High-power broadband absorptive waveguide filters

Stander, Tinus (Stellenbosch : University of Stellenbosch, 2009-12)

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch.

Thesis

ENGLISH ABSTRACT: This dissertation presents a synthesis method for broadband high-power absorptive microwave lters by cascading a wide stop-band wa e-iron lter with an absorptive harmonic pad. The classical image impedance synthesis methods for wa e-iron lters are updated to allow for non-uniform boss patterns, which enable control over both the stop-band attenuation and pass-band re ection of the lter. By optimising an accurate circuit model equivalent, computationally intensive numerical EM optimisation are avoided. The nonuniform wa e-iron lter achieves the same electrical speci cation as similar lters in literature, but in a smaller form factor. The prototype presented displays less than -21 dB in-band re ection over 8.5 - 10.5 GHz, with stop-band attenuation in excess of 50 dB over the harmonic bands 17 - 31.5 GHz and 30 dB over the 34 - 42 GHz. The prototype is designed to handling 4 kW peak power incident in the transmitted band, and is 130 mm in length. Minimal full-wave tuning is required post-synthesis, and good agreement is found between synthesised and measured responses. Additionally, a completely novel oblique wa e-iron boss pattern is proposed. For the absorptive harmonic pad, transversal broadwall slots in rectangular waveguide, coupling to an absorptive auxiliary guide, are investigated in the presence of standing wave surface current distributions. An accurate circuit model description of the cascaded structure is developed, and optimised to provide a required level of input match in the presence of an arbitrary re ective lter. Using numerical port parameter data of the wa eiron lter, a harmonic pad is developed that provides -12.5 dB input re ection match across the band 17 - 21 GHz with up to 1 kW peak incident power handling capability, yet is only 33 mm in length. Again, good agreement is found between synthesised and measured responses of the cascaded structure.

AFRIKAANSE OPSOMMING: Hierdie proefskrif stel 'n sintesetegniek voor vir wyeband, ho edrywing absorberende mikrogol lters deur 'n kaskade kombinasie van 'n verlieslose wafelyster lter met 'n wye stopband, en 'n absorberende harmoniekdemper. Die klassieke sintesemetodes vir wafelyster lters word aangepas om nie-uniforme tandpatrone toe te laat, wat beheer oor beide die lter se stopband attenuasie en deurlaatband weerkaatsing moontlik maak. Deur die optimering van 'n akkurate stroombaanmodel van die lter kan berekeningsintensiewe numeriese EM optimering vermy word. Die nieuniforme wafelyster lter behaal dieselfde spesi kasies as soortgelyke gepubliseerde lters, maar is meer kompak. Die vervaardigingsprototipe handhaaf minder as -21 dB intreeweerkaatsing oor die deurlaatband van 8.5 - 10.5 GHz, asook attenuasie van meer as 50 dB oor die stopband 17 - 31.5 GHz en 30 dB oor 34 - 42 GHz. Die prototipe is ontwerp om 4 kW intree kruindrywing te hanteer in die deurlaatband, en is 130 mm lank. Die metode vereis minimale verstellings tydens volgolf simulasie, en die meetresultate stem goed ooreen met die gesintetiseerde gedrag. 'n Nuwe skuinstandpatroon word ook voorgestel vir wafelyster lters. Vir die harmoniekdemper word transversale bre ewandgleuwe in reghoekige gol eier wat koppel na 'n absorberende newegol eier ondersoek in die teenwoordigheid van staandegolfpatrone in oppervlakstroom. 'n Akkurate stroombaanmodel van 'n gleufkaskade word ontwikkel, en geoptimeer om 'n vereiste intreeweerkaatsing te bewerkstellig in samewerking met 'n arbitr^ere weerkaatsende lter. Deur gebruik te maak van poortparameterdata van die wafelyster lter word 'n 33 mm lange hamoniekdemper ontwikkel wat 'n maksimum intreeweerkaatsing van -12.5 dB oor die band 17 - 21 GHz handhaaf vir kruindrywingsvlakke van tot 1 kW. Goeie ooreenstemming tussen gesintetiseerde en gemete resultate word weereens waargeneem vir die volledige saamgestelde struktuur.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/1157
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