“…The aperture-coupling excitation method with a microstrip feed-line has the advantage of having the feed network located below the ground plane, thus avoiding spurious radiation and the advantage of integrating DRAs with printed feed structures [38]. Therefore, this excitation method has usually been used to excite the DRAs [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,39] and the last method of designing a single-feed CP DRA (modifying the coupling aperture embedded on the ground plane) is the most popular one by designers. There are many kinds of modified coupling apertures used to design single-feed CP DRAs.…”