Lighting time

The dwell time of a target in the antenna beam of a reconnaissance radar device is called the illumination time T _D ("dwell time"). The lighting time depends mainly on the opening angle Θ _AZ and the rotation speed n of the antenna (antenna cycle time).

Duration of exposure to a target by a radar

The opening angle is given as a ratio to the full circle (360 °). Basically, the wider the main lobe of the antenna and the slower the antenna turns, the longer the radar will illuminate the object . The following formula specifies the lighting time for a panoramic radar:

${\displaystyle T_{D}={\frac {\Theta _{AZ}\cdot 60}{360\cdot n}}}$

Θ _AZ = horizontal opening angle of the antenna

n = revolutions of the antenna per minute

Since the speed of rotation is given in revolutions per minute and the lighting time in seconds , it must be multiplied by a factor of 60 in the formula.

The lighting time for height finders is not determined by the full circle, but only partly by the size of the swivel sector. Taking into account the fact that the object is detected by the radar beam twice per swivel cycle, i.e. once when swiveling up and once when swiveling down, the lighting time can be determined by the following formula, assuming that the antenna has a constant swivel speed.

${\displaystyle T_{D}={\frac {\Theta _{EL}\cdot 60}{\epsilon _{max}\cdot 2n}}}$

Θ _EL = vertical opening angle of the antenna

ε _max = maximum swivel sector of the antenna

n = swivel cycles per minute

elliptical gears

In practice, deviations arise due to the superimposition of a sinusoidal speed change, which is particularly noticeable at the turning points of the swivel. In order to obtain an approximately linear speed at least in the main direction, elliptical gears are sometimes used in the swivel gear.

This swivel gear changes its transmission ratio depending on the current angle and thus causes a change in speed of the rotary movement that is opposite to the sinusoidal speed change. To ensure smooth running, the sum of the power-transmitting partial radii of both gears must always be the same. In practice, both gears are matched to one another and can therefore only be changed in pairs.