Agilent Measurement Journal - Issue 4 - 2008 - (Page 44)

A connection between the network analyzer and the DUT may include cables, adapters, circuit traces and ﬁxtures. The variances in the characteristic impedance of each component can be caused by poor quality components and cables, dirty or damaged connectors and improper torque, to mention a few. These have a cumulative effect that will produce a signiﬁcant level of measurement uncertainty. These examples demonstrate the importance of using good measurement practices, including proper connector care, torque, cleaning, and minimizing adapters, as well as using quality cables and components during calibration and device measurements. Minimizing noise during calibration In addition to using good measurement practices during calibration, the impact of the environment and noise should be minimized. Doing so will improve the repeatability, accuracy and stability of the measurement results. When radiated or conducted electrical noise is present, ﬁltering and shielding should be employed to reduce the noise. Certain instrument settings can further reduce the effect of noise on the measurement: • Set the stimulus power of the network analyzer as high as practical to maximize the signal-to-noise ratio of the DUT. Balance this with the input requirements of the DUT and other measurement considerations. • Reduce the IF bandwidth. The tradeoff is slower sweep speed. If required, use averaging to further improve signalto-noise ratio by reducing the effect of random white noise. Averaging can be turned off after calibration but the measurement noise will increase. • To reduce the risk of procedural errors, a test run of the instrument settings and DUT connections is strongly recommended prior to performing a calibration. Proper calibration practices will ensure minimal errors. Outlining best measurement practices When using network analyzers, optimize measurement accuracy and repeatability by following the steps listed below. It is important to test run the setup before calibrating. Ensuring proper connection to the DUT and instrument settings will improve accuracy. Any changes made to the measurement or setup after calibration can decrease measurement accuracy. 1. 2. 3. 4. 5. 6. 7. 8. 9. Warm up the network analyzer Clean, inspect and gauge all connectors and cables Connect cables and adapters to the analyzer Preset the analyzer to a known condition Set up stimulus frequencies, number of points and power Set velocity factor, IF bandwidth and averaging (if required) Connect the DUT to verify setup, cables, adapters and operation Select S-parameter(s) to be measured If using special functions, select the proper setup as required 10. Select the display format 11. Scale the display 12. Remove the DUT 13. Select the proper calibration kit or calibration standards deﬁnitions 14. Calibrate 15. Conﬁrm the quality of the calibration 16. Reconnect the DUT 17. Save the instrument state 18. If required, turn off averaging, select time domain, port extensions or other modes The most important steps happen before calibration. For example, it is essential to ensure proper instrument settings, DUT connections and measurement setup prior to performing a calibration. Equally important is understanding the correct usage of the calibration kit and standards for a given application. Some network analyzers will turn off correction if parameters are changed after calibration. All network analyzers will have reduced measurement accuracy if the calibration is performed improperly. 44 Agilent Measurement Journal

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 4 - 2008

Agilent Measurement Journal - Issue 4 - 2008 Delivering Confidence through Compliance with Standards Contents Emerging Innovations Trying Early Device Implementations at the IEEE 1588 PlugFest Achieving Greater Confidence in Measurement Accuracy through Consistency in Calibration Services Overcoming the Challenges of RFID Component Testing 3GPP LTE: Introducing Single- Carrier FDMA Ensuring Reliable Operation and Performance in Converged IP Networks Testing Storage Area Networks and Devices at 8.5-Gb/s Fibre Channel Rates Choosing an Appropriate Calibration Method for Vector Network Analysis Making Traceable EVM Measurements with Digital Oscilloscopes Exploring Terahertz Measurement, Imaging and Spectroscopy: The Electromagnetic Spectrum’s Final Frontier Interpreting Quoted Specifications when Selecting Digitizers

Agilent Measurement Journal - Issue 4 - 2008

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