> DC Lost Tangent - Controlled Impedance

> I am looking for an explanation/definition of "DC Lost Tangent" in
> regards to
> Controlled Impedance.

> Can anyone suggest a reference book which may cover this?
> Thanks for any help!

I think you mistyped loss tangent though I don't know what a "DC loss
tangent" would be.  The loss tangent is defined relative to a frequency
(see below).

Any basic physics book, in the section on electromagnetic wave propagation,
will discuss the loss tangent in the same section as dielectric constant.
A (much) more detailed discussion of high frequency concepts in general can
be found in chapter 1 in "Microwave Engineering", David M. Pozar. Wiley -
get the 2nd ed.

Physically, the loss tangent is related to the loss (duh :-) :-) in the
dielectric material.  The tangent is routinely specified because of the
complex math used to describe wave propagation. (Dielectric loss is the
imaginary part of the dielectric constant which, in a mathematical
description of wave propagation becomes real and hence a loss).

From Pozar, 1.21
     tan delta = (w*e'' + conductivity)/w*e'
where tan delta is the conventional nomenclature for loss tangent, w is 2 *
pi*freq, conductivity is the conductivity of the dielectric and e' and e''
are the real and imaginary parts of the dielectric constant respectively

often this is just approximated as
     tan delta = e''/e'
with the implicit assumption that the conductivity is 0 or small compared
to w*e'' (problematic as the frequency increases).

BTW, tan delta for "good" dielectric materials are <0.001, OK materials are
arguably <0.01.  Above this loss will have some design impact.
Hope this helps.

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