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Characteristic impedance and input impedance

Question asked by SCHAEFFNER.HARALD.DA on May 24, 2007
Latest reply on Jul 31, 2007 by ALEPEREZ

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Hello to all!

Is this right: the momentum simulation of a one Dipole antenna returns reflection coefficient s11 and characteristic impedance of the antenna Z0 (modeled as transmission line).
The input impedance of the antenna is:
Zant = Zport* (1+S11)/(1-S11).

Thanks for post.
Harald :-/

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ALEPEREZ May 27, 2007 10:13 PM
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The Momentum dataset contains three S-arrays: S (normalized to the Port impedance a user can set in the Port Editor), S_50 (always 50 Ohms) and S_Z0 (computed if a Single or Differential sheet metal port is used such that a characteristic impedance can be computed). Your equation is thus correct. However, especially for dipoles, you will find that the antenna impedance is very much a function of the finite size of the dipole. Don't expect to get the ideal dipole 73 Ohms. Real dipoles with finite wire diameters are more like 68 Ohms at resonance.
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SCHAEFFNER.HARALD.DA Jun 7, 2007 9:41 PM
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I have simulated different port impedances (50 Ohm, 100 Ohm, 25 Ohm, (50 -j50)Ohm, (50+j50)Ohm) for the same dipole. I thought S11 will change that way, that Zant will be constant after multiplication of Zport*(1+S11)/(1-S11) - but the input impedance changes too?
Is there something else to mind to?
Thanks for support.
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ALEPEREZ Jun 21, 2007 3:30 AM
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All results should be self-consistent. I think your question is better handled by sending in a file with some sample simulation results to tech support at Agilent EEsof. Thanks.
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ABDUL_MATEEN Jul 31, 2007 7:33 PM
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Hello

I have a question about Gerber file format and I would appreciate you help.

I want to import a layout with the .GBR extension to Circuitcam software to fabricate a lange Coupler
However,the layout is not properly exported the spacing between the finger of lange coupler vanishes.My Question is

How can I import a .GBR file to Circuit CAM?
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ALEPEREZ Jul 31, 2007 8:25 PM
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The Gerber question does not belong in this thread, but to answer your question, when you loose features of a layout in Gerber, it is most likely due to the export format (MDA, RS274X, etc) and choice of apertures and/or precision. For details, please check with Tech Support as they need to look at your layout precision and Gerber translator settings.
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Characteristic impedance and input impedance

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