Designing Uncorrelated Multiple Antennas with Round Patterns Using Handset Metal Frames

Multiple antennas with low correlations are highly in demand in the mobile handsets for higher data rate. At the same time, the total pattern provided by the antennas should be as round as possible for reliable links. In this paper, by analysing the characteristic modes of the mobile chassis loaded by ultra-thin metal frames, a four-antenna system with a round total pattern is designed at 2.4 GHz. The gain variations are only 3.4 dB and 3.6 dB on two dominant planes. The isolations between antennas are above 15 dB, and the correlations are below 0.01, with intact ground plane and small ground clearance of 2 mm maintained. Afterwards, an eight-port antenna system is designed by taking advantage of the ground clearance and exciting modes with different phases. Low correlations of below 0.07 are obtained. The antenna system is fabricated, with the measured results agreeing well with the simulated ones.