John Ashworth Ratcliffe CB[2] CBE FRS[3] (known to intimates as "Jar";[4] 12 December 1902 – 25 October 1987) was an influential British radio physicist.

They and M A F Barnett developed methods to understand why ‘fading’ of radio signals from a fixed transmitter occurred during hour of darkness.

[3] At the outbreak of war in 1939, dozens of radar stations formed a network, known as Chain Home (CH), covering the eastern and southern coasts of Britain.

Physicists from the Cavendish and elsewhere were assigned to spend a month at one of the stations: Ratcliffe was sent to the one near Dover, but was soon made part of the Telecommunications Research Establishment (TRE) in Dundee where he was in charge of a new form of CH known as Chain Home Low (CHL), used to detect aircraft flying at altitudes below those detectable by CH stations.

At the end of the conflict, Ratcliffe was back at the Cavendish, which had been enlarged, enabling him to restart research with a larger group.