Compact small magnetic antennas an efficient technique to reduce dimensions without affecting the efficiency

The use of small radiators is growing in importance for applications related to wireless sensor networks, RFIDs, personal and body communications. In these context, the antenna must be compacted in a very narrow space, and the bandwidth of the signal is typically small. Under these conditions, radiating elements smaller (even much smaller) then the wavelength, appear as the best solution. Thanks to a compact design and a small size, these antennas can be embedded in a narrow space, with extremely limited spatial dimension. On the contrary, small antennas have limited radiating characteristics, with a light efficiency and a high mismatch. The paper introduces a design approach that reduces the overall antenna dimensions by selecting an efficient geometrical shape and embedding the matching circuit inside the antenna. The return loss has a 0.6% bandwidth at -10 dB, larger in comparison to other realizations than can be found in the literature. Although several realizations s have been carried out, two solutions working 900 MHz with simulations and measurements is presented. For their shape, they have been baptized, respectively, Smiley and Hair Antennas.