Dissimulation electromagnetique d'une membrure d'antenne par un reseau de lignes de transmission

In the world of ground and spatial telecommunications, antennas are present in all applications. One of the most used antennas is the parabolic dish that can be seen on the roofs of some buildings and also on spacecrafts. Those antennas, constituted by a parabolic reflector are generally fed by primary sources such as horn antennas, or sub-reflectors. Those elements are maintained in front of the main reflector by struts which are placed in the radiation field, and they thus contribute to signal loss due to scattering. To fix this problem, several solutions have been proposed during the last years. However, most of these solutions are often complex to realize and they provide limited results in terms of frequency bandwidth. In this project, we explore a new way to design a strut by inserting a Transmission Line Network (TLN).;The principal objective in this project is to decrease the loss of signal caused by the antenna struts by inserting a TLN. To reach this objective, we should first well understand the concept of cloaking using a TLN. In order to do so, we have reproduced the simulations done in [15] using the software HFSSRTM (High Frequency Structure Simulator) from Ansoft.;After some few modifications of the TLN used in [15] for an application in strut cloaking, several simulations have been done and different results (reflection coefficient, transmission coefficient, RCS in transmission and RCS in reflection) were noted. In the beginning, we simulated a unit cell which could be considered as an element of an infinite periodic network of cells. The results being encouraging, we continued with a finite number of cells representing an antenna strut of parallelepiped shape crossed by a RLT. These simulations also demonstrated that the TLN transmits the incident waves very efficiently through the strut. We also studied the effect of the TLN on a rhombus antenna strut for comparison since this shape is currently considered the state-of-the-art in uncloaked antenna struts. It was found that the TLN brings better improvements in the case of the parallelepiped strut. Always for comparison, we have simulated a parallelepiped antenna strut crossed by a TLN and with dielectric strips on its sides for implementing a hard surface. By doing this, we are combining two approaches for the first time, i.e. cloaking using a TLN and cloaking using hard surfaces. The results obtained are better than the results obtained with the parallelepiped strut using a TLN but over a very limited frequency band. To validate the performance of the TLN in a more realistic antenna scenario, we simulated a hollow strut crossed by a TLN. The results obtained are as satisfactory as those of the solid parallelepiped strut, but we observe a resonance phenomenon which perturbs the results at certain frequencies.;All the simulations mentioned above have been made in conditions where the strut is illuminated with a uniform plane wave, it was necessary, before validating our results by experimentation, to consider the case of source of illumination similar to that used in a real antenna and in laboratory experiments, which is with illumination from a horn antenna. These new results were certainly different from the precedent ones but we noticed that the addition of the TLN improved in an undeniable way the transmission of the incident wave through the strut. This is also what was noticed during measurements taken in laboratory on prototypes of antenna struts crossed by transmission lines.;Inserting a TLN appears as a very promising technique for cloaking an object from electromagnetic fields. When an electromagnetic wave impinges on an object (antenna strut for example) embedding a TLN, the wave is guided through the object by the transmission lines as if this one was invisible. This method of cloaking has been studied in [15] on an object of arbitrary shape and the results presented suggests that TLNs have potential for cloaking an antenna strut. The TLN is constituted of very thin microstrip lines that pass through the object and not around it. The object to cloak should however be built with the capability of embedding the TLN.;In conclusion, we were thus able to demonstrate that the insertion of a TLN in an antenna strut could considerably improve the transmission of the signal through this last one. This demonstration has been done with several simulations which were experimentally confirmed. This realization brings to light an important potential application of the TLN cloak in the design of the antenna struts.