I. Introduction
Compared to dual and other multifeed versions, the single-feed circularly polarized (CP) patch antennas are valued because their configurations are inherently simpler. Nevertheless, most reported single-feed CP patch antennas suffer from an inherent, very narrow axial-ratio (AR) bandwidth. This aspect severely limits their widespread application [1]–[4]. A popular and effective method to improve their AR bandwidths is to introduce additional parasitic patches [5]– [14]. Unfortunately, their presence also has some inescapable drawbacks. For instance, vertically stacking one or more parasitic patches with similar configurations has the desired effects, but it also significantly increases the antenna's total height [5]– [13]. On the other hand, adding parasitic patches around the main radiating patch on the same layer requires much more area than the main patch [13], [14].