Compact Second-Order LTCC Substrate Integrated waveguide Filter with Two Transmission Zeros

Abstract

A compact second-order substrate integrated waveguide (SIW) filter using low-temperature co-fired ceramic (LTCC) technology with two transmission zeros for high-selectivity application is presented. The proposed filter is composed of a Modified Doublet (MD) and input/output (I/O) SIW. The MD comprises two resonators that are not coupled to each other, whereas the two resonators are placed below and above the I/O SIW, respectively. The input and output SIW are directly coupled in order to generate up to two finite transmission zeros. The filter not only has good selectivity owing to the controllable transmission zeros by tuning the coupling manner and strength between the I/O SIWand two resonators, but also has a small size by profit from LTCC structure. A demonstration filter having a center frequency of 10 GHz and a 3 dB fractional bandwidth of 2.5% is designed and fabricated to validate the proposed structure. The measured results exhibit high selectivity, minimum passband insertion loss of 2.09 dB, and in-band return loss greater than 14 dB, agree well with simulated ones. Furthermore, based on the vertically multilayer structure using LTCC technology, the overall size of the filter is only 18 × 10 × 1.2mm³.