Introduction

A frequency synthesizer is the most versatile piece of microwave equipment. Synthesizers come in a variety of forms ranging from tiny chips to complex instruments. Single-chip synthesizers are available in a die form or as surface-mount ICs. They include the key elements (such as RF and reference dividers, phase detector, and lock indicator) required to build a simple single-loop synthesizer. Such ICs are mounted on a PCB with additional circuitry. The PCB-based modules range from small, surface-mount, “oscillator-like” designs to more complex connectorized assemblies. Such PCB assemblies can be packaged into a metal housing and are presented as stand-alone, complete synthesizer modules. Connectorized synthesizer modules can be used to build larger instruments such as signal generators for test-and-measurement applications.

Not surprisingly, frequency synthesizers are among the most challenging of high-frequency designs. Many approaches have been developed to generate clean output signals [1–17]. This chapter presents a brief overview of today's microwave synthesizer technologies. It starts with general synthesizer characteristics followed by a review of the main architectures. Direct analog, direct digital, and indirect techniques are compared in terms of performance, circuit complexity, and cost. Synthesizer parameters can be further improved in hybrid designs by combining these main technologies and taking advantage of the best aspects of each. Finally, sophisticated test-and-measurement signal generator solutions are reviewed. The signal generators come with high-end technical characteristics and extended functionality including output power calibration and control, frequency and power sweep, various modulation modes, built-in modulation sources, and many other functions.