An Impedance Matching Method for Superdirective Antenna by Characteristic Mode Manipulation

In this work, an impedance matching method is proposed for superdirective antenna through characteristic mode (CM) manipulation. Lumped loads are used to manipulate modal admittance (MA) of the target mode. At the assistance of the equivalent circuit models (ECM) of the CMs, values of the lumped loads can be effectively obtained. In this way, the input impedance of the superdirective antenna can be manipulated, and the reflection coefficient can be improved significantly. A V-shaped superdirective antenna is analyzed and measured as an example. By implementing the method, the reflection coefficient of the antenna at the operating frequency is improved from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{- 6. 5}$</tex> dB to -18.3 dB, and its front-to-back ratio at the resonant frequency achieves 7.1 dB.