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    Smith Chart: Double Stub Tuner  


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Amy Wendt

Published in 1939, long before electrical engineers had ready access to computers for rapid computations, a graphical tool created by Philip H. Smith and his Bell Labs colleagues aided engineers in the design of radio and microwave systems. The Smith Chart makes use of two overlaid coordinate systems to represent a transformation between reflection coefficient and impedance or admittance, and to compute other quantities on the horizontal axes below. This sequence of four Smith charts depicts the design of a "double stub tuner" in which transmitted power is maximized by tuning the lengths of two side branches on the transmission line feeding an antenna, to eliminate reflections. The Smith charts here are printed on fabric, and the red calculation is stitched by machine embroidery.


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