SEMICONDUCTOR MICROWAVE AMPLITUDE AND PHASE MODULATOR.
Quarterly rept. no 8, 16 Feb-15 May 65,
GENERAL TELEPHONE AND ELECTRONICS LABS INC BAYSIDE N Y
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Experiments on the amplitude modulator indicate a linear falloff of modulation depth with drive frequency from 12.5 percent at 0.9 Gcs to 8.4 percent at 1.4 Gcs. It appears from these data that the useful modulation bandwidth of this device in its present configuration falls in the 1 Gcs range. The drive power required to maintain a constant modulation index as the rf carrier power was varied over a three to one range was experimentally determined. A linear relation existed between the drive and carrier power levels. Measurements indicate that the injecting point contact can be represented by a series LCR circuit in shunt with the transmission line. On the basis of this circuit, it is possible to explain the observed decrease in insertion loss with forward bias. The stability of the GaAs varactors was improved by coating the semiconductor surface with a thin film of epoxy. However, the yield was limited, and some electrical deterioration occurred immediately after application of the epoxy coating. Author