Compact interdigital capacitor coupled dual-behavior resonator (ICDBR) filter with suppression of spurious responses

A compact interdigital capacitor coupled dual-behavior resonator (DBR) filter with high spurious responses suppression is proposed in this paper. The technique is based on two equivalent topologies of J-inverter and dual-line equivalent circuit of open- circuited stubs. The first compact equivalent topology capacitive inverter is a high pass structure and consequently, and the spurious responses can be suppressed effectively at low frequencies. The second equivalent topology 1/4-network is employed in realizing a compact size and adding new transmission zeros dedicated to the spurious responses suppression at high frequencies. Further compactness is achieved with a dual-line equivalent circuit of open-circuited stubs. The relevant equations are given in the paper. Finally, a 3rd-order compact DBR filter is designed and measured. This structure has a high degree of miniaturization (83%) in comparison to the classical one. Measurement results show good agreement with the simulated ones.