Today, aviation is unthinkable without radars. An airborne radar station (BRLS) is one of the most important elements of the radio-electronic equipment of a modern aircraft. According to experts, in the near future radar stations will remain the main means of detecting, tracking targets and pointing guided weapons at them.
We will try to answer the most common questions about the operation of radars on board and tell how the first radars were created and how promising radar stations can surprise.
1. When did the first radars appear on board?
The idea of using radar on airplanes came a few years after the first ground-based radars appeared. In our country, the ground station "Redut" became the prototype of the first radar station.
One of the main problems was the placement of the equipment on the plane - the station set with power supplies and cables weighed about 500 kg. It was unrealistic to install such equipment on a single-seat fighter of that time, so it was decided to place the station on a two-seat Pe-2.
The first domestic airborne radar station called "Gneiss-2" was put into service in 1942. Over the course of two years, more than 230 Gneiss-2 stations were produced. And in the victorious 1945 Fazotron-NIIR, now part of KRET, began serial production of the Gneiss-5s aircraft radar. The target detection range reached 7 km.
Abroad, the first aircraft radar "AI Mark I" - British - was put into service a little earlier, in 1939. Due to its heavy weight, it was installed on heavy fighter-interceptors Bristol Beaufighter. In 1940, a new model, the AI Mark IV, entered service. It provided target detection at a distance of up to 5.5 km.
2. What does an airborne radar station consist of?
Structurally, the radar consists of several removable units located in the nose of the aircraft: a transmitter, an antenna system, a receiver, a data processor, a programmable signal processor, consoles and controls and displays.
Today, almost all airborne radars have an antenna system consisting of a flat slotted antenna array, Cassegrain antenna, passive or active phased antenna array.
Modern airborne radars operate in a range of different frequencies and allow detecting air targets with an EPR (Effective Scattering Area) of one square meter at a distance of hundreds of kilometers, and also provide tracking of dozens of targets in the passage.
In addition to target detection, today radar stations provide radio correction, flight assignment and target designation for the use of guided airborne weapons, carry out mapping of the earth's surface with a resolution of up to one meter, and also solve auxiliary tasks: following the terrain, measuring its own speed, altitude, drift angle, and others. …
3. How does an airborne radar work?
Today, modern fighters use pulse Doppler radars. The name itself describes the principle of operation of such a radar station.
The radar station does not work continuously, but with periodic jerks - impulses. In today's locators, the transmission of a pulse lasts only a few millionths of a second, and the pauses between pulses are a few hundredths or thousandths of a second.
Having met any obstacle on the path of their propagation, the radio waves scatter in all directions and are reflected from it back to the radar station. At the same time, the radar transmitter is automatically turned off, and the radio receiver starts to work.
One of the main problems with pulsed radars is getting rid of the signal reflected from stationary objects. For example, for airborne radars, the problem is that reflections from the earth's surface obscure all objects below the aircraft. This interference is eliminated using the Doppler effect, according to which the frequency of a wave reflected from an approaching object increases, and from an outgoing object it decreases.
4. What do the X, K, Ka and Ku bands mean in the radar characteristics?
Today, the range of wavelengths in which airborne radar stations operate is extremely wide. In the characteristics of the radar, the station range is indicated in Latin letters, for example, X, K, Ka or Ku.
For example, the Irbis radar with a passive phased antenna array installed on a Su-35 fighter operates in the X-band. At the same time, the detection range of Irbis air targets reaches 400 km.
The X-band is widely used in radar. It extends from 8 to 12 GHz of the electromagnetic spectrum, that is, it is wavelengths from 3.75 to 2.5 cm. Why is it named that way? There is a version that during the Second World War the band was classified and therefore received the name X-band.
All names of ranges with the Latin letter K in the name have a less mysterious origin - from the German word kurz ("short"). This range corresponds to wavelengths from 1.67 to 1.13 cm. In combination with the English words above and under, the Ka and Ku bands got their names, respectively, located "above" and "below" the K-band.
Ka-band radars are capable of short range and ultra-high resolution measurements. Such radars are often used for air traffic control at airports, where the distance to the aircraft is determined using very short pulses - several nanoseconds in length.
The Ka-band is often used in helicopter radars. As you know, to be placed on a helicopter, an airborne radar antenna must be small. Considering this fact, as well as the need for an acceptable resolution, the millimeter wavelength range is used. For example, a Ka-52 Alligator combat helicopter is equipped with an Arbalet radar system operating in the eight-millimeter Ka-band. This radar developed by KRET provides the Alligator with tremendous opportunities.
Thus, each range has its own advantages, and depending on the placement conditions and tasks, the radar operates in different frequency ranges. For example, obtaining a high resolution in the forward sector of the view realizes the Ka-band, and an increase in the range of the on-board radar makes the X-band possible.
5. What is PAR?
Obviously, in order to receive and transmit signals, any radar needs an antenna. To fit it into an airplane, special flat antenna systems were invented, and the receiver and transmitter are located behind the antenna. To see different targets with the radar, the antenna needs to be moved. Since the radar antenna is quite massive, it moves slowly. At the same time, the simultaneous attack of several targets becomes problematic, because a radar with a conventional antenna keeps only one target in the "field of view".
Modern electronics have made it possible to abandon such mechanical scanning in an airborne radar. It is arranged as follows: a flat (rectangular or circular) antenna is divided into cells. Each such cell contains a special device - a phase shifter, which can change the phase of the electromagnetic wave that enters the cell by a given angle. The processed signals from the cells are sent to the receiver. This is how you can describe the operation of a phased array antenna (PAA).
To be more precise, a similar antenna array with many phase shifter elements, but with one receiver and one transmitter, is called a passive HEADLIGHT. By the way, the world's first fighter equipped with a passive phased array radar is our Russian MiG-31. It was equipped with a radar station "Zaslon" developed by the Research Institute of Instrument Engineering. Tikhomirov.
6. What is AFAR for?
Active phased array antenna (AFAR) is the next stage in the development of passive. In such an antenna, each cell of the array contains its own transceiver. Their number may exceed one thousand. That is, if a traditional locator is a separate antenna, receiver, transmitter, then in AFAR, the receiver with the transmitter and the antenna are "scattered" into modules, each of which contains an antenna slit, a phase shifter, a transmitter and a receiver.
Previously, if, for example, a transmitter was out of order, the plane would become “blind”. If in AFAR one or two cells, even a dozen, are affected, the rest continue to work. This is the key advantage of AFAR. Thanks to thousands of receivers and transmitters, antenna reliability and sensitivity are increased, and it also becomes possible to operate at several frequencies at once.
But the main thing is that the structure of the AFAR allows the radar to solve several problems in parallel. For example, not only to serve dozens of targets, but in parallel with the survey of the space, it is very effective to defend against interference, to interfere with enemy radars and to map the surface, obtaining high-resolution maps.
By the way, the first in Russia airborne radar station with AFAR was created at the KRET enterprise, in the Fazotron-NIIR corporation.
7. What radar station will be on the fifth generation PAK FA?
Among the promising developments of KRET are conformal AFAR, which can fit into the fuselage of an aircraft, as well as the so-called "smart" airframe skin. In the next generation fighters, including the PAK FA, it will become, as it were, a single transceiver locator, providing the pilot with complete information about what is happening around the aircraft.
The PAK FA radar system consists of a promising X-band AFAR in the nose compartment, two side-looking radars, and an L-band AFAR along the flaps.
Today KRET is also working on the development of a radio-photonic radar for the PAK FA. The concern intends to create a full-scale model of the radar station of the future by 2018.
Photonic technologies will make it possible to expand the capabilities of the radar - to reduce the mass by more than half, and increase the resolution tenfold. Such radars with radio-optical phased antenna arrays are capable of making a kind of "X-ray image" of aircraft located at a distance of more than 500 kilometers, and giving them a detailed, three-dimensional image. This technology allows you to look inside an object, find out what equipment it carries, how many people are in it, and even see their faces.
