Miniaturization of planar microstrip filters with coupled resonators

This paper presents a new procedure for the miniaturization of microwave filter realized in microstrip technology. This filter is coupled resonator filter and the desired selectivity is achieved by adjusting the nonadjacent coupling between resonators. The new implementation proposes replacement of open-loop resonators with modified quarter-wavelength resonators to reduce the footprint area. In order to verify the proposed procedure, the fourth-order filter with relative bandwidth of 0.1 and the center frequency at 2 GHz has been implemented. The proposed method has achieved a reduction of the footprint area for more than 40% compared to the standard implementation with the open-loop resonators.