Equivalent Circuit of an Aperture Coupled Patch Antenna for Beam Control Applications Naima Amar Touhami (1) , Lorena Cabria de Juan (1) , José Ángel García García (1) , Constantino Pérez Vega (1) , Antonio Tazón Puente (1) , Mohamed Boussouis (2) (1) Department of Communication Engineering University of Cantabria- Spain (2) Department of Physic University of AbdelMalek Essaâdi- Tétouan – Morocco Abstract: -An exhaustive study of different equivalent circuits of an aperture coupled patch permits to develop a suitable circuit model. The vast majority of these models are able to reproduce the antenna behaviour around the first resonance frequency, but the proposed equivalent circuit is also capable of duplicating the radiator input impedance in the two next harmonics. Over such model, one approach has been carried out for beamsteering purposes: a Left-Handed (LH) structure has been introduced at the patch input to obtain two variable operating bands. The agreement shown in the results obtained using the proposed circuit structure, electromagnetic simulations and experimental measurements validates the model. Key-Words: - Equivalent circuit, Left Handed structure, beamsteering, variable operating bands. 1 Introduction Modern communication systems demand beamsteering and beamforming capabilities in their radiating structures. To implement these functions, active and passive printed antennas [1], [2] stand as a promising technique, as they are able of combining the radiating properties of printed antennas with the signal processing capabilities of active devices. For instance, aperture coupled patch antenna has been widely used for arrays and reflectarrays systems with electronic beam control [3], [4]. Metamaterials are artificial structures that can be designed to exhibit specific electromagnetic properties not commonly found in nature. Recently, metamaterials with simultaneously negative permittivity (ε) and permeability (μ), more commonly referred to as left-handed materials (LHMs), have received substantial attention in the scientific and engineering communities [5]. The unique properties of LHMs have allowed novel applications, concepts, and devices to be developed. Electromagnetic simulators to design and analyze the microstrip antennas have a high computational cost and, in any cases, it is not possible to introduce the electronic control circuitry. This reason makes useful to dispose a suitable equivalent circuit to be used in circuit simulators. Many authors [6-10] have developed models which are able to reproduce the antenna behaviour around the first resonance frequency. However, in this work we propose an equivalent circuit for such radiating structure capable of also duplicating the antenna input impedance in the two next harmonics, an exhaustive study of different equivalent circuits have been made. Using the developed model, one approach has been carried out for beamsteering purposes: A Left- Handed (LH) structure has been introduced at the patch input to obtain two variable operating bands with electronic control capabilities. To ensure the validity of the equivalent circuit, comparisons among electromagnetic simulations with Ensemble, experimental results and circuit simulations with MW Office, using our circuital model, have been carried out. 2 Slot Coupled Patch Equivalent Circuits The working band of the used aperture coupled patch antenna [11-12] is around 965 MHz. The microstrip patch antenna is etched on the top of the radiating element, and the microstrip feed line is on the bottom of the feed substrate. These substrates are Arlon 25N of 3.38 of dielectric constant and 0.76 mm high. The dielectric between the patch and the ground plane is air of 21 mm and the slot is over the ground plane (figure 1). 8th WSEAS International Conference on SIMULATION, MODELLING and OPTIMIZATION (SMO '08) Santander, Cantabria, Spain, September 23-25, 2008 ISSN: 1790-2769 298 ISBN: 978-960-474-007-9