Balanced-to-balanced dual-band bandpass filter with common-mode rejection spurious suppression and independent bands

Abstract

A novel balanced-to-balanced dual-band bandpass filter is presented. The structure is obtained by combining two single-layer balanced-to-balanced bandpass filters (BBPF) with microstrip lines. Characteristics of each band can be designed independently. The final structure exhibits a reduced size with 0.4 λg × 0.22 λg where λg is the guided wavelength at the lower frequency. A good out-of-band response is achieved with a spurious frequency value of 5.6 times the lowest central frequency. Common-mode rejection is 58 and 45 dB for the first and second central frequencies, respectively.