The Impact of Excitation Technique on the Frequency Agility of Electrically Small Antennas

This work presents a study of the impact of the excitation technique on the frequency agility performance of a capacitively loaded loop (CLL) electrically small antenna (ESA). Three excitation techniques are presented and analyzed: electric-dipole based excitation, magnetic-dipole based excitation, and short-circuit based excitation. All the designs are electrically small with a maximal electrical size of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{k}\boldsymbol{a}$</tex> less than 0.4. To compare the agility performances achieved by each excitation technique, the tunable bandwidth (TBW), the fractional tunable bandwidth (FTBW) and agility efficiency (AE) are used as figures of merit. The comparison reveals that the short-circuit based excitation archives the optimal performances with a TBW of 1104 MHz, a FTBW of 146.42% and an AE of 83.15 MHz/pF. Furthermore, it presents a radiation efficiency ranging from 1.5% (for a ka = 0.06) to 94% (for a ka = 0.39).