Narrow line coupled stripline elliptic-function filter using F-form resonator for transmission zeros

In portable telephone systems for mobile satellite and cellular radio communications, elliptic-function filters are used to achieve miniaturization of filters with low loss and high isolation characteristics. In this paper, we present a narrow line coupled elliptic-function filter which has planar stripline structure. A sub-resonator, named "F-form resonator" here, is proposed for the coupling between nonadjacent main resonators. By arranging the F-form resonator on a common dielectric substrate with the main resonators, we realize a minia-turized multi-pole stripline filter with the elliptic-function response. A design procedure is presented and validated by the performances of fabricated L-band filter and diplexer.