the British WW2 system worked with two coastal radar systems, the "Chain home" and the "Chain home low" and, for the airspace inlands of the coast, a "Royal Observer Corps, which used traditional methods. like visual silouette recognition, to report aircraft movements via telephone to fighter command HQ
Chain home consisted of towers along the coast, between which antenna wires were stretched.
Transmission and reception antennas were set up seperately. The transmission antennas provided a fixed "searchlight beam", illuminating a sector of azimut, while the nearby two reception antennas were directional and mounted at an angle. Comparing the signal strength and phase difference received by these two antennas on an oscilloscope gave the rough direction of the target. Altitude of the targets was determined by again comparing the signal strength between two antennas located at different heigth on the towers. In any case, since the frequencies were between 20 and 50 MHz (usually between 20 and 30 MHz, about what CB
radio operators use today), the resolution was not great. But the range was several hundred km, so that German aircraft could be recognised while they were still in the assembly areas over France or the Low Countries. Essentially the Chain Home was an early warning radar.
Only the towers of one station above Dover survive today, all others have been scrapped after WW2.
The Chain Home Low used rotating directional antennas at a frequency of 200 MHz. While the range was much lower (about 50 km or so), the resolution was much better, so that the size of the enemy aircraft unit could be determined.
After the aircraft crossed the coastline, there was no radar coverage. The Royal Observer Corps had posts e.g. on hilltops and high buildings all over the country. They would identify aircraft visually and determine their altitude and course using a simple transit. The results would be phoned (like the sightings by the radar stations) to the local HQ
(which would filter the information) and then sent to Fighter Command HQ
in IIRC Biggin Hill.
This is a typical Chain home station with the transmission towers in the foreground and the receiving antenna towers in the back:
The operator would see something like this:
The Plan Position Indicator (which is what we know as a radar screen today) only came up with the centrimetric H2S airborne ground surveillance and bomb aiming radar, which was e.g. used on Lancaster bombers:
All pictures borrowed from http://www.alpha60.de/research/muc/DavidLink_RadarAngels_EN.htm
[Edited 2011-03-02 12:47:36]