A compact millimeter-wave CMOS bandpass filter using a dual-mode ring resonator

A stub-loaded dual-mode ring resonator is proposed to design a millimeter-wave bandpass filter using 0.18-μm CMOS Technology. By increasing the length of the open-circuited stub at the inner corner of the ring resonator, the even-mode resonant frequency is moved to a lower frequency to separate it from the odd-mode resonant frequency. Therefore, the center frequency of the passband has been shifted to a lower frequency to achieve a reduced-size filter design. At the same time, an additional transmission zero is brought in at the upper stopband that can be adjusted by the length of the stub as well. Finally, a 60 GHz bandpass filter is fabricated and characterized. The filter has achieved an ultra-compact size of 0.092 × 0.56 mm. The measured results show good passband performance with two visible transmission poles and three transmission zeros thereby verifying the design principle.