Bandwidth Enhancement of Miniaturized Slot Antennas Using Folded, Complementary, and Self-Complementary Realizations

Folded and self-complementary structures are considered as two effective approaches to increase the bandwidth of miniaturized antennas. A folded realization of a previously reported miniaturized slot antenna is devised and shown to provide more than 100% increase in the bandwidth as compared with that of the miniaturized slot antenna with the same size and efficiency. The complementary pair of the miniaturized folded slot, namely, the folded printed wire is also discussed in this paper. It is shown that the folded slot has a much higher radiation efficiency when compared with its complementary folded wire antenna. Another approach for bandwidth improvement is the implementation of the self-complementary structure of the same miniaturized topology to moderate the frequency dependence of the antenna input impedance. To examine this approach, a folded self-complementary miniature antenna is studied, where further increase in bandwidth is observed. A miniaturized folded slot, its complementary miniaturized folded printed wire, as well as their self-complementary realization, were fabricated and tested. These antennas can fit into a very small rectangular area with dimensions as small as 0.065lambda_o x 0.065lambda_o. While the folded slot ranks the highest in the efficiency/gain, the self-complementary structure falls between the slot and printed wire since it consists of equal proportions of the both slots and strips. A self-complementary H-shape antenna is also introduced to demonstrate that by relaxing the miniaturization to a moderate value, a significant improvement in bandwidth can be accomplished. With yet small dimensions of 0.13lambda_o x 0.24lambda_o, a very wide bandwidth of (2.3:1) is obtained. For the case of no dielectric substrate, even wider bandwidth of (3:1) is achievable.