An Innovative Approach In The Design Of Fast-Switching Microwave Synthesizers

By Alexander Chenakin, Suresh Ojha, and Iqbal Sihra, Phase Matrix, Inc.

Abstract — This paper presents a compact, broadband frequency synthesizer module, which covers 0.1 to 10 GHz frequency range with a 0.001 Hz step size. The synthesizer combines fast switching speed, low phase noise, and low spurious characteristics. The measured phase noise at an output frequency of 10 GHz and 10 kHz offset is –122 dBc/Hz. For an output frequency of 0.1 GHz and 10 kHz offset the phase noise is –150 dBc/Hz. Spurs do not exceed the –70 dBc level and the switching time of the main PLL is less than 10 uSec. This module can be used as a broadband, agile, high-fidelity signal source in a variety of test-andmeasurement, communication, and surveillance systems.

Introduction
The frequency synthesizer is a key element of virtually any microwave measurement setup. It generates a stimulus signal or is used as a local oscillator on the receiver side. Phase noise and spurious generated by the frequency synthesizer are critical parameters that impose the ultimate limit in the system's ability to resolve signals of small amplitude. Another key parameter of the synthesizer that impacts overall system performance is the frequency switching speed. The time spent by the synthesizer transitioning between frequencies becomes increasingly valuable since it cannot be used for data processing.