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.

When the conventional mobile communication antennas embedded in the laptop computers, it is difficult to achieve enough bandwidths or a larger antenna size is required for covering the GSM/DCS operation. To overcome this problem, three new mobile communication internal antennas, having multi-band operation capability and suitable to be embedded in the laptop computers are proposed. At first, we introduce a monopole antenna with a shorted parasitic element. This antenna can provide wide bandwidths to cover GSM900, DCS, PCS, and UMTS operations. Then, in order to additionally achieve the GSM850 operation to form the penta-band operation, we present a wideband monopole antenna with a shorted structure. Finally, we propose an open-loop antenna with a shorted parasitic element. The antenna occupies a smaller volume and is capable of providing wide bandwidths to cover GSM850, GSM900, DCS, PCS, and UMTS operations. Detailed antenna designs and experimental results are presented and discussed.

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.

In this thesis, three small-size internal multiband antennas for laptop computer application for different wireless communication systems are proposed. In the first design, the coupling feed is incorporated to the planar inverted-F antenna to achieve a dual-resonance excitation in the lower band such that the obtained bandwidths can easily cover GSM850/900/DCS/PCS/UMTS operation. The effect of the user¡¦s hand on the antenna is also studied. In the second design, we introduce the T-shaped coupling feed used in the PIFA for successful excitation of two wide operating bands to cover WLAN operation in the 2.4 GHz band and 5.2/5.8 GHz band, and the size reduction is even larger than 50%. Finally, a multiband monopole antenna with a band-notching slit is proposed. By embedding the slit of length about a quarter-wavelength at about 4 GHz, a band-notching characteristic is obtained, which leads to an additional resonance at about 3.5 GHz. Hence, three wide operating bands for covering all the desired operating bands of WLAN/WiMAX systems are achieved for the proposed antenna.

In this dissertation, a variety of multiband communication device antennas using the coupling-feed mechanism are presented. The coupling feed contributes additional capacitance to the antenna¡¦s input impedance which shows a high inductive component for the traditional case of using a direct feed. In the first and second antenna designs, with the coupling feed, the high input inductance of the antenna is effectively compensated. This behavior leads to a dual-resonance excitation for the lower band of the antenna. Two wide operating bands are achieved, allowing the antenna¡¦s lower and upper bands to easily cover GSM850/900 and GSM1800/1900/UMTS operation. For the last two antenna designs, owing to the coupling feed, the very large input impedance seen at antenna¡¦s lower band is greatly decreased and results in successful excitation of the one-eighth wavelength (£f/8) mode of the antenna. The specific absorption rate and hearing aid compatibility results for these mobile phone antennas are also analyzed. The effects of presence of the user¡¦s hand on the laptop computer antenna performance are also studied in this dissertation.

In this dissertation, thin internal antennas for mobile communication devices with a total thickness of less than 10 mm are proposed. There are mainly two differences in the antenna¡¦s construction between the proposed thin internal antennas and conventional planar inverted-F antenna. The first proposed antenna for thin internal antenna is a combo type formed by combining the conventional inverted-F antenna with the monopole antenna. The second proposed antenna is obtained by integrating two radiating arms into a radiating patch. By adjusting the tapering angle and the direction of the end portions, thin internal planar antenna with a thickness of less than 4 mm can be successfully achieved. In these two antennas, their Q-value can be lowered, and then the impedance bandwidth can be effectively improved. This kind of thin internal antennas not only has good impedance matching but also shows good radiation performance. Additionally, by adding a vertical metal wall acting as a RF shielding wall, EM fringing fields between the thin internal EMC antenna and nearby metal components can be effectively supressed. This kind of EMC antennas can effectively eliminate the isolation distance between the antenna and nearby conducting elements to increase the available space on the printed circuit board for additional functions. Besides, multi-band operation is another important function in current mobile devices. In this dissertation, we also studied the effects of the plastic casing and the user¡¦s hand and head on the antenna charateristics. For studying the antenna with the presence of the user¡¦s hand and head, the simulation model provided by SPEAG simulation software SEMCAD is used. From the results obtained, it is seen that the frequency detuning is greatly dependent on the presence of the user¡¦s hand and head. Owing to the presence of the user¡¦s hand and head, large decrease in the radiation efficiency is seen. It also indicates that the radiation efficiency decrease and radiation pattern distortion are mainly owing to the radiation power absorption by the user¡¦s hand and head.

In this dissertation, a series of multiband hybrid mobile phone antennas, incorporating the electric-current and equivalent magnetic-current excitation mechanisms are presented. The design concept of the hybrid antenna is that the multiband operation is achieved by incorporating the resonant modes generated by the two above-mentioned excitation mechanisms. In the first and the second antenna designs, they are obtained by stacking the antennas using the electric-current and equivalent magnetic-current excitations, and both can achieve multiband operations. For the last two antenna designs, the two different excitation mechanisms can be incorporated on a single metal plate or dielectric substrate. This kind of hybrid are promising for application in bar-type and folder-type mobile phones. Besides, in order to pass some required testing criterions and analyze the environmental effects, the hybrid penta-band mobile phone antenna applied in bar-type and folder-type mobile phones is analyzed. The main topics include the speaker¡¦s effects on the antenna¡¦s performances, the analysis of user¡¦s hand and head effects, and the analysis of the hearing aid compatibility.

In this dissertation, a variety of novel mutiband WWAN loop antennas are presented. By designing proper coupled-fed mechanisms for the proposed loop antennas, the impedance bandwidth of the loop antenna can be greatly enhanced to achieve two wide operating bandwidths at antenna¡¦s lower and upper bands to easily cover GSM850/900/1800/1900/UMTS operation. With two wider operating bandwidths obtained, the tolerance of frequency detuning and the capability of bandwidth tuning of the loop antennas can be improved for practical applications. In addition, in order to find methods to meet the SAR and HAC criterions, the proposed small-size chip loop antenna studied in this dissertation which is suitable for both bar-type and folder-type mobile phone applications are simulated and analyzed for SAR and HAC issues.