Advanced Design System 2011.01 - Smith Chart Utility 4 as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR. I have tried winsmith and automatch smith chart v3.0,they all easily to use.I think if you have a good basic on smithchart theory you also can realized your own smithchart application software in some math software like mathlab.
![]() Smith Chart
'Going Around in Circles to Get to the Point'
Iulian Rosu, YO3DAC / VA3IUL, http://www.qsl.net/va3iul Named after its inventor, Phillip H. Smith(Bell Laboratories), the Smith Chart was originally described in Electronics for January 1939. (Interview with Philip H. Smith)
Rs + jXs = RL - jXL
For better understanding let's give an example. Suppose we have an impedance consisting of 50 ohms resistance and 100 ohms inductive reactance (Z = 50 +j100). If we assign a value of 100 ohm to prime center, we normalize the above impedance by dividing each component of the impedance by 100 (Normalization must be used, in order to facilitate the plotting of larger impedances. Each impedance to be plotted is divided by a convenient number that will place the new normalized impedance near the center of the chart where increased accuracy in plotting is obtained). The normalized impedance is then 50/100 + j(100/100) =
0.5 + j1.0. This impedance is plotted on the Smith Chart at the intersection of 0.5 resistance circle and the +1.0 reactance circle. Instead of assigning 100 ohms to prime center, we assign a value of 50 ohms. With this assignment, the 50 + j100 ohm is plotted at the intersection of the 50/50 = 1.0 resistance circle, and the 100/50 = 2.0 positive the same impedance value, 50 + j100 ohms. This example shows that the same impedance may be plotted at different points on the chart, depending upon the value assigned to prime center. But two plotted points cannot represent the same impedance in the same time. Prime center is a point of special significance. It is customary when solving problems to assign the Zo value of the line to this point on the chart, 50 ohms for a 50 ohms line, for example. The center point of the chart now represents 50 + j0 ohms, a pure resistance equal to the characteristic impedance of the line, that it represents a perfect match, with no reflected power and with a 1.0 to 1 SWR. When plotting impedances two cases can be. These are short circuits and open circuits. A true short circuit has zero resistance and zero reactance, or 0 + j0. This impedance is plotted at the left of the chart, at the intersection of the resistance and reactance axes. An open circuit has infinite resistance, and therefore is plotted at the right of the chart, at the intersection of resistance and reactance axes. In other words the zero ohms circles (r = 0) is the largest one and the infinite resistor circle is reduced to one point at (1,0). There should be no negative resistance. If one (or more) should occur, we will be faced with possibility of oscillatory conditions. Gamma = Vref / Vinc Thus , to locate the impedance Z = 1 +j1, you would find R = 1 constant resistance circle and follow until it crossed the X = 1 constant reactance circle. The junction of these two circles would then represent the needed impedance value)
The Smith Chart has the following futures:
References:
1. RF Circuit Design - C. Bowick ![]()
2. RF and Microwave Wireless Systems - K. Chang
3. Microwave Communications Engineering - Glover, Pennock, Shepherd
4. RF Design Magazine, 1988-2000
5. Microwave Journal, 1998-2000 6. Applied Microwave Magazine, 1995-2000 7. ARRL Handbook, 1990-2000
8. Ham Radio Magazine, 1970 - 1980
![]() Comments are closed.
|
AuthorWrite something about yourself. No need to be fancy, just an overview. Archives
March 2023
Categories |