ENHANCEMENT OF THE POWER RADIATED BY A DIPOLE ANTENNA AT BORESIGHT BY MEANS OF A LEFT HANDED SUPERSTRATE E. Sáenz (1) , I. Ederra (1) , R. Gonzalo (1) , P. de Maagt (2) (1) Electrical and Electronic Engineering Department, Public University of Navarra Campus Arrosadía, E-31006, Pamplona, Navarra, Spain. Tel: +34 948 169023 Fax: +34 948 169720 E-mail: elena.saenz@unavarra.es , ramon@unavarra.es (2) European Space Research and Technology Centre, ESTEC, PO Box 299, NL 2200 AG Noordwijk, The Netherlands Tel: +31 71 565 5906 Fax: +31 71 565 4999 E-mail: Peter.de.Maagt@esa.int Abstract: In this paper a comparison between the measured radiation performances of a single dipole and a dipole with a left handed superstrate based on a finite periodic repetition of a unit cell is presented. First of all the return losses and resonant frequency of the dipole has been measured for different sizes of the superstrate, having a good impedance matching and a decrease in the resonant frequency as the number of cells increase. By using an anechoic chamber and a receiver horn antenna, the power transmitted at boresight has been measured for different frequencies, observing a filtering behaviour due to the resonant characteristic of the superstrate and an improvement of the power transmitted at the resonant frequency of around 3 dB. Comparing the H and E plane radiation patterns of a dipole and the dipole with superstrate, more symmetrical and directive radiation patterns can be observed. Finally, a comparison between the simulated and measured aperture efficiency is presented with a good agreement. I. INTRODUCTION Nowadays, the study of the so-called metamaterials (MTMs) has been increasing due to the enormous potential of this technology. Examples of MTMs include Photonic Band Gap (PBG) structures and Left Handed Material (LHM). Several recent papers have exposed the usefulness of these MTMs for different applications [1]-[9]. LHMs can be understood as resonators with pass band and stop band properties at which the power is transmitted or reflected respectively. Up to now, volumetric MTMs have been used to create Artificial Magnetic Conductor (AMC) for antenna applications [6]. Working in the rejection bands as substrate of dipole antennas instead of a perfect electric conductor (PEC) ground plane, an enhancement of the directivity and reduction of the back radiation is obtained. Recently, applications of LHMs have shown the benefits of their pass band properties using them as superstrate of planar antennas with the goal of improving their radiation behaviour [5]-[9]. In this paper a comparison between the radiation properties of a single dipole and a dipole with a LH superstrate is presented. Measurements of the S 11 parameter and the radiation pattern have been carried out for different sizes of the superstrate, i.e., varying the number of unit cells that form the superstrate. Finally, a comparison between the aperture efficiency obtained with these measurements and the one predicted by the simulations with Ansoft-HFSS is shown. II. LHM SUPERSTRATE The left handed media used as superstrate is a finite periodic structure based on the unit cell described in [3]-[5]. It consists of one Split Ring Resonator (SRR) between two pairs of Capacitively Loaded Strips (CLSs) all embedded in a dielectric slab (see Fig. 1). (a) (b) (c) (d) Fig. 1. (a) Geometry of the LHM unit cell (b) Layers of one period (c) Detail of the SRRs (d) Detail of the CLSs. In order to construct a unit cell, a layer by layer technique described in detail in [5] is followed. Each period is created by stacking six layers, 2 layers of each of the three types, following the pattern 123321 (see Fig. 1(b)). Using this fabrication technique, the number of periods that constitute the superstrate is not fixed, but can be modified by varying the number of layers stacked.