An internal antenna for mobile phones with small volume is proposed. The proposed antenna is based on a planar inverted F-antenna (PIFA) with a coupled feeding structure. The proposed antenna realized on a printed circuit board to reduce fabrication costs. The coupled feeding structure helps the antenna have broadband characteristic which includes all commercial service bands, GSM850 / GSM900 / GPS / GSM1800 / GSM1900 / WCDMA2100 / 802.11b/g / LTE2600 (824-2690 MHz) as well as 802.11a/n (5150-5825 MHz). The antenna gain is in the range of -0.1-3.5 dBi over 824-2690 MHz and 2.3-2.8 dBi over 5150-5825 MHz. And the antenna efficiency is in the range of 61-93 % over 824-2690 MHz and 69-81 % over 5150- 5825 MHz. In addition, the effect of SAM head phantom is tested using a simulation. As a result, it was verified that the performance does not change significantly. The total size including system circuit area and no-ground area is 100 × 40 × 0.8 mm 3. The SAR results for the proposed antenna are presented as proper values. As a result, the designed antenna is suitable for small mobile devices and slim wireless applications.