here to go to our main page on phase shifters
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New for February 2006!
In April 1958 the IRE MTT published a paper by Bernard M. Schiffman
titled A New Class of Broadband Microwave 90 Degree Phase Shifters.
Schiffman's contribution to phase shifter science was that
the phase difference between a quarterwave coupled section, compared
to a 3/4 wave straight section, would provide a nearly flat 90 degree
phase differential. Schiffman went on to publish a second article
extending the analysis to multi-section coupled lines. We've added
Bernard Schiffman to the
Microwave Hall of Fame!
Although Schiffman's original
analysis was for a three-port network, we prefer to think of a Schiffman
phase shifter as a fourport network to which you can add switches
to achieve a "digital" phase shift, or cascade it with
a Wilkinson power divider to achieve a very broadband 90 degree
coupler (better than a branchline!)
Below is a picture of two paths
of the Schiffman 90 degree phase shifter:
Here's the phase
difference that is calculated by MeasEqn "Meas1". There
is only about ten degrees of error over xxx bandwidth.
Schiffman 90 degree
This is a great
application of the Schiffman technique. You can get performance
that exceeds the bandwidth of a branchline
quadrature hybrid, although you need a little more area.