![]() The susceptance of point A is -j0.95 mho, so I add an open-circuit stub with susceptance +0.95 mho. I rotate point B* towards the load on a constant VSWR circle, which corresponds to adding a length of TL, until it intersects the circle with admittance = 1 at point A. I plot point B*, which is the complex conjugate of the S 22 parameter of the amplifier, and plot the 50 Ω load at the center. I think I could not go wrong on this one, but anyway. The last thing to to is match the 50 Ω load to the output of FET B. Next, add an open-circuit stub with susceptance equal to the opposite of point C. Point C has the same conductance as point A*. This corresponds to adding a length of TL. Rotate point B towards the generator A* on a constant VSWR circle to point C. My solution: Plot point A* = complex conjugate of the source impedance point B is the load impedance. The input of FET B has S 22 = 0.75∠-140° and needs to be matched to the input of FET A which has S 11 = 0.5∠-70°. Here is the Smith chart:įET A Output matching: The circuit shows the S values which need to be used. To go from point A to B, a QWT is used its impedance is equal to Z T=√(50*15.75) = 28 Ω. Impedance at point B is 0.315 * 50 = 15.75 Ω unnormalized. The VSWR circle intersects the horizontal line after a length of 0.112 λ at point B. Next, I have rotated the impedance corresponding to Γ opt towards a constant VSWR circle towards the load (which is plotted at the center). ![]() My solution: I have plotted Γ opt on a Smith chart and assume the center of the chart is where the load Z lies everything is normalized to 50 Ω. The input of the FET needs to be matched using a quarter-wave transformer (QWT) and a piece ot transmission line (TL). The schematic is here:įET A Input matching: The input needs to see impedance equal to Γ opt and is driven by a generator with 50 Ω impedance. So I would like to post my problem and solution here and let people who are more experienced take a look and tell me if I am on the right track. However, an inexpensive modern calculator can handle the complex algebra in less time and with much less effort than are needed to use the Smith chart. However, this has happened many times before and I have learned to double check everything. Although the results obtained using the Smith chart are only approximate, for engineering purposes they are close enough to the exact ones obtained by Method 1. I have made an attempt to solve the problems, and actually I think I got them right. I have a homework which involves impedance matching using Smith charts.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |