How to detect targets

The history of radar, from aircraft radio detectors to airborne radar

Aviation today is impossible without radar, as it helps navigate ships and spacecraft alike. Over the past decades, radar technology has changed beyond recognition. How were the first radars created, and how can modern radars today recapture our imagination?

The first ideas

Aircraft was first used in the wartime hostilities of the early twentieth century. With the advent of combat aircraft, there was also a need to detect them.

At the time, instruments based on optical principles were first used. Subsequently emerged sound detectors that could note the sound of an aircraft engine. Work was then conducted on a system to detect an airplane by the thermal radiation of its engine. The greatest disadvantage of these detection methods was their dependence on weather conditions. It soon became clear that radio waves could help to find a plane in the air, regardless of the weather.

Detection of aircraft by radio waves, or radar, has been used since the 1930s, with the idea originating even earlier. In 1886, the German physicist Heinrich Hertz discovered that radio waves can affect bodies, and in 1897, working with his radio transmitter, Alexander Popov discovered that radio waves reflected off the metal parts of ships.

One of the first radar devices for aerial objects was demonstrated on February 26, 1935, by Scottish physicist Robert Watson-Watt, about a year before he received the first patent for the invention of such a system.

Even though this patent was the first in the world, Watson’s device cannot be called a technical novelty. Research into radar began in the Soviet Union in 1933. 13 years later, American experts Raymond and Hacherton, former employees of the US Embassy in Moscow, wrote: “Soviet scientists successfully developed the theory of radar several years before it was invented in England.”

Radio detection of aircraft

Soviet professor Pavel Oschepkov was the first to apply the Popov effect in practice. In 1934, Soviet specialists successfully conducted an experiment to detect aircraft radar with this method. A plane flying at an altitude of 150 meters was discovered 600 meters from the radar installation. This can be considered the birthday of Russian domestic radar.

The first radar stations adopted for military use and mass-produced in Russia were the RUS-1 (radio detection of aircraft) in 1939 and RUS-2 Redut in 1940.

The technical characteristics of the Redut station had no analogues anywhere the world. It became the most popular Soviet-made radar during World War II, with only 607 units produced.

Redut served the war effort well, especially in the defense of Moscow from attacks by enemy aircraft. These Soviet radio aircraft detectors were used in Mozhaysk against enemy aircraft to identify the direction of flight and distance of targets. German planes were then greeted with Russian anti-aircraft guns and fighter planes. After five hours of fighting, and losing 20 airplanes, German fighter aircraft turned away from Moscow.

Incidentally, the Redut station, so necessary for the Russian army, was made commercially available during the war by Factory № 339. Today this enterprise is known as PHAZOTRON-NIIR and is part of KRET.

How to detect targets
How to detect targets

First time onboard  

The idea of ​​installing radar in aircraft came a few years later after the first ground radar systems, although navigation systems and blind landing radio aids were used since 1933.

The Redut ground station served a prototype for the first onboard radar. One of the main problems was the placement of the equipment on the plane, as the station with its power supplies and cables weighed about 500 kg. There was no place to install such equipment on the single-seat fighter of the time. A solution was found, though, by placing the station not on a single-seat aircraft, but on the two-person Pe-2.

The first Russian airborne radar was called Gneiss-2, and it entered into service in June 1943. More than 230 Gneiss-2 stations were produced by the end of 1944.

In the victorious year of 1945, what is now PHAZOTRON-NIIR began mass production of the Gneiss-5s aircraft radar. Its target detection range expanded to 7 km, but its primary novelty was that from 1.5 km out, the data was duplicated on special indicators in the cockpit. This allowed the pilot to position his own aircraft for attack.

Principles of operation

Although modern radar stations cannot be compared with the first radars in their complexity, the operating principles remain the same.

Radar stations do not operate continuously, but rather through periodic pulses. The transmitters of the first stations sent pulses 25 times per second. Modern radars are also built with this pulse format. While hard to imagine, today's radars send pulses lasting only a few millionths of a second, with the pause between pulses only a few hundredths or thousandths of a second.

Having sent these radio waves into space, the radar transmitter automatically turns off and the radio starts to work. When radio waves spread out and meet an obstacle, they scatter in all directions and are reflected back to the radar.

This can be compared with the reflection of sound waves, known as echoes. Radio waves travel at a speed almost a million times faster than sound waves. If the echo from rocks at a distance of 3,500 meters returns after 20 seconds, radio waves take two-thousandths of a second. Therefore, the main feature of the radar is its fast measurement time, at up to a millionth of a second.

One of the main problems of pulse radars is avoiding signals reflected from stationary objects. For example, for on-board pulse radars, the problem is that reflection from the Earth’s surface obscures all objects below the plane.

The Doppler effect, according to which the frequency of the wave reflected from an approaching object increases and that of a passing object decreases, eliminates this interference.

These kinds of Doppler pulse radars, which can successfully detect low-flying targets, are used in modern fighter jets. PHAZOTRON-NIIR, which is part of KRET, develops such multi-functional and airborne radars.