The HP 8360 synthesizer architecture is shown in Figure 8.59.
The four subsystems in this synthesizer are a 2–7.8 GHz YIG-tuned oscillator (YTO), a
reference PLL, a fractional-N PLL, and a sampler loop. A portion of the RF output from
the YTO is sent to a sampler, where it is mixed with a high order harmonic of the
200–220 MHz PLL, forming a 20–40 MHz IF signal. A phase detector compares this IF
signal to the output of the fractional-N PLL. This phase detector output is summed into
the tuning control for the YIG oscillator. The sampler loop can be incremented in 500 kHz
steps, and the fractional-N loop can be stepped in 0.001 Hz increments. This mode of
operation permits this family of microwave frequency synthesizers to maintain 1 Hz
resolution over their entire output range.