“…Later, in 2017 and 2019, the author then respectively investigated the propagation characteristics and the radiation properties of the 2-D LWA in the microwave regime and also the optical regime. 14,15 In 2020, a two-dimensional (2-D) annular periodic LWA with metal strip gratings printed on a grounded dielectric slab is proposed, suppressing the open stopband and achieving high-gain broadside radiation over a wide bandwidth. 16 It is easy to see that in these studies about 2-D LWA, most of them can be classified into the array antenna, 9,[11][12][13][14][15] and few of them are about the real 2-D structure.…”