In this thesis we introduce a half-wavelength loop antenna for operation as an internal antenna for mobile phones. First, we introduce a single loop antenna for single-band operation (eg., UMTS band), and experimental and simulated results are presented. Next, we introduce a dual-band loop structure which covers the operating bandwidths of the GSM/DCS dual-band mobile phone. The proposed dual-loop antenna is studied, especially for the effects between the two loops of the antenna. Both of the single-loop and dual-loop antennas have the characteristics of generating similar surface currents on the ground plane with that of the conventional monopole and planar inverted-F mobile phone antennas.

In this dissertation, EMC antennas for mobile communication device applications are proposed. This kind of EMC antennas can overcome the problem that happens to the conventional antenna; in practical application, when electronic components are placed very close to the conventional antenna, large degradation of the antenna performance will occur. In the proposed EMC antennas, by adding a vertical antenna ground plane functioning as a shielding metal wall, EM coupling between the EMC antenna and nearby components can be reduced. Thus, it leads to no degradation or only negligible variations of the antenna performance. Also, the concept of EMC antennas can be applied to the monopole antenna. One of the examples suitable for the future thin (< 10 mm) mobile communication device is demonstrated. Further, the user¡¦s hand effects on EMC antenna performance are analyzed. Even when the mobile phone is hand-held at the bottom, large radiation efficiency drops are observed, especially for the GSM band.

In this dissertation, different from the conventional PIFA structure, the novel internal loop and slot antennas suitable for multiband mobile phone application are proposed. The loop antennas here use the technique of meandering the loop pattern to control the frequency ratio of the three resonant loop modes, and then the multiband operation can be obtained. For the slot antenna, different from the conventional slot antenna operating in a half-wavelength, the monopole slots antenna operating in it¡¦s quarter-wavelength mode are proposed. By properly adjusting the position of the monopole slot and the tuning stub of the microstrip feedline, the monopole slot antenna can achieve the multiband operation with a small occupied area in the mobile phone. In addition, the user¡¦s hand and head effects on the loop antenna are also studied. The obtained results indicate that, when the user¡¦s hand and head is close to or cover a certain portion of the antenna, large decrease in the antenna¡¦s radiation efficiency and great distortion in the antenna¡¦s radiation pattern will occur for all the three excited resonant modes of the loop antenna, no matter the unbalanced or balanced modes. Further, the efficiency drops caused by the user¡¦s hand and head over the GSM900 band are much larger than that over the GSM1800/1900 bands.

A mobile phone antenna with a radiating coupling feed is presented. By using the radiating coupling feed, the conventional coupled-fed loop antenna and coupled-fed shorted monopole antenna can be efficiently incorporated into the antenna structure and respectively excite a wide band resonant mode to cover GSM850/900 and GSM1800/1900/UMTS/LTE2300/2500 for the seven-band operation. Besides, the antenna can be in compact integration with the extended ground plane such that more electronic components in the mobile phone can be accommodated in the practical applications. In order to study the near-field radiation characteristics of the antenna, SAR and HAC are also simulated and analyzed.

A variety of internal mobile phone antennas with a coupling feed are proposed. The antennas are suitable to be embedded in the mobile communication devices. At first, the coupling feed is incorporated to the conventional dual-band PIFA (planar inverted-F antenna) to achieve a dual-resonance excitation at about 900 MHz such that the obtained bandwidths can easily cover GSM850, GSM900, DCS and PCS operations. Then, the coupling feed is further applied to the PIFA with a single resonant path close to about one-eighth wavelength at 900 MHz. In this design, the large input impedance at 900 and 1900 MHz can be greatly decreased to allow the PIFA to generate two operating bands at about 900 and 1900 MHz to cover GSM900, DCS, PCS and UMTS operations. Finally, a compact quad-band folder-type mobile phone antenna with a coupling feed is proposed. The one-eighth wavelength mode can be excited, and the obtained bandwidths cover GSM850, GSM900, DCS and PCS operations.

In this thesis, an internal mobile phone antenna with a distributed matching circuit for eight-band LTE/WWAN operation is presented. By selecting proper dimensions of the distributed matching circuit, the bandwidth of the proposed antenna can be greatly enhanced. Good radiation characteristics are also obtained, and the proposed antenna occupies only 60 ¡Ñ 10 ¡Ñ 3 mm^3 and is very suitable for slim mobile phone applications. Effects of the human body including user¡¦s head and hand are also studied, and the SAR and HAC issues are simulated and analyzed in this thesis.

Bandwidth enhancement of the LTE/WWAN handset antenna achieved by improving the excited surface current distribution in the system ground plane is presented. To achieve this goal, the system ground plane is shaped to be of a C-shape in this thesis. In this case, the longitudinal excited surface current in the system ground plane can have a smooth distribution. The proposed antenna is disposed at one edge of the C-shaped system ground plane, and the antenna comprises a driven monopole strip, a shorted monopole strip and a distributed parallel resonance (PR) circuit. By controlling the resonant frequency of the distributed PR circuit, it can result in dual-resonance excitation of the lowest resonant mode contributed by the shorted monopole strip to cover the LTE700/GSM850/900 operation. The antenna also occupies a small volume of 44 ¡Ñ 10 ¡Ñ 5 mm3 (about 2.2 cm3). Good radiation characteristics of the antenna are also obtained. For practical applications, effects of the electrical connection between the system ground plane and the surrounding metal elements such as the battery¡¦s metal casing and the handset metal midplate are studied. The simulated SAR (Specific Absorption Rate) and HAC (Hearing Aid Compatibility) results are also analyzed.

There are large groundplane variations for the folder-type mobile phone in the talk and idle conditions, which makes its embedded antennas not easy to maintain good radiation characteristics in the two states. The radiation efficiencies in the idle condition are often less than 15%. To solve this problem, two novel antennas for the folder-type mobile phone are proposed. The first antenna is the coplanar coupled-fed planar inverted-F antenna. The antenna can cover GSM850/900/DCS/PCS operation in the talk condition, and the radiation efficiencies over the desired operating bands in the idle condition is larger than 32%, which is acceptable for practical applications for the folder-type mobile phone. The second antenna is the ultra-wideband coupled-fed loop antenna. The antenna can cover GSM850/900/DCS/PCS/UMTS penta-band operation in the talk condition. In the idle condition, good performances over the five operating bands can still be obtained, and the radiation efficiencies are better than 53%. The effects of the housing and the user's hand and head on the antenna are also studied. From the obtained results, it is seen that the effects of the housing on the radiation efficiencies are small. However, since the user's hand and head are high-loss materials, large decrease in the radiation efficiencies is usually observed.