The size of antenna becomes large because it is necessary to periodically arrange many unit cells. For example, an antenna using an AMC that Kyocera developed in the past as a substrate measures 8 x 8cm and has a thickness of 3.8mm. It was made by arranging 13 x 13 unit cells like a lattice.
This time, Kyocera solved this problem by using a "three-fold mirror" as a hint, the company said. When a three-fold mirror is set at a certain angle and looked from the side, it looks that the face of the person is infinitely reflected.
Likewise, by making improvements to the boundary of 2 x 2 unit cells, for incident electromagnetic waves, it looks that many unit cells are spreading even outside the boundary. As a result, 2 x 2 unit cells became enough, enabling to reduce antenna area to 1/60.
Strictly speaking, the principle that enabled to realize the small size of the Amcenna is different from that of three-fold mirror. In the case of three-fold mirror, there look to be many faces because light is actually reflected from the mirror many times.
On the other hand, in the case of the Amcenna, electromagnetic waves are not repeatedly reflected in the antenna. By "producing a periodic boundary condition on the boundary of the AMC," Kyocera realized an effect similar to the effect of arranging many unit cells, the company said.
AMC functions as antenna element
Kyocera made one more improvement to an antenna prototyped by using a previous AMC. Specifically, the company used the new AMC itself as an antenna element. The previous AMC was used mainly for blocking the influence of metal.