Vanadium Oxide Bandstop Tunable Filter for Ka Frequency Bands Based on a Novel Reconfigurable Spiral Shape Defected Ground Plane CPW

• Published in: IEEE access Vol. 6; pp. 12206 - 12212
• Main Authors: Casu, Emanuele Andrea, Muller, Andrei A., Fernandez-Bolanos, Montserrat, Fumarola, Alessandro, Krammer, Anna, Schuler, Andreas, Ionescu, Adrian M.
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 01.01.2018; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Bandstop filters; CMOS; Coplanar waveguides; Extremely high frequencies; Frequencies; Ground plane; Insertion loss; Microwave filters; millimeter wave technology; Resonant frequencies; Resonant frequency; Resonator filters; Silicon substrates; Spirals; Switches; thin films; Tunable filters; Tuning; vanadium oxide; Vanadium oxides
• ISSN: 2169-3536; 2169-3536
• DOI: 10.1109/ACCESS.2018.2795463

This paper proposes and validates a new principle in coplanar waveguide (CPW) bandstop filter tuning by shortcutting defected ground plane (DGS) inductor shaped spirals to modify the resonant frequency. The tunable filter is fabricated on a high-resistivity silicon substrate based on a CMOS compatible technology using a <inline-formula> <tex-math notation="LaTeX">1\,\,\mu \text {m}\times 10\,\,\mu \text {m} </tex-math></inline-formula> long and 300 nm thick vanadium oxide (VO 2 ) switch by exploiting its insulator to metal transition. The filter is designed to work in K a band with tunable central frequencies ranging from 28.2 GHz to 35 GHz. The measured results show a tuning range of more than 19 %, a low insertion loss in the neighboring frequency bands (below 2 dB at 20 GHz and 40 GHz in on/off-states) while a maximum rejection level close to 18 dB in off-state, limited by the no RF-ideal CMOS compatible substrate. The filter has a footprint of only <inline-formula> <tex-math notation="LaTeX">0.084\cdot \lambda _{0} \times 0.037\cdot \lambda _{0} </tex-math></inline-formula> (where <inline-formula> <tex-math notation="LaTeX">\lambda _{0} </tex-math></inline-formula> represents the free space wavelength at the highest resonance frequency) thus making it the most compact configuration using CPW DGS structures for the K a frequency band. In addition, a more compact filter concept based on the Peano space filling curve is introduced to increase the tuning range while minimizing the DGS area.