Using A Programmable Microwave Tuner For Custom Amplifier And RFID Testing

Testing of microwave devices and assemblies has traditionally been performed under matched conditions, and most of the specifications were defined for a quite narrow VSWR range, since isolators were often used to embed the assemblies.

Today, specifications have to be verified for a much wider VSWR range, and test stations have to be retrofitted to allow ongoing testing under variable load (and sometimes also source) conditions.

Mechanical microwave slide screw tuners are well suited for such applications, since they offer comprehensive and solid performance over a wide VSWR tuning range and a wide frequency band. Mechanical tuners exhibit very low loss at the low VSWR setting, enabling the test station to perform under 50W conditions, as before incorporating the tuners. Tuner loss increases with increasing VSWR and has to be known (calibrated) in order to de-embed the test results to the device reference plane. Manual tuners allow coarse adjustment of the VSWR, but require permanent manual operator interaction, and the actual tuner loss is unknown.

Computer-controlled electro-mechanical microwave tuners have been available for nearly 20 years but generally require an external controller and application software to set the tuner and calculate VSWR and loss.

Focus Microwaves' iTuner is a traditional electro-mechanical slide screw tuner. However, it includes sophisticated control electronics that allow it to become a self-contained and fully calibrated test instrument that is well suited for integration into an existing or new test station. A micro-controller inside the tuner housing is used to administer ASCII format communication via an industry standard TCP/IP interface, to control up to six stepper motors and to perform mathematical operations in order to determine the stepper motor positions required for user specified values of VSWR and impedances at the device reference plane. In addition, microstepping motor control virtually eliminates tuner vibration.