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60-405: The AESA is a more advanced, sophisticated, second-generation of the original PESA phased array technology. PESAs can only emit a single beam of radio waves at a single frequency at a time. The PESA must utilize a Butler matrix if multiple beams are required. The AESA can radiate multiple beams of radio waves at multiple frequencies simultaneously. AESA radars can spread their signal emissions across

120-453: A beam in the direction of the line (endfire beam) will be produced. Using an intermediate value of phase shift between elements will produce a beam at some angle intermediate between these two extremes. In a Butler matrix, the phase shift of each beam is made and the angle between the outer beams is given by The expression shows that θ {\displaystyle \theta } decreases with increasing frequency. This effect

180-475: A company named Transis-tronics released a solid-state amplifier, the TEC S-15. The replacement of bulky, fragile, energy-hungry vacuum tubes by transistors in the 1960s and 1970s created a revolution not just in technology but in people's habits, making possible the first truly portable consumer electronics such as the transistor radio , cassette tape player , walkie-talkie and quartz watch , as well as

240-442: A different phase-mode. A circular antenna array can be made to simultaneously produce an omnidirectional beam and multiple directional beams when fed through two Butler matrices back-to-back. Butler matrices can be used with both transmitters and receivers. Since they are passive and reciprocal , the same matrix can do both – in a transceiver for instance. They have the advantageous property that in transmit mode they deliver

300-602: A display as if there was a single powerful beam being sent. However, this means that the noise present in each frequency is also received and added. AESAs add many capabilities of their own to those of the PESAs. Among these are: the ability to form multiple beams simultaneously, to use groups of TRMs for different roles concurrently, like radar detection, and, more importantly, their multiple simultaneous beams and scanning frequencies create difficulties for traditional, correlation-type radar detectors. Radar systems work by sending out

360-409: A few cubic centimeters in volume. The introduction of JFETs and MESFETs did the same to the transmitter side of the systems as well. It gave rise to amplifier-transmitters with a low-power solid-state waveform generator feeding an amplifier, allowing any radar so equipped to transmit on a much wider range of frequencies, to the point of changing operating frequency with every pulse sent out. Shrinking

420-568: A much simpler radar whose primary purpose was to track the outgoing Sprint missiles before they became visible to the potentially distant MAR. These smaller Missile Site Radars (MSR) were passively scanned, forming only a single beam instead of the MAR's multiple beams. While MAR was ultimately successful, the cost of the system was enormous. When the ABM problem became so complex that even a system like MAR could no longer deal with realistic attack scenarios,

480-519: A portion of the sky, the radar antenna must be physically moved to point in different directions. Starting in the 1960s new solid-state devices capable of delaying the transmitter signal in a controlled way were introduced. That led to the first practical large-scale passive electronically scanned array (PESA), or simply phased array radar. PESAs took a signal from a single source, split it into hundreds of paths, selectively delayed some of them, and sent them to individual antennas. The radio signals from

540-456: A rotating antenna, or similar passive array using phase or amplitude comparison . Typically RWRs store the detected pulses for a short period of time, and compare their broadcast frequency and pulse repetition frequency against a database of known radars. The direction to the source is normally combined with symbology indicating the likely purpose of the radar – airborne early warning and control , surface-to-air missile , etc. This technique

600-439: A sealed tube. Although the first solid-state electronic device was the cat's whisker detector , a crude semiconductor diode invented around 1904, solid-state electronics started with the invention of the transistor in 1947. Before that, all electronic equipment used vacuum tubes , because vacuum tubes were the only electronic components that could amplify —an essential capability in all electronics. The transistor, which

660-441: A sensitive receiver which amplifies any echos from target objects. By measuring the time it takes for the signal to return, the radar receiver can determine the distance to the object. The receiver then sends the resulting output to a display of some sort . The transmitter elements were typically klystron tubes or magnetrons , which are suitable for amplifying or generating a narrow range of frequencies to high power levels. To scan

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720-451: A signal and then listening for its echo off distant objects. Each of these paths, to and from the target, is subject to the inverse square law of propagation in both the transmitted signal and the signal reflected back. That means that a radar's received energy drops with the fourth power of the distance, which is why radar systems require high powers, often in the megawatt range, to be effective at long range. The radar signal being sent out

