**From:** Chris Rokusek (*crokusek@innoveda.com*)

**Date:** Tue May 29 2001 - 18:12:56 PDT

**Next message:**Ashok Prabhu Masilamani: "[SI-LIST] : It is not a virus"**Previous message:**BIBICHA: "Re: [SI-LIST] : Please read this, it is a virus"**In reply to:**Doug McKean: "Re: [SI-LIST] : Antenna Problem on the Board"**Next in thread:**Doug McKean: "Re: [SI-LIST] : Antenna Problem on the Board"**Reply:**Doug McKean: "Re: [SI-LIST] : Antenna Problem on the Board"

Doug,

The formula I used for E(f) can be found in both Clayton Paul and Henry

Ott's text. If is essentially the superposition of two electric (Hertzian)

dipoles carrying purely differential currents. Paul provides a derivation

while Ott references Weeks 1964, p.565, Eq 91. They would probably shoot me

if I did not mention that their are limitations to these models to which I

will refer you to their texts. Most notable are far field and constant

current segment. Beyond these (>200 MHz on a typical PCB) it is an

approximation for non-elemental structures (integration could be used).

The terms that account for field pattern were replaced with worst case

(sin(x) = 1) to simplify the expression.

I can't comment as to the applicability of the folded dipole structure

(non-elemental) but just wanted to provide some rebuttal for the concern

over use of the "Max-Electric-Magnitude-in-far-field" formula.

Chris Rokusek

Innoveda

*> -----Original Message-----
*

*> From: owner-si-list@silab.eng.sun.com
*

*> [mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Doug McKean
*

*> Sent: Tuesday, May 29, 2001 1:58 PM
*

*> To: si-list@silab.eng.sun.com
*

*> Subject: Re: [SI-LIST] : Antenna Problem on the Board
*

*>
*

*>
*

*> Chris,
*

*>
*

*> This E(f) relation being used looks like the magnetic
*

*> dipole equation. My question is in terms of radiation,
*

*> why is the magnetic dipole equation being used and
*

*> any more valid than the electric dipole equation?
*

*>
*

*> Now, I understand the loop circuitry of a trace over a
*

*> ground plane, but traces can also act very much like
*

*> dipoles. Especially folded dipoles in some cases.
*

*>
*

*> Where you have
*

*>
*

*> H(f) = k(H) * [ I * f^2 * A / d ] (Amps/meter)
*

*>
*

*> where
*

*>
*

*> k(H) = 1.316*10^-14
*

*> I = amps
*

*> f = frequency in Hertz
*

*> A = area in meters squared
*

*> d = distance from antenna in meters.
*

*>
*

*> You also have for the electric field
*

*>
*

*> E(f) = k(E) * [ I*f*l/d ] (Volts/meter)
*

*>
*

*> k(H) = 6.3*10^-6
*

*> I = amps
*

*> f = frequency in Hertz
*

*> A = area in sq. meters
*

*> d = distance from antenna in meters.
*

*>
*

*> Two points:
*

*>
*

*> One - I've seen this loop equation used quite a lot and
*

*> I have to disagree with it. There has to be some sine
*

*> or cosine factor in there as well as to compensate for
*

*> position from the loop.
*

*>
*

*> Second, even if the magnetic relation is accepted, the
*

*> constant factors alone show that there are orders of
*

*> magnitude differences in amplitude between the two.
*

*>
*

*> My bottom line here is that where people seem to
*

*> assume a loop, I see quite clearly a folded dipole.
*

*>
*

*> - Doug McKean
*

*>
*

*>
*

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*>
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*>
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**Next message:**Ashok Prabhu Masilamani: "[SI-LIST] : It is not a virus"**Previous message:**BIBICHA: "Re: [SI-LIST] : Please read this, it is a virus"**In reply to:**Doug McKean: "Re: [SI-LIST] : Antenna Problem on the Board"**Next in thread:**Doug McKean: "Re: [SI-LIST] : Antenna Problem on the Board"**Reply:**Doug McKean: "Re: [SI-LIST] : Antenna Problem on the Board"

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