Radar active phased antenna array. American aircraft radar with a phased array antenna

Amplitude, phase shift and wavelength (frequency) are the main characteristics of any wave

During interference, depending on the wavelength and the phase difference between them, the waves mutually reinforce or weaken each other in different points space

For the first time on a fighter: the airborne radar of the MiG-31 aircraft with the Zaslon PFAR

PFAR "Irbis-E" is installed on Su-35 aircraft

Last peep: AFAR "Zhuk-AE" on MiG-35

Western competitors also have their own AFARs - for example, the American AN / APG-81, which is planned to be installed on promising F-35s

With the help of AFAR, you can also conduct topographic surveys of the area - without being distracted from the main work of the onboard radar (the picture was taken by AFAR AN / APG-81)

HEADLIGHTS are used not only on aircraft, but also on ground-based radars (in the picture - the Don-2N multifunctional radar) ...

... and on naval ships - like the four 348 radars on the Chinese destroyer Haikou

Phased array antennas (PAR) are the most important tool for modern radars, and the most vigilant "eye" of modern fighters. It is worth noting that two possible types- passive (for example, "Barrier" - the world's first PFAR installed on MiG-31 fighters) and active (for example, "Zhuk-AE" on the new MiG-35). It is believed that AFAR - required element 5th generation aircraft. But to understand what it is and how it works, you have to start from afar.

Keyword here is antenna. Recall that any antenna is a device for emitting and receiving radio waves. Antennas are used both for communications and for detecting enemy equipment. In the simplest case, the antenna works in the manner of a bat, emitting ultrasound into space, inaudible to our ear, which, reflected from surrounding objects, gives the animal an idea of ​​​​them.

This is how the very first radars operated, protecting the British Isles from Luftwaffe raids: they emitted radio emission into space and “listened” to the reflected signal. According to the reflection characteristics, it is possible to mathematically calculate some properties of the object that reflected the radio wave - for example, its coordinates. However, since then, both science and technology have made a big step forward, and modern HEADLIGHTS are no more like their ancestors than a new computer is like the Colossus encryption machine (we talked about it in the article “ British Colossus”).

Unlike a simple antenna, antenna array represents whole array from hundreds (and sometimes thousands) of individual emitters. All these emitters work in concert, in such a way that the phases of the radio waves emitted by them change in a complex way (hence the definition of “phased”).

Recall that a radio wave, like any other wave, is a transverse oscillation of electric and magnetic fields. And, like any “decent” oscillation, it is characterized by:

Amplitude, which determines the "strength" of the oscillation.

The wavelength and associated frequency of oscillation. This value determines the nature of the electromagnetic oscillation. Radio waves have wavelengths ranging from tenths of a millimeter to tens of meters. For radar, centimeter wavelengths are used, with a frequency of about 3-30 GHz.

Phase - that is, the state of the oscillatory system in this moment time. Since the wavelength and frequency are, in principle, constant, the phase of the radar signal shows the current "position" of the wave on the amplitude scale.

Of these characteristics, we are especially interested in the phase, or rather, the phase difference of the oscillations. From the school physics course, we remember that waves, meeting at different points in space, interfere, that is, “recombine” with each other in accordance with the difference in their phases at these points. They can both mutually reinforce and weaken each other.

Let's finish a small theoretical digression and return to the HEADLIGHTS. As we remember, each antenna in the array radiates separately from the others, but in coordination with them - so that the phase difference of the radio signals emitted by them can be controlled - which means that it is possible to control the interference of waves at the points of space we need. By doing this, we will immediately achieve a lot of advantages.

Firstly, we will be able to make the signal, at will, either wide or very narrowly focused, and, in principle, give it the most varied form we need. This allows us to significantly save energy, strengthening the "scanning" only in the directions of interest to us.

To narrow the beam, you can, of course, use a conventional hyperbolic “dish” antenna, but it is problematic to install it on an airplane, and controlling its beam requires rotating the entire antenna - and this is not an easy task. Such antennas, in principle, are put on earlier aircraft, but it is both cumbersome and slow, and if you start rotating the antenna fast enough, controllability problems will inevitably arise.

This brings us to the second advantage of headlamps: in order to change the direction of the radio beam, we do not need to rotate the headlamp itself: it is enough to change the phase difference of the signals emitted by the antennas. This means that bulky and complex hydraulic equipment is not required, and the loss of time for the rotation of a bulky antenna also goes away: the phase switching is controlled by electronics, and the movement of the narrowly focused “attention” of the HEADLIGHTS occurs almost instantly.

At the same time, the PAR receives a signal from all directions - but in some of them it becomes much more sensitive, which makes it especially useful, say, for conducting a detected target. This is already a thing that is not a shame to put on any plane!

First, passive phased antenna arrays (PFAR) with one emitter and one receiver were used for this purpose. Its cells contain not separate emitters and receivers, but special phase shifters, which, receiving a signal from the emitter, change its phase properly. But a more modern version is an active headlamp (AFAR), each cell of which has its own emitter and receiver, although, of course, they all work under the control of a single electronic center. Each APAA cell itself emits a signal controlled in phase and frequency, and in the most difficult versions- and amplitude.

Unlike PFAR, they are much more sensitive and reliable: the failure of the emitter or receiver does not make the entire AFAR a useless heap of iron, it continues to work: there are hundreds of such receiver-transmitters in the AFAR! Well, modern powerful computers further expand the capabilities of this tool, allowing you to simultaneously conduct dozens of targets, including ground ones - and even map the area in parallel with the main work.

Moreover, it becomes possible to work with different frequencies radiation, increasing noise immunity or, say, using AFAR to interfere with the enemy: one part of the cells works as a radar, and the other as a jammer. Finally, they are more economical: in the PFAR there are high signal losses during transmission to the phase shifters, but in the AFAR they simply do not exist.

Of course, in this sea of ​​\u200b\u200bhoney there was a place for a fair amount of tar. The main headache for radar developers with AFAR is cooling. Such a mass of emitters overheats extremely strongly, and even in flight air cooling is completely insufficient, and a liquid system filled with special refrigerants has to be used.