780-419: A wide band even in a single pulse, a technique known as a "chirp". In this case, the jamming will be the same frequency as the radar for only a short period, while the rest of the radar pulse is unjammed. AESAs can also be switched to a receive-only mode, and use these powerful jamming signals to track its source, something that required a separate receiver in older platforms. By integrating received signals from

840-458: A wider angle of total coverage. This high off-nose pointing allows the AESA equipped fighter to employ a crossing the T maneuver, often referred to as "beaming" in the context of air-to-air combat, against a mechanically scanned radar that would filter out the low closing speed of the perpendicular flight as ground clutter while the AESA swivels 40 degrees towards the target in order to keep it within

900-409: A wider range of frequencies, which makes them more difficult to detect over background noise , allowing ships and aircraft to radiate powerful radar signals while still remaining stealthy, as well as being more resistant to jamming. Hybrids of AESA and PESA can also be found, consisting of subarrays that individually resemble PESAs, where each subarray has its own RF front end . Using a hybrid approach,

960-572: Is a major drawback for aircraft use. Another choice that is less bulky, but still less lossy than microstrip, is substrate-integrated waveguide . A typical use of Butler matrices is in the base stations of mobile networks to keep the beams pointing towards the mobile users. Linear antenna arrays driven by Butler matrices, or some other beam-forming network, to produce a scanning beam are used in direction finding applications. They are important for military warning systems and target location. They are especially useful in naval systems because of

1020-411: Is a simple radio signal, and can be received with a simple radio receiver . Military aircraft and ships have defensive receivers, called " radar warning receivers " (RWR), which detect when an enemy radar beam is on them, thus revealing the position of the enemy. Unlike the radar unit, which must send the pulse out and then receive its reflection, the target's receiver does not need the reflection and thus

1080-458: Is also used as an adjective for devices in which semiconductor electronics that have no moving parts replace devices with moving parts, such as the solid-state relay , in which transistor switches are used in place of a moving-arm electromechanical relay , or the solid-state drive (SSD), a type of semiconductor memory used in computers to replace hard disk drives , which store data on a rotating disk. The term solid-state became popular at

1140-545: Is called beam squint . Both the Blass matrix and Butler matrix suffer from beam squint and the effect limits the bandwidth that can be achieved. Another undesirable effect is that the further a beam is off boresight (broadside beam) the lower is the beam peak field. The total number of circuit blocks required is Since n {\displaystyle n} is always a power of 2, we can let n = 2 m {\displaystyle n=2^{m}} , then

1200-417: Is common on ships, for instance. Unlike the radar, which knows which direction it is sending its signal, the receiver simply gets a pulse of energy and has to interpret it. Since the radio spectrum is filled with noise, the receiver's signal is integrated over a short period of time, making periodic sources like a radar add up and stand out over the random background. The rough direction can be calculated using

1260-454: Is much less useful against a radar with a frequency-agile (solid state) transmitter. Since the AESA (or PESA) can change its frequency with every pulse (except when using doppler filtering), and generally does so using a random sequence, integrating over time does not help pull the signal out of the background noise. Moreover, a radar may be designed to extend the duration of the pulse and lower its peak power. An AESA or modern PESA will often have

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1320-399: Is required. The elements are commonly arranged in a linear array . A Butler matrix can also feed a circular array giving 360° coverage. A further application with a circular antenna array is to produce n {\displaystyle n} omnidirectional beams with orthogonal phase-modes so that multiple mobile stations can all simultaneously use the same frequency, each using

1380-415: Is the simplicity of the hardware. It requires far fewer phase shifters than other methods and can be implemented in microstrip on a low-cost printed circuit board . The antenna elements fed by a Butler matrix are typically horn antennae at the microwave frequencies at which Butler matrices are usually used. Horns have limited bandwidth and more complex antennae may be used if more than an octave

1440-527: Is unavoidably some coupling between the lines being crossed. An alternative which allows the Butler matrix to be implemented entirely in printed circuit form, and thus more economically, is a crossover in the form of a branch-line coupler . The crossover coupler is equivalent to two 90° hybrid couplers connected in cascade . This will add an additional 90° phase shift to the lines being crossed, but this can be compensated for by adding an equivalent amount to

