Design of Coupled Slow-Wave CPW Millimeter-Wave Bandpass Filter Beyond 100 GHz in 55-nm BiCMOS Technology

The design and experimental results of millimeter-wave bandpass filters (BPFs) implemented in 55-nm BiCMOS technology and operating around 120 GHz are presented in this article. Slightly modified coupled line filters' structures are used in the designs. It allows generating the transmission zero at the upper stopband, leading to the selectivity of enhanced filters. The coupled line structure is implemented in two technologies, microstrip coupled lines and coupled slow-wave (SW) coplanar waveguides (CS-CPWs). The latter shows more design flexibility, allowing to reach a better filtering performance than the microstrip filters, i.e., better in-band flatness and higher selectivity. Good agreement is achieved between simulation, modeling, and measurement results. Also, the overall length of the filter based on CS-CPWs is smaller as compared to the filters based on the microstrip lines, thanks to the SW propagation.