Another problem is the cost: in modern AFARs, the number of individual cell elements reaches hundreds, or even 1-1.5 thousand. And if each of them does not cost too much - say, a couple of hundred dollars - then in total it comes out fairly.

Active phased array antenna (AFAR) - a kind of phased antenna array (PAR).

In an active phased array antenna, each array element or group of elements has its own miniature microwave transmitter, eliminating the need for the single large transmitter tube used in passive phased array radars. In an active phased array, each element consists of a module that contains an antenna slot, a phase shifter, a transmitter, and often also a receiver.

Comparison with passive grating

In an ordinary passive array, a single transmitter with a power of several kilowatts feeds several hundred elements, each of which emits only tens of watts of power. A modern microwave transistor amplifier can, however, also produce tens of watts, and in an active phased array radar, several hundred modules, each with a power of tens of watts, produce an overall powerful radar main beam of several kilowatts.

While the result is identical, active arrays are much more reliable, since the failure of one transceiver element of the array distorts the antenna pattern, which slightly degrades the performance of the locator, but in general it remains operational. Transmitter lamp catastrophic failure, which is a problem with conventional radars, simply cannot happen. Additional benefit - weight savings without a large lamp high power, an associated cooling system and a large high voltage power supply.

Another feature that can only be used in active arrays is the ability to control the gain of individual transmit/receive modules. If this can be done, the range of angles through which the beam can be deflected is greatly increased, and thus many of the array geometry limitations that conventional phased arrays have can be bypassed. Such gratings are called supermagnification gratings. It is not clear from the published literature whether any existing or planned antenna array uses this technique.

disadvantages

AFAR technology has two key problems:

Power dissipation
The first problem is power dissipation. Due to the shortcomings of microwave transistor amplifiers (monolithic microwave integrated circuit, MMIC (English) Russian ), the transmitter efficiency of the module is typically less than 45%. As a result, AFAR allocates a large number of The heat that must be dissipated to keep the transmitter chips from melting and turning into liquid gallium arsenide - the reliability of GaAs MMIC chips improves at low operating temperatures. Traditional air-cooling used in conventional computers and avionics is poorly suited to the high packing density of AFAA cells, resulting in modern AFAAs being liquid-cooled (American designs use a polyalphaolefin (PAO) coolant similar to synthetic hydraulic fluid). A typical liquid cooling system uses pumps that introduce coolant through channels in the antenna and then discharge it to a heat exchanger - this can be either an air cooler (radiator) or a heat exchanger in the fuel tank - with a second liquid cooling the heat exchange loop to lead high temperature from the fuel tank.

Compared to conventional fighter aircraft radar with air-cooled, AFAR is more reliable, but will consume more electricity and require more cooling. But AFAR can provide much more transmitting power, which is necessary for a greater range of target detection (increasing transmitting power, however, has the disadvantage of increasing the trace along which enemy radio intelligence or RWR can detect the radar).

Price
Another problem is the cost of mass production of modules. For a fighter radar requiring typically 1000 to 1800 modules, the cost of AFAR becomes unacceptable if the modules cost more than one hundred dollars each. Early modules cost approximately $2,000, which prevented the mass use of AFAR. However, the cost of such modules and MMIC chips is constantly decreasing, as the cost of their development and production is constantly decreasing.

Despite the disadvantages, active phased arrays are superior to conventional radar antennas in almost every way, providing greater tracking capability and reliability, albeit at some increase in complexity and possibly cost.

Receiving-transmitting module

AFAR transceiver module

Receiving-transmitting module- this is the basis of the spatial signal processing channel in APAA.

Its composition includes active element is an amplifier that makes this device electrodynamically non-reciprocal. Therefore, to enable the device to work both for reception and for transmission, it separates the transmitting and receiving channels. Separation is carried out either by a commutator or a circulator.

receiving channel

Part receiving channel includes the following devices:

• Receiver protection device- usually either a spark gap or another threshold device that prevents overloading of the receiving channel.
• Low noise amplifier- two or more stages of active signal amplification.
• Phase shifter- device for the phase delay of the signal in the channel to set the phase distribution over the entire opening of the grating.
• Attenuator- a device for setting (reducing, attenuating) the signal amplitude for setting the amplitude distribution along the grating opening.

Transmitting channel

The composition of the transmitting channel is similar to the composition of the receiving channel. The difference lies in the absence of a protection device and lower noise requirements for the amplifier. However, the transmit amplifier must have more output power than the receive amplifier.

Produced radar with AFAR

• AN/APG-63(V)2/3 (F-15 C/E)
• AN/APG-79 (F/A-18 E/F)
• AN/APG-80 (F-16 Block 60)
• AN/APG-81 (F-35)
• AN/APQ-181 (B-2 Spirit)
• EL/M-2052 (F-15 , MiG-29 , Mirage 2000)

see also

Links

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Yuri Ivanovich Bely was born in 1951. He graduated from the Moscow Higher Technical School. N.E. Bauman. Since 1974 - on military service. He served as a military representative at the Research Institute of Instrument Engineering, deputy head of the Air Force ordering department. Since 1987 - head of the military representation at the NIIP. Military rank - Colonel. Since March 1998 - Director of NIIP. Currently - CEO JSC "NIIP im. V.V. Tikhomirov. Doctor of Science (engineering), academician of the International Informatization Academy, member of the STC of the military-industrial complex under the Government of the Russian Federation. Cavalier of the Orders of Friendship and "For Merit to the Fatherland" IV degree.

One of the main components of the high combat capabilities of modern fighters is a perfect weapon control system, which is based on a powerful airborne radar station. All fighters of the Su-27 and Su-30 family supplied to the world market and serving in the domestic Air Force are equipped with weapon control systems developed at the Research Institute of Instrument Engineering named after I.I. V.V. Tikhomirov. NIIP is a pioneer in the development of phased array radars (PAR). For the first time, the "Tikhomirovskaya" radar with PAR was used on the MiG-31 fighter-interceptor. Starting with the Su-30MKI aircraft, PAR radars are already being installed on Sukhoi fighters. This year, tests of the new Su-35 multifunctional fighter began, for which NIIP is creating the Irbis-E passive phased array radar, the most advanced in its class. And for a promising fifth-generation fighter, the Tikhomirovites are developing their first radar with an active phased antenna array (AFAR). To find out how work on these topics is developing, Rise correspondent Andrey Fomin met with the general director of JSC Research Institute of Instrument Engineering. V.V. Tikhomirov” Yuri Bely, who kindly agreed to give an interview to our magazine.

