SMITH CHART AND APPLICATIONS
Smith chart is a polar plot of the reflection coefficient in terms of normalised impedance, r + jx. In other words, it is a graphical plot of normalised resistance and reactance in the reflection coefficient plane.
Smith Chart Tool : LINK
Construction of Smith Chart
It is constructed within a circle of unit radius
It can be used to:
1. find the parameters of mismatched transmission lines
2. find normalised admittance from normalised impedance or vice-versa
3. find VSWR for a given load impedance
4. design stubs for impedance matchings
5. find the reflection coefficient.
6. locate a voltage maximum on the line
7. find the input impedance of a transmission line.
STUBS :
A stub is a piece of transmission line. It can be short circuited at the far end or open circuited. It has a pure reactance or susceptance. It is used to cancel out reactance or susceptance of a transmission line. In other words, it is used for impedance matching.
In general, shorted stubs are more frequently used since open ended stubs tend to radiate. The design parameters of stubs are (1) stub length and (2) stub distance from the load. The matching of transmission lines is done by the design of a single stub or a double stub.
Design of Single Stub Matching :
DOUBLE STUBS:
or the design of any device, it is convenient to have more parameters in designer ’s control for more freedom. For this purpose, to match the load with the transmission line, a second stub of adjustable position is included. A typical double stub is
shown in Figure.
Problems on Smith Chart:
