Subharmonically injection-locked dual-gate FET VCO frequency synthesizer

By employing a high-frequency dual-gate FET VCO and a low-frequency PLL synthesizer, a new approach to obtain a wideband higher frequency synthesizer with a lower frequency PLL system is introduced in this letter. For a demonstration, a 4.0 GHz frequency synthesizer was designed and tested. It is a 4.0 GHz dual-gate FET VCO that is fourth subharmonically injected locked by a 1.0 GHz PLL synthesizer, with the FET VCO being controlled by the PLL controlling voltage at the same time. Thus, the free-running frequency of an FET VCO can follow proportionally that of the 1.0 GHz synthesizer, and wideband subharmonic injection locking can be achieved. The output power of the demonstration synthesizer is more than 15.0 dBm, with a bandwidth more than 30% and the phase noise is -102 dBc/Hz at an offset frequency of 100 kHz.