First order diplexer using SIW-based circular cavity resonator

A design of Substrate Integrated Waveguide (SIW) diplexer is proposed. The diplexer is formed using two SIW circular cavity resonators designed individually and combined through a T-junction. The circular cavity structure using TM
₀₁₀
mode is employed in the design of this diplexer. To prove the concept, the diplexer is fabricated using Rogers RT5880 with dielectric constant, □
_r
= 2.2 and height of substrate 1.57 mm. The diplexer is fabricated with standard printed circuit board technology and will be operating at 2.4 GHz and 2.6 GHz each suitable for LTE/WiFi applications. The performances of the proposed design are verified through both simulation and measurement. The measured results are in good agreement with simulated result. Slight frequency shift and losses are still in acceptable range.