Abstract: A novel broadband cylindrically conformal microstrip antenna with a single substrate is presented. A patch with a U-shaped slot is employed as the radiating element, and the incurrence of the slot changes the current distribution on the patch. Through this the impedance bandwidth is extended to about 39%. A full-wave hybrid algorithm that combines the finite difference time-domain (FDTD) method and the dyadic Green's functions for cylindrically stratified media is used to analyze the impedance and radiation characteristics of this antenna, as well as the mutual coupling effects between the two antenna elements. Compared with the broadband microstrip antenna with stacked structure, the profile of this type of antenna is reduced by the order of about 30%. Thus it is very suitable for use on the situations where rigorous limitation on the size of the antenna profile is required, because only a single dielectric layer is involved in its structure.