Miniature loop antennas with balanced and unbalanced feeds

Loop antennas have been shown to exhibit characteristic of self-balance. In this paper, however, we extended the study to include unbalanced-feeds, which excited various additional modes. The purpose of the study was to see how feeds can minimize the ground current perturbation, thus, reducing the overall antenna size. We found that, for loop antennas which are of a balanced configuration, balanced-feed can only excited self-balanced current modes. Such antennas are more stable (i.e., immune to the external variations), suitable for products such as notebook or tablet computers. Unbalance-fed loop antenna excited both self-balanced and quasi self-balanced modes. Such antennas are suitable for handsets where multi-bands are required. We also analyzed the effects of ground size and human finger proximity effect on these antennas.