Browsing by Author "Johnson, Leanne"

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    Advances in pedestal substrate integrated waveguide filters
    (Stellenbosch : Stellenbosch University, 2022-04) Johnson, Leanne; Meyer, Petrie; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: This dissertation presents a set of advances to the recently proposed Pedestal Substrate Integrated Waveguide (SIW) structure as a solution to various problem areas in the field of microwave filters. The structure consists of an evanescent-mode SIW cavity that is loaded with a square pedestal connected to the ground with a metal post. This structure is firstly investigated and compared to other common microwave resonators. It is then utilized in 3 different ways. The work includes the design of a coupled resonator filter with both positive and negative cross-coupling. Electric coupling is obtained with an I-shaped line between pedestal tops, while positive coupling is obtained in the traditional manner with inductive irises. Both types of couplings offer large ranges of coupling values and are easily implemented in this structure. The proposed structure can also introduce mixed coupling. A proof-of-concept sixth order cross-coupled bandpass filter, with a 5 % bandwidth at 5 GHz, and both real and imaginary axis transmission zeros, is designed and measured. Secondly, the dissertation presents a novel partially air filled pedestal resonator. The pedestal SIW topology is adapted to create partially air filled pedestal SIW resonators to reduce losses and increase Q factors while maintaining small sizes. A comparison of three different types of pedestal resonators is done between a totally filled pedestal SIW resonator, a partially air-filled pedestal resonator and an empty pedestal resonator, show ing the increase in Q factor for the same size. Then the use of micro-machining to create these novel resonators is illustrated and explained. A resonator and second order filter prototypes are manufactured, using the manufacturing process explained, and tested. It was shown that the Q factor can be increased from 186 for a fully filled dielectric resonator to 285 for a partially air filled resonator. This shows a 34.7 % increase. The last application of the pedestal resonator is in the use of tunable structures. The pedestal resonator is shown to be made easily tunable by the addition of PIN diodes to the pedestal post, seperated with an annular ring. Four separate stages of frequency are obtained in this manner. Two resonators and one third order filter are designed, manufac tured and tested. Good frequency tunability is obtained in simulation and measurement, but high losses were observed in the measured prototypes.