Contents I. Introduction
Annular-ring slot antennas have been of great interest to many researchers and engineers in recent decades [1]–[4]. In [1] and [2], by introducing the asymmetry of the ring slot, the degenerate resonant modes are excited. Le Bolzer and A. Louzir presented a nonconcentric microstrip-fed multiannular slot antenna in [3]. However, due to the nonconcentric configuration of the antenna, the frequency ratio is large for some applications where a lower frequency ratio is required. In [4], triplate line-fed dual-loop slot antennas for linear polarization and for circular polarization are investigated.
