How high can a radar operate?

Radar is just another pulsed electromagnetic wave, and may travel freely

throughout space. Radar transponders are left on our Moon and measure

orbital variations.

The upper frequency limit is only defined by our ability to operate technology at

high frequencies. Light radar (lidar) is commonly used on the highway, albeit in

Doppler mode.

There appears to be no practical limit to operational height.

-- The Doppler Weather Radar units operated by NOAA/NWS are routinely mounted

on towers at least 100-ft off the ground.

-- Air Route Surveillance Radar (ARSR) installations are routinely constructed on mountaintops.

-- All commercial airliners and military aircraft are equipped with Radar units, which

function quite satisfactorily while in flight.

-- Side Aperture Radar (SAR) has been used aboard the Space Shuttles and other artificial

Earth satellites to map the Earth's surface, with spectacular success.

-- Radar units have been used very successfully to map the surfaces of the moon

and several planets.