The unloaded Q of a varactor-tuned cavity is derived from a solution of Maxwell's equation. The deri¬vation takes into account the Q multiplying properties of a length of transmission line loaded with a varactor.nAn equation is written which relates the tuning range of a cavity to the cavity length for a given ratio of maximum to minimum varactor capacitance. The equation was solved on a computer and the results are given in graphical form. Using the general Q equation, a plot is made of Q multiplication factor as a function of cavity length.nThese results, in graphical form, can be used to determine the maximum unloaded Q obtainable over a given tuning range for a varactor of known cut-off frequency and capacitance.nTwo types of varactor-tuned TEM cavities are discussed and design procedures given. Methods of controlling bandwidth over a tuning range are discussed for both bandpass and bandstop filters.
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