Electrically small antennas design challenges

The Electrically Small Antennas (ESAs) perform well compared to larger antennas under matched conditions. In this paper, we study the difficulties in achieving a good design of an ESA matched to 50 O system. These difficulties are summarized in three topics: First, the Quality (Q) factor of an ESA, in general, is high and cannot be less than the Chu limit. The Q factor of an antenna is inversely proportional to the bandwidth of the antenna so this will impose a limit on the bandwidth of the antenna. Second, losses are always there in the impedance matching network, these losses associated with the matching network can dominate the small radiation resistance of an ESA which will degrade the efficiency of the ESA. Third, we are limited by the Fano-Bode gain-bandwidth limit when using the lossless passive matching network techniques. To overcome these issues, several solutions are presented briefly, either we try to alter the shape of the ESA so as to make the Q factor of the antenna close to the optimum lower limit or to use the concept of non-Foster matching networks to overcome the Fano-Bode limit. Finally, we design a four-arm meander line folded monopole which is considered an ESA at 1 GHz; it is shown that this design is matched to 50 Ω with low quality factor.