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UBC Theses and Dissertations

Ultra wideband coplanar waveguide based impedance transformer with slow-wave electrodes Yao, Xia


A new type of broadband impedance transformer loaded with capacitive fins (ITF) and suitable for use up to 100 GHz is presented. The development of ITF is motivated due to the growing demand for the ever increasing transmission speed in the telecommunications industry. At millimetre wave frequencies, impedance matching is crucial to reduce reflections between mismatched loads, allowing for cleaner signal transfer and higher bit rates. Conventional tapered impedance transforms have been used in the past to achieve wideband impedance matching. In order to improve the performance of tapered impedance transformers, we adopted a slow-wave electrode design approach. A typical ITF structure utilizes capacitive loading fins to control the impedance along the line. This increases the effective microwave index of the impedance transformer. Compared with conventional, unloaded, tapered impedance transformers, ITF structures extend the impedance matching range and the operating bandwidth for the same amount of on-chip real-estate. We have designed ITFs capable of impedance matching resistive loads from ~ 10 Ω to ~ 229 Ω, on a 650 μm thick GaAs substrate, for frequencies up to 70 GHz. Several design examples are used to demonstrate the performance and flexibility of these ITF structures. The ITF design technique can be used to make impedance transformers that operate up to 100 GHz.

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