Center frequency stability and bandwidth reconfigurability in microstrip filters for advanced radio systems

Dual-mode resonators are particularly attractive because they offer size-reduction as well as the ability to achieve tunable filters. Tuning the bandwidth of the filter by adjusting dimensions of its perturbation element is commonly used. It is shown in this paper that different shapes of cuts, which are used as perturbation element, have different effects on stability of the filter center frequency when the dimensions of the cut are tuned. Also it is proved that the center frequency can be kept fix when tuning filter bandwidth by choosing an appropriate value for one dimension and changing the other one.