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Analysis of Specially Doped Varactors for Direct Frequency Tripling

01 February 1975

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The varactor fabrication technique recently evolved is a notable beneficiary of the IMPATT developments. Such a transfer of technology from IMPATT to varactors1 has resulted in diodes with a zero bias capacitance of 7.7 pF, a breakdown voltage of 160 V, and a series resistance of 0.66 ohm. These diodes have been utilized in the construction of a coaxial frequency doubler yielding 8.2 W1 at 3990 mHz and 80-percent efficiency. Further, if these diodes are used for frequency tripling, they yield about 10 W1 at 6.345 GHz and 72- to 76-percent efficiency. When the doping density is also controlled (as is done in high-low-high profile IMPATT'S), it is possible to generate varactor diodes with any predefined relation between the charge and the voltage across the varactor. Conventional frequency tripling studied by Penfield and Rafuse2 asserts the presence of an idler frequency excitation at twice the input frequency to mix with the input frequency, thus creating a third harmonic voltage. In the proposed tripler, the doping density is adjusted to directly convert the power at incident frequency to power at 317