Single-Oscillator Wideband VCO.

The effort on this program was aimed at fabricating a low-voltage, high-speed VCO to cover the 11- to 18-GHz frequency range for use in a set-on VCO-type of frequency memory in place of an arrangement requiring three VCOs and a multiplexer. The most important accomplishments were 1 The development of a low-power VCO covering the 11- to 18-GHz range using a GaAs hyperabrupt junction varactor diode and requiring a very small tuning voltage requirement 2 The fabrication of a new type of frequency discriminator which uses the roll-off characteristic of a microwave FET 3 Measurements leading to an understanding of the behavior of GaAs hyperabrupt varactors at high input levels. GaAs hyperabrupt varactors were produced having capacitance ratios in excess of 101, but less than the expected frequency tuning ranges were orginally obtained from VCOs with these hyperabrupt varactors used as the tuning diode. Special network analyzer measurements with varying levels of input drive power showed the impedance of the hyperabrupt varactors to be unusually sensitive to the incident power level resulting in a significant reduction in maximum capacitant at levels consistent with those to which the varactors are exposed in the oscillator.