Thus an imaginary signal that you send through a transmission line of one quarter wavelength must travel fully half a wavelength, since it travels down the quarter-wave line, gets reflected, then returns down the quarter-wave line. Here's a frequently asked question: if a quarter-wave is 90 degrees in phase length, why does it transform you 180 degrees on a Smith chart? Consider that here we are plotting reflection coefficients on the Smith chart.
It's Opposite Day, Sponge Bob! That's the magic of a quarter-wavelength But there's much more that you can do, as you will see on this page. Adding one quarter-wavelength moves you 180 degrees to the right side of the chart, to an open circuit. Suppose your network was a short circuit, the left "corner" of the Smith Chart. By the time you have added a quarter-wavelength, you have gone 180 degrees about the center of the Smith chart. Further, the rotation occurs at a fixed radius (and VSWR or return loss magnitude) if the transmission line has the same characteristic impedance as the source impedance Z 0. But if the reflection coefficient of your network (S11 for example) is at some non-ideal impedance, adding transmission line between the network and the reference plane rotates the observed reflection coefficient clockwise about the center of the Smith chart. Referring to a Smith chart, if you are already at a matched impedance condition, any length of transmission line at the system characteristic impedance Z 0 does nothing to your input match. Quarter-wave coupled lines (coming soon) What's so special about a quarter-wavelength? How to use constructive interference when designing with PIN diodes
Maximally flat transformers (new for November 2008!)Ĭonstructive interference of two equal VSWRs (featuring more wisdom from Wally!) Quarter-wave transformers (separate page) What's so special about a quarter-wavelength? Here is a clickable index to our material on quarterwave transformers:
How do you turn a short circuit into an open circuit, or a capacitor into an inductor? Here we will describe some of the magic that happens when you use the distributed properties of transmission lines, in particular when you use lines of length one-quarter wavelength, or multiples of a quarter-wavelength. Click here to go to our page on basic concepts of microwavesĬlick here to learn about a rule of thumb for measuring the length of cablesĬlick here to go to our page on the Smith ChartĬlick here to go to our page on Schiffman phase shiftersĬlick here to go to our page on Lange couplers
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