Radar is an abbreviation of the term "Radio Detection and Ranging". As for the country it could be argued that it was the English, American, German or French. I think Marconi in Italy discovered he could measure range with Radio waves, but Radar was not made really very practical and the ranges he could do it where very short, the Americans tried to build death ray, concentrating RF energy into a beam, but this again was not really practical and range limited, but they noted that they observed reflections. However it was the UK that innovated the PPI display and the Magnetron that gave the RF power required in a rugged form and therefore made Radar practical. So it is generally accepted the UK gets the credit for it.
It was named after Luigi Galvani, the Italian scientist.
Applique was first used in Egypt and India but the word comes from France.
Terrestrial radar, using over-the-horizon techniques, around 3000~5000 km. Astronomical radar, at least as far as Venus.
The smallest object most radar can pickup is a bird. Radar used by air traffic control and civilians is less accurate than that of the military.
Typical radar operates in the 50 to 330 megahertz bands. However, long range radar uses ultra high frequencies in the 300 to 1,000 megahertz range.