A cross-coupled substrate integrated waveguide filter for 28 GHz millimeter wave communications

Abstract

The design of a cross-coupled substrate integrated waveguide (SIW) filter with three transmission zeros (TZs) for 28 GHz millimeter wave application is presented in this paper. The filter consists of an oversized cavity and a cascaded triplet (CT). The oversized cavity introduces a TZ in the lower stopband by the cross-coupling between higher/lower order modes. The location of this TZ can be adjusted by changing the offset distance of input/output ports to the center of the cavity. The CT section consist of three cavities. By analyzing the phase model, two TZs in the upper stopband are predicted, which is verified by the simulation. Measured results show that the filter has a center frequency of 28 GHz with the bandwidth of 600 MHz. The minimum insertion loss in the passband is 2.7 dB, and the return loss is better than 15 dB. Due to the TZs, the SIW filter has sharper transition performance at both lower and upper sidebands, good selectivity is achieved.