What Are Network Analyzers?

Network analyzers are test and measurement instruments used to characterize the electrical behavior of radio frequency and microwave networks by measuring how signals propagate through or reflect from a device under test. The instruments apply a calibrated stimulus signal across a range of frequencies and capture the response in terms of transmission, reflection, and impedance, providing a quantitative description of the network's high-frequency properties. Network analyzers are fundamental tools in RF and microwave engineering, enabling characterization of passive components such as filters, couplers, and transmission lines, as well as active devices including amplifiers and transistors.

The conceptual basis for network analyzers lies in the theory of linear two-port networks and the scattering parameter (S-parameter) formalism developed in microwave engineering from the 1940s onward. By expressing input and output signal relationships as ratios of incident and reflected power waves, S-parameters provide a complete description of a device's behavior that is independent of the source and load impedances connected to it.

Vector Network Analyzers

A vector network analyzer (VNA) measures both the amplitude and phase of signals, allowing it to compute the full complex S-parameter matrix of a device under test. This capability distinguishes VNAs from simpler instruments: phase information is required to reconstruct time-domain responses through inverse Fourier transform, to extract equivalent-circuit models, and to perform the error-correction routines that remove the systematic effects of cables, connectors, and adapters from the measurement. Modern VNAs span frequency ranges from a few kilohertz to hundreds of gigahertz, with vector network analyzer calibration and check standards work at NIST defining the metrology practices that underpin traceable measurements at microwave frequencies. The instruments typically present results as Smith charts, polar plots, and Cartesian magnitude or phase displays.

Scalar Network Analyzers

A scalar network analyzer (SNA) measures only the amplitude of transmitted and reflected signals, without recording phase. While simpler and less expensive than a VNA, an SNA is sufficient for applications that require only gain, insertion loss, or return loss measurements and do not need the full complex response. Scalar analyzers were common in production-line testing of amplifiers and filters through the 1990s, though they have largely been supplanted by VNAs as the cost of vector hardware has fallen. The Keysight scalar network analyzer selection guide documents the typical frequency coverage, dynamic range, and accuracy specifications that define the instrument class.

S-Parameter Measurement and Calibration

Accurate S-parameter measurement requires a rigorous calibration procedure to establish a reference plane at the device ports and remove the errors introduced by the test fixture and cabling. The standard calibration methods, SOLT (short-open-load-thru), TRL (thru-reflect-line), and LRM (line-reflect-match), each use a set of well-characterized reference standards to solve for the systematic error terms of a 12-term error model. The accuracy of the final measurement depends directly on the accuracy of these standards. For on-wafer measurements, probing systems combine precision micropositioners with calibration substrates to bring the reference plane to the device pads, a technique surveyed in a novel vector network analyzer paper in IEEE Transactions on Microwave Theory and Techniques.

Applications

Network analyzers have applications in a wide range of disciplines, including:

• RF and microwave component design, including filters, couplers, and power dividers
• Antenna characterization for gain, bandwidth, and impedance matching
• Amplifier and transistor large-signal and small-signal testing
• Cable and connector quality assurance in production environments
• Electromagnetic compatibility pre-compliance testing
• On-wafer probing of integrated circuits at millimeter-wave frequencies