A computer aided numerical iteration technique is presented which would be suitable for optimum design and realisation of Impatt amplifiers with circular resonant cap cavities. The dependence of the centre frequency of the amplifier on the device and circuit impedance with the device placed at the centre of the circular resonant cap cavity has been studied. The real part of the impedance seen at the cap edge by an incoming signal has been studied along with the geometrical parameters of the cavity using a numerical iteration process through solution of related electromagnetic field equations. The dependence of the centre frequency on the cap radius, cap height, post radius and the cap thickness has also been studied. © 1998 Taylor & Francis Group, LLC.