Compact Millimeter-Wave CMOS Wideband Three-Transmission-Zeros Bandstop Filter Using a Single Coupled-Line Unit

This brief presents the design and implementation of millimeter-wave ultra-wide bandstop filter (BSF) using a standard 0.18-μm CMOS technology. The BSF configuration consists of a single coupled-line resonator shorted at the middle, which operates as not only a resonant element but also an open stub. The BSF realizes three transmission zeros in the stopband that results in sharp skirt selectivity. The overall width of the filter is less than the width of a 50-Ω line and occupies a compact area of 0.0066λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> × 0.443λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> is the guided wavelength at 60 GHz. Explicit design equations are derived analytically using lossless transmission model. A prototype wideband BSF with a 3-dB bandwidth of 110% at 60 GHz is realized on a thin-film microstrip structure. The impact of several CMOS process parameters on the designed filter is also examined.