This application note contains a variety of hints to help you understand and improve your use of network analyzers, along with a quick summary of network analyzers and their capabilities.
Overview of network analyzers
Network analyzers characterize active and passive components, such as amplifiers, mixers, duplexers, filters, couplers, and attenuators. These components are used in systems as common and low-cost as pagers, or in systems as complex and expensive as communications or radar systems. Components can have one port (input or output) or many ports. The ability to measure the input characteristics of each port, as well as the transfer characteristics from one port to another, gives designers the knowledge to configure a component as part of a larger system.
Types of network analyzers
Vector network analyzers (VNAs) are the most powerful kind of network analyzer and can measure frequencies from 5 Hz up to 120 GHz. Designers and final tests in manufacturing use VNAs because they measure and display the complete amplitude and phase characteristics of an electrical network. These characteristics include S-parameters, magnitude and phase, standing wave ratios (SWR), insertion loss or gain, attenuation, group delay, return loss, reflection coefficient, and gain compression VNA hardware consists of a sweeping signal source (usually internal), a test set to separate forward and reverse test signals, and a multichannel, phase-coherent, highly sensitive receiver (Figure 1). In the RF and microwave bands, typical measured parameters are referred to as S-parameters and are also commonly used in computer-aided design models.
Scalar network analyzers
A scalar network analyzer (SNA) measures only the amplitude portion of the S-parameters, resulting in measurements such as transmission gain and loss, return loss, and SWR. Once a passive or active component has been designed using the total measurement capability of a VNA, an SNA may be a more cost-effective measurement tool for the production line to reveal out-of-specification components. While SNAs require an external or internal sweeping signal source and signal separation hardware, they only need simple amplitude-only detectors, rather than complex (and more expensive) phase-coherent detectors.
A network/spectrum analyzer eliminates the circuit duplication in a bench test setup of a network and spectrum analyzer. Frequency coverage ranges from 10 Hz to 1.8 GHz. These combination instruments can be economical alternatives in design and test of active components like amplifiers and mixers, where analysis of signal performance is also needed.
Hint 1. How to boost and attenuate signal levels when measuring high-power amplifiers
Testing high-power amplifiers can sometimes be challenging since the signal levels needed for test may be beyond the stimulus/response range of the network analyzer. High-power amplifiers often require high input levels to characterize them under conditions similar to actual operation. Often these realistic operating conditions also mean the output power of the amplifier exceeds the compression or burn-out level of the analyzer’s receiver.