A novel design method of microstrip dual-band filter using feed line with SIR

In this paper, a new design method of the dual-band bandpass filter which consists of Stepped-Impedance Resonators (SIRs), Open-Loop Ring Resonators (OLRRs) and feed lines with SIRs is proposed. The length of feed line with SIR electrically becomes half wavelength at the first resonance frequency and one wavelength at the second resonance frequency, and so the size of filter may be reduced. And to improve the attenuation at the stopband and minimize the coupling between the first band resonator and the second band resonator, the second harmonic frequency of the SIR constituting the first band resonator may be moved out of operating frequency range. The proposed design method may be confirmed to be useful from measured results for dual-band bandpass filter operated at 2.45 GHz and 5.8 GHz.