| dc.description.abstract | Phase shifters are indispensable components in modern radar and communications phased-array antenna systems. A typical phased array employs a large number of phase shifters. Using MMIC technology to implement the phase shifters helps the miniaturization of phased-array systems.
In this thesis, two distributed analog phase shifters implemented using two different IC processes are introduced. First, we design an X-band phase shifter based on artificial transmission lines using TSMC 0.35-μm SiGe BiCMOS process. The measurement results at 11 GHz show that, biased between 0 and 3.3 V, the circuit provides a phase shift of 46° and its return losses are greater than 12 dB. At 11 GHz, the measured maximum insertion loss and the minimum input P1dB of the phase shifter are 6.3 dB and 11.7 dBm, respectively.
Next, a Ku-band distributed phase shifter is designed and implemented using WIN 0.15-μm GaAs pHEMT technology. The measurement results at 13 GHz show that, biased between 0 and 1.8 V, the circuit exhibits a phase shift of 60.5°, a maximum insertion loss of 1.9 dB, an input P1dB of 10.7 dBm, and a return loss greater than 15 dB.
In distributed analog phase shifters, variable capacitors are indispensable circuit elements. Though conventional varactor diodes are most widely used for implementing the variable capacitors in phase shifter design, ferroelectric varactor technology offers a viable and potentially better alternative, having the advantages of low loss and high tunability in microwave regime. In this thesis, we fabricate coplanar waveguide (CPW) transmission lines based on ferroelectric barium strontium titanate (BST) thin films and use the CPW lines for extracting the electrical properties of the BST thin films. The S parameters of the CPW lines are measured and carefully compared with full-wave electromagnetic simulation results. The extracted dielectric constant and loss tangent of the BST thin films are approximately 300 and 0.1, respectively.
In summary, we have designed and implemented distributed analog phase shifters using two different IC processes. Implementing phase shifters in MMIC forms helps to miniaturize phased-array systems. We have also developed a ferroelectric thin-film fabrication process. Based on the thin-film process, we have fabricated CPW lines and used them in the extraction of electrical properties of the films. This work provides a basis for ferroelectric-based tunable microwave circuit design in the future.
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