here to go to our page on permittivity
here to go to our page on filling factor
New for June 2010! Here
we will explain the term "Keff" which is short for "K
"Dk" is often used
as the "dielectric constant". Why not "DC" you
ask? Unless you are not an electrical engineer, you'd realize that
DC was already taken as "direct current!"
In this context, "k"
refers to the effective "dielectric constant", which might
also be called Epsilon effective.
The dielectric constant Dk, also
known as epsilon relative (ER) is a material property, a measure
of the material's property of slowing electromagnetic waves down.
The parameter ER is usually nearly constant with frequency, which
is why it is called the dielectric constant. Sometimes ER
Given that a two-conductor transmission
line is transverse electromagnetic
(TEM) and is fully encased in a uniform material, the speed
would be c/SQRT(ER). Dk is also the parameter used in capacitance
calculations, Dk is proportional to capacitance value for a given
area and plate separation.
Epsilon effective (Ee), a.k.a.
Keffective, takes into account geometry of a transmission line,
which makes it less than ER (or Dk) in many cases. For microstrip,
part of the wave is in air, and part is in the substrate material.
Once a "filling factor"
is calculated for what percentage is in the material, then the Epsilon
effective is equal to ERxFF+1x(1-FF). The second term comes from
the percentage that is in air (ER=1). Most calculations for microstrip
ignore filling factor and directly provide Keff and Z0.
a page that explains filling factor.
a page on how to extract Dk from transmission line measurements.