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In recent years, the rapid decrease in size of personal communication devices has lead to the need for more compact antennas. At the same time, expansion of wireless systems has increased the applications for multi-functional antennas that operate over broad frequency bands or multiple independent bands. The civilian GPS system is quickly becoming the standard for personal and commercial navigation and position location. The difficulty with GPS is that there is no return link. That is, a GPS terminal determines its position, but that position is known only to the terminal user. A return link enables positional information derived from GPS to be communicated to a remote location. This is especially desirable for unmanned terminals. The next wide scale technology area for GPS is the integration of a GPS receiver with some type of wireless service to provide communication of the GPS - derived position as well as messaging. One of the most popular uses for this service is tracking of mobile cargo. This paper presents a design for a compact, low-profile antenna that operates at both the conventional cellular telephone band of 824 to 894 MHz and the civilian GPS L1 frequency of 1575 MHz. The combined antenna unit has a lateral diameter of less than 4 inches (10 cm) and its height is less than 2 inches (5 cm). The integrated unit is a hybrid design of two collocated antennas that operate at the two different bands. The planar inverted F antenna, PIFA, meets the specifications which are required in a reduced size environment. The PIFA is capable of achieving a bandwidth of 8% in the cellular band. The GPS portion of the hybrid unit consists of a dielectrically loaded patch located in a "piggyback" configuration on top of the top PIFA element. Computer simulation and design were performed using a combination of IE3D, a 2.5 dimensional commercial moment method code, and Fidelity, a commercial full 3D finite difference time domain code. Results will be presented from these calculations along with measurements on prototype antennas using both the Virginia Tech outdoor antenna range and the Virginia Tech near-field antenna range. / Master of Science

Yes / The paper presents a new modeling and design concept of antennas using polar- ization diversity of 2 £ 2 and 3 £ 3 Multiple Input Multiple Outputs (MIMO) system that is proposed for future mobile handsets. The channel capacity is investigated and discussed over Raleigh fading channel and compared to a linear/planner antenna array MIMO channel. The capacity is also discussed over three types of power azimuth spectrums. The results are compared to the constraints capacity limits in which the maximum capacity observed.

Electrically small, low profile antennas have become the new frontier in wireless communication research. With the pressure to miniaturize wireless communication devices, engineers are turning to small low profile antennas as a way to reduce their antennas and hence their devices. Ideally, one would also like to at least maintain antenna bandwidth and efficiency while reducing size. However, in theory, antenna performance degrades when it is miniaturized—impedance bandwidth decreases with the reduction in antenna size. This thesis investigates the possibility of increasing the input impedance bandwidth without enlarging the volume of the antenna. This thesis attempts to break the fundamental tradeoff between antenna size and bandwidth by loading it with a nonlinear element. First, a brief summary of antenna background definitions is presented. Next, the analytical framework of the thesis is presented using a model of a narrowband antenna. A literature review of various narrowband electrically small antennas is studied, including the pros and cons of the Inverted-F antenna (IFA), Inverted-L antenna (ILA), and the Planar Inverted-F antenna (PIFA).Next, the analysis and the methodology leading to results are discussed and simulated results are presented. Simulated results show that the PIFA is able to achieve a higher bandwidth with a loaded nonlinear element. However, it is difficult to sustain the efficiency of the antenna due to harmonics generated by nonlinearity in the antenna. Results indicate that an increase in nonlinearity tends to generate harmonics which leads to losses in the antenna. / Master of Science

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