Design of 2-in-1 bandpass filter using common dual mode resonators

This paper proposes a new design concepts for 2-in-1 bandpass filter in millimeter-wave, based on substrate integrated waveguide (SIW) cavities resonators implemented on low temperature co-fired ceramic (LTCC) substrate. Two filters at same center frequency but for different polarizations are integrated and designed using common dual mode cavity resonators in order to reduce the circuit size. Due to the concept of modal orthogonality in the SIW cavities, the filter response could not only be controlled in different paths by different modes, but also provides good isolation to each path. With center frequency at 73.5 GHz and fractional bandwidth 6.8%, the filter exhibits 16dB return loss and 2.2dB insertion loss while occupying area of 1.15λ_g × 1.16λ_sr As compared to two typical SIW filters with the same order and cavity arrangement, 31.2% size reduction is achieved.