The first smart antennas were developed for military communications and intelligence gathering. The growth of cellular telephone in the 1980s attracted interest in commercial applications. The upgrade to digital radio technology in the mobile phone, indoor wireless network, and satellite broadcasting industries created new opportunities for smart antennas in the 1990s, culminating in the development of the MIMO (multiple-input multiple-output) technology used in 4G wireless networks.
Directional antennas The earliest success at tracking and controlling wireless signals relied on the antennas’ physical configuration and motion. The German inventor and physicist Karl F. Braun demonstrated beamforming for the first time in 1905. Braun created a phased array by positioning three antennas to reinforce radiation in one direction and diminish radiation in other directions. Guglielmo Marconi experimented with directional antennas in 1906. Directional antennas were rotated to detect and track enemy forces during World War I. The British admiralty used goniometers (radio compasses) to track the German fleet. Edwin H. Armstrong invented the superheterodyne receiver to detect the high frequency noise generated by German warplanes’ ignition systems. The war ended before Armstrong's creation was ready to help direct antiaircraft fire. Multiple elements (a fed dipole, a director, and reflectors) were assembled in the 1920s to create narrow transmit and receive antenna patterns. The Yagi-Uda array, better known as the Yagi antenna, is still widely used. Edmond Bruce and Harald T. Friis developed directional antennas for shortwave and microwave frequencies during the 1930s.
AT&T's decision to use microwave to carry inter-city telephone traffic led to the first large-scale commercial deployment of directional antennas (based on Friis’ horn reflector design) in 1947. Directional antennas with alternating polarization enabled a single pair of frequencies to be reused over many consecutive hops. Microwave links are less expensive to deploy and maintain than coaxial cable links.
Phased array radar The first mechanically scanned phased array radar (using a rotating Yagi antenna) was demonstrated in the 1930s. The first electronically scanned radars used electromechanical devices (such as mechanical tuners or switches) to steer the antenna's beam.
Germany built the Wullenweber circular array for direction finding during the early years of World War II. The Wullenweber could electronically scan the horizon 360° and determine the direction of any signal with reasonably good accuracy. Circular arrays were enhanced during the Cold War for eavesdropping purposes. The American Physicist Luis Walter Alvarez developed the first ground-controlled approach (GCA) system for landing aircraft in bad weather based on an electronically steered microwave phased array antenna. Alvarez tested and deployed the system in England in 1943. Near the end of the war, Germany's GEMA built an early warning phased array radar system (the PESA Mammut 1) to detect targets up to 300 km away. The polyrod fire control antenna was developed by Bell Laboratories in 1947 using cascaded phase shifters controlled by a rotary switch (spinning at ten revolutions per second) to create a continuous scanning beam.
A major push to meet national security response time and coverage requirements called for the development of an all-electronic steerable planar phased array radar. The USSR's launch of Sputnik in 1957 suggested the need for ground-based satellite surveillance systems. Bendix Corporation responded by building its Electronically Steerable Array Radar (ESAR) in 1960. Enhanced beamforming techniques, such as multiple-beam Butler matrices, were developed for detecting and tracking objects in space.
The launch of Explorer 1 by the United States in 1958 suggested another application: space-based radar systems for detecting and tracking aircraft, ships, armored vehicles, ballistic missiles, and cruise missiles. These systems required the development of special techniques for canceling the radar clutter seen from space, nulling ground-based jammers, and compensating for Doppler shifts experienced by fast-moving satellites.
Space-based radar systems spurred the development of smaller, lighter weight, and less costly components: monolithic microwave integrated circuits (MMICs) for operation at frequencies in the 1 GHz to 30 GHz (microwave) and 30 GHz to 300 GHz (millimeter wave) ranges. The high power levels needed for detection are easier to achieve at microwave frequencies. The narrow beams required for high resolution target tracking are best achieved at millimeter wave frequencies. Companies such as Texas Instruments, Raytheon, RCA, Westinghouse, General Electric, and Hughes Electronics participated in the early development of MMICs.
The first all-solid state radar was built for the United States Marines in 1972 by General Electric. It was a mobile 3-D radar system with its array mounted on a rotating platform for scanning the horizon. The first all-solid state phased array radar was the PAVE PAWS (precision acquisition vehicle entry - phased array warning system) UHF radar built in 1978 for the United States Air Force. Phased array antennas are also used in radio astronomy. Karl Jansky, discoverer of the radio waves emanating from the Milky Way galaxy, used a Bruce array for experiments he conducted in 1931. Modern phased array radio telescopes typically consist of a number of small, interconnected antennas such as the Murchison Widefield Array in Australia, constructed in 2012.
