CPW bandpass filter with serially-connected series-stub resonators

This paper proposes a new type of series resonator with serially-connected series-stubs (SCSS). They are proposed to design bandpass filter in finite-ground coplanar waveguide (FGCPW). With the proposed SCSS series resonators, transmission zeros close to the resonant frequency could be obtained so that the size of the filter can be decreased by reducing the orders. Moreover, this kind of structure is capable of 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, two 2-order CPW bandpass filters with attenuation poles are designed, one is designed with two serially-connected short-circuit series-stub (SCSSS) resonator, another is with combination of serially-connected short-circuit and open-circuit series-stub (SCSOSS) resonator. The simulations and experiments results are presented which show that the proposed resonators can be used to improve the skirt selectivity of the filters.