Vector Network Analyzers

Vector Network Analyzers are used to characterize electromagnetic devices. They are used to measure S Parameters of one port and two port devices. The Vector Network Analyzer measures both the amplitude and phase of each S Parameter.

A Vector Network Analyzer works by sending a voltage wave into the device under test and measuring the reflected and transmitted waves.

For example for a two port device the voltage wave is sent at port1 and its reflection is measured to compute S11 and its transmitted voltage is measured at port 2 to compute S21. Similarly a voltage wave is sent on port 2 and its reflection is measured to compute S22, and the voltage wave at Port 1 is measured to get S12.

Test fixtures and their calibration

For the characteristics of the device to be accurately measured by the VNA, the response of the device must be separated from the response of the fixture and the cables used to connect the device under test to the Vector Network Analyzer.

One can either

• calibrate the test fixture
• Buy pre calibrated test fixtures from a company like Agilent

Acquiring Vector Network Analyzers

Vector Network Analyzers are expensive devices. There was cheap kit available from Tuscon Amatuer Packet Radio (TAPR) good to 100 MHz but that has been discontinued. You can probably get an used Vector Analyzer cheaper. Ebay is good and one can pick up cheap deals there. One has to be careful - it really is a buyers beware kind of auction. One has to check that

• The VNA is in a working condition
• It comes with all probes and cables

If you only need a Vector Network Analyzer for a short time, a good option might be to lease a VNA from one of the test equipment leasing companies.

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