Coaxial Resonators with Helical Inner Conductor

The use of coaxial or reentrant resonators is practical at frequencies down through the high-frequency band and even lower. By introducing a helical inner conductor, a Q of several thousand can be achieved in relatively small volume. Design equations are simple and are the basis for an alignment chart. The unloaded Q is equal to 50 times shield diameter in inches times square root of resonance frequency in megacycles. Shield length is about 30 per cent greater than its diameter. Experimental results confirm the accuracy of the predicted Q. The method is also applicable to miniaturized UHF resonators, and to the design of high-Q radio-frequency inductors and LC resonators. Additional formulas and a chart relate frequency, Q, volume, voltage gradient and power rating.