Wide-Range Electronic Tuning of Microwave Cavities

Methods for electronically tuning microwave cavities using the principles of space-charge tuning and of spiral-beam electronic tuning in the presence of a low-pressure gas are described. The use of a low-pressure gas permits tuning over frequency ranges several times larger than those obtainable in vacuum. An S-band cavity was tuned over a frequency range from 3,280 to 4,350 mc, and from 3,280 to 2,540 mc, or ±30 per cent. An X-band cavity was tuned over a frequency range from 9,170 to 10,800 mc, or 18 per cent. These values are compared to measurements made in vacuum. A semi-quantitative theory for electronic tuning in gas atmospheres is presented. Limitations of the method are given.