While measuring passive matched noise standards can be useful for verifying a test system setup, as well as the noise extraction algorithm, it might not always represent the reflection characteristics of practical active devices such as field effect transistors (FETs). In the case of a FET, the input and output terminals exhibit capacitive behavior and often represent a nearly open circuit at frequencies to tens of gigahertz. To mimic this behavior, a two-port, passive non-matched bandpass filter was built and used as a non-matched standard for noise measurements.
Figure 5 shows the S-parameter response of such standard and a photograph of the prototype network. Measured results of passive, non-matched standards further confirm the repeatability and extraction accuracy of the Focus Microwaves measurement system under extreme mismatched conditions—a very important figure of merit for evaluating a noise-parameter measurement system.
Mismatched attenuators are generally difficult to measure because there is no DUT gain, and the noise power reaching the receiver is reduced due to the impedance mismatch. The dynamic range of the measurement system must be wide so that the noise level being measured remains above the detection limit of the receiver. Extraction algorithms in this case must be more robust compared to what was required under matched conditions, pushing the limits of the measurement system accuracy to the extreme levels. If the extracted noise parameters based on measured data correspond to the noise parameters calculated out of the S-parameter for the DUT (the mismatched attenuator), the system is considered accurate.
For those working with noise measurement systems from Focus Microwaves, the matched and non-matched passive noise standards developed at the company serve to verify the repeatability and accuracy of those test systems. By using these passive standards, those using the test systems can gain confidence in the accuracy of their measurements on active devices.
Hoang V. Nguyen, Manager, RF Engineering
Neven Misljenovic, Supervisor, Installations and Training
Bryan Hosein, Manager, Software Engineering
Christos Tsironis, President
Focus Microwaves, Inc., 1603 St. Regis, Dollard-des-Ormeaux, Quebec, Canada H9B 3H7; (514) 684-4554, FAX: (514) 684-8581.
1. Hoang V. Nguyen, Neven Misljenovic, Bryan Hosein, and Christos Tsironis, “Noise System Verification using Noise Passive Standards,” 18th Journees Nationales Microondes, Paris, France, May 14-17, 2013.
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5. Hoang V. Nguyen, Neven Misljenovic, and Bryan Hosein, “Efficient noise extraction algorithm and wideband noise measurement system from 0.3 GHz to 67 GHz,” Automatic RF Techniques Group (ARFTG), 81st Microwave Measurement Conference, Seattle, WA, June 2013.
6. Anonymous, “Noise measurements using the computer controlled microwave tuner system,” Application Note 1-90, Focus Microwaves, Inc.