1500-442: Is used. Target motion analysis can estimate these quantities by incorporating many directional measurements over time, along with knowledge of the position of the receiver and constraints on the possible motion of the target. Since each element in an AESA is a powerful radio receiver, active arrays have many roles besides traditional radar. One use is to dedicate several of the elements to reception of common radar signals, eliminating

1560-404: Is why AESAs are also known as low probability of intercept radars . Modern RWRs must be made highly sensitive (small angles and bandwidths for individual antennas, low transmission loss and noise) and add successive pulses through time-frequency processing to achieve useful detection rates. Jamming is likewise much more difficult against an AESA. Traditionally, jammers have operated by determining

1620-402: The AESA each module generates and radiates its own independent signal. This allows the AESA to produce numerous simultaneous "sub-beams" that it can recognize due to different frequencies, and actively track a much larger number of targets. AESAs can also produce beams that consist of many different frequencies at once, using post-processing of the combined signal from a number of TRMs to re-create

1680-464: The AESA system of a Raptor to act like a WiFi access point, able to transmit data at 548 megabits per second and receive at gigabit speed; this is far faster than the Link 16 system used by US and allied aircraft, which transfers data at just over 1 Mbit/s. To achieve these high data rates requires a highly directional antenna which AESA provides but which precludes reception by other units not within

1740-513: The AESA's 60 degree off-angle limit. With a half wavelength distance between the elements, the maximum beam angle is approximately ± 45 {\displaystyle \pm 45} °. With a shorter element distance, the highest field of view (FOV) for a flat phased array antenna is currently 120° ( ± 60 {\displaystyle \pm 60} °), although this can be combined with mechanical steering as noted above. The first AESA radar employed on an operational warship

1800-641: The Nike-X concept was abandoned in favor of much simpler concepts like the Sentinel program , which did not use MAR. A second example, MAR-II, was abandoned in-place on Kwajalein Atoll . The first Soviet APAR, the 5N65 , was developed in 1963–1965 as a part of the S-225 ABM system. After some modifications in the system concept in 1967 it was built at Sary Shagan Test Range in 1970–1971 and nicknamed Flat Twin in

1860-579: The West. Four years later another radar of this design was built on Kura Test Range , while the S-225 system was never commissioned. US based manufacturers of the AESA radars used in the F-22 and Super Hornet include Northrop Grumman and Raytheon. These companies also design, develop and manufacture the transmit/receive modules which comprise the 'building blocks' of an AESA radar. The requisite electronics technology

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1920-523: The Zeus program ended in favor of the Nike-X system in 1963. The MAR (Multi-function Array Radar) was made of a large number of small antennas, each one connected to a separate computer-controlled transmitter or receiver. Using a variety of beamforming and signal processing steps, a single MAR was able to perform long-distance detection, track generation, discrimination of warheads from decoys, and tracking of

1980-447: The ability to produce several active beams, allowing them to continue scanning the sky while at the same time focusing smaller beams on certain targets for tracking or guiding semi-active radar homing missiles. PESAs quickly became widespread on ships and large fixed emplacements in the 1960s, followed by airborne sensors as the electronics shrank. AESAs are the result of further developments in solid-state electronics. In earlier systems

2040-454: The antennas beamwidth, whereas like most Wi-Fi designs, Link-16 transmits its signal omni-directionally to ensure all units within range can receive the data. AESAs are also much more reliable than either PESAs or older designs. Since each module operates independently of the others, single failures have little effect on the operation of the system as a whole. Additionally, the modules individually operate at low powers, perhaps 40 to 60 watts, so

2100-429: The beam of radio transmission is in the desired direction. The beam direction is controlled by switching power to the desired beam port. More than one beam, or even all n {\displaystyle n} of them can be activated simultaneously. The concept was first proposed by Butler and Lowe in 1961. It is a development of the work of Blass in 1960. Its advantage over other methods of angular beamforming

2160-400: The beginning of the semiconductor era in the 1960s to distinguish this new technology. A semiconductor device works by controlling an electric current consisting of electrons or holes moving within a solid crystalline piece of semiconducting material such as silicon , while the thermionic vacuum tubes it replaced worked by controlling a current of electrons or ions in a vacuum within

