Building a Microwave Frequency Synthesizer — Part 5 : Advanced Techniques

T his is the final article in a five-part series on microwave frequency synthesizers. It concludes with a review of advanced synthesizer solutions. Although synthesizers can be found in virtually any microwave system, test and measurement (T&M) is probably the most challenging application that calls for advanced synthesizer techniques. This final article addresses some specific T&M requirements and possible solutions. Broadband operation, very fine frequency resolution, low spurious and low phase noise are the key specifications for T&M applications. More recently a lot of interest has been focused on fast frequency switching. This has been motivated by a need for increased data throughput of ATE systems, and the frequency agility demands of wide bandwidth receivers and transmitters [2, 3]. Besides the spectral purity and switching characteristics, the T&M applications require extended func-tionality that include output power leveling and control, frequency and power sweep, modulation , etc. These options can be realized by adding additional separate modules or can be incorporated into the synthesizer core module. For example, the amplitude and pulse modu-lators can be either external or internal to the synthesizer itself (Figure 49), while the phase and frequency modulation components are usually included into the synthesizer as a part of the PLL circuitry. Test and measurement applications are usually associated with big bench-top instruments , which can be found in every engineering lab. Synthetic instrumentation is a cost-effective alternative for building complex test and measurement equipment [48-49]. It enables the emulation of various traditional bench-top instruments employed in automatic test systems using a reconfigurable combination of core hardware components (such as a signal generator shown in Figure 50).