A broadband VCO using dielectric resonators

An approach for obtaining broadband negative resistance in designing single-port voltage controlled oscillators (VCOs) is described. The circuit uses a varactor in the feedback path to obtain a variable reactance for maximizing the negative resistance. The concept is demonstrated by designing and fabricating a circuit that oscillates in the 3.5-6.5-GHz band, depending only on the selection of the dielectric resonator. Electronic tuning for automatic frequency control is provided by a tuning varactor coupled to the tank circuit. The VCO was used in a prototype broadband downconverter for 4-6-GHz microwave digital radio.<
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