New Reconfigurable mmWave Filters Enabled by Vanadium Dioxide

Abstract

This article presents fundamental research of new on-chip reconfigurable bandpass filters for mmWave applications. Two designs for a 2-band, 2-pole bandpass filter in coplanar waveguide (CPW) on a $430~\mu $ m sapphire substrate, incorporating silicon dioxide metal-insulator-metal (MIM) capacitors and bridges are presented. Vanadium dioxide (VO2) is integrated directly into the filter to enable 2-band reconfiguration. The wide-tuning filter design has two bands centered at 38.5 and 49 GHz, with 3 dB bandwidths of 4.7 and 6.0 GHz, respectively. The wideband filter design has two bands centered at 30.1 and 36.5 GHz, with 3 dB bandwidths of 22.0 and 22.3 GHz, respectively. In-band insertion loss (IL) was measured to be 2.7 and 4.4 dB, respectively. The 2-pole 2-band filter has the typical 40 dB per decade increase of IL as designed. The filter’s input, referred to as 1 dB compression point, is measured to be above 22 dBm at 26.5 GHz, for both bands. The filter has an area of 0.184 mm2, which is 2% of the interelement area of a typical 50 GHz tiled array. The passband shifts by 21.2% from low-band to high-band center frequency. Subcomponent testing of shunt VO2 switches has shown a switching time averaging $2.2~\mu $ s, which indicates a filter tuning speed of 3.16 GHz/ $\mu $ s. The novel reconfigurable mmWave on-chip filter’s combination of power handling and small size is, to the best of the authors’ knowledge, the current state of the art.