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RF Test Equipment Series: Signal Analyzers (Vector Signal Analyzers) 101

Unlike spectrum analyzers of the past, modern signal analyzers provide additional phase (time) information that can be used for much more expansive analysis than a power sweep across frequency. Though modern signal analyzers are often still called spectrum analyzers, the capability of signal analyzers includes many features beyond what a spectrum analyzer can perform. For example, the phase and amplitude data captured by a signal analyzer can be used to provide modulation analysis, which are features that also lead to these instruments being called vector signal analyzers (VSAs).

Hence, many VSAs have complex modulation analysis tools, displays, and features, which can provide measurements such as error vector magnitude (EVM), display IQ data, demodulate various known modulation standards, pre-compliance analysis, and more. This is possible as VSAs use a different signal capture approach than typical spectrum analyzers, which involves the use of digitization shortly after the signal reception. Digital signal capture allows for fast Fourier transform (FFT)-based analysis and deeper digital processing that yields signal data that can readily be processed with digital hardware and modern display technology. Some VSAs are also designed with overlapping capture windows that allows for real-time signal analysis, which is incredibly useful for modern signal hunting, EMC precompliance testing, interference hunting, and analysis of transient system performance. This is why real-time spectrum analyzers, or real-time signal analyzers (RTSAs), are becoming increasingly common as field instruments or laboratory instruments for analyzing transient signal standards and communication systems that use spread spectrum modulation techniques.

Many VSAs are also able to store the digitized signal information for later analysis, which can include mapping and tracking features. VSAs are also often available with additional optional analysis tools that can provide even greater analysis of specific communication standards, and may also be extensible with custom programming features to enable testing automation.

Similar with a spectrum analyzer, VSAs include almost all of the hardware necessary for their operation. However, external interconnect, antennas, adapters, attenuators, and sometimes amplifiers are also useful for some testing scenarios. Typical VSAs and RTSAs come with N-type, SMA, or 3.5mm coaxial connector ports, which may require additional adapters to be compatible with external antennas or DUT coaxial interconnect.  As with spectrum analyzers, an inline attenuator may be useful when working with signal levels beyond the threshold of the VSA, as the internal attenuators of a VSA are limited to the extent they can attenuate external signals.

Pasternack In-series and Between-series Adapters

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References
  1. Spectrum Analysis Basics - Keysight