Characterization of indirectly measurable antenna balun/impedance-matching device

This paper presents a novel approach for the S-parameter characterization of an indirectly measurable antenna balun/impedance-matching device. A back-to-back measurement set-up is proposed and a system of complex variable nonlinear equations is derived to relate the measurable undesired parameters and the unmeasurable desired parameters. Then the genetic algorithm (GA) is proposed to solve the system of complex variable nonlinear equations to obtain the desired S-parameters. Unlike conventional GA, the chromosomes in our approach are represented directly by complex numbers instead of normal binary coding. The representation of chromosome in complex number increases the efficiency and flexibility of GA in engineering applications. With the GA-solved S-parameters, we are able to characterize the antenna input impedances. The simulated and measured results of the antenna system show that the proposed GA approach is valid and this approach can also be extended to some other indirect measurement.