NEW CONCEPTS FOR HIGH-FREQUENCY AND HIGH-POWER FREQUENCY-MULTIPLIERS AND THEIR IMPACT ON QUASI-OPTICAL MONOLITHIC ARRAY DESIGN

Varactors have been extensively employed for harmonic generation, where high cut-off frequency is dependent upon small C(min), which is typically achieved using small device active area. However, small area limits the output power. Furthermore, the power and frequency dependences of the series resistance in the epitaxial region degrade the efficiency and cut-off frequency as well. As a result, currently utilized varactors are only efficient for relatively low power generation and limited output frequency. Herein, we describe our new approach where by epitaxially stacking single quantum barrier structures, more than an order of magnitude improvement in cut-off frequency and power handling ability may be possible. Alternatively, by combining a Schottky barrier with stacked single quantum barriers, superior performance can also be achieved. These concepts can be readily employed for quasi-optical frequency multiplier arrays, and appear to result in simplified fabrication compared to other devices. The design of high performance quasi optical arrays requires optimization of the passive (metalization) grid as well as the embedded semiconductor devices. Recent work has resulted in an improved impedance model for the standard diode-loaded strip array, including a quantitative estimate of the shunt capacitance introduced across the diode by the discontinuity of the metal strip at the diode site ("gap"). The value of this capacitance exceeds the predicted C(min) for these new devices. We discuss two grid design approaches that can suppress this capacitance.