applications of the Internet of Things (IoT). By incorporating stub-loaded coupled line resonators, the diplexer achieves significant enhancements in its passband performance. Specifically engineered to operate at precise frequencies of 2.55 and 3.94 GHz, the diplexer demonstrates improved isolation and selectivity through the integration of five transmission poles (TPs). A comprehensive analysis is conducted, evaluating crucial parameters, such as size, insertion loss, return loss, and isolation. The diplexer is fabricated on a compact Rogers Duroid 5880 substrate, and experimental measurements validate its effectiveness, exhibiting a low insertion loss of 0.3 dB at 2.55 GHz and 0.4 dB at 3.94 GHz, in close agreement with simulated predictions. The proposed design, featuring stub-loaded coupled line resonators, showcases highly promising passband characteristics, making it a compelling solution for efficient multiplexing of diverse frequency bands in wireless communication applications within the IoT and network-on-chip (NoC) domains.