This thesis includes the design, production and measurement of a wideband dualpolarized X-band aperture-coupled microstrip patch antenna. The wideband and dual-polarized operation is achieved through the use of H-shaped coupling slots. Therefore, the equivalent circuit modeling of a microstrip line fed H-shaped slot is also studied in this thesis. A step-by-step procedure is followed during the design process of the dual-polarized aperture-coupled microstrip antenna. First, an aperture-coupled microstrip antenna with a single rectangular slot, that exhibits a wideband characteristic for single polarization, is designed. Then, the design procedure is repeated for an antenna with H-shaped slot in order to satisfy the same specifications with a shorter slot. Finally, dual-polarized aperture-coupled microstrip antenna is designed. At this configuration, two H-shaped slots are used and they are placed orthogonal to each other. During the design process, the effects of antenna parameters on the input impedance characteristics of the antenna are investigated. These parametric analyses are done in CST Microwave Studio&reg / . The v designed dual-polarized wideband aperture-coupled microstrip antenna is manufactured. Simulation results and measurement results are compared. During the equivalent circuit modeling of an H-shaped slot fed by a microstrip line, an approach based on the reciprocity theorem is utilized. The method was originally proposed for rectangular shaped slots, in this thesis it is generalized for arbitrarily shaped slots. Software codes are developed in MATLAB to calculate the equivalent impedance of the slot.