2220-606: The benefits of AESA (e.g., multiple independent beams) can be realized at a lower cost compared to pure AESA. Bell Labs proposed replacing the Nike Zeus radars with a phased array system in 1960, and was given the go-ahead for development in June 1961. The result was the Zeus Multi-function Array Radar (ZMAR), an early example of an active electronically steered array radar system. ZMAR became MAR when

2280-428: The capability to alter these parameters during operation. This makes no difference to the total energy reflected by the target but makes the detection of the pulse by an RWR system less likely. Nor does the AESA have any sort of fixed pulse repetition frequency, which can also be varied and thus hide any periodic brightening across the entire spectrum. Older generation RWRs are essentially useless against AESA radars, which

2340-475: The entire assembly (the transmitter, receiver and antenna) into a single "transmitter-receiver module" (TRM) about the size of a carton of milk and arraying these elements produces an AESA. The primary advantage of an AESA over a PESA is the capability of the different modules to operate on different frequencies. Unlike the PESA, where the signal is generated at single frequencies by a small number of transmitters, in

2400-413: The first practical computers and mobile phones . Other examples of solid state electronic devices are the microprocessor chip, LED lamp, solar cell , charge coupled device (CCD) image sensor used in cameras, and semiconductor laser . Also during the 1960s and 1970s, television set manufacturers switched from vacuum tubes to semiconductors, and advertised sets as "100% solid state" even though

2460-424: The full power of the transmitter to the beam, and in receive mode they collect signals from each of the beam directions with the full gain of the antenna array. The essential components needed to build a Butler matrix are hybrid couplers and fixed-value phase shifters . Additionally, fine control of the beam direction can be provided with variable phase shifters in addition to the fixed phase shifters. By using

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2520-488: The independent variable rather than time. Assuming a sinc function beam shape, the beams must be spaced so that their crossovers occur at 2 / π {\displaystyle 2/\pi } of their peak value (about 4 dB down). Solid state (electronics) Solid-state electronics are semiconductor electronics: electronic equipment that use semiconductor devices such as transistors , diodes and integrated circuits (ICs). The term

2580-414: The junctions. The device has n {\displaystyle n} input ports (the beam ports) to which power is applied, and n {\displaystyle n} output ports (the element ports) to which n {\displaystyle n} antenna elements are connected. The Butler matrix feeds power to the elements with a progressive phase difference between elements such that

2640-562: The need for a large high-voltage power supply is eliminated. Replacing a mechanically scanned array with a fixed AESA mount (such as on the Boeing F/A-18E/F Super Hornet ) can help reduce an aircraft's overall radar cross-section (RCS), but some designs (such as the Eurofighter Typhoon and Gripen NG ) forgo this advantage in order to combine mechanical scanning with electronic scanning and provide

2700-464: The need for a separate radar warning receiver. The same basic concept can be used to provide traditional radio support, and with some elements also broadcasting, form a very high bandwidth data link . The F-35 uses this mechanism to send sensor data between aircraft in order to provide a synthetic picture of higher resolution and range than any one radar could generate. In 2007, tests by Northrop Grumman , Lockheed Martin, and L-3 Communications enabled

2760-433: The one to be used to jam. Most radars using modern electronics are capable of changing their operating frequency with every pulse. This can make jamming less effective; although it is possible to send out broadband white noise to conduct barrage jamming against all the possible frequencies, this reduces the amount of jammer energy in any one frequency. An AESA has the additional capability of spreading its frequencies across

2820-472: The operating frequency of the radar and then broadcasting a signal on it to confuse the receiver as to which is the "real" pulse and which is the jammer's. This technique works as long as the radar system cannot easily change its operating frequency. When the transmitters were based on klystron tubes this was generally true, and radars, especially airborne ones, had only a few frequencies to choose among. A jammer could listen to those possible frequencies and select

2880-471: The outbound interceptor missiles. MAR allowed the entire battle over a wide space to be controlled from a single site. Each MAR, and its associated battle center, would process tracks for hundreds of targets. The system would then select the most appropriate battery for each one, and hand off particular targets for them to attack. One battery would normally be associated with the MAR, while others would be distributed around it. Remote batteries were equipped with

