An inline coaxial quasi-elliptic filter with controllable mixed electric and magnetic coupling

Based on the concept of using controllable mixed electric and magnetic coupling to design planar filters in our earlier work, we propose a novel inline coaxial filter, in which the electric and magnetic coupling can be separately controlled. Due to this controllable mixed coupling, the filter can operate with a quasi-elliptic characteristic. By modifying resonator structure and inserting additional coupling components, the filter size is substantially reduced and the coupling becomes more easily controllable, thus being able to produce a highly selective filter with a compact size. In addition, asymmetric response can be easily achieved. For the N-order filter, a maximum of N - 1 finite transmission zeros can be realized. Practical designs, concerning a global system for mobile communication specification, show the advantages of this filter. Index Terms--Coaxial, elliptic filtering characteristic, inline filter, mixed coupling.