Agilent Techniques for Time Domain Measurements - Application Note 5991-0420EN c20140723 [15] free download

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Keysight Technologies Techniques for Time Domain Measurements Using FieldFox Handheld Analyzers Application Note Abstract This application note will introduce time domain and distance-to-fault (DTF) measurement techniques for identifying the location and relative amplitudes of discontinuities while operating in the field. This application note will describe the relationship between frequency domain measurements and time domain transforms and their relationships to time resolution and range. Also shown will be VNA configurations for characterizing band-limited devices such as couplers, filters, antennas and waveguide components, and broadband devices such as cables and connectors. This note will also discuss time domain "gating," a powerful feature that effectively isolates discontinuities in the time domain just as a filter would isolate signal energy in the frequency domain. Measurement examples will be provided using the Keysight Technologies, Inc. FieldFox vector network analyzer. Introduction Testing and qualifying components and systems that function as part of a communications or radar system often requires that the electrical performance of these devices achieve a certain level of specified performance across the operating frequency range. Specifications include Voltage Standing Wave Ratio (VSWR), return loss and insertion loss to name a few. These specifications provide a clear distinction when the device under test (DUT) has passed or failed its performance requirements as a function of frequency. Figure 1a shows the measured VSWR of a system where the VSWR has exceeded the specification at several places across the measured frequency range of 8.5 to 12 GHz. The Keysight FieldFox vector network analyzer (VNA) used in this example was configured with limit lines to help the operator quickly identify whether the DUT has passed or failed the test. While a frequency measurement provides useful information into the proper functioning of a system, having only swept frequency may not provide enough information to determine the root cause of the problem. When a system fails to meet specification, troubleshooting is often difficult as components would then need to be swapped in and out of the system until performance once again meets the specified requirements. Fortunately, there is another measurement technique that provides details into the location and magnitude of any such problems. This technique relies on measurements in the time domain and a vector network analyzer, such as the Keysight FieldFox, has the capability of displaying