Yuri Ivanovich, please tell us how the Irbis-E radar with the headlights is being tested.

The program is progressing well. We continue to fly on the Su-30MK2 flying laboratory with an experimental Irbis-E radar set with a 1 kW transmitter - we have been flying for almost a year and a half and have received confirmation of the main characteristics. Most of the modes have been worked out, in particular - the multipurpose air-to-air mode, the early warning mode, the air-to-surface modes with low, medium and high resolution. In addition, a set of radar units was manufactured, including a standard 5-kilowatt transmitter for the serial Irbis-E, which is undergoing laboratory tests - we are completing them in in full this year

In addition, we have produced two models of the radar control system in a complete set for installation on experimental Su-35 aircraft. The first of them, which has already been tested in the laboratories of NIIP, and then in the relevant units of KnAAPO, was installed on board the second copy of the Su-35. When, according to the aircraft test schedule, the turn of flight testing of the radar complex comes, we will turn it on. To ensure the testing of the Irbis on the Su-35, a control and repair vehicle station (KRAS) with jobs has been prepared - therefore, we will soon begin flying on a real aircraft with a full-scale complex of the Irbis. The second set for the next experimental aircraft has also already been manufactured, tested by us and handed over for acceptance. Soon it will also be installed on board. Thus, the Irbis test program is in full swing, and by the time the Su-35 is ready for mass production, its radar system will be fully developed.

Radar control system with headlights "Bars", which is now in large-scale production. It is equipped with the Su-30MKI, Su-30MKM and Su-30MKA fighters supplied by the Air Forces of India, Malaysia and Algeria. In addition, the licensed production of "Bars" is being mastered in India, and "NIIP named after V.V. Tikhomirov is working on its further phased modernization

Is it possible to install the Irbis on previously produced Su-27 aircraft in the process of their modernization?

This option has been worked out as part of the Su-27SM2 ​​program. In fact, this is the configuration of the radar control system, which is now being tested in a flying laboratory with a kilowatt transmitter (the power of the aircraft does not allow the use of a 5 kW transmitter on previously produced Su-27s). Therefore, the version of the Irbis that is now on the flying laboratory is an almost ready-made kit for the modernization of combat aircraft. However, apparently due to financial considerations, it was decided to develop the modernization of the Su-27SM without changing the type of radar, but only increasing its capabilities - introducing new modes, ensuring the use of new types of weapons, etc. Such an aircraft was built and entered flight tests this year. But it should be borne in mind that tests may take more than one year, and the remaining calendar resource of combat fighters, the "youngest" of which were released in the early 90s, is steadily declining in the meantime. The only way out of this situation can be the purchase of new aircraft - such as the Su-35, which immediately have on board the radar with the Irbis PAR. The Russian Air Force has already come close to such a decision. At the presentation of the Su-35 at the FRI for the press in July this year, the Commander-in-Chief of the Air Force, Colonel-General Alexander Zelin, said that the possibility of ordering new Su-35 aircraft to rearm two or three regiments of the Russian Air Force with them is being considered.

Is there any plan to develop the predecessor of the Irbis - the Bars radar control system used on Su-30MKI aircraft? Is there any way forward on this topic?

There is still some way to go. Let's take, for example, the Su-30MKI. Passed evaluation tests of the current configuration of "Bars" on Su-30MKI aircraft in India, which confirmed the elimination of all comments. And now the Indian Air Force is raising the question: to make all 140 aircraft according to licensed program, calculated until 2014, in the form approved in the late 90s. - unreasonable. Therefore, they offer us to carry out the modernization of Bars in the process of licensed production, incl. demanding to use AFAR on it. For our part, we have developed proposals that provide for a two-stage modernization. At the first stage, "Bars" remains with a passive phased array, but the capabilities of the radar in terms of operating modes and characteristics will be increased. And at the second stage, taking into account the groundwork for AFAR received by that time as part of work on the fifth generation aircraft, Bars can already be equipped with an active phased antenna array. The Indian Air Force is currently considering these proposals of ours, and we hope that a decision on how to modernize Bars will be made soon.

Irbis-E radar control system aboard the Su-35 = at the MAKS-2007 air show (above) and the Su-30MK2 flying laboratory (below)

If the conversation has already turned to modernization, please tell us how the work on the modernization of the Zaslon SUV of the MiG-31 fighter-interceptors is progressing. The Russian Air Force has already officially announced that this spring they received the first modernized aircraft of this type ...

Turning to the topic of "Barrier", we must first note that this is our basic development, with which we began the use of electronic scanning on board the aircraft, the use of digital computers - this was the first time in our domestic practice. SUV "Zaslon" with PAR on board the MiG-31 fighter is an unconditional priority not only for NIIP them. V.V. Tikhomirov, but throughout our country. Since then (and the MiG-31 was put into service in 1981), many years have passed, and the complex, of course, requires modernization. This work is ongoing. Last year, the first stage of state joint tests (GSI) of the upgraded MiG-31 was completed. The Leninets plant began supplying the modified systems to production aircraft, and the first of them went into operation this year. At the same time, tests on the second stage of the CSI are ongoing at the GLITS in Akhtubinsk, which is scheduled to be completed by the end of this year.

What has already been done? Firstly, the modernization touched on the information and control field of the navigator's cabin: made new system indications on the LCD with new types of information display. Secondly, the range of the complex has been increased. Thirdly, the range of weapons used has been expanded. At the same time, the antenna itself remains unchanged, but some SUV units are changed, and the computer system is completely replaced. Already discontinued vehicles used on the MiG-31 are giving way to modern new-generation on-board computers. In the future, we plan to further increase the capabilities of the complex.

