Multiband loaded inverted-F antennas suitable to be applied in a portable device as an internal antenna having high gain property for mobile WiMAX , Wi-Fi, Bluetooth and WLAN operations are presented. Numerical simulation is carried out using method of moments in Numerical Electromagnetic Code (NEC-2). The proposed dual inverted-F antenna is suitable for 3.5/5 GHz and compact triple band inverted-F antenna is for 2.4/3.5/5.2 GHz operations. Total areas occupied by the antennas are 24mm×37mm and 29mm×37mm in case of dual IFA and triple IFA respectively. The antennas contain an incredibly high peak gain of 7.72 dBi at 5 GHz band and the gain variations at all frequency bands are less than 1 dBi. In addition, the antennas have satisfactory radiation characteristics at all the frequency bands. Due to compact area occupied, the proposed antennas are promising to be embedded within the different portable devices.