Synthesis and Realization of Multisection Tandem Stripline Bandpass Filters

A bandpass filter is described which is made up of two identical multi-element coupled symmetrical striplines in tandem connection. For the filter, a precise synthesis procedure is presented reducing the design to the synthesis of a directional coupler. The required equal-ripple polynomials are calculated by an iterative method. Relations for the polynomial extreme values are provided, derived from the attenuation requirements in passband and stopband. On the basis of this procedure the coupling factors of two 21-element filters are calculated and realized three-layer polyolefin. Measurements show good agreement with theoretical results.