Electrically Small Antennas under matched conditions

In this paper, we study the performance of the Electrically Small Antennas (ESAs) versus larger antennas in both transmitting and receiving modes. We conclude that the ESAs perform well compared to larger antennas under matched conditions where the input power to the antenna is real (input power is S = VinIin, Vin and Iin are the phasor domain Root Mean Square (RMS) input voltage and input current, respectively). The difficulties in achieving a good design of an ESA matched to 50 Ω system 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.