Accuracy of the equivalent circuit model using a fixed beam impedance for klystron gain cavities

Most small-signal calculations of the modulation in a klystron's gain cavit y use an equivalent circuit which includes a fixed beam impedance. Comparin g this calculation to the gain calculated self-consistently, we note there are appreciable errors in both the calculated amplitude and phase of the ca vity's modulation. These errors may lead to large accumulated errors in det ermining either the tube's small-signal or large-signal gain, Both techniqu es are used in a comparison with an existing S-band klystron.