Design of a high outband rejection cross-coupled SIW filter for millimeter wave communications

Substrate integrated waveguide (SIW) technology provides an attractive solution to the integration of planar and nonplanar circuits by using a planar circuit fabrication process. In this paper, a 6-order cross-coupled SIW bandpass filter is designed by coupling matrix synthesis, electromagnetic simulation, coupling matrix extraction and optimization of filter size. The relative bandwith of the filter is 10.5% and the insertion loss is less than 2.65dB in the passband of 24.75GHz-27.5GHz. The transmission zero is introduced by cross-coupling, so that the filter obtains a steep transition band and good sideband suppression characteristics, while having low insertion loss and in-band fluctuation. The filter circuit has a small area and a simple structure, and can be widely applied to the microwave millimeter wave communication system.