And finally, we come to the most important thing - work on AFAR. A little over a year ago, at the MAKS-2007 air show, full-scale fragments of prototypes of active phased arrays developed by NIIP were shown for the first time. As you know, your institute is the lead developer of the radio-electronic system with AFAR for the fifth generation aircraft. How are these works progressing?

The work is proceeding according to the schedule, under the contract that we signed with Sukhoi. By this schedule in November of this year, the first full-sized fully equipped with transceiver modules and tuned AFAR will be delivered to the stand for docking with the rest of the station. Today, the first antenna has already been fully assembled, completed and handed over for tuning. The production of transceiver modules based on monolithic microcircuits has been launched at Istok Research and Production Enterprise, the assembly of the second sample is underway, and the acquisition of parts and modules of the third sample has begun. Thus, today we already have three antennas in production. They will successively go to trials - the first, as I said, in November, the second - in March-April of the next year, and so on. As early as next year, the AFAR is expected to be installed on one of the first prototypes of the fifth generation aircraft, which are currently being built at KnAAPO, and in 2010 to begin its flight testing. Today, we can confidently say that all technical problems in the development and manufacture of transceiver modules have been overcome. Now we are resolving issues related to the antenna as a whole - cooling, pairing, beam control, but, I emphasize, everything is moving in accordance with the approved schedule. As the tests progress, we will gradually increase the composition of the complex - first on the stands, then on the aircraft, as a result - we will come to the configuration fully provided for by the terms of reference.

Fragment of a full-scale prototype of the X-band AFAR developed by the NIIP. V.V. Tikhomirov, first shown publicly at the MAKS-2007 air show in August 2007.

How much time may be needed for the entire cycle of testing and fine-tuning AFAR?

As you know, the development of a modern radar usually takes 5-7 years. Therefore, if we take the current 2008 as the starting point, when the actual development of the equipment began, then we can assume that our system will be completely ready for operation by about 2014-2015. The situation is similar abroad: even the F-22, which has been put into service for quite some time, has not yet fully developed all the AFAR modes. In this regard, it should be noted that NIIP them. V.V. Tikhomirov has a wealth of experience in the field of phased antenna arrays. The Americans at one time skipped the stage of passive HEADLIGHTS - moving from slotted gratings directly to AFAR. We also have extensive experience in the field of phased array, which has been around for about 40 years (and we argue that AFAR differs from passive phased array essentially only in the technological design of the emitters, and we take the rest of the mathematical and modeling apparatus from the phased array already well mastered by us) , which gives us serious advantages, incl. and in terms of completion. We have such developments in PAR that no one else in the world has!

You probably follow the work on AFAR, which is being carried out both abroad and in our country. Can you name some features of your project relative to the others, its advantages?

Well, it is rather difficult to compare with the Americans, since there is very little real (and not advertising) information, and one can only judge by some indirect signs. But we believe that we have laid down and are implementing characteristics that are at least not inferior, but in fact in some way superior to those possessed, for example, by the AFAR radars of the F-22 and F-35 aircraft. As for the work carried out by other domestic radar developers, the main difference lies in the technology. We rely on the most modern technologies of monolithic microwave microcircuits in the world, while our domestic colleagues use the so-called hybrid technologies, which, for example, have already been abandoned in Europe. Like us, the Americans are building their AFARs on monolithic microcircuits, with the prospect of increasing the degree of their integration and moving in the future to what is called “intelligent skin” - i.e. The transceiver modules can be located anywhere in the aircraft, forming the required radiation field. Thus, we are on the main world path of AFAR development.

Is it possible to say that the technologies obtained during the development of the AFAR under this program can be used in the future to create radars for other aircraft and, in general, other types of equipment?

Certainly. For example, sooner or later the question may arise of developing a new fifth-generation light fighter or equipping AFARs with modernized 4+, 4++ generation aircraft, etc. And in this case, instead of “reinventing the wheel” again, it is better to use already proven technologies, while simultaneously ensuring the loading of production (after all, the larger the production scale of transceiver modules, the lower their cost). The task in this case will simply come down to scaling: all the same technologies and components will remain, and it will only be necessary to reduce the diameter of the antenna. This is no longer a scientific task, but a purely constructive-technological one. Further. Transceiver modules that have already been mastered in production can be used in radar stations, for example, in anti-aircraft missile systems. So, the more applications we find for already proven technologies, the better. After all, if earlier we had the task of creating and “promoting” production, now the opposite situation may arise: capacities are “promoted”, and consumption is low. Only under conditions of good production load, the cost of modules can be acceptable.

And what is your vision - in the future there will be a place for both directions of PAR development (active and massive), or with the development of AFAR, the line of passive PAR will be forgotten?

I believe that, at least in the foreseeable future, both directions will have their own niche. AFAR will be able to displace conventional PAR only if its element base becomes very cheap. In the meantime, even in the conditions of mass serial production, at the current level of technology, the cost of AFAR and PAR differs significantly. So it is too early for passive HEADLIGHTS to go down in history.

Vladimir SHCHERBAKOV Sikorsky company photo

Eli Bruckner

A constantly rotating radar antenna, which directs high-frequency signals towards the horizon in order to detect distant objects, is an integral element of the panorama of a modern airfield. However, in many of the most well-known radar applications, such as aviation, air defense and intelligence, the mechanically controlled antenna mirror is beginning to be replaced by a new type of device. Located in the same plane, a set of small identical antennas, each of which is capable of transmitting and receiving signals, replaces the concave reflector. The beam created by this set of antennas moves around the airspace, while the antenna system itself remains stationary. The direction of the electromagnetic radiation generated by the radar is set by a special electronic device, and the beam control is based on the use of the phenomenon of electromagnetic wave interference. This technical innovation used in radar systems is called phased array antennas. The basic principles of building radar stations remain the same.

The operation of all radar stations is based on directional radiation of radio signals. As a rule, the frequency of the radiation lies in the microwave range, from 3108 to 1010 Hz, although some types of radar stations with very long range actions operate in the high frequency (HF) range and microwave frequencies(UHF), or respectively in the ranges from 3106 to 3107 Hz and from 3107 to 3108 Hz. Depending on the shape, the antenna emits a narrow, highly directional beam, suitable for precise target tracking, or a wide fan-shaped beam, most suitable for viewing wide areas of airspace.

