Design of Three-pole Single-to-balanced Bandpass Filters

A novel procedure for designing single-to-balanced filters is proposed. The proposed procedure can effectively convert a coupled resonator filter into a single-to-balanced filter without changing the frequency characteristics. Such conversion involves dealing with only a 2-port prototype. The most valuable benefit is the great decrease in the EM simulation time. A 3-pole cross-coupled filter topology is introduced to generate a transmission zero that enhances the side-band rejection. Applying the conversion to the 3-pole topology yielded a 2.4 and a 5 GHz single-to-balanced filter using LTCC technology