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Hello everyone,
I'm trying to understand how Ansoft Designer makes the link with HFSS when one uses the "push excitation" command.
My final goal is to plot with HFSS the electric field into an antenna which is loaded by a complex admittance (actually, a plasma). HFSS can't calculate this particular admittance (the medium in front of the antenna is a complex full tensor permittivity...), but I have a code which do it very well : this code gives me the scattering matrix of this load. Ansoft designer seems adapted to my problem, since I can easily import a scattering matrix and connect it to the ports of my antenna. Using the "push excitation" option in Designer, I should obtain the correct loading into HFSS, then the correct Efield.
Anyway, before going into complex things, I'd tried to model a simple case : a rectangular waveguide connected to a complex load. This problem can be solved by hand (see also attached for a presentation of the test case)
Let \[ \left[ S^{WG} \right] \] the scattering matrix of a regular section of a rectangular waveguide. I've modelled a simple rectangular waveguide in HFSS and solve for a frequency : as expected, the scattering matrix is close from the ideal case which is \[S^{WG}_{11}=S^{WG}_{22}=0\] and \[S_{12}^{WG}=S^{WG}_{21}=1\]
Let \[ S^{L} \] the scattering parameter of a complex load. For example, I took \[S_L=0.5+0.3i \].
Using the network theory, one founds that the reflected power \[a^{WG}_2\]wave from the load into the waveguide is :
\[a_{2}^{WG} = b^L = S^L a^L = S^L b_2^{WG}=S^L (S_{21}^{WG} a_1^{WG} + S_{22}^{WG} a_2^{WG}) \approx S^L a_1^{WG}\]
(see the attached .ppt for a sketch)
Thus, using the scattering parameters of the waveguide calculated by HFSS, I find :
\[a_2^{WG} \approx ~ (0.5+0.3i)*(0.9678-0.25103i) = 0.5593 + 0.1649i = (0.583, 16.42°) \]
According to the HFSS documentation, the "scaling factor" should be :\[SF=1/2 \left|a_2^{WG}\right|^2\]
which should give :
However, using Designer and pushing excitation in HFSS, I find a scaling factor of SF=0.2596 ! (And a non-zero phase, which I do know how Designer/HFSS calculate it...)
Is someone here know what's wrong with this simple test case ?
I've attached the Designer and HFSS file in case.
Many thanks in advance,
Best regards
I'm trying to understand how Ansoft Designer makes the link with HFSS when one uses the "push excitation" command.
My final goal is to plot with HFSS the electric field into an antenna which is loaded by a complex admittance (actually, a plasma). HFSS can't calculate this particular admittance (the medium in front of the antenna is a complex full tensor permittivity...), but I have a code which do it very well : this code gives me the scattering matrix of this load. Ansoft designer seems adapted to my problem, since I can easily import a scattering matrix and connect it to the ports of my antenna. Using the "push excitation" option in Designer, I should obtain the correct loading into HFSS, then the correct Efield.
Anyway, before going into complex things, I'd tried to model a simple case : a rectangular waveguide connected to a complex load. This problem can be solved by hand (see also attached for a presentation of the test case)
Let \[ \left[ S^{WG} \right] \] the scattering matrix of a regular section of a rectangular waveguide. I've modelled a simple rectangular waveguide in HFSS and solve for a frequency : as expected, the scattering matrix is close from the ideal case which is \[S^{WG}_{11}=S^{WG}_{22}=0\] and \[S_{12}^{WG}=S^{WG}_{21}=1\]
Let \[ S^{L} \] the scattering parameter of a complex load. For example, I took \[S_L=0.5+0.3i \].
Using the network theory, one founds that the reflected power \[a^{WG}_2\]wave from the load into the waveguide is :
\[a_{2}^{WG} = b^L = S^L a^L = S^L b_2^{WG}=S^L (S_{21}^{WG} a_1^{WG} + S_{22}^{WG} a_2^{WG}) \approx S^L a_1^{WG}\]
(see the attached .ppt for a sketch)
Thus, using the scattering parameters of the waveguide calculated by HFSS, I find :
\[a_2^{WG} \approx ~ (0.5+0.3i)*(0.9678-0.25103i) = 0.5593 + 0.1649i = (0.583, 16.42°) \]
According to the HFSS documentation, the "scaling factor" should be :\[SF=1/2 \left|a_2^{WG}\right|^2\]
which should give :
Code:
1/2*abs((0.5+0.3i)*(0.9678-0.25103i))^2=0.1699
Is someone here know what's wrong with this simple test case ?
I've attached the Designer and HFSS file in case.
Many thanks in advance,
Best regards