Properties of Near Field Focusing for Cylindrical Dipole Arrays in Enclosed Array Volume

Motivated by large intelligent surface applications, the electric field properties of near field focusing using phase conjugation method are analyzed for cylindrical dipole arrays. Firstly, for the transmitting antennas featuring vertical polarization, the polarization characteristic is decomposed along the x, y, and z directions. Three typical cases are studied when the focal points are at (xf , 0, 0), (0, yf , 0), and (0, 0, zf ). When the length of the cylindrical dipole array is significantly larger compared to its radius, certain unique insights emerge. When the focal point is positioned along (0, 0, zf ), apart from the region on both sides, the ratio between Ez and Ex/Ey remains {\pi}/2. Additionally, When the focal point is located within the cylinder, the electric field of each polarization is approximately the same everywhere. In other words, beam focusing does not incur losses due to different positions. The focusing resolution of Ez is the same in the transverse and longitudinal directions. Different from the situation where the 3 - dB focal beam depth is much smaller than the focal beam width for the most of arrays, the resolution in the longitudinal can be improved, respectively. Through a comprehensive grasp of these design principles, we can gain a deeper understanding of the specific areas with significant potential for practical applications.