A vector signal analyzer is an instrument that measures the magnitude and phase of the input signal at a single frequency within the IF

bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...

of the instrument. The primary use is to make in-channel measurements, such as

error vector magnitude The error vector magnitude or EVM (sometimes also called relative constellation error or RCE) is a measure used to quantify the performance of a digital radio transmitter or receiver. A signal sent by an ideal transmitter or received by a receiver ...

, code domain power, and

spectral flatness Spectral flatness or tonality coefficient, also known as Wiener entropy, is a measure used in digital signal processing to characterize an audio spectrum. Spectral flatness is typically measured in decibels, and provides a way to quantify how muc ...

, on known signals. Vector signal analyzers are useful in measuring and demodulating digitally modulated signals like

W-CDMA The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS is a component of the Inte ...

, LTE, and

WLAN A wireless LAN (WLAN) is a wireless computer network that links two or more devices using wireless communication to form a local area network (LAN) within a limited area such as a home, school, computer laboratory, campus, or office building ...

. These measurements are used to determine the quality of

modulation In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informatio ...

and can be used for design validation and compliance testing of electronic devices.

Operation

The vector signal analyzer spectrum analysis process typically has a down-convert & digitizing stage and a

DSP DSP may refer to: Computing * Digital signal processing, the mathematical manipulation of an information signal * Digital signal processor, a microprocessor designed for digital signal processing * Yamaha DSP-1, a proprietary digital signal ...

& display stage.

Down-convert and digitize stage

A vector signal analyzer operates by first down-converting the signal spectra by using superheterodyne techniques. A portion of the input signal spectrum is down-converted (using a

voltage-controlled oscillator A microwave (12–18GHz) voltage-controlled oscillator A voltage-controlled oscillator (VCO) is an electronic oscillator whose oscillation frequency is controlled by a voltage input. The applied input voltage determines the instantaneous oscilla ...

and a mixer) to the center frequency of a

band-pass filter A band-pass filter or bandpass filter (BPF) is a device that passes frequencies within a certain range and rejects (attenuates) frequencies outside that range. Description In electronics and signal processing, a filter is usually a two-por ...

. The use of a

allows consideration of different carrier frequencies. After the conversion to an

intermediate frequency In communications and electronic engineering, an intermediate frequency (IF) is a frequency to which a carrier wave is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier sign ...

, the signal is

filtered Filtration is a physical separation process that separates solid matter and fluid from a mixture using a ''filter medium'' that has a complex structure through which only the fluid can pass. Solid particles that cannot pass through the filter m ...

in order to band-limit the signal and prevent

aliasing In signal processing and related disciplines, aliasing is an effect that causes different signals to become indistinguishable (or ''aliases'' of one another) when sampled. It also often refers to the distortion or artifact that results when a ...

. The signal is then

digitized DigitizationTech Target. (2011, April). Definition: digitization. ''WhatIs.com''. Retrieved December 15, 2021, from https://whatis.techtarget.com/definition/digitization is the process of converting information into a digital (i.e. computer- ...

using an

analog-to-digital converter In electronics, an analog-to-digital converter (ADC, A/D, or A-to-D) is a system that converts an analog signal, such as a sound picked up by a microphone or light entering a digital camera, into a digital signal. An ADC may also provide ...

Sampling rate In signal processing, sampling is the reduction of a continuous-time signal to a discrete-time signal. A common example is the conversion of a sound wave to a sequence of "samples". A sample is a value of the signal at a point in time and/or spac ...

is often varied in relation to the frequency span under consideration.

DSP and display stage

Once the signal is digitized, it is separated into quadrature and in-phase components using a quadrature detector, which is typically implemented with a discrete Hilbert transform. Several measurements are made and displayed using these signal components and various

processes, such as the ones below.

Signal spectrum from FFT

FFT A fast Fourier transform (FFT) is an algorithm that computes the discrete Fourier transform (DFT) of a sequence, or its inverse (IDFT). Fourier analysis converts a signal from its original domain (often time or space) to a representation in the ...

is used to compute the frequency spectrum of the signal. Usually there is a windowing function option to limit

spectral leakage The Fourier transform of a function of time, s(t), is a complex-valued function of frequency, S(f), often referred to as a frequency spectrum. Any linear time-invariant operation on s(t) produces a new spectrum of the form H(f)•S(f), which chang ...

and enhance frequency resolution.Keysigh

''Keysight Vector Signal Analysis Basics'', Published September 30, 2019. This window is implemented by multiplying it with the digitized values of the sample period before computing the FFT.

Constellation diagram

constellation diagram A constellation diagram is a representation of a signal modulated by a digital modulation scheme such as quadrature amplitude modulation or phase-shift keying. It displays the signal as a two-dimensional Cartesian plane, ''xy''-plane scatter dia ...

represents a signal modulated by a digital

scheme such as

quadrature amplitude modulation Quadrature amplitude modulation (QAM) is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications to transmit information. It conveys two analog message signal ...

phase-shift keying Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). The modulation is accomplished by varying the sine and cosine inputs at a ...

. This diagram maps the magnitude of the quadrature and in-phase components to the vertical and horizontal directions respectively. Qualitative assessments of signal integrity can be made based on interpretation of this diagram.

Error vector magnitude

By representing the quadrature and in-phase components as the vertical and horizontal axes, the

can be computed as the distance between the ideal and measured constellation points on the diagram. This requires knowledge of the modulated signal in order to compare the received signal with the ideal signal.

Typical functionality

Typical vector signal analyzer displays feature the

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...

of the signal measured within the IF

, a

of the demodulated signal,

measurements, and a

time-domain Time domain refers to the analysis of mathematical functions, physical signals or time series of economic or environmental data, with respect to time. In the time domain, the signal or function's value is known for all real numbers, for the cas ...

plot of the signal. Many more measurement results can be displayed depending on the type of modulation being used (symbol decoding,

MIMO In radio, multiple-input and multiple-output, or MIMO (), is a method for multiplying the capacity of a radio link using multiple transmission and receiving antennas to exploit multipath propagation. MIMO has become an essential element of wir ...

measurements, radio frame summary, etc.).

References

Communications Systems Analysis Using Hardware and Software-Based Vector Signal Analyzers

Footnotes

{{Reflist Measuring instruments Electronic test equipment Signal processing