Editing Radar (section)

====Beam path and range====
{{see also|Beam forming|Over-the-horizon radar}}
[[File:Radar-hauteur-en.svg|thumb|upright=1.5|Echo heights above ground<br /><math>H=\left (\sqrt{r^{2}+(k_{e}a_{e})^{2}+2rk_{e}a_{e}sin(\theta _{e})} \right )-k_{e}a_{e}+h_{a}</math> <br />Where : <br />&nbsp;&nbsp;r : distance radar-target <br />ke : 4/3 <br />ae : Earth radius <br />θe : elevation angle above the radar horizon <br />ha : height of the feedhorn above ground]]
A radar beam follows a linear path in vacuum but follows a somewhat curved path in atmosphere due to variation in the [[refractive index]] of air, which is called the [[radar horizon]]. Even when the beam is emitted parallel to the ground, the beam rises above the ground as the [[Figure of the Earth|curvature of the Earth]] sinks below the horizon. Furthermore, the signal is attenuated by the medium the beam crosses, and the beam disperses.

The maximum range of conventional radar can be limited by a number of factors:
* Line of sight, which depends on the height above the ground. Without a direct line of sight, the path of the beam is blocked.
* The maximum non-ambiguous range, which is determined by the [[pulse repetition frequency]]. The maximum non-ambiguous range is the distance the pulse can travel to and return from before the next pulse is emitted.
* Radar sensitivity and the power of the return signal as computed in the radar equation. This component includes factors such as the environmental conditions and the size (or radar cross section) of the target.