The angle of arrival (AoA) of a signal is the direction from which the signal (e.g. radio, optical or acoustic) is received.

Measurement

Measurement of AoA can be done by determining the direction of propagation of a radio-frequency wave incident on an

antenna array An antenna array (or array antenna) is a set of multiple connected antennas which work together as a single antenna, to transmit or receive radio waves. The individual antennas (called ''elements'') are usually connected to a single receiver o ...

or determined from maximum signal strength during antenna rotation. The AoA can be calculated by measuring the

time difference of arrival Time of arrival (TOA or ToA) is the absolute time instant when a radio signal emanating from a transmitter reaches a remote receiver. The time span elapsed since the time of transmission (TOT or ToT) is the ''time of flight'' (TOF or ToF). Time diff ...

(TDOA) between individual elements of the array. Generally this TDOA measurement is made by measuring the difference in received phase at each element in the antenna array. This can be thought of as

beamforming Beamforming or spatial filtering is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in an antenna array in such a way that signals at particular angles e ...

in reverse. In beamforming, the signal from each element is weighed to "steer" the gain of the antenna array. In AoA, the delay of arrival at each element is measured directly and converted to an AoA measurement. Consider, for example, a two element array spaced apart by one-half the wavelength of an incoming RF wave. If a wave is incident upon the array at boresight, it will arrive at each antenna simultaneously. This will yield 0° phase-difference measured between the two antenna elements, equivalent to a 0° AoA. If a wave is incident upon the array at broadside, then a 180° phase difference will be measured between the elements, corresponding to a 90° AoA. In

optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultrav ...

, AoA can be calculated using

interferometry Interferometry is a technique which uses the '' interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber o ...

Applications

An application of AoA is in the

geolocation Geopositioning, also known as geotracking, geolocalization, geolocating, geolocation, or geoposition fixing, is the process of determining or estimating the geographic position of an object. Geopositioning yields a set of geographic coordinates ...

cell phone A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive telephone call, calls over a radio freq ...

s. The aim is either for the cell system to report the location of a cell phone placing an emergency call or to provide a service to tell the user of the cell phone where they are. Multiple receivers on a base station would calculate the AoA of the cell phone's signal, and this information would be combined to determine the phone's location. AoA is generally used to discover the location of

pirate radio stations Pirate radio or a pirate radio station is a radio station that broadcasts without a valid license. In some cases, radio stations are considered legal where the signal is transmitted, but illegal where the signals are received—especially ...

or of any

military A military, also known collectively as armed forces, is a heavily armed, highly organized force primarily intended for warfare. It is typically authorized and maintained by a sovereign state, with its members identifiable by their distinct ...

radio transmitter. In

submarine A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...

acoustics Acoustics is a branch of physics that deals with the study of mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acousticia ...

, AoA is used to localize objects with active or passive

ranging Length measurement, distance measurement, or range measurement (ranging) refers to the many ways in which length, distance, or range can be measured. The most commonly used approaches are the rulers, followed by transit-time methods and the in ...

Limitation

Limitations on the accuracy of estimation of angle of arrival signals in digital antenna arrays are associated with

jitter In electronics and telecommunications, jitter is the deviation from true periodicity of a presumably periodic signal, often in relation to a reference clock signal. In clock recovery applications it is called timing jitter. Jitter is a signific ...

ADC and DAC.

References

{{Reflist Angle Signal processing

Measurement

Applications

Limitation

See also

References