Gain Optimization of an Electrically Small Huygens Source Antenna

Electrically small antennas typically suffer from significant ohmic losses. To achieve optimum gain, the antenna should be able to distribute the power into the most efficient modes. Aiming to verify and apply the above mentioned optimal theory of electrically small antenna, this work further reduces the size of an existing single-substrate Huygens source antenna design. Traditionally, the feeding power of a Huygens source antennas is equally distributed to two fundamental modes to achieve higher gain and front-to-back-ratio (FTBR). However, when the antenna size is considerably small, the ohmic losses differ across two modes and equal power distribution no longer results in the maximum gain. In this work, the power ratio between TE10 (loop) and TM10 (dipole) modes is optimized by adjusting the coupling between the loop and the dipole. By adjusting the FTBR, the proposed Huygens source antenna achieves a gain of 0.88 dB within a small size of ka=0.36.