Equivalent circuit design of multilayer parallel-coupled line filter

LTCC filters have been widely used for wireless LAN terminals. They generally adopt the multilayer structure. Some multilayer LTCC filters are made of symmetrical parallel-coupled lines and anti-symmetrical parallel-coupled lines to reduce the length of resonators. The equivalent circuit of parallel-coupled lines was analyzed and applied to bandpass filters using multilayer parallel-coupled line resonators. A three-pole bandpass filter with a center frequency of 2.45 GHz is designed by using the proposed equivalent circuit and the measured results have good agreement with the design results.