Dual-band filter design using L-shaped stepped impedance resonators

This study demonstrates the feasibility of using microstrip L-shaped stepped impedance resonators in a dual-band filter, in conjunction with one of two coupled fed structures. Traditional single-band coupled filter design theory is used and each design parameter of the filter is controlled by two suitable physical parameters. Thus, the specifications, such as the central frequencies and the bandwidth of the two bands, can be fulfilled simultaneously. The filter maintains the geometry of the resonators without the need for additional matching networks. Design curves are constructed systematically, and used to obtain an appropriate pair of physical parameters that meet the desired specifications without trial and error. The L-shaped resonator makes the required values of the physical parameters possible to be found. Two dual-band filters operated at 2.4/5.2 GHz bands are fabricated and measured to verify the design concept.