Design of balanced band pass filters with one transmission zero using an asynchronously coupled dual-mode resonator

A novel quasi-elliptic balanced bandpass filter (BBPF) designed on microstrip technology that uses Asynchronously Coupled Dual-Mode Resonator (ACDMR) is proposed. The filter is based on a novel Balanced Asynchronous Box (Basybox), which has five couplings and three resonators (two λ/2 resonators and a dual-mode grounded λ/2 resonator). By changing a conventional triplet with the use of dual-mode resonators, we can generate a non-resonant mode that generates a transmission zero (TZ). In addition, the filter has a balanced response. In this paper, full design methodology is presented along with a practical implementation. The filter has a center frequency in differential-mode of 950 MHz, a bandwidth of 53 MHz and a transmission zero at 975 MHz. For the common-mode, there is a rejection higher than 15 dB throughout the band up to 3 GHz. Good agreement between simulation and measurement is observed.