A built-in antenna for a portable terminal is provided. The built-in antenna includes a substrate including a ground region and a non-ground region, an antenna radiator formed in a pattern with a preset shape within the non-ground region of the substrate, at least one sub-radiation pattern formed in a pattern type while including a preset spacing distance from the antenna radiator, and a conductive plate with a preset height, electrically connecting the sub-radiation pattern to the antenna radiator and/or the sub-radiation pattern.