| 摘要 |
A frequency synthesizer is described which operates over a wide frequency range at high resolution and variable step size without trading off between spurious frequency rejection and phase noise suppression. The synthesizer includes a magnetically-turned YIG oscillator which generates a desired output frequency from a received tuning signal. The output signal is fed back into a phase locked loop which generates the tuning signal. The phase locked loop includes a harmonic mixer for mixing the output signal with a reference frequency F2. The mixer receives a base frequency signal and a harmonic select signal resulting in the generation of the reference signal, F2. The mixed signal is input to a programmable divider, then to a phase detector which receives another reference signal, F1. The phase detector output is the tuning signal which is coupled to the YIG oscillator. Both reference frequencies, F1 and F2, are derived from a common base frequency. A base frequency source includes a voltage-controller oscillator coupled to another phase locked loop. This other phase locked loop receives two reference signals, Fx and Fy. Reference Fx preferably is generated by a direct digital synthesizer that receives programmable tuning parameters. Reference Fy may be generated with a fixed, switched or other frequency source. A microprocessor is included for selecting the programmable divider factors, the direct digital synthesizer tuning parameters, and other variable factors.
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