A Characteristic Mode View of Electrically Small Unidirectional Antenna Design

Maximum available directivity (D
_max
) for any arbitrary structure can be found using characteristic modes. It is theoretically achievable by placing multiple ports properly. This paper proposes the procedure of determining the voltage of each port by deriving the numerical expression of modal weighting coefficients. Numerical experiments for achieving D
_max
of electrically small structures could provide guidelines for practical unidirectional small antenna design.