Radar technology has no single inventor. It can more appropriately be recognized as a joint effort by scientists from several nations who have often worked collaboratively. In the past there were nevertheless some interesting milestones, with the discovery of important basic knowledge and important inventions. Let’s take a minute to explore some of these. 

James Clerk Maxwell – Scotland

1865 – The Scottish physicist James Clerk Maxwell presents his electromagnetic theory of light, a description of electromagnetic waves and their propagation properties. 

James Clerk Maxwell (1831–1879) was a physicist and mathematician from Scotland. He became famous for his mathematical description of the magnetic and electric fields known as Maxwell’s equations.

Maxwell relied on the relationship between the movement of a magnet and the voltage induced in an electrical conductor, which later became the law of induction, discovered experimentally by Michael Faraday.

Faraday spoke of individual lines of force, which the moving magnet pulls behind it. Maxwell, on the other hand, imagined that the entire space around the magnet was filled with a force field. Complicated differential equations were required to calculate this force field. Maxwell also attempted to define laws governing the behavior of any system of electrically charged particles, given their current position and velocity and the value of the field at all its points.

Having achieved this, he found that Faraday’s experimentally found laws could not be complete, that the equations were ambiguous and led to no definite resultexcept assuming that not only a magnet in motion generates an electric field (and thus an electric current in the conductor), but also a moving electric charge creates a very small magnetic field. With this additional knowledge, scientists could now set up closed unique equations.

• Equation 1: The distribution of an electric charge gives rise to an electric field. The electric flow through the closed surface ∂ V of a volume V is directly proportional to the electric charge inside it.

• Equation 2: Magnetic field lines form closed circles. The magnetic flux through the closed surface of a volume is equal to the magnetic charge in its interior, which is zero since there are no magnetic monopoles.

• Equation 3: A time-varying magnetic field creates an electric field. The electrical circulation across the boundary curve ∂ A of an area A is equal to the negative change with time of the magnetic flux through the area.

• Equation 4: A moving charge or an alternating electric flow both create a magnetic field. The magnetic circulation over the boundary curve ∂ A of an area A is equal to the sum of the (electric) current and the change in electric flux through the area with time.

One of the most surprising results of these equations was that electric fields and magnetic fields can be set in motion in waves with a well-defined velocity that depends on the strength of the electric field created by a moving magnet. This means that the desired speed of the waves is equal to the speed one gives to a magnet if the generated electric field is to be of the same energy as its own magnetic field. This speed was already known, and Maxwell pointed out that it was in close agreement with speeds then attributed to light. He therefore made the assertion that the light waves were of electromagnetic origin.

These purely mathematical equations thus predict the existence of electromagnetic waves. Their existence was only confirmed 20 years later by experiments by Heinrich Rudolf Hertz and forms the basis of all radio and radar technology. Today, Maxwell’s equations are no longer used in this complicated integral representation. The so-called Nabla representation (mathematical sign: ∇ ) is preferred.