A microstrip bandpass filter using a line periodically loaded with unbalanced SIRs for size reduction and spurious suppression

A bandpass filter using a microstrip line periodically loaded with new unbalanced stepped-impedance resonators (SIRs) is proposed. With the proposed resonators, size reduction of approximately 16 % when comparing with the conventional SIR has been obtained. The bandpass filter has been designed at the operating frequency of 2 GHz with a narrow bandwidth of 60 MHz. The filter provides a lower insertion loss than that of parallel or cross-coupled structure with conventional SIRs. The upper stopband performance of the proposed filter has been drastically improved that the first spurious suppression of better than 20 dB has been measured.