Project Diana
Project Diana, named for the Roman moon goddess Diana, was an experimental project of the US Army Signal Corps in 1946 to bounce radar signals off the Moon and receive the reflected signals. This was the first experiment in radar astronomy and the first active attempt to probe another celestial body. It was the inspiration for later EME (Earth-Moon-Earth) communication techniques.
At a laboratory at Camp Evans (part of Fort Monmouth), in Wall Township, New Jersey, a large transmitter, receiver and antenna array were constructed for this purpose. The transmitter, a highly modified SCR-271 radar set from World War II, provided 3 kilowatts (later upgraded to 50 kilowatts) at 111.5 MHz in 1⁄4-second pulses, applied to the antenna, a "bedspring" reflective array antenna composed of an 8x8 array of half wave dipoles in front of a reflector which provided 24 dB of gain. Reflected signals were received about 2.5 seconds later, the time required for the radio waves to make the 768,000-kilometre (477,000 mi) round-trip journey from the Earth to the Moon and back. The receiver had to compensate for the Doppler shift in frequency of the reflected signal due to the Moon's orbital motion relative to the Earth's surface, which was different each day, so this motion had to be carefully calculated for each trial. The antenna could be rotated in azimuth only, so the attempt could be made only as the moon passed through the 15 degree wide beam at moonrise and moonset, as the antenna's elevation angle was horizontal. About 40 minutes of observation was available on each pass as the Moon transited the various lobes of the antenna pattern.
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