cst calculate impedance
This question puzzled me for a long time and i post it here since i noticed another similar problem on impedance is discussed these days.
As we know the input impedance is an extremely important parameter to antenna design.But can we check this parameter directly in CST?
In 2D result, there are two items called "wave impedance" and "line impedance" respectively. I examined the help file which gives the definition to them.
The wave impedance is defined as the average ratio of the transversal electric field to the transversal magnetic field for all grid points. But i don't find any importance of this because i've not found any book on electromagnetic theory or microwave engineering which gives definition to the "wave impedance" in this way.
The line impedance is defined as the ratio of of the power to the squre of total current in the port. According to my understanding, for TEM or QTEM modes, it is the input impedance at the port since Z=P/(I*I)==>Z=U/I. I'm not sure whether it is correct.But when i examined the example of the "rectangular patch antenna" that CST itself provides, i noticed the "line impedance" is almost exactly equal to the characteristic impedance of the microstrip feedline, which means the impedance of the patch is not considered if the patch is treated as a terminal load of the transmission line!
what are your comments? Thank you!
In HFSS, I write an equation calculating the input impedance of an antenna using the port impedance and the S11 which has given me reliable results until now. Maybe you could do the same in CST..
Hope this helps and Happy New Year to all..
Ananth.
Hi ananth,
this is exactly the same procedure in CST. The Line and wave Impedace are purly port values. The get teh Z-Parameter (Impedace of the antenna) You can calcaulte them under Resut-> S-Parameter Calculation -> calculate z and Y Parameter..
F.
yes, The line impedance or the wave impedance are the charateristic impedance of the feeding waveguide that has the same cross-section as the device cross-section, not the imput impedance of the device, that's the tricky thing
say thanks to ananth, RFSimulator and arthury!
But could you tell me what is this "wave impedance" used for, as is calculated in the way that the help file describes?
Initially i suppose it is the wave impedance of the plane wave transmitting in that kind of medium. However, if we take the "Rectangular Patch"(CST example) for example, it should be squa(Mu/Epsilon)=255, as the relative permitivity used is 2.2, but the "wave.Imp"=277.536Ohms, as is shown in 2D/3D Results.
U can check the input impedance of antenna in CST with both Real and Image part.
From the menu
Results -->S parameter calculations --> calculate Z and Y matices
Then, in the result tree, u will see two new folders Y and Z. Z folder contents the input impedance with real and image part u need.
Thank you and i've seen the results of Z and Y matrix.
