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Keysight VNA Glossary

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A

Accurate measurements

A phrase that describes an approach to measurement in which the devices under test (DUTs) are characterized at their fundamental frequency, often needed for frequency-domain measurements.

Active components

The devices in an electronic circuit that perform the basic operation of the circuit, such as amplifiers, resistors, capacitors, and inductors.

Analyzer Module

Hardware that is used to control the VNA. This module may be part of a larger PNA or MXA modular test system. The controller sends commands to the other modules in the system to move them into position, perform measurements, and store data. For example, an analyzer module may include a spectrum analyzer used for amplitude measurements or a dynamic range analyzer for measuring noise.

Antidot arrays

A method by which distortion can be measured in a VNA using an array of pre-distorted tone generators. The device under test (DUT) is connected to the tone generator array, which has been designed so that each tone generator has equal amplitude but opposite phases. A special reference probe converts the signals from this array back into single-ended signals. A vector network analyzer is needed to analyze the paired single-ended reference probe outputs to determine the distortion caused by the DUT.

Aperture

The time interval over which the VNA measures the amplitude of a pulse or group of pulses. You can configure the aperture to be symmetrical or asymmetrical in order to capture rising and falling edges separately.

C

Complex transmission components (Magnitude and Phase)

A technique used to determine the magnitude and phase for a number of transmission components in a circuit. The DUT is represented as a linear network to calculate its response. In this case, vector network analyzer (VNA) measurements can be made without measuring amplitude or frequency responses individually for each transmission component, allowing complex circuits to be analyzed more quickly and easily.

Compression

A technique that reduces the dynamic range of a system or signal. For example, in an electrical circuit, high input amplitudes may clip (distort) signals before they reach their final value. A compressor can be used to reduce this distortion. The result is improved accuracy and repeatability of measurements not otherwise possible with large input signals.

Conversion loss

The loss of power when a signal is converted from one type to another. For example, when converting between analog and digital signals in an electrical circuit, some power is always lost in the conversion process.

D

Directional coupler

A device that splits a measurement signal into two or more signals, according to a directional pattern.

Directivity

The ratio of the maximum to minimum gain of an antenna in a desired direction.

Dynamic range

The ratio between the minimum detectable signal power and the maximum specified input power (or voltage). Dynamic range also affects amplitude accuracy, noise floor, and signal attenuation measurements. Instruments with high dynamic ranges are required for measuring small signals with high accuracy and low noise floors.

E

Error correction

Error correction is the process of resolving or correcting errors in data that has already been transmitted. In vector network analysis, error correction is used for correcting errors in magnitude and phase.

F

Ferromagnetic material

A type of material that exhibits a strong positive influence on a magnetic field. Ferromagnetic materials are used in antennas and wireless devices, because of their ability to support high amplitude voltage swings while maintaining low loss characteristics.

Few-mode fiber

A special type of fiber optic cable that uses an extremely small aperture for transferring optical data. It is used in a number of applications for its high bandwidth and large operating wavelengths.

Frequency-dependent

A term used to describe one behavior of an electronic circuit or device. For example, a filter is frequency-dependent if its performance varies depending on the operating frequency.

Frequency extenders

Frequency extenders are used to add or expand frequency spans of a VNA.

Frequency range

The total range of frequencies that can be applied to a network analyzer or vector network analyzer without causing any limitations in the performance specification. For example, VNAs are usually specified for measurement ranges between DC and 18 GHz.

Frequency resolution

A term used to refer to the ability of an analyzer to correctly display closely spaced frequencies. For example, the resolution of the spectrum analyzers is about 1/2 Hz. This means that two signals at 2 GHz and 2.005 GHz would be visible as one signal whose reading is between 1.995 and 2.005 GHz.

G

Group delay

A test used to measure the amount of time required for a signal to transit through or around an object, circuit, or network. It is considered to be one of the most important measurements in the test and measurement industry because it provides information about how fast signals travel within various types of test objects.

H

Holographic mode generation

A method used for creating transmission and reflection test setups that can be measured using transmission/reflection coefficients available on the VNA. This type of setup uses a holographic pattern generator to split the transmission and reflection test signals in order to measure transmission and reflection coefficients simultaneously.