When the signal sent by the antenna reaches the object, it is reflected. If the power of the transmitted pulse, the sensitivity of the antenna and the reflectivity of the object are large enough, the reflected signal that hits the antenna can be detected by the radar station. Depending on the type of radar and the type of emitted pulse, the reflected signal carries various information about the goal.

The direction from which the reflected signal comes determines the location of the object, and if the radar station emits pulses of energy, and not continuous signal, then the time delay between sending the pulse and receiving the reflected signal can also be used to judge the distance to the object. Some radars provide a measurement of the Doppler shift in the frequency of the reflected signal (i.e., the difference between the frequencies of the direct and reflected signals), which occurs when the radiation source (in this case target) and the receiver (radar) are moving relative to each other. The value of the Doppler shift calculates the speed of the object towards or away from the antenna.

For a given distance to an object, the intensity of the reflected signal gives some idea of ​​the size of the object. The word "representation" is used here deliberately: two objects of the same size, if they have a different shape or are made of different materials, will send out reflected signals that differ significantly in intensity. To get more exact information about the size of objects, some radars transmit pulses so short that they are physically shorter than the targets they might encounter along their path. If the radar station radiates energy only for a few billionths of a second, then by the time the transmission of the pulse is over, its front will pass the distance in a space of the order of one or several meters. Such an impulse in space has a shorter extension than, for example, an airplane. Radio signals are reflected from both the far and near surfaces of the target, and in the case of an extremely short pulse, two reflected signals are formed. The time interval between these two reflected signals corresponds to the length of the target.

Since the radar conventional type surveys wide areas of airspace, it can collect information on a large number of objects. However, between successive moments when the same target is in the field of view of the radar, there is inevitably some (sometimes significant) time interval. Target information update rate, i.e. the frequency with which the same target is fixed by the radar, for most stations with a rotating antenna, does not exceed the speed of rotation of the antenna mirror around its axis. In air traffic control radars, for example, the green line of the radial scan, which moves across the screen, leaving marks on it characterizing the new position of the aircraft and carrying other information about it, rotates at the same speed as the antenna mirror itself rotates. Updating information about the observed object in such radar stations is usually done every six seconds, and even in the most advanced military stations, information is rarely updated more than twice in one second.

There are circumstances in which new information information on the position and movement of targets is required to be obtained more frequently. A single mechanically steerable radar can provide continuous data on one or more closely spaced objects by constantly tracking them by rotating the antenna system. However, for many combat and reconnaissance missions, such as tracking from a warship several missiles moving towards it from various directions, or closely observing the flight of several components of a disintegrated warhead in an ICBM test, each of a large number of targets must be observed continuously. Until recently, in such cases, resorted to the use of several radar stations, each of which was intended to track one or more targets. With the advent of radar stations with a phased array antenna, the need to use several radars with mechanically controlled antennas in such cases has disappeared. Now they can be replaced by just one station, equipped with a new antenna system. An example is a radar station with the code name COBRA DANE, which has a phased antenna array; it is installed on the shores of the Bering Sea and can simultaneously monitor hundreds of targets dispersed in a space limited by 120 ° in azimuth and approximately 80 ° in elevation. In fact, the radar station observes these targets simultaneously by automatically transferring its beam from one target to another in a time measured in microseconds.

The electronic beam control that achieves these remarkable features is based on the use of a simple physical phenomenon. When nearby sources radiate energy simultaneously at the same frequency, the waves coming from these sources add up. This phenomenon is called interference. The nature of the interaction of two waves from two sources separated in space depends on the phase shift between these waves. If the crests and troughs of one wave respectively coincide with the crests and troughs of another wave (the phase shift is 0), then the resulting oscillation will have a total amplitude. If the waves are out of phase and their crests and troughs do not match, then the resulting signal will be attenuated or (with a 180° phase shift) equal to 0.

A phased antenna array is usually assembled from radiating elements located in the same plane and at the same distance from each other, to which microwave signals of equal amplitude and phase are supplied. A master oscillator generates a signal, and transistors and special tubes designed for microwave operation, such as traveling wave tubes, amplify it. If signals are emitted in phase from all array elements, then their amplitudes are added at certain points in space along a line perpendicular to the array plane. Consequently, the emitted signal will be strong, and the signal reflected from objects lying in the path of its propagation along the axis perpendicular to the plane of the antenna array and within a small angle to the side of it will have sufficient intensity to detect it.

At large angles of deviation from the perpendicular axis of the antenna array, signals from different radiating elements must travel unequal distances to the target. As a result, the ratio of their phases changes and they interfere, weakening or completely destroying each other. Thus, outside the narrow cone, the axis of which coincides with the perpendicular axis of the antenna array and in which interference occurs with amplification of the resulting wave amplitude, the signals reflected from the objects are of low intensity and cannot be detected. The physical principles underlying the formation of interference patterns make it possible to determine the width of this cone. It is directly proportional to the operating wavelength of the radiation and inversely proportional to the size of the antenna array. If each element of the antenna array emits signals in phase with the others, then the radar beam propagates in a direction strictly perpendicular to the plane of the array.

Now suppose that the signals of each radiating element are delayed by a time that increases uniformly from element to element along the plane of the array. In this case, the signal emitted by each element will lag behind the signal of the neighboring element by a part of the wavelength. As a result, all signals will be phase shifted relative to each other. Now the zone in which the individual signals are in phase and, when added, give a signal of the total amplitude, with which it is possible to detect targets, is not located along the perpendicular axis of the array, but is shifted in the direction of increasing signal delay. The beam deflection angle depends on the phase shift of the signals emitted neighboring elements antenna array, the size of the latter and the wavelength. And in this case, the beam takes the form of a narrow cone, surrounded by areas of debilitating interference. Thus, the radar beam is deflected without changing the position of the antenna.

When the reflected signal returns from a target that is in this new direction, determined by the progressive phase shift, the circuit providing the time delay transmitted signal, introduces new series delays of individual signals arriving at each of the radiating elements. Since the front of the returning wave reaches the antenna array at an angle to its plane, the antenna elements that emitted the signal last (they are closer to the target) receive the reflected pulse first. Therefore, the same series of delays, due to which a given radiation directivity is created, ensures that all components of the reflected signal arrive at the receiving device in one phase, which makes it possible to process them to obtain information about the target.

