Tunable Substrate Integrated Waveguide Diplexer With High Isolation and Wide Stopband

A tunable multilayer diplexer using substrate integrated waveguide (SIW) technology is proposed in this letter. A multilayer design is chosen to easily control the electric and magnetic coupling through circular slots in order to achieve a wide-stopband response. The proposed diplexer works at two unique frequencies (centered at 10.5 and 13.5 GHz) with high isolation (>42 dB) and a wide stopband (up to 21 GHz). A varactor diode is used in the proposed diplexer for tuning. The varactor diode is placed in the structure in such a way that both channels can be tuned independently without affecting one another. The results show the flexibility of the diplexer in achieving desired responses and its suitability for integration with any tunable component. Simulated and measured results obtained are in good agreement.