Phase Measurement and Analysis System

Phase measurement of microwave signals may seem off the subject from our main business, which is designing and building vacuum tubes. But there is a connection. Broadband traveling wave tubes have significant phase deviations between input and output signals as one sweeps the frequency band. This problem limits their performance for certain applications. For example, it limits spatial and temporal resolution for radars where the tube is the amplifier.

In our work on TWTs in the 1980's and 1990's, we saw a need for fast and accurate capture of phase, especially in pulse modulated tubes. The result was PMAS, or Phase Measurement and Analysis System. It consists of two parts. First, an acquisition section that rapidly acquires phase across the designated frequency band. Second, an analysis section which consists of a computer and proprietary software. It analyzes the phase data in various ways and plots it against frequency. The types of analysis that are most useful are, first, to normalize out calibration error. A special phase plot is stored in memory that contains the test system phase without the traveling wave tube in place. This plot is subtracted from test data to remove spurious phase ripple - that is, phase ripple caused by the test system itself. Another analysis feature is removal of slope and bowing in phase plots, i.e., linear and quadratic components, because these are correctable outside the TWT. Finally, third order and above phase ripple can be plotted in fourier space, and the number of degrees of phase quantified for each order.

Phase measurement system

If you have had a phase problem with an active component, you probably know that these kinds of problems are not trivial, even to accurately characterize. We recommend the versatility and simplicity of the Phase Measurement and Analysis system. Because it is a system dedicated to solving just one problem, it has features and capabilities you won't find on any network analyzer, and it is a lot less expensive.

Copyright 2005, ebeam, Inc.