Dielectric Varactor Tunable Matching Network And The Microstrip Antenna Development,

Barium strontium titanate thin films are potential candidates for application in frequency-agile microwave electronic components due to their large field-dependent dielectric constant. BST thin film varactor integrating with microwave circuit can effectively reduce the size of circuit,such as tunable matching network, tunable microstrip patch antennas,tunable filters,phase shifters and other tunable microwave devices et al.In this thesis, the dielectric properties of barium strontium titanate thin films using for tunable microwave devices have been optimized,and tunable matching networks and tunable microstrip patch antennas have been studied.The major conclusions are as follow:(1) We have produced good quality BST thin film with the relative tunablility rate 52.7% (40V) and dielectric loss 0.8%, through optimizing RF magnetron sputtering parameters. The BST thin films varactor with the relative tunablility rate 37% (30V) and dielectric loss 0.7% were fabricated using micro-fabricated techniques in this paper.(2) A tunable matching network with coplanar waveguide (CPW) structure was fabricated on LaAlO₃ substrate by using the micro-fabrication technique. The fabricated network was aπ-type network with a capacitor-inductor-capacitor (C-L-C) configuration, and the tunable capacitor components used in this network are the barium strontium titanate (BST) thin film varactors. The simulation and measurement results show that, by tuning the capacitance of BST varactors by applying DC bias voltage to the varactors, good impedance matching between the network and the source can be achieved in the range of 720 MHz⁸40 MHz. The reflection coefficient S₁₁ of the network measured at 780 MHz reaches-40.3 dB.(3) A tunable microstrip patch antenna that utilizes BST films varactor is presented. The antenna is fabricated on FR-4 substrate with a dielectric constant and thickness of 2.65 and 1.5mm, respectively. The simulation and measurement results show that the microstrip patch antenna can be tunned by applying DC bias voltage for the capacitance of BST varactors. The antenna resonant frequency can continuously be shifted from 1.525 GHz up to 1.622 GHz. The reflection coefficient S₁₁ of tunable microstrip patch antenna at GPS(1.575GHz) frequency reaches–17.2 dB.