Question: In which area did this French engineer and physicist, whose name became synonymous to one of a series of concentric prolate ellipsoidal regions of space between and around a transmitting antenna and a receiving antenna system, contribute significantly?

Context paragraphs:
Periscope antenna: In telecommunication, a periscope antenna is an antenna configuration in which the transmitting antenna is oriented to produce a vertical radiation pattern, and a flat or off-axis parabolic reflector, mounted above the transmitting antenna, is used to direct the beam in a horizontal path toward the receiving antenna.

Two-ray ground-reflection model: The Two-Rays Ground Reflected Model is a radio propagation model which predicts the path losses between a transmitting antenna and a receiving antenna.  Generally, the two antenna each have different height.  The received signal having two components, the LOS (line of sight) component and the multipath component formed predominately by a single ground reflected wave.

Feed line: In a radio antenna, the feed line is the cable or other transmission line that connects the antenna with the radio transmitter or receiver.  In a transmitting antenna, it feeds the radio frequency (RF) current from the transmitter to the antenna, where it is radiated as radio waves.  In a receiving antenna it transfers the tiny RF voltage induced in the antenna by the radio wave to the receiver.  In order to carry RF current efficiently, feed lines are made of specialized types of cable called transmission line.  The most widely used types of feed line are coaxial cable, twin-lead, ladder line, and at microwave frequencies, waveguide.

Driven element: In a multielement antenna array (such as a Yagi-Uda antenna), the driven element or active element is the element in the antenna (typically a metal rod) which is electrically connected to the receiver or transmitter.  In a transmitting antenna it is "driven" or "excited" by the RF current from the transmitter, and is the source of the radio waves.  In a receiving antenna it collects the incoming radio waves for reception, and converts them to tiny oscillating electric currents, which are applied to the receiver.  Multielement antennas like the Yagi typically consist of a driven element, connected to the receiver or transmitter through a feed line, and a number of other elements which are not driven, called parasitic elements.  The driven element is often a dipole.  The parasitic elements act as resonators and couple electromagnetically with the driven element, and serve to modify the radiation pattern of the antenna, directing the radio waves in one direction, increasing the gain of the antenna.

Free-space path loss: In telecommunication,free-space path loss (FSPL) is the attenuation of radio energy between the feedpoints of two antennas that results from the combination of the receiving antenna's capture area plus the obstacle free, line-of-sight path through free space (usually air).  The "Standard Definitions of Terms for Antennas", IEEE Std 145-1993, defines "free-space loss" as "The loss between two isotropic radiators in free space, expressed as a power ratio."  Despite this name and definition, the FSPL includes a receiving antenna aperture component in the total attenuation.  It does not include any loss associated with hardware imperfections, or the effects of any antenna gains.  A discussion of these losses may be found in the article on link budget.  The FSPL is rarely used standalone, but rather as a part of the Friis transmission formula, which includes the gain of antennas.

Fresnel zone: A Fresnel zone ( ), named for physicist Augustin-Jean Fresnel, is one of a series of concentric prolate ellipsoidal regions of space between and around a transmitting antenna and a receiving antenna system.  The concept is used to understand and compute the strength of waves (such as sound or radio waves) propagating between a transmitter and a receiver.

Tunnel transmitter: A tunnel transmitter allows wireless reception in tunnels.  It consists of a receiving antenna which receives the signal to be radiated in the tunnel, and a transmitting antenna installed in the tunnel, which is either a Yagi antenna or a line antenna.  In principle, a tunnel transmitter can work purely passively, in which case the received signal is passed over a cable to the antenna in the tunnel.  Active systems, however, are more often used.  In some cases the radio frequency inside the tunnel is different from the one used by the broadcaster.  More often the program inside is transmitted on the same frequency as outside, in which case the information signal should be demodulated or converted to an intermediate frequency in the outside receiver, and then modulated/shifted back in the transmitter.  Otherwise feedback may occur.

Augustin-Jean Fresnel: Augustin-Jean Fresnel ( ; ] ; 10 May 1788 – 14 July 1827) was a French engineer and physicist who contributed significantly to the establishment of the theory of wave optics.  Fresnel studied the behaviour of light both theoretically and experimentally.

Radar: Radar is an object-detection system that uses radio waves to determine the range, angle, or velocity of objects.  It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain.  A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna (often the same antenna is used for transmitting and receiving) and a receiver and processor to determine properties of the object(s).  Radio waves (pulsed or continuous) from the transmitter reflect off the object and return to the receiver, giving information about the object's location and speed.

Antenna gain: In electromagnetics, an antenna's power gain or simply gain is a key performance number which combines the antenna's directivity and electrical efficiency.  In a transmitting antenna, the gain describes how well the antenna converts input power into radio waves headed in a specified direction.  In a receiving antenna, the gain describes how well the antenna converts radio waves arriving from a specified direction into electrical power.  When no direction is specified, "gain" is understood to refer to the peak value of the gain, the gain in the direction of the antenna's main lobe.  A plot of the gain as a function of direction is called the radiation pattern.

Supporting paragraphs: Fresnel zone Augustin-Jean Fresnel
Answer: theory of wave optics