Back in the 1930s the Germans were using something called the Lorenz beam as a Navigational Aid at landing strips. Simplified, this consisted of 2 antennas on either side of the runway with one transmitting "dits" and the other transmitting "dahs". Each aircraft had a receiver for these transmissions. An approaching aircraft would line up on the runway and he drifted too far left or right he would only hear the dits or only the dahs. If he were centered on the runway he would hear both dits and dahs. This worked well. Here is an image from the Wikipedia Lorenz Beam page.
Jump ahead to WWII. Bombers were slow large aircraft and were easy targets for anti-aircraft weapons so bombing raids were generally held under the cover of darkness. The problem with this is that it made it very difficult for the bomber pilots to see their targets below. The British had blackouts in place so that the town showed no light should bombers be overhead. The bombing raids tended to take place during the full moon so there would be a lot better vision however this made the raids more predictable. Nighttime flying was generally difficult with minimal navigational aids at their disposal.
What the Germans did was use the technology of the Lorenz beam and beef it up. Very large directional antennas were built and high power was used to provide the German pilots with a secret navigational aid. The antennas were aimed at a specific target and the pilots would fly so that they were on course by listening for the dits and the dahs. The receivers had to be hidden very cleverly in the aircraft so that if a bomber were shot down their secret would not be discovered. This method of flying at night and finding their targets was extremely clever and quite successful. There were different versions and names of this system as well as different antennas as the system was improved.
Wartime generates a lot of technological advancements and the German/English air battle really spurred on the development of Radio and RADAR technologies including countermeasures such as jamming. If this interests you as much as it did me you should look up the history of the Knickebein, Freya, and the Battle of the Beams.
Cheers for now,