I

IF bandwidth

The total range of frequencies that can be sent through a device or circuit without significant distortion. For example, a transmitter is said to have an IF bandwidth of 100 MHz if it can send signals over the full range of frequencies between 0 and 100 MHz without significant distortion.

Impedance

Impedance is the general term used to describe the opposition to current flow in an alternating current (AC) circuit; it combines both magnitude, and phase information. It is a vector quantity, with both magnitude and phase as components.

Incident power

The power applied to a device, circuit, or network. In order to test a device or circuit, the incident power must be sufficient to measure that device or circuit. For example, if an RF switch with a known insertion loss is being tested with a VNA, the incident power applied at the port of this RF switch must be great enough so that its insertion loss can successfully be measured.

Insertion loss

The amount of signal power that is lost during transmission through or around a network or device. Insertion loss describes the worst case scenario in which all of the signal’s power is lost due to reflection, impedance mismatches, and other factors. It is usually measured with large signals using vector network analyzers with tracking generators.

Interferometer

A device used to determine the characteristics of an object or circuit by splitting a signal into two parts, sending them through or around this object or circuit separately and then combining them back to one signal.

L

Load reflection coefficient

A term used to describe the ratio of reflected power divided by incident power. This is one of many types of reflection coefficients that can be used in a vector network analyzer for transmission and reflection measurements.

Logarithmic sweeps

An analytical method used to measure the performance of a device or system. A logarithmic sweep is a broad range of frequencies swept over in some manner, usually linearly. The result is a display of how performance changes with frequency, and/or input signal amplitude (power level).

Low-dimensional structures

A description of an object or device that has a dimensionality less than three, which means it can be described as a surface (two dimensional) or as a line (one-dimensional). Examples include thin films and wires.

M

Magnetic field

The area in which a magnetic object influences other objects. Magnetic fields are created by current flowing through wires, microwave signals, and devices that generate microwaves.

Magnetic force microscopy

A microscopy technique that can be used to study the magnetization of an object, including its direction and strength. It is often used for studying magnetic structures, such as ferromagnets or antiferromagnets.

Magnitude

A scalar value that describes the strength of a signal, usually measured in either voltage or power. The magnitude of an electromagnetic field can be provided by its electric or magnetic components.

Maximum frequency

The highest possible frequency for which a scalar network analyzer can be used. This is one of the key specifications for scalar network analyzers, especially when measuring components such as inductors and capacitors that have high self-resonances.

Measurement accuracy

The degree of agreement between the results of a measured quantity and the true or accepted value. It is usually quantified by how much an error can vary from one test to another, which is called repeatability. Measurement accuracy often depends on many factors, including time, environmental conditions, type of component being measured, etc.

Measurement application

The use of network analyzers to determine the characteristics of a deviceor circuit and provide these measurements as a function of frequency. For example, rf and microwave vector network analyzers can be used for impedance, return loss, and transmission line analysis by making S-parameter measurements over a range of frequencies.

Measurement plane

A virtual plane in a vector network analyzer (VNA) on which measurements are performed. Measurements on each point of the measurement plane give rise to a two-port S-parameter, such as reflection and transmission.

Microwave frequency

The band of frequency that spans from 300 MHz to 300 GHz, which includes frequencies used for mobile phone transmissions. It is the range of frequency used by microwave network analyzers and rf network analyzers.

Mode multiplexer

An rf device used with vector network analyzers to select a single rf signal from among different rf signals or rf sources. A mode multiplexer enables the instrument to measure the rf characteristics of devices that have multiple ports, such as power dividers and directional couplers.

Mode transfer matrix inversion

A scalar network analyzer measurement technique that uses a specially developed model to calculate the impedance of a device. This method is called mode transfer matrix inversion because it involves inverting the mode transfer matrix (M), which relates the reflection coefficient (S11) values at two ports of a device to the impedance of those ports.

N

Noise floor

The minimum signal level that is detectable by an instrument. A network analyzer with low noise floor measurement capability can detect much weaker signals than one with high noise floor capabilities. This is because the measured value of a weak signal may be significantly affected by the presence of noise, which reduces its accuracy. Noise floor is often specified as a minimum detectable power.

O

Operating frequency

The range of frequency over which a network analyzer can be used to make power measurements. This is one of the key specifications when choosing a network analyzer for making power measurements, especially when measuring components such as inductors and capacitors that have high self-resonances.

