PCB Design

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  3. In HFSS 3D, the default port impedance is 50 ohms. However, the user may want set the port impedance to a complex number like R-jX ohms to account for matching circuits. At times, if reactance is set in the port settings, it may trigger positive S parameters. In this document we explore how correctly set the port to a non 50-ohm termination and obtain the correct S parameters.

In HFSS 3D, the default port impedance is 50 ohms. However, the user may want set the port impedance to a complex number like R-jX ohms to account for matching circuits. At times, if reactance is set in the port settings, it may trigger positive S parameters. In this document we explore how correctly set the port to a non 50-ohm termination and obtain the correct S parameters.

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    • May 25, 2023 at 7:30 am
      SolutionSolution
      Participant

      To model R-jX ohms for port impedance, the recommended method to modeling complex port impedance is to 1.Divide the port into 3 rectangles; two rectangles for the capacitors and one for the port itself. We use two capacitors instead of one for a balanced feed as shown in the attached PDF. 2.The port and two capacitors are in series. 3.Calculate the capacitance C= 1/(2*pi*f*X) and where X is the imaginary part of the required port impedance. C1 = C2 = 2C 4.The port should be set to the real part of the required port impedance (R) and be normalized to 50 ohms (network analyzer).

      Attachments:
      1. How%20to%20Set-up%20a%20non%2050%20Ohm%20Port.pdf

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