High-power broadband absorptive waveguide filters

[摘要] ENGLISH ABSTRACT: This dissertation presents a synthesis method for broadband high-power absorptive microwave lters by cascading a wide stop-band wa e-ironlter with an absorptive harmonicpad.The classical image impedance synthesis methods for wa e-ironlters are updated toallow for non-uniform boss patterns, which enable control over both the stop-band attenuationand pass-band reection of thelter. By optimising an accurate circuit modelequivalent, computationally intensive numerical EM optimisation are avoided. The nonuniformwa e-ironlter achieves the same electrical speci cation as similarlters inliterature, but in a smaller form factor. The prototype presented displays less than -21dB in-band reection over 8.5 - 10.5 GHz, with stop-band attenuation in excess of 50 dBover the harmonic bands 17 - 31.5 GHz and 30 dB over the 34 - 42 GHz. The prototype isdesigned to handling 4 kW peak power incident in the transmitted band, and is 130 mm inlength. Minimal full-wave tuning is required post-synthesis, and good agreement is foundbetween synthesised and measured responses. Additionally, a completely novel obliquewa 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 standingwave surface current distributions. An accurate circuit model description of the cascadedstructure is developed, and optimised to provide a required level of input match in thepresence of an arbitrary reectivelter. Using numerical port parameter data of the wa eiron lter, a harmonic pad is developed that provides -12.5 dB input reection matchacross 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 andmeasured responses of the cascaded structure.

[发布机构] Stellenbosch University