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.