Читать книгу Handbook of Microwave Component Measurements - Joel P. Dunsmore - Страница 17

Throughout the discussion of measurements, a six‐step procedure will be followed that applies to most measurement problems. When approaching a measurement, these steps are as follows:

 Pretest: This important first step is often ignored, resulting in meaningless measurements and wasted time. During the pretest, measurements of the device‐under‐test (DUT) are performed to coarsely determine some of its attributes. During pretest, it is also determined if the DUT is plugged in, turned on, and operating as expected. Many times the gain, match, or power handling is discovered to be different than expected, and much time and effort can be saved by finding this out early.

 Optimize: Once the coarse attributes of the device have been determined, the measurement parameters and measurement system can be optimized to give the best results for that particular device. This might include adding an attenuator to the measurement receivers, adding booster amplifiers to the source, or just changing the number of points in a measurement to capture the true response of the DUT. Depending upon the device's particular characteristic response relative to the system errors, different choices for calibration methods or calibration standards might be required.

 Calibrate: Many users will skip to this step, only to find that something in the setup does not provide the needed conditions and they must go back to the first step, retest, and optimize before recalibration. Calibration is the process of characterizing the measurement system so that systematic errors can be removed from the measurement result. This is not the same as obtaining a calibration sticker for an instrument but really is the first step, the acquisition step of the error correction process that allows improved measurement results.

 Measure: Finally, some stimulus is applied to the DUT, and its response to the stimulus is measured. During the measurement, many aspects of the stimulus must be considered, as well as the order of testing and other testing conditions. These include not only the specific test conditions but also pre‐conditions such as previous power states to account for non‐linear responses of the DUT.

 Analyze: Once the raw data is taken, error correction factors (the application step of error correction) are applied to produce a corrected result. Further mathematical manipulations on the measurement result can be performed to create more useful figures of merit, and the data from one set of conditions can be correlated with other conditions to provide useful insight into the DUT.

 Save data: The final step is saving the results in a useful form. Sometimes this can be as simple as capturing a screen dump, but often it means saving results in such a way that they can be used in follow‐up simulations and analysis.