CMOS Millimeter-Wave Ultra-Wideband Bandpass Filter With Three Reflection-Zeros Using Compact Single TFMS Coupled-Line Hairpin Unit

Abstract

In this brief, a modified coupled-line (CL) hairpin unit topology with short-circuited ends is proposed to design a compact millimeter-wave ultra-wideband (UWB) bandpass filter (BPF). Thin film microstrip configuration is used for the implementation of CL hairpin unit. The passband return loss bandwidth is enhanced by three attenuation poles achieved by appropriately selecting a single set of CL impedances. Explicit design equations along with graphs are provided by using even-and-odd mode analysis. A prototype filter is fabricated using 0.35- ${\mu }\text{m}$ BiCMOS technology. The fabricated UWB BPF achieves an extended passband from 25 GHz to 95 GHz around 60 GHz with more than 115% fractional bandwidth along with a wide return loss bandwidth. The filter size is very small with the overall width comparable to the width of a 50 ${\Omega }$ line. The measured results are in good agreement with those of predicted ones up to 110 GHz.