On the feasibility of using an active tuner for measuring microwave noise parameters

The advantages of using an active tuner to vary the source impedance in a m icrowave noise parameter measurement system are investigated. The additiona l noise figure measurement error introduced by the use of an active tuner ( rather than a conventional passive tuner) is analyzed and shown to be negli gible, compared to those errors common to both types of tuner, provided tha t the tuner excess noise output is kept within certain limits. A modificati on to the standard one-port active tuner design is described which signific antly reduces the amount of excess noise produced by such a tuner, and a pr ototype of this design has been built and tested. Measurements performed ov er a limited range of impedances indicate that the tuner is capable of synt hesizing any impedance on the Smith Chart while keeping well within the acc eptable noise levels. The use of this active tuner would facilitate a wider constellation of source impedances to be used in microwave noise parameter measurement systems than has been previously possible with a passive tuner , thus increasing noise parameter measurement accuracy.