Radar: history and evolution of this technology widespread in every area

The term Radar derives from a reduction of the American words " Radio Detection And Ranking ", that is, radio detection and positioning. The basic concept of radar was first demonstrated in classical experiments conducted by a German physicist, Heinrich Hertz from 1885 to 1888. Herz experimentally verified Maxwell's theory of electromagnetism, published in 1864. Although Hertz's acknowledgments for the his work, he did not continue his experiments.

Research on the detection and localization of reflected objects was then developed in the early 1900s by a German engineer, Christian Hulsmeyer who assembled an instrument now known as monostatic radar (" single site ") and in 1904 a patent was issued for a detector of obstacles and an apparatus for maritime navigation in various countries. However, Hulsmeyer's idea had no follow-up, mainly due to the technological poverty of the time.

Guglelmo Marconi: precursor of the radar system

Radar: history and evolution of this technology widespread in every area

The first who clearly saw the possibilities offered by short waves as a means of detecting targets was Guglielmo Marconi , observing during his experiments that it is possible to detect targets by means of radio waves. In a speech given at the Institute of Radio Engineers (now IEEE), in 1922 he said:

I believe that it should be possible to design apparatuses by which a ship can spread waves in a desired direction and find a metal assembly such as an opposite ship, by receiving on a receptor shielded from the transmitter of the transmitting ship, promptly indicating whether a other ship is present, through its detection in fog and bad weather.

However, it was necessary to wait at least a decade before studies were carried out in a systematic way to realize the apparatus he described and at least 15 years before these apparatuses worked satisfactorily.

Pulse radar: first application and research from the early 1900s

The first application of the impulse technique in distance measurement occurred in the experiments of Breit and Tuve in 1925, to determine the height of the ionosphere , while the first revelations of objects (often only random ). The body that took on the financial burden of this first phase was the Naval Research Laboratory: since there was no immediate interest, the studies proceeded slowly and the first patented apparatus dates back to 1934, of the continuous wave type, given the practical difficulties encountered in the implementation of pulse radars.

The first pulsed devices date back to 1936, with an operating frequency of 28.3MHz and a pulse duration of 5 seconds. The range, which was initially only 2.5 miles, was increased to 25 miles in a few months. A new impulse to the evolution of the technology of these radars was obtained with the development of high-power tubes ; however, the installation of a series of pulse radars on the major units of the US Navy dates back to 1941. The other countries in which studies and research on the construction of radar equipment were developed are Italy, England, Germany. Independent studies also began in France but were interrupted due to setbacks suffered at the beginning of the Second World War.

Application of radar systems during the Second World War

Radar: history and evolution of this technology widespread in every area
Naval radar photo taken at the military museum in Gothenburg. Credits: Rossella Miele

The Germans arrived at the construction of excellent radar systems during the war, which however did not play the decisive function of the American and British radars , probably due to different (and erroneous) assessments of the German General Staff on the development of the war. The history of the British radar deserves a separate mention, as this country has invested considerable resources in the development of such equipment, bringing it in a few years to a level similar to that achieved by the United States.

This effort was due in addition to the foresight of its rulers, to the particular geographical position in which England is located , vulnerable to German attacks, therefore in 1935 the government agreed to invest for the first time in research in the radar sector. The first continuous wave prototype was built at the end of 1935 while the first prototypes of pulse radars with a frequency of 25 MHz date back to 1936 and in 1939 on that of 200 MHz. In the mid-1940s, following the alliances with the Americans, there was a transfer of technical knowledge which accelerated the realization of the technology. However, a fundamental contribution was made by the construction of the multiple cavity magnetron, built by the British Randall and Boote.

The Italian panorama

Radar: history and evolution of this technology widespread in every area

As for Russia and Japan, these states probably did not engage in a concrete way in the study and practical implementation of radar equipment. Just as for these two states , Italy too did not enjoy the same success as the USA and England, above all because of the short-sightedness of the rulers of the time and not so much because in Italy no radar research had started . In 1933 Marconi, in an experience made in the presence of the Italian military authorities, demonstrated the possibility of revealing obstacles through the reflection of electromagnetic waves.

After Marconi's experiments, in 1935 a report was issued to the Interministerial Committee for Military Electrical Services which reported a research by U. Tiberio intended to clarify "if and in what way the ionospheric sounding apparatuses could adapt to the detection of airplanes and of long-distance ships ". This report described both the theoretical equation of radar in free space and the characterization and basic data for continuous wave and pulse systems. Unfortunately, the military managers preferred the construction of a 10000-ton cruiser to financing the project with adequate means and men: in practice, until 1940 the only person who dealt with the problem was U. Tiberius.

Subsequently in 1935, the Royal Electrotechnical and Communications Institute, today Mariteleradar carried out the tests and the first prototypes in Livorno . Only in 1941, after the disaster suffered in the naval battle of Capo Matapan, was the contract to perfect and build a first series of impulse devices entrusted to the company SAFAR of Milan. Unfortunately, in the absence of a national electronics industry and adequately trained technical personnel, it did not allow to obtain the results that could potentially have been achieved. The centimeter wave radar of the 70s came from a huge financial effort made by the USA during the last war period.

The 28-volume treatise on radar technology published by the Massachusetts Institute of Technology's Radiation Laboratory after the war testifies to the progress made in those few years. It should be noted that the research activity in the radar sector, being of high military interest, has always been the subject of strong funding from the various military bodies even after the end of the Second World War.

Interest in space research and evolution in the telecommunication field

Radar: history and evolution of this technology widespread in every area

Another notable source of funding in this field came after 1950 from space research. All this explains the continuous and rapid progress achieved up to our days, both in radar equipment and in related technologies. After the war period in which it was imperative to build and immediately, the many theoretical aspects connected with the development of this new apparatus were also addressed, the solutions of which have brought considerable benefits to related disciplines, first of all telecommunications . Some of the most significant theoretical aspects faced by radarists were:

  • reduction of the effect of thermal noise in the processing of the return echo (adapted filter);
  • systematic development and application of decision and estimation theory;
  • systematic use of probability theory, which among other things led to the development of modern statistical communication theory, application of information theory to radar;
  • development of digital signal processing techniques, which led to modern DSP (Digital Signal Processing);
  • development of ever faster computing techniques and architectures for real-time processing.

From the technological point of view, the remarkable advances obtained in the field of antennas (up to modern electronic scanning antennas or phased-arrays ), in the generation of power at an ever higher frequency, in the development of microwave technology, now reached 100GHz, should be remembered. (examples of tracking radar and discovery radar).

Perhaps the greatest revolution compared to the 1950s lies in the different conception of radar, which from a simple instrument that had to detect the presence or absence of a possible target is increasingly considered as a real sensor of the surrounding space , therefore able to provide a variety of information, previously unthinkable. This new philosophy forced researchers to develop all the techniques that would allow the radar to fulfill this new function. From this point of view, perhaps the most relevant results have been the massive use of numerical processing and computers (the radar becomes an automatic sensor that estimates the characteristics of the surrounding environment in real time, adapting to them).

Curated by Rossella Miele

The article Radar: history and evolution of this widespread technology was written on: Tech CuE | Close-up Engineering .