Differentially Fed, Self-Resonant, High-Efficiency, Superdirective Mixed-Multipole Antennas

This paper presents three compact differentially-fed, self-resonant, mixed-multipole antenna (MMA) designs that achieve superdirective performance while maintaining high overall efficiency (OE) values. Symmetric coupled resonators are utilized to facilitate configurations in which precise control of their current magnitude and phase distributions is obtained. A “structure-mode-impedance” co-design methodology is developed that bestows the elements in these MMAs with optimal reactive loading characteristics to realize their exceptional impedance match to a 50-Ω source. Three related single-feed topologies and their design evolution are reported: a two-element electrically small MMA with an OE = 91.8% and peak directivity <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> = 7.32 dB that exceeds the Harrington <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ka</i>-directivity bound, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Harrington</sub> = (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ka</i>)2 + 2 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ka</i>, by 2.81 dB; a compact three-element MMA with OE = 82.2% and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> = 10.09 dB that exceeds <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Harrington</sub> by 4.38 dB, and an electrically small three-element MMA with OE = 78.8% and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> = 8.59 dB that exceeds <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Harrington</sub> by 3.88 dB. The consequent peak realized gains of these MMAs are outstanding. Experimental prototypes of all three MMAs were fabricated; the measured results confirm their extraordinary radiation performance characteristics. They establish MMAs as excellent candidates for narrow-band Internet of Things (IoT), wireless sensors, and portable terminal applications.