Reduced size single and dual-band diversity antennas for portable devices

The reliability of communication in mobile wireless systems can be improved by using diversity combining. This technique can be realized by using independent antenna elements as the branches to form a MultiElement Antenna array (MEA). Diversity reception at the mobile requires physically small antennas. Two techniques to reduce the physical size of rectangular and circular microstrip patch antennas are presented. Firstly, slits are inserted within the antenna which are perpendicular to the resonant current. This forces the current to flow around the obstacles which has the effect of reducing the resonant frequency. Using slits, a four element MEA with one-fourth the area of the original MEA is demonstrated. Secondly, by utilizing the symmetry of the resonant current distribution the size of the circular patch antenna can be reduced by one-half of the original patch. Finally, using two semi-circular patches displaced laterally an antenna with dual band capabilities can be realized. The two frequency bands, f₀=5.2, 5.7 GHz, are chosen to lie within the existing PCS and the two future Bluetooth frequency bands. The antenna geometry is an aperture coupled microstrip antenna. The reduced size and thin substrate thicknesses will allow the compatibility with portable communications systems