Miniaturized dual-band bandpass filter with wide stopband using stepped impedance resonators

A compact dual-band bandpass filter with wide stopband based on stepped impedance resonators has been presented. The proposed filter consists of two quarter-wavelength modified SIRs which share a common grounded via-hole and two symmetrical open-end stubs. This structure without the open-end stubs can generate four transmission zeros (TZs) to achieve strong passband selectivity and the additional two transmission zeros can be obtained to improve the wide stopbabnd characteristics by using the symmetrical open-end stubs. The center frequencies and bandwidths of the two passband can be controlled by adjusting the geometric dimensions of the proposed SIRs. Moreover, The filter with passbands operated at 2.4/5.2 GHz can finely meet the wireless local area network (WLAN) bands requirements. The circuit only occupies 0.07 λg×0.11 λg.