Tunable microstrip dual-band bandpass filter for WLAN applications

In this paper, based on a new stub-loaded open loop resonator, a compact microstrip dual-band bandpass filter is presented. The proposed filter is designed using two stub-loaded open loop resonators to create two pass bands at 2.39 GHz and 5.7 GHz for multimode wireless LANs applications. Two high impedance sections are used in the main loops and the internal stubs are two low impedance microstrip cells. A method is presented to control the mode resonance frequencies. By increasing the internal stubs’ dimensions, the resonance frequencies are adjusted without size increment. The proposed filter has a good performance. The insertion losses at 2.39 GHz and 5.7 GHz frequencies are 0.1 dB and 0.4 dB, respectively, while the return loss at the two pass bands is better than –16.6 dB. The filter size is 251 mm . The designed filter is fabricated and measured. The results show that there is a good agreement between the simulation and measurement.