Optical mode transfer matrix

A mathematical model that relates the s-parameters of a device at two ports to the impedance of the two ports. The optical mode transfer matrix is used to calculate impedance measurements by inverting it and then multiplying by the measured reflection coefficients (S21, S12).

Output signal

A fundamental rf signal that is sent from an rf source to a device under test or equipment under test. The output signal may be modulated for making measurements of the frequency, phase and level of modulation.

P

Passive components

A category of electrical components that does not contain active electronic circuitry, such as diodes and transformers. They include resistors, capacitors, inductors, attenuators, and directional couplers.

Phase noise

Low-frequency noise components that may be present in an RF signal. This is sometimes referred to as "phase jitter". The Rohde Schwarz glossary explains that phase noise is caused by a multitude of varying phenomena, such as voltage temperature drift, resistor thermal drift, and even the age of a resistor. These items contribute to the noise “floor”, or that overall "hiss" heard when tuning through a spectrum analyzer setting that lets you view an RF signal.

Phase shift

The time displacement of signals in a system. The phase shift between two signals can be used to describe the difference, or mismatch, between the signals themselves, and/or the effect that one signal has on another.

Phase synchronization

A technique to make phase measurements with one or more vector network analyzers using two separate ports of a device under test. The measurement can be based on either the absolute or relative phase difference between the rf signals applied to each port.

Phase variation

The change in phase of an rf signal, measured as a degree. Whether the network analyzer is connected to one or two ports of a device under test, or whether an absolute or relative measurement technique is used, phase variation must be considered when making impedance measurements.

Power sweeps

A common measurement technique for network analyzers. Sweeping the power applied to both or all ports of a device under test is typically performed at many frequencies over the operating frequency range of the instrument. The result is a curve showing how much voltage and current was delivered at each frequency.

Precision cables

Cables used to connect network analyzers with components under test, which means they must have low loss and maintain phase coherence. They are also required to have a very high common-mode rejection ratio for accurate measurements of differential mode components.

R

Raw port parameters

The individual S-parameters of each port that are measured with a vector network analyzer. They are then converted into total device S parameters using mode-coupling theory, which enables admittance measurements to be made at different frequencies.

Reduced-reflectometer calibration

A technique used to make impedance measurements with vector network analyzers. It is used to adapt one or more vector network analyzers into a reduced-reflectometer that can produce accurate impedance measurements without requiring an expensive calibration fixture.

Reference channel

A high-frequency path in a vector network analyzer that provides a stable calibration signal. The power of the reference channel path must be 50 dB more than the device under test in order to achieve an accurate impedance measurement. Since using two or more ports for measurements can increase their accuracy, the reference channel path can be combined with one or more calibration ports to accomplish this.

Reference multiline

A network analyzer feature that allows one to easily switch between four different signals in the time domain. Having multiple signals also helps characterize how the signals being measured are interfacing with each other, or what signals are present across a demodulated output.

Reflection coefficient

A value that describes how much of the power of an rf signal is reflected from a device under test. The reflection coefficient can be expressed in terms of either voltage or current and tells you the ratio between incident (forward) and reflected (backward) energy. It is sometimes referred to as SWR (standing wave ratio).

Reflection measurements

Measurements used to determine the impedance of a device under test. Accurate reflection measurements can be made with vector network analyzers using one of two techniques: absolute technique and relative technique. In both cases, reflections from two or more calibrated ports on a device under test are measured at different frequencies. Relative measurements account for phase and amplitude differences in the calibration ports to accurately provide impedance measurements.

Relaxation oscillation frequency

A value that describes the lowest frequency at which an oscillation will occur when measuring port parameters. Relaxation oscillations are caused by reflection measurement errors and can make accurate measurements difficult or impossible to obtain.

Residual port parameters

The difference between the total device S-parameters and raw port parameter measurements. They become smaller as the vector network analyzer's noise figure decreases, calibration accuracy

Return Loss

A measure of the power reflected from a device under test due to impedance mismatches. Return loss is expressed in decibels (dB) and represents how many dB are lost at each reflection interface. Typically, return loss is measured at individual frequencies in order to determine if the device under test might be damaged by high-power signals.

RF cables

Cables used to connect the rf ports of network analyzers. They are made with low-loss, high-impedance coaxial cables that minimize signal loss.

