Determining Bandwidth Estimators and Matching Circuits for Evaluation of Chassis Antennas

This paper presents a procedure for determining the practically achievable bandwidth of a strongly frequency-dependent load impedance when using a simple matching circuit. The main target application is mobile handset antennas, which might be inherently nonresonant and thus the achievable bandwidth is not known from the input impedance. A straightforward and efficient algorithm for determining various bandwidth estimators is presented. A compact dual-band WLAN antenna is then designed, manufactured, and measured as an example application of utilizing the bandwidth estimators. Another example demonstrates how the bandwidth estimators can be used to determine a matching and decoupling circuit for a symmetrical dual-element antenna. The results show that the bandwidth estimators can be used as a supplementary tool in antenna design, transferring a part of the design challenge from electromagnetics to circuit design.