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Schiffman 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!)

Schiffman basics

Below is a picture of two paths of the Schiffman 90 degree phase shifter:

Schiffman Phase Shifters

Here's the phase difference that is calculated by MeasEqn "Meas1". There is only about ten degrees of error over xxx bandwidth.

 

Schiffman Phase Shifters

Schiffman 90 degree power divider

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.

Schiffman Phase Shifters

Schiffman Phase Shifters

 

 

Author : Unknown Editor

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