[SI-LIST] Re: Loss tangent calculation
- From: "Tabatchnick, Justin" <justin.tabatchnick@xxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 3 Apr 2003 16:38:11 -0800
er" is called the dielectric loss constant - not to be confused with
loss tangent which is e"/e'
Justin
-----Original Message-----
From: Robert Plant [mailto:rplantsprint@xxxxxxxxxxxxx]=20
Sent: Thursday, April 03, 2003 4:29 PM
To: ashamim@xxxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Loss tangent calculation
According to Wadell's venerable book "Transmission Line Design Handbook"
(page 21), the precise definition of loss tangent is:
tand =3D=3D (er") / (er')
where er' is the real part of er (relative permittivity) and
er" is the imaginary part of er...normally we just pay attention
to er' because er" is small.
THEN(!): on page 27 the loss factor (what we're all really interested
in anyway!) is given by:
ad =3D [pi * f * qtand * tand * sqrt(eeff)]
------------------------------------
co
where ad =3D=3D dielectric loss constant (proportional to f =3D=3D> =
important!)
qtand =3D=3D "filling factor" approximately 1 but different fo=20
non-homogenous materials
tand =3D=3D loss tangent
eeff =3D effective relative permittivity.
co =3D speed of light in a vacuum.
What Wadell doesn't say but you might be able to approximate is:
qtand ~ 1 (assume the material is approximately homogenous)
eeff ~ er (same assumption)
ad =3D [pi * f * tand * sqrt(er)]
--------------------------
co
I think those are the operative equations you want to use.
As far as determining tand, the only way I know how to do this is to
either
calculate the loss factor and do a reverse calculation of tand
or else look up on the web or in a book for the material in question.
There's no other way I'm aware of.
Good luck,
Drew Plant
=20
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of atifshamimkhan
Sent: Thursday, April 03, 2003 11:58 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Loss tangent calculation
Hi
I am designing an antenna on Si substrate at 24 GHz.I want to
calculate the Loss tangent for this substrate .I have the following
info
Resistivity =3D 300 ohm-cm (for silicon substrate )
I calculate it as follows: conductivity =3D 1/ resitivity
Also loss tangent (Tan d)=3D conductivity / (epsilon * 2 *pi * f )
where Epsilon (r) for silicon is 12 and f is 24 GHz.In this way I get
=20
Tan d =3D 0.25=20
I dont know whether this calculation is right or not.My question is if
this is not the right way then how can I calculate the Loss tangent
from resistivity only and secondly if this is right then why the loss
tangent decreases with the increase in fequency.
Thanks=20
Atif
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