Adaptive antenna arrays L. C. van Atta was first to describe a retrodirective antenna, the van Atta array, which redirects (rather than reflects) a signal back in the direction from which it came, in his 1959 patent. The signal can be modulated by the redirecting host for purposes such as radio-frequency identification and traffic control (radar target echo enhancement). The first adaptive array, the side-lobe canceller, was developed by Paul Howells and Sid Applebaum at General Electric in 1959 to suppress radar jamming signals. Building on Norbert Wiener’s work with analog filters, in 1960 Stanford University professor Bernard Widrow and PhD student Ted Hoff developed the least mean squares (LMS) algorithm that automatically adjusts an antenna's directivity pattern to reinforce desired signals. Ted Compton at Ohio State University developed an adaptive antenna technique for recovering direct sequence spread spectrum signals in the presence of narrowband co-channel interference. Compton's method, reported in 1974, only requires knowledge of the desired signal's pseudorandom noise (PN) code—not its direction of arrival. In the late 1970s, Kesh Bakhru and Don Torrieri developed the maximin algorithm for recovering frequency hopping signals in the presence of narrowband co-channel interference. A 1977 paper by Bell Labs researchers Douglas O. Reudink and Yu S. Yeh described the advantages of scanning spot beams for satellites. The authors estimated that scanning spot beams could save 20 dB in link budget which in turn could be used to reduce transmit power, increase communication capacity, and decrease the size of earth-station antennas. Satellite spot beams are used today by direct broadcast satellite systems such as DirecTV and Dish Network.
The Strategic Defense Initiative (SDI), proposed in 1983, became a major source of funding for technology research in several areas. The algorithms developed to track intercontinental ballistic missiles and direct x-ray laser weapons were particularly relevant to smart antennas.
Digital antenna arrays
These are antenna arrays with multi channels digital beamforming, usually by using FFT.
The theory of the 'digital antenna arrays' (DAA) started to emerge as a theory of multichannel estimation. Its origins go back into methods developed in the 1920s that were used to determine direction of the arrival of radio signals by a set of two antennas based on the phase difference or amplitudes of their output voltages. Thus, the assessment of the directions of arrival of a single signal was conducted according to pointedtype indicator readings or according to the Lissajous curves, drawn by beam on the oscilloscope screen.Slyusar V. I. Origins of the Digital Antenna Array Theory.// International Conference on Antenna Theory and Techniques, 24–27 May 2017, Kyiv, Ukraine. – Pp. 199 - 201
In the late 1940s this approach caused the emergence of the theory of three-channel antenna analyzers that provided the solution to the problem of signal separation of air target and “antipode” reflected from the underlying surface by solving system of equations which were obtained with the help of complex voltages of three-channel signal mix.
The growing complexity of solving such radar challenges, as well as the need to implement effective signal processing by the end of the 1950s predetermined the use of electronic computers in this field. For example, in 1957, Ben S. Meltont and Leslie F. Bailey published a very significant article in this field, where authors offered options of implementation of algebraic operations for signal processing with the help of electronic circuits, their equivalents, with the aim to develop signal correlator on the base of certain analogue computer.
The replacement of analogue computer facilities by digital technologies three years after in 1960 was embodied in the idea of using high-speed computers to solve directional finding problems, initially to locate earthquake epicenter. B. A. Bolt was one of the first who implemented this idea in practice, he has developed a program for IBM 704 for seismic direction finding based on the method of least squares. Almost simultaneously a similar approach was used by Flinn, research fellow of the Australian National University.E. A. Flinn. Local earthquake location with an electronic computer.//Bulletin of the Seismological Society of America. - July 1960. - Vol. 50, No. 3. – Pp. 467 - 470
Despite the fact that in the mentioned experiments the interface between sensors and computer was implemented with the help of data input cards, such decision was a decisive step on the way of the appearance of the DAA. Then, there was only to solve the problem of direct digital data, obtained from sensing elements, input into computer, excluding the stage of preparation of punch card and operator assistance as a surplus link.
Apparently, it was Polikarpov B.I. who first drew attention to the potential possibilities of multichannel analyzers in the former USSRPolikarpov B.I. On some possibilities of application of independent channels of signal reception and the use of electronics and computer technologies to improve antijamming capabilities and resolution characteristic of radar measurement//Express Information, BNT, № 23, 1961. Polikarpov B.I. shows the principal possibility of signal sources resolution with an angular distance less than aperture angle of the antenna system.
However, a specific solution to the problem of superRayleigh resolution of the emission sources was proposed by Varyukhin V.A. and Zablotskiy M.A. only in 1962, they invented corresponding method of measuring of directions to sources of electromagnetic field.A.S. USSR № 25752. Method of measuring of directions to sources of electromagnetic field. // Varyukhin V.A., Zablotskiy M.A. – 1962 This method was based on the processing of information contained in the distribution of complex voltage amplitudes at the outputs of amplitude, phase and phase-amplitude multichannel analyzers and it permitted to determine the angular coordinates of sources within the width of the main lobe of the receiving antenna system.