Highly Directive Fabry-Pérot Cavity Antennas: A Review and Our Developments F. Capolino (1) , D. R. Jackson (2) , P. Burghignoli (3) , G. Lovat (4) , M. Albani (5) , A. Vallecchi (1,5) , S. A. Hosseini (1) , and F. De Flaviis (1) (1) Dept. of Electrical Engineering and Computer Science, University of California, Irvine, CA, 92697-2625, USA. Tel. 1-949-824 2164, email: f.capolino@uci.edu (2) Dept. of Electrical and Comp. Engineering, University of Houston, Houston, TX, 77204-4005, USA (3) Dept. of Electronic Engineering, “La Sapienza” University of Rome, 00184 Roma, Italy (4) Dept. of Electrical Engineering, “La Sapienza” University of Rome, 00184 Roma, Italy (5) Dept. of Information Engineering, University of Siena, 53100 Siena, Italy Abstract We review the history of Fabry-Pérot Cavity (FPC) antennas (which may be particular cases of EBG or leaky-wave antennas), and present and discuss our developments compared to those made by other research groups. An FPC antenna is a highly directive radiator consisting of a cavity and a surface, that allows power to be leaked in free space and that forms a large radiating area. The usual drawback is the small pattern bandwidth. 1. Introduction A Fabry-Pérot Cavity (FPC) antenna is an antenna made by a resonator, large in the transverse direction (say, in the xy plane) and resonating in the z direction. A variety of FPC antennas have been designed, as explained in detail, e.g., in the introduction of [1]. Generally, they are made by a ground plane underneath a dielectric (or artificial-material) slab that resonates in the z direction because of an impedance mismatch at the top surface. For example, various designs are made by covering a grounded dielectric either with a high-density dielectric layer or by a partially reflective surface (PRS) that partially inhibits radiation to es- cape from the slab. Therefore the resonant mode is kept inside the slab and leaks a small amount of power while it travels along the xy plane. During the presentation we will cover the history of FPC antennas, which are actually a particular case of leaky-wave antennas as well explained in the referenced papers and in some of their references. Below we highlight some of our developments that will be thoroughly dis- cussed during the presentation. 2. Fabry-Perót Cavity (FPC) antennas using different metamaterial concepts Wire media have been used for long time as artificial dielectrics. Under the conditions of small (compared to the wavelength) period and wire radius and for suitable field polarization, they behave as an artificial plasma. In particular, when the electric field is parallel to the wires and slightly above the plasma frequency (depending on the geometric characteristics of the wire arrangement), they exhibit a small permittivity 0<  r < 1. We have used this feature to design FPC antennas made by a wire-medium slab as shown in Fig. 1. Various design formulas have been derived in [1]. A more realistic dipole excitation was considered in [2]. In [3], concepts have been generalized and we have determined the slab material properties that could lead to high directivity. Low  r cases are shown in Figs. 1 and 2, while in Fig. 3 we show the radiation pattern of a source inside a structure with small  r . Fig. 1: A grounded wire-medium slab excited by a line source, and its homogenized equivalent slab with permittivity 0<  r < 1. Broadside ( = °) directivity varying the slab thickness, at f = 20.16 GHz. (This is a high-impedance slab, therefore the thickness that leads to high directivity is half wavelength.) Parameters and plots from [1]. 3rd International Congress on Advanced Electromagnetic Materials in Microwaves and Optics ISBN 978-0-9551179-6-1 ©2009 Metamorphose-VI ISBN 978-0-9551179-6-1 ISBN 978-0-9551179-6-1 ©2009 Metamorphose-VI 379