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Investigation of Ferroelectric Thick-Film Varactors for Microwave Phase Shifters

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5 Author(s)
Wenfei Hu ; Sch. of Eng., Univ. of Birmingham ; Dou Zhang ; Michael J. Lancaster ; Tim W. Button
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This paper presents a novel cost-effective microwave phase-shifter technology using thick-film ferroelectric varactors as the tuning component. The devices are fabricated by conventional screen-printing techniques with silver/platinum as the conducting layers and Ba0.7 Sr0.3TiO3 as the tunable dielectric layer. The microwave performance of the ferroelectric varactors is optimized in terms of both material process parameters and the varactor gate area dimensions. S-parameter measurements on a tunable reflective circuit are used to evaluate the performance of the varactor at around 2 GHz. The varactor parameters such as RF capacitance, tunability, and the Q factor of the varactor are studied as a function of the gate dimension. At 100-V dc-biasing voltage, the BSTO varactor loaded tunable reflective circuit exhibits a differential phase shift of 70deg with a return loss of -1.2 dB. This is equal to a figure-of-merit value of 58deg/dB. Full analog reflection-type and all-pass network phase shifters are also implemented in order to explore the monolithic integration of phase control devices into the RF system based on low-cost ceramic thick-film technology

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IEEE Transactions on Microwave Theory and Techniques  (Volume:55 ,  Issue: 2 )