Browsing by Author "Swart, Hein"
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- ItemWideband axially symmetric power combiners based on short step filters(Stellenbosch : Stellenbosch University, 2021-03) Swart, Hein; De Villiers, Dirk; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: This thesis presents a technique for the design of compactN-way coaxial line powercombiners. By incorporating short-step-stub Chebyshev impedance transformers into thedesign, a noteworthy reduction in the physical size, compared to existing axially symmet-ric combiners, is achieved. This feature is especially advantageous at lower microwavefrequencies for which combining structures are typically large.An 8-way coaxial combiner atL-band, with a 10th order short-step-stub Chebyshevimpedance transformer is designed and simulated. The simulation results show a−12 dBreturn loss bandwidth of 112%. The total size of the structure is 0.22λat the lowest pass-band frequency. Due to the optimisation framework used, very few full wave calculationsare required which makes the design simple and relatively fast to execute.Network analysis techniques are investigated and the different circuit parameter descrip-tions for lossless circuits are presented. This forms the foundation for the realisabilityconditions of short-step filters in terms of circuit parameters. A detailed examination onthe theory of network synthesis is done. Short-step impedance transformers are analysedand synthesized and accompanied by complete design examples, demonstrating the proce-dure for extracting element values from the synthesised transfer functions. The short-stepimpedance transformers are designed and synthesised with specified operating bandwidthsand transmission line lengths well suited for the purposes of waveguide power combinersat lower microwave frequencies. A general configuration for coaxial combiner designs and geometrical parameter descrip-tions are presented. Special considerations for combiners with short-step-stub impedancetransformers are discussed and the methods for implementing different parts of the designis analysed. A back-short is included in the synthesis that allows a short-step transformerto be incorporated into coaxial combiners. A method for realising shunt stub lines withinthe combiner configuration is demonstrated. A space-mapping optimisation frameworkis used to extract mathematical models describing the relationship between physical pa-rameters and circuit element values for optimising the design.