Single-loop synthesizer for C-band with ultra fine frequency step

The work considers the results of a C-band simple frequency synthesizer design based on a single loop PLL. The Skyworks CX72302 fractional-N PLL IC was chosen for the exciter and LO design. A high-Q dielectric resonator oscillator (DRO) is used to obtain better noise performance out of the PLL passband. A linear frequency sweep is carried out using a varicap having weak coupling with the DR. The output power of DRO generator is 50 mW. The weak coupling between the varicap and dielectric resonator in the tuned generator provides rather good noise parameters, but the synthesized frequency band is too narrow (approximately 50 MHz within the varicap tuning range of 1-25 V). The single chip fractional-N PLL allows small size single-loop frequency synthesizers to be constructed for frequencies up to the maximum operating PLL IC frequency with the frequency step less than 400 Hz and acceptable phase noise level.