Phase delay control makes it possible to deflect the beam of a conventional type antenna array at an angle of up to 60 ° from the perpendicular axis, which provides a field of view of 120 ° in azimuth, i.e., keeping the antenna stationary, the radar surveys the third part of the circular horizon line, and if the plane the lattice has a sufficient slope, then from the horizon to the zenith and far beyond it. Since the beam control is not associated with any mechanical adjustments, the movement of the beam within the entire field of view takes only a few microseconds. By using a computer to calculate the necessary phase shifts to deflect the beam to the desired angle and to control the signal delay circuit, a phased array radar such as COBRA DANE can simultaneously track several hundred targets.

An electronic device that provides control of the radar beam and creates the required delay of the microwave signal when applied to each element of the antenna array is called a phase shifter. It consists of pieces of cable or waveguide of very precise dimensions. An increase in the length of the cable, through which the signal from the generator or amplifier is fed to the radiating element, leads to a delay in the signal transit time. In practice, it is impossible to make sure that the length of all cables, through which signals are fed to the radiating elements of a phased antenna array, changes smoothly, ensuring a continuous change in phase delays. Therefore, the phase shift is performed in jumps. Each element of the antenna array is connected to several cables of various lengths. To obtain phase shifts that provide a given beam deflection, each circuit includes certain combination cables.

The COBRA DANE radar used for reconnaissance purposes, for example, uses three-element phase shifters. Each such device has three strip lines of various lengths, a kind of waveguides, which provide the transmission of microwave vibrations along a narrow copper strip located between two grounded copper plates. One of the strip lines increases the length of the signal path by an amount equal to half the wavelength, about 15 cm, since operating frequency radar station COBRA DANE is approximately 1 GHz. This provides a 180° phase shift of the signal with respect to the non-delayed signal. Another stripline provides a signal delay of a quarter wavelength, i.e. provides a phase shift of 90°. The length of the third strip line is such that it creates a delay equal to one-eighth of the wavelength, which corresponds to a phase shift of 45°. In various combinations, these three striplines can change the phase of the signal by any multiple of 45 degrees, from 0 to 315°.

A step change in the phase delay should probably lead to the appearance of dead zones. How, then, using eight different phase lags at 45° intervals, can a radar beam move continuously? The answer to this question lies in the properties of the interference patterns. Whenever the phase difference between the signals emitted from opposite sides of the antenna array reaches 360°, or one wavelength, the interference region where the beam with the total amplitude is formed will shift in space by a distance approximately equal to its own width. Therefore, in order to shift a beam perpendicular to the plane of the antenna array (it has such a direction when all signals are radiated in phase) to an adjacent position without forming a dead zone between these two positions, the total phase shift along the plane of the antenna array must be approximately 360 °.

Whether the phase shifts along the grating plane increase continuously or stepwise (through 45°) does not matter. A step change in phase shifts leads only to a slight decrease in the radiation power and some loss of sensitivity of the antenna system. To ensure smoother beam movement of an antenna array with three-element phase shifters, you can set a smaller total phase shift value, for example, 180°, i.e. four times at 45°.

If the beam is to be deflected from the perpendicular direction by more than its width, the total phase change along the plane of the antenna array must exceed 360°. Due to the periodic nature electromagnetic oscillations phase shift by a multiple of wavelengths is equivalent to 360°. For a total phase change of more than 360°, the linear increase in the phase delay from zero to 360° must be repeated several times over the entire plane of the antenna array. The first series of delays provides a total phase shift of one wavelength, the second series increases it to two wavelengths, and so on. Graphically, the change in the phase delay along the plane of the antenna array is represented as saw teeth: the steeper their bevels and the greater their number, the sharper the beam is deflected.

From simple geometric rules it follows that with increasing beam deviation from the perpendicular direction effective area antenna is reduced. As a result, the sensitivity of the phased antenna array to signals reflected from the target rapidly decreases at angles of deviation of the beam from the perpendicular axis by more than 60°. Therefore, a single phased array antenna cannot provide the same visibility in all directions as mechanically rotated antennas. One of the solutions to this problem is the use of several antenna arrays with their planes turned into different sides. Another way to expand the field of view of a phased antenna array is to place it in a horizontal plane under a domed lens that reflects radiation, and due to this, the beam deflection angle of the radar station increases. When the antenna array forms a beam at an angle of 60° to the zenith, the use of a lens can provide an even greater deviation of it, up to 90° to the zenith, i.e. towards the horizon. Thus, the lens allows you to view the entire hemisphere of airspace using an antenna array. The lens can be made of a special ceramic or plastic that reflects microwave radiation. It can also act as second stage phase shifters to further delay the phase of the signal emitted by the antenna array.

When phase control is used to send a short pulse at a large angle to the perpendicular axis of the antenna array, the radiated pulse will inevitably be distorted - stretched in time and space. Let us assume that the antenna emits a pulse with a duration of 5 nsec. If the radiation of a radar station is directed strictly perpendicular to the plane of the antenna array, then the pulse has a rectangular longitudinal section in space; its width is equal to the width of the antenna array, and its length is equal to the distance that an electromagnetic wave travels in 5 ns, i.e. 1.5 m. If, on the other hand, due to the phase shift, the beam deviates significantly from the perpendicular axis, then the longitudinal section of the pulse will have the shape of a parallelogram. In relation to the target, the pulse length will be more than 1.5 m, since the signals emitted by the individual elements of the antenna array do not reach the target simultaneously, but sequentially. The reflected pulse that returns to the antenna array will also be stretched.

Much longer pulses, such as 1000 ns, are typically used to detect and track targets, and distortion within a few nanoseconds is of little value. Pulse stretching, in turn, has little effect on the ability of the radar station to determine the location and speed of the target from the nature of the reflected signal. For separate observation of targets moving in close formation, however, it is required to emit short pulses. They are also necessary to determine the size of the target from the signals reflected from its front and rear surfaces. If the transmitted short pulse is stretched, then the reflected signals no longer arrive separately, but merge, which makes it difficult to obtain the required information.

