RF Test Equipment Series: Network Analyzers
Network Analyzers, and Vector Network Analyzers (VNAs), are one of the cornerstone RF test instruments, and virtually every test center or lab usually employs some type of VNA. These test instruments are able to send electromagnetic energy into a component, device, antenna, assembly, etc. and accurately measure the power transmitted and reflected through the device-under-test ports. This function enables the generation of incident, reflected, and transmitted waves from each port of a DUT. The result is the ability to measure and perform mathematical functions on these measurements is the key capability of VNAs.
With the RF network measurements and analysis important measurements, such as insertion loss, reflection, transmission, and multi-port S-parameter information can be taken. These measurements enable the characterization of a DUT network, and critical information about the behavior of a DUT. With VNA measurements, a device can be accurately modeled, and that information can be fed into system simulators, aiding greatly in the design and engineering of RF and microwave systems.
At its roots, a network analyzer is merely a generator and receiver, or several generator/receiver combinations depending on the port count of the instrument.
Moreover, network analyzers also employ circuitry that reduces noise, harmonics, phase error, and non-linearities and circuitry (often software now) that enables calibration and other measurement refinement techniques. Hence, the result are instruments with high dynamic range and broad bandwidth that are used in the testing of virtually all RF/Microwave devices and systems. Many NAs/VNAs are also able to measure the time delay, or phase shift, of incoming signals compared to outgoing signals, which enables time-domain reflectometry (TDR) functionality.
Network analyzers, which are single port devices, and VNAs, which have multiple ports, come in a very wide range of system configurations. Some are very large and sophisticated bench-top/rack-mount instruments complete with their own screens, CPUs, network infrastructure, storage, and other accessory capabilities. Others are highly compact and portable units powered and connected to a PC via USB, as PXI cards, and everything in-between. The diversity of configurations and designs of NAs/VNAs is indicative of their utility to designers, engineers, technicians, and even hobbyists.
In order to use an NA/VNA properly a calibration kit is needed to remove the test interconnect from the measurements, so that the measurement plane is brought to the DUT ports. It is also important to have a quality of coaxial, or waveguide, interconnect that matches the desired quality of the measurements to be taken. Hence, there are a wide range of coaxial interconnect and adapters that are designed with extreme precision and other capabilities to ensure that they are the least detrimental to NA/VNA testing as possible. As NAs/VNAs are also used to test wafers, RFICs, and MMICs, there are even probe kits and wafer-level calibration standards for network analyzes.
Useful VNA Accessories and Equipment