Abstract :
Resonant-cavity techniques provide a powerful method for evaluating circular-electric-mode waveguide performance, particularly attenuation, mode conversion and bend-loss characteristics. The waveguide to be tested forms the side wall of the resonator. Thus, a few samples of special waveguide may be sufficient to check design parameters. Cavity measuring equipment operating at frequencies between 50 and 60 Gc/s has been designed and used to study 7/16 in, 7/8 in and 2 in-inner-diameter copper, helix and dielectric-lined waveguide. Q-factors as high as 3.5×106 have been measured for a 30 ft-long 2in-diameter copper cavity at room temperature. Attenuation characteristics are obtained by measuring several cavities of different lengths to obtain end-wall and coupling corrections. A pure-mode coupler is used to excite the cavity, allowing mode-conversion effects caused by power transferred from the circular electric to other modes generated by side-wall imperfections to be measured when both modes are resonant simultaneously.
