Frequency Switching Speed In Microwave Signal Generators

From calibrating cellular receivers to agile Electronic Warfare transmitters, the ability to change from one frequency to another and settle within a specified amplitude and frequency is a key requirement for microwave signal generators. But what actually defines the frequency switching speed? What components in the block diagram contribute? What is the specification trade-off, with respect to architecture and technology choices? To help answer all these questions, and hopefully generate a few more, let’s take our signal generator apart and see what contributes, and why.

First let’s define what we mean by “frequency switching speed.” For the purposes of this article we will define it as the time it takes to move the output frequency of a signal generator from frequency A to frequency B. By the end of that time we will specify how close we are in Hz to the desired frequency and to within tenths of dB’s of amplitude the output of the source signal generator is to the desired absolute amplitude.