Compact dual-band bandpass filter using open loop resonator for multimode WLANs

A compact and low insertion loss microstrip filter, designed and fabricated using the open loop resonator to achieve a dual-band bandpass response with controllable centre frequencies, is presented. The coupling structures, consisting of three coupled lines with different widths, are used to control resonance frequencies that lead to the creation of two passbands at 2.4 and 5.2 GHz for wireless LANs application. In the design process, the admittance and impedance of the input are used to adjust the resonance frequencies for even and odd modes. Good agreement between the simulation and measurement results is achieved.