The Influence of Harmonic Injection on Power, Efficiency and Stability of Trapatt Amplifiers

It is shown by an analytical model, that power and efficiency of TRAPATT diodes are limited by the fact, that the optimum diode impedances cannot be matched with a passive load circuit at some harmonics of the oscillation. These restrictions can be overcome by injection of a small amount of power at the respective harmonics. The experimental verification of this method has been performed with an unique lumped element circuit. By injection of the third harmonic fundamental power and efficiency could almost be doubled. At 1,7 GHz a peak power of 230 Wwith a total efficiency of 46% has been achieved. The maximum gain (from the third to the first harmonic) was 23 dB. The good symmetry of the output spectrum indicates high phase and amplitude stability.