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Dissimulation électromagnétique d'une membrure d'antenne par un réseau de lignes de transmission

Francis Siaka

Master's thesis (2010)

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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). 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. 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 HFSS® (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.


Dans le monde des télécommunications terrestres ou spatiales, les antennes sont présentes dans toutes les applications. Parmi les antennes les plus utilisées, on compte les antennes paraboliques que l'on peut voir sur les toits de certains bâtiments et qui se trouvent aussi dans l'espace. Ces antennes, constituées d'un réflecteur parabolique sont généralement alimentées par des sources primaires telles que des antennes de type cornet, ou des sous-réflecteurs. Ces éléments sont maintenus devant le réflecteur principal à l'aide de supports ou membrures (« strut » en anglais) qui se situent dans le champ de rayonnement, et ils contribuent donc à une perte de signal. Pour remédier à ce problème, différentes solutions ont été proposées durant ces dernières années. Malheureusement, la plupart de ces solutions sont souvent complexes à réaliser et elles fournissent des résultats assez limités en largeur de bande. Dans ce projet, nous explorons une nouvelle façon de concevoir une membrure d'antenne en y insérant un réseau de ligne de transmissions (RLT). Insérer un RLT dans un objet est une technique très intéressante pour masquer un objet des ondes électromagnétiques. Lorsqu'une onde électromagnétique arrive sur un objet (une membrure d'antenne par exemple) traversé par un RLT, elle est guidée à travers l'objet par les lignes de transmission comme si celui-ci était invisible. Cette technique de masque électromagnétique (ME) a été étudiée en [15] sur un objet quelconque et les résultats obtenus sont très intéressants pour l'appliquer sur une membrure d'antenne. Le RLT en question est constitué de paires de rubans métalliques très minces qui passent à travers et non autour de l'objet. L'objet à masquer doit donc être au préalable construit de façon à pouvoir y insérer les lignes de transmission.
Department: Department of Electrical Engineering
Program: Génie électrique
Academic/Research Directors: Jean-Jacques Laurin
PolyPublie URL: https://publications.polymtl.ca/277/
Institution: École Polytechnique de Montréal
Date Deposited: 23 Jun 2010 15:31
Last Modified: 11 Nov 2022 04:35
Cite in APA 7: Siaka, F. (2010). Dissimulation électromagnétique d'une membrure d'antenne par un réseau de lignes de transmission [Master's thesis, École Polytechnique de Montréal]. PolyPublie. https://publications.polymtl.ca/277/


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