Study of the total Q of antennas in terms of modal Qn provided by Characteristic Modes Theory

An expression of the total radiation Q in terms of the Q_n of characteristic modes for an arbitrary antenna is presented. The theory of Characteristic Modes (CM) was used to expand the total Q in terms of Q_n (quality factor of each mode) including the effect of each mode and the interaction between them. This expression is very useful because it provides physical insight; therefore, it is very helpful in antenna design and analysis. The expression was obtained using the expansion of the total input admittance of the antenna in terms of the individual admittances of the CM in conjunction with the well-known expression for Q by Yaghjian and Best [1]. Numerical examples will be provided to illustrate the expression and compare it with the original expression by Yajian and Best.