The Adcock antenna is an antenna

Antenna (radio)

An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...

 (British English

British English

British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...

 aerial) array consisting of four equidistant vertical elements which can be used to transmit or receive directional radio waves. It was invented and patented by British engineer Frank Adcock in 1919 as British

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

  Patent No. 130,490, and has been used for a variety of applications, both civilian and military, ever since. Although originally conceived for receiving Low Frequency

Low frequency

Low frequency or low freq or LF refers to radio frequencies in the range of 30 kHz–300 kHz. In Europe, and parts of Northern Africa and of Asia, part of the LF spectrum is used for AM broadcasting as the longwave band. In the western hemisphere, its main use is for aircraft beacon,...

 (LF) waves, it has also been used for transmitting, and has since been adapted for use at much higher frequencies, up to Ultra High Frequency

Ultra high frequency

Ultra-High Frequency designates the ITU Radio frequency range of electromagnetic waves between 300 MHz and 3 GHz , also known as the decimetre band or decimetre wave as the wavelengths range from one to ten decimetres...

 (UHF).

In the early 1930s, the Adcock antenna (transmitting in the LF/MF bands) became a key feature of the newly created radio navigation

Radio navigation

Radio navigation or radionavigation is the application of radio frequencies to determine a position on the Earth. Like radiolocation, it is a type of radiodetermination.The basic principles are measurements from/to electric beacons, especially...

 system for aviation. The Low Frequency radio range

Low Frequency radio range

The low-frequency radio range , also known as the four-course radio range, LF/MF four-course radio range, A-N radio range, Adcock radio range, or commonly "the range", was the main navigation system used by aircraft for instrument flying in the 1930s and 1940s, until the advent of the VHF...

 (LFR) network, which consisted of hundreds of Adcock antenna arrays, defined the airways used by aircraft for instrument flying

Instrument flight rules

Instrument flight rules are one of two sets of regulations governing all aspects of civil aviation aircraft operations; the other are visual flight rules ....

. The LFR remained as the main aerial navigation technology until it was replaced by the VOR

VHF omnidirectional range

VOR, short for VHF omnidirectional radio range, is a type of radio navigation system for aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice , and navigation signal. The identifier is typically a two- or three-letter string in Morse code...

 system in the 1950s and 1960s.

The Adcock antenna array has been widely used commercially, and implemented in vertical antenna heights ranging from over 130 feet (40 meters) in the LFR network, to as small as 5 inches (13 cm) in tactical direction finding

Radio direction finder

A radio direction finder is a device for finding the direction to a radio source. Due to low frequency propagation characteristic to travel very long distances and "over the horizon", it makes a particularly good navigation system for ships, small boats, and aircraft that might be some distance...

 applications (receiving in the UHF band).

Radio direction finding

Frank Adcock's original work was focused on the receiving mode of radio antennas, and specifically in identifying the azimuth of remote sources of electromagnetic radiation

Electromagnetic radiation

Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...

, which became known as radio direction finding. Prior to Adcock's invention, engineers had been using loop antenna

Loop antenna

A loop antenna is a radio antenna consisting of a loop of wire, tubing, or other electrical conductor with its ends connected to a balanced transmission line...

s to achieve directional sensitivity. They discovered that due to atmospheric disturbances and reflections, the detected signals included significant components of electromagnetic interference

Electromagnetic interference

Electromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...

 and distortions: horizontally polarized radiation contaminating the signal of interest and reducing the accuracy of the measurement. Adcock—who was serving as an Army officer in the British Expeditionary Force in wartime

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

 France at the time he filed his invention—solved this problem by replacing the loop antennas with symmetrically inter-connected pairs of vertical monopole

Monopole antenna

A monopole antenna is a class of radio antenna consisting of a straight rod-shaped conductor, often mounted perpendicularly over some type of conductive surface, called a ground plane. The driving signal from the transmitter is applied, or for receiving antennas the output voltage is taken,...

 or dipole antenna

Dipole antenna

A dipole antenna is a radio antenna that can be made of a simple wire, with a center-fed driven element. It consists of two metal conductors of rod or wire, oriented parallel and collinear with each other , with a small space between them. The radio frequency voltage is applied to the antenna at...

s of equal length. This created the equivalent of square loops, but without their horizontal members, thus eliminating sensitivity to much of the horizontally polarized distortion. The same principles remain valid today, and the Adcock antenna array and its variants are still used for radio direction finding.

Low Frequency radio range

In the late 1920s, the Adcock antenna was adopted for aerial navigation, in what became known as the Low Frequency radio range (LFR), or the "Adcock radio range". Hundreds of transmitting stations, each consisting of four or five Adcock antenna towers, were constructed around the U.S. and elsewhere. The result was a network of electronic airways, which allowed pilots to navigate at night and in poor visibility, under virtually all weather conditions. The LFR remained as the main aerial navigation system in the U.S. and other countries until the 1950s, when it was replaced by VHF-based VOR

VHF omnidirectional range

VOR, short for VHF omnidirectional radio range, is a type of radio navigation system for aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice , and navigation signal. The identifier is typically a two- or three-letter string in Morse code...

technology. By the 1980s all LFR stations were decommissioned.