This application note serves as a primer on the vector signal analyzer (VSA).
This chapter discusses VSA measurement concepts and theory of operation;
Chapter 2 discusses VSA vector-modulation analysis and, specifically,
digital-modulation analysis.
Analog, swept-tuned spectrum analyzers use superheterodyne technology
to cover wide frequency ranges; from audio, through microwave, to millimeter
frequencies. Fast Fourier transform (FFT) analyzers use digital signal
processing (DSP) to provide high-resolution spectrum and network analysis,
but are limited to low frequencies due to the limits of analog-to-digital
conversion (ADC) and signal processing technologies. Today’s wide-bandwidth,
vector-modulated (also called complex or digitally modulated), time-varying
signals benefit greatly from the capabilities of FFT analysis and other DSP
techniques. VSAs combine superheterodyne technology with high speed
ADCs and other DSP technologies to offer fast, high-resolution spectrum
measurements, demodulation, and advanced time-domain analysis.
A VSA is especially useful for characterizing complex signals such as
burst, transient, or modulated signals used in communications, video,
broadcast, sonar, and ultrasound imaging applications.
Figure 1-1 shows a simplified block diagram of a VSA analyzer. The VSA
implements a very different measurement approach than traditional
swept analyzers; the analog IF section is replaced by a digital IF section
incorporating FFT technology and digital signal processing. The traditional
swept-tuned spectrum analyzer is an analog system; the VSA is fundamentally
a digital system that uses digital data and mathematical algorithms to
perform data analysis. For example, most traditional hardware functions,
such as mixing, filtering, and demodulation, are accomplished digitally,
as are many measurement operations. The FFT algorithm is used for
spectrum analysis, and the demodulator algorithms are used for vector
analysis applications.