The modified aperture coupled MicroStrip Antenna (MSA) and Planar Inverted F Antenna (PIFA) for mobile applications are studied and presented in this dissertation. The designed antennas are improved multi-band and broad-band characteristics by the modification of radiating elements and/or the ground plane. The novel modified aperture coupling annular-ring antenna fed by stripline is the hybrid structure of the aperture coupling feed MSA and the proximity feed MSA. The proximity feed enable to concentrate the field strength toward the direction of the radiating element and the modified aperture layer contributes to provide the maximum coupling to the radiating element. The measurement bandwidths of the Aperture Coupling Proximity Feed Hybrid MSA #1(ACPF-HMSA#1, design #1) and ACPF-HMSA #2 (design #2) are 185MHz (7%) and 105MHz (4.1%), VSWR in less than 2, respectively. Two layers Planar Inverted F Antenna (PIFA) with the modification of the ground and radiating element was studied. The inserted T-shaped or L-shaped ground and inserted a slot and slits on radiating elements help to adjust the resonant frequencies to the target applications. The result of PIFA #3 (design #3) is presented a significant board-band characteristic on the upper band by 910MHz (from 1.45GHz to 2.36GHz) with VSWR less than 2.5. It covers GPS, DCS, PCS, and UMTS bands. Novel internal loop planar inverted F antennas (L-PIFA) with Inserted Concentrated Annular Rings (ICAR) and Inserted Loop Inductors (ILI) are presented as design #4 (ICAR-L-PIFA #4) and design #5 (ILI-L-PIFA #5), respectively. The simple loop structure consists of a meandered line. It increases the capacitance between adjacent lines. The Inserted annular-rings and loop inductors provide inductance values to the main loop antennas. Therefore, the impedance bandwidth of the design #4 is 570MHz (from 1.69GHz to 2.26GHz) with VSWR less than 2.5. And, the impedance bandwidth of the design #5 is 275MHz (from 1.63GHz to 1.905GHz) and 465MHz (from 2.19GHz to 2.655GHz) with VSWR less than 2.5.