Chapter 10High Impedance Surface Close toa Radiating Dipole1




10.1. Introduction

High impedance surfaces seem to be very attractive for design engineers who at first glance see the opportunity to reduce the thickness of all kinds of antennas using dipoles. The reason is that at the frequency at which the impedance of the surface reaches a high value, it is possible to get a good dipole radiation with an input impedance of the dipole close to 50 Ohms.

In order to check this attractive property, we have studied, fabricated and measured a circuit made of a dipole placed very close to a high impedance surface (HIS). This HIS contains resonant line patterns called 2LC which have been studied by L.Y. Zhou, H. Ouslimani from GEA Université Paris Ouest Ville d’Avray France. We will present in the following sections, firstly the description of the circuits, secondly the main results obtained and after that we will discuss the difficulties encountered and propose some physical explanations for the phenomena.

10.2. Antenna study

The antenna which has been defined is made of a dipole fed by a balun and placed above a dielectric substrate. On one side of the substrate there is a ground plane and on the other side, the microstrip lines that make up the resonant circuits called 2LC. The dipole has been initially designed in order to have a length close to half a wavelength at the central frequency. Later, after the introduction of the HIS below the dipole, it was necessary to reduce the ...

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