A superstrate is able to significantly increase the gain of an antenna, and this superstrate based technology has been widely used. However, the studies about the effects of superstrates on the return loss of the antenna are limited. In this work, taking homogenous dielectric superstrates and a probe-fed microstrip antenna as examples, using numerical simulations, the effect of superstrates on the return loss of an antenna is investigated. The simulation results show, by proper design of some structural parameters, such as the distance between the superstrate and the antenna, the feeding location of the antenna and so on, the dielectric superstrate can improve both the gain and the impedance bandwidth. A prototype is fabricated and measured, and the measured results shows that it has a gain of 14.5 dBi and a |S11|
