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 research we attempted several modifications to microstrip ring/loop antennas to design multi-frequency antennas through systematic approaches. Such multi-frequency antennas can be useful while building compact terminals to operate at multiple wireless standards. One of the primary contributions was the use of a capacitive feed arrangement that enables simultaneous excitation of multiple concentric rings from an underlying transmission line. The combined antenna operates in the same resonant bands as the individual rings and avoids some of the bands at harmonic frequencies. A similar feeding arrangement is used to obtain dual band characteristics from just one ring, with improved bandwidth. This is made possible by widening two adjacent sides of a square ring antenna symmetrically, and attaching an open stub to the inner edge of the side opposite to the feed line. Use of fractal segments replacing the side with the stub also results in a similar performance. Use of fractal geometries has been widely associated with multi-functional antennas. It has been observed from the parametric studies that, the ratio of the resonant frequencies can range from 1.5 to 2.0. This shows some flexibility in systematically designing dual-band antennas with a desired pair of resonant frequencies. An analysis technique based on multi-port network modeling (MNM) has been proposed to accurately predict the input characteristics of these antennas. This approach can make use of the ordered nature of fractal geometries to simplify computations. Several prototype antennas have been fabricated and tested successfully to validate simulation and analytical results.