Method, like that, which is used to control the beam by shifting the phases of the signals, helps in this case too; it allows you to save the shape of the pulse. To ensure the required phase shift, it is necessary to delay the signals only for a time corresponding to parts of the wavelength. The delays required to avoid pulse stretching are equivalent to an integer number of wavelengths. In this case, the radiation of signals by individual elements of the antenna array is carried out sequentially, and the lead in the radiation of each signal with respect to the next one is proportional to the distance that the signal must travel to the target. The result is the same effect as if the antenna array rotated, keeping the target in the direction of the perpendicular axis. This technique is known as beam steering with time delays. Similar to the method that uses increasing phase delays, it makes it possible to send in given direction a signal of coherent and therefore powerful radiation.

Such large delays, equivalent to a distance of several meters that the signal travels, require the inclusion of cable segments of the appropriate length in the signal path from the generator or amplifier to the radiating element. A large phased array antenna can include many thousands of radiating elements, and if each had its own time delay circuit, then the radar installation would be extremely complex and expensive. Therefore, designers of radar stations seek to find a compromise solution that would simultaneously achieve the desired pulse shape, even at large angles of deviation of the radiation direction from the perpendicular axis of the antenna array, and structural simplicity. As a result, in modern radars with phased antenna arrays, beam control is carried out using both phase shift and time delays.

In the COBRA DANE radar, for example, each of the 15,360 radiating elements is associated with a separate three-element phase shifter, so each signal is phase shifted separately. In target detection mode, the radar station emits pulses with a duration of 1000 ns, and the beam is controlled only by introducing phase delays. Since the purpose of the radar station is to track ballistic missiles, it must provide information about their size after detection. For this purpose, the antenna array is divided into 96 sections, each of which includes 160 radiating elements. After the target is detected, the station begins to emit pulses of very short duration, and the signals supplied to each section of the antenna array first pass through the time delay circuit. These circuits are similar to phase shifters, but much larger. They consist of a set of coaxial cables of various lengths, and any combination of them can be included in the circuit to create time delays corresponding to the signal propagation distance from one to 64 wavelengths, or about 19.2 m, since the operating frequency of the COBRA DANE radar is approximately 1 GHz.

Since the transverse size of individual sections of the antenna array is about 2.7 m, which is small compared to its diameter of 29 m, the distortions that occur in each section of the array at large angles of beam deviation from the perpendicular axis lie within acceptable limits. Each section of the antenna array emits a signal that occupies a volume in space, the longitudinal section of which has the shape of a parallelogram. Due to time delays, these signals are summed up so that the distortions of the individual signals do not add up. As a result, the pulse shape is preserved quite well, and devices that provide time delays of signals are used only 96, and not 15 360. As for the consumption of materials, ensuring beam control of the COBRA DANE radar station by introducing time delays required the additional use of cables with a total length a little more than 1500 m. If the division of the antenna array into separate sections, then an additional 165 km of cable would be required.

Replacing a mobile antenna with a set of fixed radiating elements, in addition to the possibility of electronic beam steering, can provide other advantages. One of these advantages is to provide high reliability in operation. The operation of a fixed antenna array is independent of the condition of wearable mechanical components such as bearings and motors. In addition, most mechanically controlled radars use one or more very large vacuum tubes to amplify microwave signals.

An example is the Marconi Martello radar, made in the UK and intended for use in the air defense system. The main circuit element in this station is a vacuum tube with an output power of about 3 MW. If it fails, the entire system fails. True, in such radar stations intended for operation in reconnaissance and air defense systems, it is always possible to quickly switch to auxiliary sources of microwave radiation energy.

In contrast, in the COBRA DANE radar station, the radiated energy is generated by 96 lamps, each with a power of 160 kW. The output signal from each lamp is fed to a divider, and then to 160 radiating elements that make up one section of the antenna array. The failure of one lamp in this case leads to the failure of only one of the 96 parts of the antenna array, and the radar station as a whole remains operational, although the quality of its work is somewhat deteriorating. What's more, the smaller lamps are easier to replace in the event of a failure than the single large lamp used in the Martello radar.

Solid-state phased array radars have an even higher level of reliability and ease of operation. Transistor circuits of generators and amplifiers are used, for example, in radar stations code-named PAVE PAWS, designed to detect ballistic missiles launched from ships and submarines (such stations have already been installed on Cape Cod and California, and their placement planned in the states of Georgia and Texas). IN individual modules four 100 W transistors connected in parallel were mounted. Each module provides excitation of one radiating element. Thus, the signals fed to each of the two surfaces of the dual antenna are amplified simultaneously by 1792 modules in the antenna element chain, rather than 96 lamps, so that the failure of one element affects the performance of the radar station as a whole even less. In addition, the mean time between two failures for a single semiconductor module is significantly longer than for the lamp used in the COBRA DANE radar station. In the first case, this figure is 100,000 hours, in the second - 20,000 hours. In case of failure of modules that are 30 cm long and operate from a 28 V voltage source, it is much easier to replace them than lamps in the COBRA DANE radar station, which have a length of 1, 5 m and operating under voltage of 40,000 V.

In the PAVE PAWS radar, as in many others built on semiconductor elements, the signals are amplified after they are distributed over the antenna elements and shifted in phase. Therefore, the power losses that occur during the passage amplified signal through the divider and phase-shifter circuits are excluded. However, along with this efficiency gain and all the other advantages, semiconductor technology also has a disadvantage. It generally provides lower peak powers than can be achieved with vacuum tubes.

Limitations associated with the possibility of obtaining signals in radars based on semiconductor elements high power, increased the importance of the so-called pulse coding and compression method, with which it is possible to simulate short pulses of high power when emitting less powerful and longer signals. This technique does not lose its importance in the case of using powerful radar stations on electronic tubes both with mechanically controlled antennas and with phased antenna arrays, when it is required to obtain certain information about distant objects.

