Wideband axially symmetric power combiners based on short step filters

Swart, Hein (2021-03)

Thesis (MEng)--Stellenbosch University, 2021.

Thesis

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.

AFRIKAANSE OPSOMMING: Hierdie verslag lewer ’n ontwerptegniek vir kompakte,N-rigting, koaksialelyn drywingskombineerders. Met ingeboude kort-stap-stomplyn Chebyshev impedansie transformatorsis die ontwerp se fisiese grootte noemenswaardig kleiner as bestaande soortgelyke kom-bineerders. Hierdie eienskap is veral voordelig by laer mikrogolf frekwensies, wat tipiesgroot kombineerings strukture vereis.Die ontwerp en simulasie resultate van ’n 8-rigting koaksiale kombineerder byL-band,met ’n 10de orde Chebyshev impedansie transformeerder word voorgelˆe. Die simulasieresultaat vertoon ’n−12 dB weerkaatsko ̈effisi ̈ent bandwydte van 112%. Die totale lengtevan die kombineerder is 0.22λby die laagste frekwensie van die deurlaat band. Met dieoptimerings raamwerk wat gebruik is, word baie min volgolf berekeninge benodig wat dieontwerp eenvoudig en relatief vinnig maak om uit te voer.Kort-stap impedansie transformeerders word gesintetiseer om spesifieke bandwydtes entransmissielyn lengtes te vertoon. Die teorie van netwerk sintese word sorgvuldig on-dersoek. Die tegnieke vir netwerk analiese met verskillende parametetriese stroombaanbeskrywings word voor gelˆe. Die realiseerbaarheidsvereistes word weergegee in termevan die stroombaan beskrywings wat belangrik is in die ontwerp van kort-stap trans-formeerders. Die ontwerpprosses vir kort-stap transformeerders word deeglik ondersoekwaarna ’n paar verskillende voorbeelde gesintetiseer word tydens ’n volledige ontwerpsvoor-beeld wat ook die stroombaanelement waardes onttrek. Die algemene konfigurasie vir ’n koaksiale kombineerder met die geometriese beskrywingdaarvan word gegee. Aanvangs vereistes vir die ontwerp word bespreek en die metodeswaar volgens verskillende dele van die ontwerp geimplementeer word, word geanaliseer.Die sintese word aangepas om ’n kortgesluite transmissielyn in te sluit en stomplyne wordgerealiseer met ge ̈etste stroombane op di ̈elektriese skywe wat versoenbaar is met die kom-bineerder se konfigurasie. Modelle wat die wiskundige verhouding beskryf tussen fisieseveranderlikes en stroombaanelemente word onttrek met ’n optimeeringsraamwerk wat ookgebruik word vir die optimering van die volledige ontwerp.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/109825
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