Serially-connected-series-stub resonators and their applications in coplanar stripline bandpass filter design

This paper proposes three types of series resonators which serially connect two or more series stubs and investigate their applications in coplanar stripline (CPS) filter design. With the proposed resonators, transmission zeros close to the resonant frequency could be obtained. The key concept to obtain the transmission zeros is the utilization of serially-connected-series-stub (SCSS) in the series resonators. Moreover, this kind of structure is capable of increasing and adjusting the equivalent total line impedance of the resonator so as to ease the design procedure to meet the Q-values requirements of the resonators in filter design. Based on this concept, a CPS 5-order bandpass filter with attenuation poles is designed and fabricated. The simulations and experiments results are presented which show that the proposed resonators can be used to improve the skirt selectivity and stopband performance of the filters.