A Compact and Embedded Balanced Bandpass Filter With Wideband Common-Mode Suppression on Wireless SiP

A compact balanced bandpass filter is proposed using a novel circuit topology, which includes a differential resonator and a common resonator in the conventional quasi-lumped coupled-line circuit, instead of adopting quarter-wavelength or half-wavelength transmission lines in the filter design. Based on this circuit topology, the balanced bandpass filter can support bandpass filtering function under differential-mode operation and exhibit bandstop filtering function under common-mode noise. By employing the advantage of the low-temperature co-fired ceramic fabrication technology, a compact balanced bandpass filter is centered at 3.42 GHz with fractional bandwidth 10.4% for differential signals and rejection band is from 1.48 to 7.4 GHz for the common-mode noise. Moreover, the proposed filter is able to introduce a transmission zero with excellent common-mode suppression (>;40 dB) within the differential-mode passband. The electrical size of this filter is 5.6 × 5.4 mm with the corresponding electrical size 0.113 × 0.109 λ_g, where λ_g is the guided wavelength at the center frequency 3.42 GHz. This compact balanced bandpass filter is suitable to be applied to the system-in-package technology for wireless application.