High-efficiency series operation of Gunn devices

Successful series operation of two Gunn devices, differing by about 10% in threshold current, has been achieved at X band (8.5¿12GHz). The devices were mounted in a resonant cavity and biased to approximately six times the threshold voltage of a single device before both became active. At that point, the output power of the series combination was nearly equal to the sum of the powers observed previously for each device operating alone at its measured bias voltage. For one particular set of diodes, the observed efficiency (for series operation with N/f = 1.3 × 105 s/cm3) was 28.2% at 8.3GHz with 3.4W of peak pulsed power output. This is the highest efficiency ever reported for Gunn devices at such frequencies.