The electromagnetic field focusing capabilities of non-continuous periodic Mikaelian lens is considered. Theoretical continuous Mikaelian lens has the electromagnetic field focusing properties and concentrates incident wave field in one point on the border. Also this lens has sophisticated structure and cannot be implemented using current technologies. The alternative way to implement similar structure is by using periodic layers of constant permittivity which are separated by the periodic layers of air. The idea is to replace continuous lens with the another one, which structure could be easily implemented in practice. Continuous lens has permittivity reducing from 2.56 on the axis of symmetry to 1.0 at the borders. The new lens is a periodic structure, that does not have the same redundancy of permittivity as the continuous one. Such lens has layers containing both the non-conductor and the air, and the ratio of thickness of air to thickness of material increases in the direction from axis of symmetry towards the borders. Thickness ratio of air to thickness of material in each layer is calculated according to the permittivity in the continuous lens on the same distance from the axis of symmetry. Material and air create necessary permittivity in total. It is shown, that the ratio of wavelength to the one period length should be higher than specific value. FDTD method is used for the numerical simulation. The thickness of one layer expressed in the number of grid points is important numerical parameter. When this number is too small, structure of lens close to the axis of symmetry cannot be resolved, and this leads to loss of focusing capabilities. To avoid this, the number of grid points per layer should be at least equal to 10, but the higher this number is the better result would be achieved. The problem with increasing the number is that grid size should also be increased, and the amount of needed memory will also significantly rise. Number of computational experiments is performed and electromagnetic-field focusing capability of layered lens is obtained.
展开▼