The range at which a radar station with a given sensitivity of the receiving path can detect objects of a certain size and with a certain reflectivity depends on the total pulse energy. The shorter the pulse, the higher the peak radiation power should be at a given range. The COBRA DANE radar can detect metal objects the size of a grapefruit at a distance of about 2000 km. To do this, with a pulse duration of 5 ns, the peak radiation power must be at least 3 1012 W, which is more than enough to destroy all the radar circuits.

Nevertheless, it is possible to determine the size of an object or to separately observe a number of objects flying at a close distance from each other only with the help of pulses of short duration. The fact that the range of the radar station is determined not by the peak power, but by the total pulse energy, helps to find a solution. It consists in the following. When the radar is in transmit mode, the transmitted pulse is stretched and the peak power is reduced accordingly. This technique is called pulse coding. In the receive mode, the reflected signal is compressed in order to extract from it all the information that could be obtained by transmitting a really short pulse. In the COBRA DANE radar, for example, a 5 ns pulse is stretched 200,000 times before it is amplified and emitted, and its duration becomes 1 ms. The required peak power is reduced by the same factor - from 3 1012 W to 15 MW, the actual emission power of COBRA DANE.

With a conventional coding technique, a 5 ns pulse, which includes a frequency spectrum, passes through a dispersion delay line, which causes different delays in the individual components of this spectrum: the higher the frequency of the component, the greater the delay; the component of the signal with the lowest frequency is radiated without delay, while the component with the highest high frequency receives a maximum delay of 1 ms. After that, the pulse, which already has a duration of 1 ms, is amplified and emitted; the received reflected signal has the same duration.

The received signal is passed through a compression chain, which introduces a number of additional delays. This time, the length of the delays is inversely related to the frequency. The lowest frequency component of the pulse spectrum receives a delay of 1 ms, and the highest frequency component receives no delay. Thus, in the process of performing the operation of encoding and compressing the pulse, each of the components of the signal spectrum receives the same total delay. As a result, the reflected signal is undistorted, having a duration of 5 ns.

If a radiated pulse with a duration of 1 ms, which in space has a length equal to 300 km, during propagation encounters an object that is much shorter than it, then the pulse returns back in the form of two overlapping reflected signals. In the usual way such reflected signals cannot be separated, and it is impossible to determine the size of the object from their relative position. However, when the encoded, overlapping echoes are compressed, the output is two different signal with a duration of 5 ns.

Encoding and compression of pulses perform the same role in radar stations built on semiconductor elements. Even when it is not necessary to determine the size of the object from which the signal is reflected, accurately determining the distance to the object requires the use of fairly short pulses. If compression is not used, then using pulses with a duration of 1 ms, it is possible to determine the distance to the object with an accuracy of only 150 km. In addition, when emitting long pulses, the effect of local interference due to reflection from precipitation and from the ground affects. At the same time, semiconductor technology cannot provide such powers, which are necessary when operating with short pulses, so that the range of the radar is the same as when emitting long pulses. Therefore, in order to obtain a long range and high resolution at low radiation power, it is necessary to use coding and pulse compression in radars based on semiconductor elements.

The first radar stations with phased antenna arrays, which began to be used in the 60-70s, were intended for military and intelligence purposes. There are circumstances in which the civilian sectors of the economy dictate the needs that stimulate the development of military equipment. In particular, civil aviation needs to obtain data on fast-moving objects in the airfield area, where arriving aircraft align their course for landing approach. Radar stations that control the approach of aircraft to the runway direct them to land, while monitoring the range of the aircraft and their position relative to the runway. The increasing intensity of air traffic creates an increasing need to equip civil aviation with phased array radars.

With a decrease in the number of radiating elements, the cost of a phased array antenna decreases. In most applications of radar technology antenna systems should have a large number of radiating elements. A small antenna array has a less focused and therefore wider beam. This reduces its resolution in angular coordinates, and a small area cannot provide high sensitivity to reflected signals. When a large area of ​​airspace is not required to be viewed, both of these disadvantages of a small antenna array can be overcome by combining it with a large reflector.

The field of view of the aircraft approach control radar should not be large. Typically, such a radar station must scan the space within about 10 ° in azimuth and from 7 to 14 ° in elevation. Therefore, for these purposes, you can use a hybrid system consisting of a phased antenna array and a traditional reflector. One of the radar designs uses an antenna array with 443 radiating elements, which works in conjunction with a reflector measuring 3.96x4.57 m. The array is located near the focus of the reflector, which reflects the beam at any angle of radiation of the antenna array. In this case, the reflector acts as a lens, focusing the beam and reducing its side scatter. The reflected rays become narrower and fit into a narrower angle in space. As a result, the ability of the array to resolve two targets within a small angle and to determine the exact bearing of a single target is improved. The reflector also increases the sensitivity to the reflected signal. In the future, new achievements in the field of circuitry will find application in radar. Use in radar technology element base, similar to digital integrated circuits used in computer science, will significantly reduce the number and size of components needed to generate, receive and process signals. New elements on gallium arsenide crystals, known as monolithic microwave integrated circuits, combine phase shifters, switches and transistor amplifiers. The transceiver module, which contains all the circuits necessary to create one radiating element of a phased antenna array, can now be completely assembled on only 11 such microcircuits. In the meantime, hundreds of parts are required to build transceiver modules based on semiconductor elements.

The development of electronics over time will allow

RADAR COMPLEX WITH AFAR PAK FA

RADAR SYSTEM WITH AESA PAK FA

04.03.2014


One of key elements for a promising long-range aviation complex (PAK DA) - a radar system - is already being developed in Russia, Yuri Bely, director general of the V.V. Tikhomirov Research Institute of Instrument Engineering, said in an interview with RIA Novosti.
Earlier, the Ministry of Industry and Trade announced the conclusion of a contract with the Ministry of Defense on the start of financing the project to create PAK DA. It is planned that this aircraft will be included in the state armament program for 2016-2025.
“If you understand a radar system as an element, then at the moment we are just considering this proposal,” Bely said, answering a question from RIA Novosti about participating in the PAK DA development project. “We completed the preliminary project, handed it over to the Tupolev company, defended it,<..>we are waiting for the go-ahead and the final TOR,” explained the director of NIIP.