A compact bandpass filter with two tuning transmission zeros using a CMRC resonator

This paper presents a new compact, low-insertion loss, sharp-rejection, and narrow-band microstrip bandpass filter (BPF) using a compact microstrip resonant cell (CMRC) as the resonator. Experimental results show that the filter only has 1.3- and 1.5-dB insertion losses when using the symmetrical and asymmetrical CMRC resonators, respectively. The effect of varying the length of the resonator to the notch frequencies of the filter has been studied. Furthermore, due to the CMRC characteristic, the size of this filter is only 0.1λ_g by 0.29λ_g. Based on the same design methodology, a microstrip BPF with a coplanar-waveguide feed is also designed with an increased bandwidth. All the proposed filters have been verified by simulation and measurement with good agreement. These filters are attractive for hybrid microwave integrated circuit and monolithic-microwave integrated-circuit implementation.