Importance of transversal and longitudinal symmetry/asymmetry in the fundamental properties of periodic leaky-wave antennas

This paper classifies periodic leaky-wave antennas (LWAs) into four groups based on the symmetries or asymmetries of their unit cell. It first presents the fundamental properties and limitations of LWAs whose unit cell is symmetric with respect to both the longitudinal (long.) and transversal (trans.) axes, which constitutes the first group. It next shows that breaking the symmetry with respect to the long. axis, which leads to the second group, allows to equalize the antenna gain through broadside. This group is generally elliptically polarized. The third group is formed by breaking the symmetry with respect to the trans. axis. Here, the degree of asymmetry is a powerful design parameter to selectively control the LWA characteristics at broadside while maintaining linear polarization. Finally, it speculates on the characteristics on the last group, that is currently under investigation.