2940-406: The path through the Butler matrix goes through a large number of hybrids and phase shifters. The cumulative insertion loss from all these components in microstrip can make it impractical. The technology usually used to overcome this problem, especially at the higher frequencies, is waveguide which is much less lossy. Not only is this more expensive, it is also much more bulky and heavier, which

3000-429: The phase shifters in lines not being crossed. An ideal branch-line crossover theoretically has no coupling between the two paths through it. In this kind of implementation, the phase shifters are constructed as delay lines of the appropriate length. This is just a meandering line on the printed circuit. Microstrip is cheap, but is not suitable for all applications. When there are a large number of antenna elements,

3060-458: The required number of hybrids is 2 m − 1 m {\displaystyle 2^{m-1}m} and phase shifters 2 m − 1 ( m − 1 ) {\displaystyle 2^{m-1}(m-1)} . To be orthogonal (that is, not interfere with each other) the beam shapes must meet the Nyquist ISI criterion , but with distance as

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3120-466: The separate antennas overlapped in space, and the interference patterns between the individual signals were controlled to reinforce the signal in certain directions, and mute it in all others. The delays could be easily controlled electronically, allowing the beam to be steered very quickly without moving the antenna. A PESA can scan a volume of space much quicker than a traditional mechanical system. Additionally, thanks to progress in electronics, PESAs added

3180-477: The signal drops off only as the square of distance. This means that the receiver is always at an advantage [neglecting disparity in antenna size] over the radar in terms of range - it will always be able to detect the signal long before the radar can see the target's echo. Since the position of the radar is extremely useful information in an attack on that platform, this means that radars generally must be turned off for lengthy periods if they are subject to attack; this

3240-530: The targets' own radar along with a lower rate of data from its own broadcasts, a detection system with a precise RWR like an AESA can generate more data with less energy. Some receive beamforming-capable systems, usually ground-based, may even discard a transmitter entirely. However, using a single receiving antenna only gives a direction. Obtaining a range and a target vector requires at least two physically separate passive devices for triangulation to provide instantaneous determinations, unless phase interferometry

3300-439: The transmitted signal was originally created in a klystron or traveling wave tube or similar device, which are relatively large. Receiver electronics were also large due to the high frequencies that they worked with. The introduction of gallium arsenide microelectronics through the 1980s served to greatly reduce the size of the receiver elements until effective ones could be built at sizes similar to those of handheld radios, only

3360-463: The variable phase shifters in combination with switching the power to the beam ports, a continuous sweep of the beam can be produced. An additional component that can be used is a planar crossover distributed-element circuit . Microwave circuits are often manufactured in the planar format called microstrip . Lines that need to cross over each other are typically implemented as an air bridge . These are unsuitable for this application because there

3420-428: The wide angular coverage that can be obtained. Another feature that makes Butler matrices attractive for military applications is their speed over mechanical scanning systems. These need to allow settling time for the servos . A linear antenna array will produce a beam perpendicular to the line of elements (broadside beam) if they are all fed in phase. If they are fed with a phase change between elements of then

3480-465: Was developed in-house via Department of Defense research programs such as MMIC Program. In 2016 the Congress funded a military industry competition to produce new radars for two dozen National Guard fighter aircraft. Radar systems generally work by connecting an antenna to a powerful radio transmitter to emit a short pulse of signal. The transmitter is then disconnected and the antenna is connected to

3540-509: Was invented by John Bardeen and Walter Houser Brattain while working under William Shockley at Bell Laboratories in 1947, could also amplify, and replaced vacuum tubes. The first transistor hi-fi system was developed by engineers at GE and demonstrated at the University of Philadelphia in 1955. In terms of commercial production, The Fisher TR-1 was the first "all transistor" preamplifier , which became available mid-1956. In 1961,

3600-816: Was the Japanese OPS-24 manufactured by Mitsubishi Electric introduced on the JDS Hamagiri (DD-155), the first ship of the latter batch of the Asagiri-class destroyer , launched in 1988. Butler matrix A Butler matrix is a beamforming network used to feed a phased array of antenna elements . Its purpose is to control the direction of a beam, or beams, of radio transmission . It consists of an n × n {\displaystyle n\times n} matrix ( n {\displaystyle n} some power of two) with hybrid couplers and fixed-value phase shifters at

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