A compact, single-layer, wideband, tilted-beam microstrip antenna with customized tilt angle is presented. The antenna is comprised by one subwavelength driven patch and several subwavelength parasitic patches. The tilt angle of the antenna is determined by the index distributions of those subwavelength patches. The detailed index-modulation principle is developed from the generalized law of refraction, wherein the reflection phase is mapped to the index by utilizing the equivalent transmission-line theory and the transverse resonance technique. As a result, the tilt angle could be customized by allocating patch cells following specific index distributions. On top of that, as a new degree of freedom in design, one could choose subwavelength patches with low dispersion characteristics as unit cells to further enhance the operational bandwidth and improve the stability of radiation pattern. For demonstration, two types of I-shaped patch units with different dispersion characteristics have been utilized to configure tilted-beam antennas that follow the same index distributions. In addition, the effectiveness of the developed tilted-beam antenna for array application has been proven. Experiments have been carried out to verify their performance.