Radars; basic principles - constitutive components

In this article, readers will discover the basic principles of electromagnetic detection, the function performed by Radar (short for Radio Detection And Ranging), and its constituent parts.

A brief history, from the telemobiloscope of German scientist Christian Hülsmeyer (1904) to the modern theories of British scientist P.M. Woodward (1950), outlines the major stages in the discovery and development of radar.

This is followed by a presentation of the basic principles of pulse radar: the principles of range measurement and angular measurement, leading to a definition of the typical composition of a radar, with a brief description of each of its components. This is followed by an overview of the different types of radar:

• panoramic ;

• volumetric ;

• pursuit ;

• landing ;

• airborne.

For each of them, we describe the corresponding typical organizations and/or their outstanding features.

Following this brief overview, the criteria used to characterize the operational performance of radars are defined:

• discriminating power and precision ;

• notions concerning the "confusion volume" of a radar and its impact on the detection of natural "clutter" parasites, which can alter their vision of useful objects;

• notion of the Doppler effect, which makes it possible to characterize motions by their speed.

This is followed by a description of the transmit-receive technologies specific to radar. It begins with a description of the general organization of radar transmit-receive chains, followed by an examination of the active elements involved in signal transmission:

• microwave tubes ;

• solid-state power stages ;

And the special power supply devices for these instantaneous high-power elements: modulators.

The description continues with the antennas used in radar. Following a classic pattern, we begin by establishing the concepts that lead to an understanding of how these antennas work, before continuing with an overview of the different types of radar antennas:

• with reflectors ;

• Cassegrain ;

• for tracking radar ;

• planes ;

• electronic scanning ;

• active....