Optimum dual‐resonant impedance matching of coupling element based mobile terminal antenna structures

This article presents a theoretical study on optimum dual‐resonant impedance matching of coupling element based mobile terminal antenna structures. First, optimum tuning of the system of two series‐resonant circuits connected to each other with an ideal impedance transformer and an impedance inverter is studied. Simple, explicit equations are derived for optimum circuit parameters of the resonator system. After this, design rules are presented for a practical discrete‐component realization of a matching circuitry specifically optimized for nonresonant antenna structures. Special emphasis has been put on minimizing the complexity of the matching network. Discussion is also given on equivalent circuit modeling of the combination of chassis and a coupling element. The presented matching network design methodology is shown to work well when applied with a realistic coupling element based mobile terminal antenna structure. The results of this article also indicate that the combination of the chassis of a mobile terminal and a simple coupling element can be with a good enough accuracy approximated as a series‐RLC equivalent circuit.