Derivation of cavity coupling to feeder from tuning curves

A method of finding a cavity coupling factor Qx from the separation in wavelength between branches of tuning curves obtained by moving a short circuit in the feeder is described. This is complementary to a derivation from slopes proposed earlier. The alternative method is suitable over a large range of Qx (from about 30, where the formulas obtained for Qx are least accurate, to 105 or more). The highest value of Qx that can be resolved is limited by losses in the cavity, feeder or short circuit. Experimental results obtained for a magnetron coupled to a waveguide are given, and Qx found by the above method is compared with that derived from standing-wave measurements. Good agreement in the values of Qx was obtained.