I. Introduction
Planar antennas with reconfigurable beam direction have opened the way to meet the ever-evolving requirements of many wireless applications, such as cellular and satellite communications and radar systems. Pattern-reconfigurable antennas offer diverse performances and are efficient in noisy environments, robust to electronic jamming, in addition to their capability to save energy by directing signals toward the intended directions. Phased antenna arrays are traditionally used to meet these requirements, but they are large in volume, need complex feeding structures, and are expensive to manufacture for many applications [1]. Electronically steerable parasitic array radiator (ESPAR) antennas can also provide beam steerabilty, but their three-dimensional structures or large profiles limit their compatibility with the requirement to build compact systems [2], [3]. Thus, compact low-profile configurations are quite desirable for ease of fabrication and system integration.