Synthesis of symmetric and asymmetric triple-stopband microwave filter using frequency transformation

This paper presents the synthesis of direct coupled triple-stopband filters using coupling matrix approach. This design method is applicable to both symmetric and asymmetric triple stopband filter.The frequency transformation techniques has been applied for finding the locations of poles and zeros of a direct coupled triple stopband filter. By properly combining several single-band filtering functions, the multiband filtering function of various bandwidth are generated. Prescribed real or complex transmission zeros can also be employed in the triple-band filtering function. Finally 12-pole symmetric and asymmetric triple-stopband filters have been synthesised in cul-de-sac configuration to validate the proposed method.