S

S-parameters

A value that describes how an rf signal responds to a device's ports, by specifying the magnitude and phase of the reflected signal. The name comes from S for "scattering." S-parameters can be represented in either tabular or graphic form and are valuable measurements because they provide insight into the overall performance and health of a device.

S-parameter measurements

Measurement used to determine rf input/output characteristics, device stability (harmonic distortion), and efficiency (return loss or noise figure). They can be made using either the absolute technique or relative technique.

Signal source

A device that generates electromagnetic energy at a specific wavelength. A signal source can be used to measure parameter data such as frequency and magnitude. Signal sources for use with vector network analyzers contain calibrated, well-defined properties such as noise figure, output power, output impedance, and frequency stability.

Simultaneous measurement

The act of simultaneously measuring the reflection coefficients (S-parameters) for all ports on a device. This measurement is performed using one or more calibrated rf sources that are time-shared between other vector network analyzers, test equipment or devices under test. These measurements can be made using either the absolute technique or relative technique.

Slow sensitivity fluctuations

As measurements are performed on a device under test, the noise figure of the vector network analyzer might not be constant. Instead, it can vary as a function of frequency and temperature. This malfunction is referred to as slow sensitivity fluctuation (SSF) and is often caused by defective components in the vector network analyzer's front-end. SSF can be caused by poor cabling, poor probe connections, dirty connectors, and even defective or missing calibration waveforms.

Smith chart

A type of chart, with each axis representing a different quantity, used to graphically calculate impedance by using S-parameter data. This is useful for characterizing impedance mismatches in components and circuits. Using the Smith chart can minimize round-off errors when performing complex mathematical operations on digital computers. The Smith chart allows graphical representation of impedance matching problems, component models for synthesis, filter design, and circuit analysis.

Source match

The manner in which the power supplied to each input port of a network analyzer is adjusted. Since both transmitter and receiver must use the same reference, source match calibration ensures that this requirement has been satisfied. A noise contribution other than that supplied by the source should be minimized without disturbing other essential conditions (such as probe matching). The source match is usually adjusted so that the total reflected power and noise level at all ports on the device under test are equal.

Standing wave ratio

The ratio of the voltage of a wave to that of another wave traveling in the same direction, measured at any point along the transmission line. This ratio is expressed as either an open-circuit or short-circuit value depending on whether it is measured with respect to current flow (an open-circuit standing wave) or potential (a short-circuit standing wave).

T

Test-set controller

A stand-alone, programmable controller used for testing and programming system components. The test-set controller is designed to support a variety of digital generators and oscilloscopes, including vector network analyzers.

Trace noise

The random fluctuation in measured amplitude and phase that occurs as a vector network analyzer is subjected to varying environmental conditions such as temperature, humidity, and power-line frequency. This may affect the accuracy of measurements done with the vector network analyzer.

Transmission coefficients

The product of the reflection coefficients for all ports on a device. This is one common parameter used to characterize complex-number impedance values. Transmission coefficients are usually expressed as either magnitude and phase angle or real, imaginary, and magnitude components.

Transmission measurements

The process of measuring transmission coefficients at all frequencies of a device under test. Transmission measurements are usually made by performing reflection coefficient measurements with a vector network analyzer. Reflection coefficients measure the magnitude and phase angle of the reflected signal. Transmission coefficients then provide greater detail about impedance matching, as they provide both magnitude and phase components, rather than the S-parameter values, which only provide magnitude.

TRL/LRM calibration

A method of calibrating the vector network analyzer by comparing an unknown device to one with known parameters at two separate frequencies. Ideally, this calibration determines both the linear and nonlinear (extrapolation) errors between the reference and unknown devices. The resulting data can be represented as either a table or by using extrapolated values with a look-up table.

V

Vector Network Analyzer

A signal-analysis instrument that provides S-parameter, Smith chart, and network representations of a device under test. A vector network analyzer can provide high levels of performance by allowing the user to measure both magnitude and phase components for complex impedance measurements. The resulting data can be displayed as either a list of frequency responses or as a Smith chart.

Vector Network Analyzer architecture

The system that results from the various components and operations that make up a vector network analyzer. The architecture of a vector network analyzer is what allows it to measure both magnitude and phase components, provide high levels of performance, and display its data in several forms (such as list format or Smith chart). It includes such components as sources, vector network analyzers, detectors, computer-aided test equipment interfaces, and displays.