In this dissertation, the study mainly focuses on small-size multiband mobile phone antennas for practical applications. Loop antenna is chosen to be the antenna type for designing the compact internal multiband antenna. Four antenna designs are presented, including ¡§Compact Multiband Folded Loop Chip Antenna for Small-Size Mobile Phone¡¨, ¡§Very-Small-Size Folded Loop Antenna with a Band-Stop Matching Circuit for Penta-Band Mobile Phone Application¡¨, ¡§Very-Small-Size Printed Loop Antenna for GSMDCSPCSUMTS Operation¡¨, and ¡§Printed Loop Mobile Phone Antenna with an Internal Printed Matching Circuit¡¨. The first two antenna designs occupy a volume of 1.0 cm3 and 0.6 cm3 respectively and the last two antenna designs are to be directly printed on the system circuit board of the mobile phone. Either of them can operate as a quad-band antenna for GSM/DCS/PCS/UMTS operation or as a penta-band antenna for GSM850/900/1800/1900/UMTS operation.

An internal small antenna usually suffers from degradation in performance of impedance bandwidth and radiation patterns. In this thesis, we design and fabricate a broadband interior type planar monopole with an omni-directional radiation pattern over a wide operation band using a slant feeding strip. It has a measured impedance bandwidth about 465MHz with center frequency at 1.66GHz (1427 ¡V 1892MHz) and the maximum cross polarization level about -13dB at 1800MHz, which is GSM1800 band in mobile communications. A modified design is an interior planar monopole with a slant slit. It has a measured impedance bandwidth about 455MHz with center frequency at 1.71GHz (1487 ¡V 1942MHz), including GSM1800 and PCS1900 band, and the maximum cross polarization level about -15dB at 1800MHz. The antennas have the dimensions of 40mm*15mm which occupies a small size on the system board and they are suitable to be mounted within the mobile handset device.

This thesis focuses on mobile phones antenna design with brief description about the historical development, basic parameters and the types of antennas which are used in mobile phones. Mobile phones antenna design section consists of two proposed PIFA antennas. The first design concerns a single band antenna with resonant frequency at GPS frequency (1.575GHz). The first model is designed with main consideration that is to have the lower possible PIFA single band dimensions with reasonable return loss (S11) and the efficiencies. Second design concerns in a wideband PIFA antenna which cover the range from 1800MHz to 2600MHz. This range covers certain important bands: GSM (1800MHz & 1900MHz), UMTS (2100MHz), Bluetooth & Wi-Fi (2.4GHz) and LTE system (2.3GHz, 2.5GHz, and 2.6GHz). The wideband PIFA design is achieved by using slotted ground plane technique. The simulations for both models are performed in COMSOL Multiphysics.  The last two parts of the thesis present the problems of mobile phones antenna. Starting with Specific absorption rate (SAR) problem, efficiency of Mobile phones antenna, and hand-held environment.