Design of tri-band filtering power divider with out-of-band transmission zeros based on frequency transformation method

In this brief, a novel tri-band filtering power divider with a pair of out-of-band transmission zeros is presented. It mainly consists of tri-band filter matching structures, transmission lines introducing transmission zeros, and isolation resistors. Through even-and odd-mode analyses, general design equations for the three parts can be derived separately. By applying coupled lines, the circuit size is further compact. For verification, a third-order tri-band filter PD working at three independent bands with a pair of out-of-band TZs & theta;z= 60 degrees is designed. Good agreement between the measured and simulated results is attained so as to successfully validate the correctness of the proposed design approach.