# Transmission Line Basics

## Field Quantities

E
Electrical field intensity (V/m).
Defined as the electric force on a unit charge. Only vector needed in discussing electrostatics (effects of stationary electric charge) in free space.
D
Electric flux density or electric displacement (C/m2).
Useful in the study of electric field in material media.
B
Magnetic flux density (T, Tesla, V-sec/m2).
Magnetic force acting on a charge moving with a given velocity. Only vector is needed in discussing magneto statics (effects of steady electric currents) in free space.
H
Magnetic field intensity (A/m).
Useful in the study of magnetic field in material media.

## Universal Constants in Free Space

$c\text{\hspace{0.17em}}=\text{\hspace{0.17em}}\frac{1}{\sqrt{{\epsilon }_{0}{\mu }_{0}}}\text{ }\text{m/s}$
Or,
${\epsilon }_{0}\text{\hspace{0.17em}}=\text{\hspace{0.17em}}1\text{\hspace{0.17em}}/\text{\hspace{0.17em}}\left({c}^{2}{\mu }_{0}\right)$
$\approx \text{\hspace{0.17em}}{\left(1\text{\hspace{0.17em}}/\text{\hspace{0.17em}}36\pi \right)}^{\prime }\text{\hspace{0.17em}}{10}^{-9}\text{ }\text{F/m}$
Where,
$c$
Velocity of electromagnetic wave (including light).
$c\text{\hspace{0.17em}}\approx \text{\hspace{0.17em}}{3}^{\prime }{10}^{8}\text{ }\text{m/s}$
${\epsilon }_{0}$
Permittivity of free space.
$D\text{\hspace{0.17em}}=\text{\hspace{0.17em}}{\epsilon }_{0}E$
${\mu }_{0}$
Permeability of free space.
$H\text{\hspace{0.17em}}=\text{\hspace{0.17em}}\left(1\text{\hspace{0.17em}}/\text{\hspace{0.17em}}{\mu }_{0}\right)\text{\hspace{0.17em}}B,\text{ }{\mu }_{0}\text{\hspace{0.17em}}=\text{\hspace{0.17em}}4{\pi }^{\prime }{10}^{-7}\text{ }\text{H/m}$

${\epsilon }_{0}$ and ${\mu }_{0}$ are not independent.