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rgcox
Joined: 31 Jul 2008
Posts: 2
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 31 Jul 2008 14:54 How to simulate a ferrite bead in HFSS? |
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Has anyone successfully simulated an antenna design that incorporates ferrite EMI suppression beads? I am trying to use a bead (or beads) as a broadband choke on a coaxial transmission line in an HFSS 11.1 model. I want to prevent the current flow on the outside of the coax sheild near a broadband dipole element. This is to control the radiation properties and impedance. I can't use quarter-wavelength chokes because the antenna is broadband.
My main problem is what values to use for relative permittivity, magnetic saturation, Lande G factor and delta H. I think that I have figured out the relative permeability, bulk conductivity and magnetic loss tangent. Amidon type 64 ferrite is what I plan to use. Amidon has not been helpful.
Thanks for any help.
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FvM
Joined: 22 Jan 2008
Posts: 2694
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Location: Bochum, Germany
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| 31 Jul 2008 18:42 How to simulate a ferrite bead in HFSS? |
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Most manufacturers, e.g. Ferroxcube or Epcos give sufficient data for this application, I think. Are you modelling the chokes as lumped elements or are you intending an EM simulation of antenna + feed structure including the exact ferrite bead geometry?
In a real antenna measurement, I could effectively isolate the feeding cable by ferrite tubes. http://www.edaboard.com/viewtopic.php?t=318914
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rgcox
Joined: 31 Jul 2008
Posts: 2
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| 31 Jul 2008 18:57 Re: How to simulate a ferrite bead in HFSS? |
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Thanks! I still have not received much information from Amidon. I also tried Fair-Rite, but no reply yet. These are my primary sources for ferrites, however I can try others.
I am using HFSS to simulate the full antenna 3D geometry, including semi-rigid feedline and ferrite bead. I have had better luck today, as I reduced the size of the ferrite bead (hollow cylinder).
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FvM
Joined: 22 Jan 2008
Posts: 2694
Helped: 439
Location: Bochum, Germany
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| 31 Jul 2008 19:24 How to simulate a ferrite bead in HFSS? |
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To my opinion, the data of NiZn or MnZn ferrites used for EMI suppression are very similar among manufacturers, so you can basically use material data from any manufacturer.
I think, that a one or two inch ferrite tube can already be regarded as an effective ground breaker with an impedance of 1000 ohm order of magnitude in UHF band. It may be interesting to learn from your simulation what's the influence of the remaining first inch stub.
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Griogair
Joined: 07 Nov 2006
Posts: 3
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| 25 Aug 2008 14:50 Re: How to simulate a ferrite bead in HFSS? |
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Hi,
I looked into using a ferrite clamp (Fair-Rite 61 material snap-it kit) to suppress leakage current being excited by a UWB dipole. To be honest it didn't really have much effect. Though I do have some data I obtained of Fair rite, which I have attached, and gives material properties up to 3 GHz.
I think using a ferrite bead or clamp is just hiding away from actually desiging the antenna properly. You are much better of designing a wideband balun such as a microstrip to parallel plate (Duncan and Minerva, "100:1 Bandwidth Balun Transformer" Proc of IRE 1960). Proper balun design will remove leakage current and as a result reduce losses and any degradation of the radiation pattern.
I am presuming you are working at the 3.1 - 10.16 GHz band?
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Azulykit
Joined: 18 Feb 2007
Posts: 795
Helped: 100
Location: All over the Map.
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| 25 Aug 2008 17:15 Re: How to simulate a ferrite bead in HFSS? |
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I was amused to see comments about the effectiveness of ferrite in the supression of currents on a cable.
I have likewise generally found them ineffective in this frequency band although many engineers swear that they are magnificent. I think that it is all in the frequency band.
Your comment about not being able to use chokes caught my attention. Do some experimentation and consider a set of chokes tuned to various frequencies. You may have a degree of success that is better than you think. Try wide chokes to get more bandwidth.
Another road to explore is RAM. Cumming (among others) has a line of absorbing materials and you may find something that may work in your situation to quiet the feed line.
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