Vector Signal Generator

- details or tutorial about vector signal generators - what they are, how they work and how they are different to other RF signal generators.

The vector signal generator, VSG has appeared as a result of the need for the generation of far more complicated waveforms.

The vector signal generators or VSG has arisen to meet the need to radio or wireless and cellular systems from W-CDMA / UMTS to Wi-Fi - IEEE 802.11, WiMAX - IEEE 802.16, LTE and many others.

These systems utilise very complicated waveforms using digital modulation. As a result it has been necessary to develop what are termed vector signal generators or digital signal generators to be able to generate the radio frequency waveforms required.

R&S SMBV100a vector signal generator
A typical vector signal generator

Vector signal generator, VSG basics

Previous generations of RF signal generator often had facilities for being able to add modulation to the signal. However to meet the needs of some of the new cellular and wireless systems, it is necessary to be able to add complex forms of modulation. This often requires the use of a vector signal generator, VSG.

The key element of a vector signal generator is that it is able to be modulated by complex signals, i.e. those containing In-phase and Quadrature, I-Q signals. As the signal generator can accommodate IQ phase information rather than just amplitude information, this means that there is a vector element to the signal rather than just the scalar or basic phase modulation.

Vector signal generator block diagram
Vector signal generator block diagram

Vector signal generators typically incorporate a high end RF signal generator with an IQ modulator. In addition to this, they often include an arbitrary waveform generator in one form or another. This is used to generate the complicated baseband modulation signals required to modulate the RF signal. In this way a vector signal generator includes the capability to generate all the signals required for some of the advanced communications systems that use modulation formats including OFDM, CDMA and many others.

Spectrum of signal produced by vector signal generator
Spectrum of example signal produced by vector signal generator

With the increasing complexity of many radio communication systems from cellular phones to Wi-Fi and more, the use of vector signal generators in the development and production test areas is only likely to increases to enable engineers to generate the test waveforms they require.

By Ian Poole

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