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Recently, a section-spherical dielectric resonator has been reported to be an efficient and low-profile radiator by using high-dielectric constant materials. In this article, the high-permittivity section spherical dielectric is used as the superstrate layer for a circular microstrip antenna. It has been reported that, by adding a high permittivity superstrate to the microstrip antenna, the antenna gain can be increased. That is, it can be predicted that the gain of the antenna structure proposed here can be enhanced. To verify such predictions, the structure of a probe-fed circular microstrip antenna with a high permittivity section-spherical dielectric loading is studied by using the three-dimensional finite-difference time-domain (FDTD) method. The rectangular coordinate rather than spherical coordinate is used due to the offset probe feed and section-spherical structure. The boundary between the section-spherical dielectric and free space is approximated by staircased Yee cells. The calculations are compared with the method of moment results of conventional patch antennas and the experimental results of hemispherical DRAs to check the accuracy of the theory. Results of input impedance, radiation pattern and antenna gain are discussed.