Quad-band dual-mode resonator with dual-square-loop for WLAN and WiMAX systems

We propose the improved configurations with dual-mode dual-square-loop resonators (DMDSLR) for quad-band applications. The resonant frequency equations of DMDSLR are introduced for simply designing quad-band bandpass filter (BPF). Resonant frequencies can be controlled by tuning the perimeter ratio of the square loops. To obtain lower insertion loss, higher out-of-band rejection level and wider bandwidth of quad-band, the improved dual-mode perturbations are designed. The proposed filter is successfully simulated and measured showing frequency responses and current distributions. It can be applied to WLAN and WiMAX GHz systems.