Characteristic Mode of a 3D Printing Hollow Sphere Antenna Fed by Conformal Wires

3D printing technology is promising for fabricating dielectric antennas. In this work, characteristic mode analysis (CMA) is adopted for analyzing 3D printing antennas. A hollow sphere made of low permittivity PLA material is considered for economic reasons but it is not resonant when its diameter equals to a half wavelength. Therefore, it is not efficient to excite those modes. Instead, a conformal wire feeds the hollow sphere. Based on the CMA, its properties such as the resonant frequency, Q factor, and power contributions by the metallic and dielectric parts are investigated. The hollow sphere works as a load to the conformal feed, and it has an optimum thickness. The antenna is resonant at 520 MHz and 350 MHz with different feeding wires.