I am trying get results from the hfss after design information an antenna and wanted to find if my impedance is matched or not.at 50om .so how can I do that....thanks in advance
goto results->solutiondata->click on Z0 for port impedence-> click on Z matrix for input impedence.
Please look on Z-parameter Z(1,1)) real and Imaginary. Real value must be near to 50 ohms and Imaginary to be 0 ohms. In fact, if matching is good then you will get good S11.
In HFSS, there is direct option for displaying Zin (R + jX) with frequency. If you want to exact data from smith chart, the took print out. from its center draw diff. radius. Measure the distance from the center the point xo (xo is the point where radial line and Zin curve intersect each other.) Measure the corresponding angle also. Then calculate R and X.
Go to results-> Modal solution data report -> rectangular plot -> Z-parameter -> Z11 (im, re). Real part is to around 50 and imaginary part should be around 0. Good impedance matching decrease the capacitance due to air gap microstrip line. hence the variation of imaginary part is decreased. It may also enhance the bandwidth but not all the time.
Be aware that HFSS DOES NOT display input impedance for wave-ports. It displays the feed-line(2D model, aka PORT) impedance, which is NOT influenced by the model solution. 2D ports are simulated separately in order to determine excitation fields.
But, you can ESTIMATE input impedance using Z, or S parameters, knowing port characteristic impedance, which is Zo(). See formulas for S/Z parameters conversion. For 2-port network it is Zin=Z11-Z12Z21/(Z22-ZL); ZL can be guessed as a port impedance at the out...but it is better if you determine it explicitly as a load. Either, it can be calculated as
Zin=Zo(1)*(S11*exp(2*Gamma(1)*l_feed)+1) / (1−S11*exp(2*Gamma(1)*l_feed))
If I did not miss anything, the result should be ALMOST the same (different amounts of calculation introduce different errors)
For 4-port network you stack four 2-port [matrices] (See Pozar, Fusco, etc.) , and solve them using the same formula for Z as above, then extract Zin from element [Zin](1,1), and (2,2). If it is 3-port network, you shunt the port 2 on port 1 writing INF in its diagonal, and Zero to 21 and 12 components. Again, [Zin](1,1) will be the estimate for input impedance.
Now, for antenna there is no second port, so input impedance is ALMOST Z(1,1), which you can plot on the chart. I don't know how fair it is, but we can say that the impedance of free space diminishes the second deductible of the formula for Zin.
You don't even need to know Zo(1). But the 3D-simulated section of the feeding line introduces its loss, and phase shift, so you should use DEEMBEDDING option in the port configuration dialog (HFSS knows its Zo and Gamma internally), which also accepts parametric data. But it is just a multiplication by 4-component matrix of transmission line. So do NOT make deembedding distance longer than the said UNIFORM feeding section.
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