# Ansoft Design Users Unite: Q on Modeling a Magnetic Dipole - RF Cafe Forums

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Ebit
 Post subject: Ansoft Design Users Unite: Q on Modeling a Magnetic Dipole Posted: Fri Aug 05, 2005 10:41 pm
 Lieutenant

Joined: Fri Aug 05, 2005 8:25 pm
Posts: 2
Location: Santa Barbara
Hello,

I have just begun interfacing with Ansoft's Designer (SV). I am trying to model a magnetic dipole in free space, operating at 10GHz and extract the radiation resistance.
This is well known theory:
Rrad=197*((a*omega)/c)^4 [Ohms]
where: a=the radius of the loop
omega = 2*pi*f
c=the speed of light
For a<<lambda

Here is what I have thus far:

Two layers of air dielectric both of thickness = lambda/2 =15mm
A lossless conductor for my signal layer. The signal layer is sandwiched between the two dielectrics.

Defined "Drawing extent" (Layout>>Settings) such that each edge (Left, right, top, bottom) are 2*lambda from the center where the dipole is located. I have done this too provide adequate space for the far-field approximation to be accurate, but I would like to know if this is necessary. Any thoughts?

The geometry:
I have constructed a square loop (at this level of approximation (a<<lambda) it shouldn’t matter if the geometry is square or circular) by making a square cell 60x60 microns^2. I copied and pasted this cell four times then assembled to form a square horseshoe. I closed the loop with two rectangles 60x90microns^2. This leaves a void of 60x60 microns^2 in the middle.

I would like to have one port located between the two rectangles (centrally located rather than on a corner) to provide a voltage potential and setup circulating currents. Is there a better design choice? Any suggestions?

Results (so far):
I tried the single edge port (which then defaulted to a gap source) and Ansoft gave me the following error:
“Edge port is not represented in the mesh: port 1”

Then I tried separating the loop just slightly and defined two ports one on each edge (now facing each other) so the geometry looks like square “C”. No errors. However, the currents are virtually non-existent.

I would appreciate any suggestions:

Meshing: Fixed (with or with out edge mesh) vs. Adaptive
Port placement ideas
etc…

Posted  11/12/2012

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