A Microstrip Bandpass Filter Using Asymmetrical Stepped-Impedance Resonators for a Wide Upper Stopband Performance

This paper proposed a new asymmetrical microstrip stepped-impedance resonator (SIR) used for constructing a narrow band bandpass filter. With the proposed resonator, a desired bandpass response has been realized and a bandstop characteristic in the upper stopband has been obtained resulting in high spurious suppression. The size of the resonator is also reduced approximately 16 % when comparing with a conventional SIR. A bandpass filter using a microstrip stepped-impedance line periodically loaded with the proposed SIRs has been designed at the operating frequency of 2 GHz with a bandwidth of 60 MHz. The proposed filter has a low insertion loss with a wide upper stopband characteristic that the spurious suppression of better than 20 dB has been measured for a frequency range up to 7.6 GHz