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--- un:dipole [2024/06/23 04:02] – asad
+++ un:dipole [2024/07/10 23:19] (current) – removed asad
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-====== Dipole antenna ======
-The simplest radiator of [[light|electromagnetic waves]] (hereafter 'light') is a **short dipole**, which was used for this purpose by [[Hertz]] for the first time, in 1887. Short, because its physical length is much shorter than the wavelengths at which it transmits or receives light.
-{{https://www.cv.nrao.edu/~sransom/web/x238.png?nolink&400}}
-Here is a Hertzian dipole that generates radio light due to an oscillating current $I$. It is called a dipole because the currents in the two conductors are exactly out of phase, they have a $180^\circ$ phase shift. Now the alternating current (AC) $ I = I_0 \cos \omega t $ is better expressed in exponential notation:
-$$ I = I_0 e^{-i\omega t} $$
-where $e^{-i\omega t} = \cos\omega t - i\sin\omega t$. The current $I=dq/dt$ can be rewritten as $I=(dq/dz)(dz/dt)=(dq/dz)v$ for a wire or rod on the $z$ axis. Here $v$ is the [[drift velocity]] of the electrons. Note that the electrons flow like water molecules in a hose, very slowly, but that does not hinder current.
-Now using the perpendicular electric field ($E_\theta$) derived in the article [[radiation from acceleration]], we can find that
-$$ \Rightarrow dE_\theta = \frac{dq}{dz}dz \frac{a\sin\theta}{rc^2} =  $$
-{{https://upload.wikimedia.org/wikipedia/commons/d/dd/Dipole_receiving_antenna_animation_6_800x394x150ms.gif?nolink&400}}