On wideband matching circuits in handset antenna design

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Anu Lehtovuori Name of the doctoral dissertation On wideband matching circuits in handset antenna design Publisher School of Electrical Engineering Unit Department of Radio Science and Engineering Series Aalto University publication series DOCTORAL DISSERTATIONS 123/2015 Field of research Circuit Theory Manuscript submitted 21 May 2015 Date of the defence 2 October 2015 Permission to publish granted (date) 22 July 2015 Language English Monograph Article dissertation (summary + original articles) Abstract Transferring the growing amount of data calls for wider bandwidths in new wireless standards. For the mobile antennas, which have to be squeezed to a very limited space, this poses quite a challenge for impedance matching, if efficiency is not to be sacrificed. Earlier, wideband matching was studied as a rather theoretical problem, but this work takes a practical viewpoint to produce readily applicable results. The goal is to utilize circuit elements to improve the performance of handset antennas. Because the number of matching elements is to minimized in practical designs, this work focuses particularly on three-element matching circuits. The presented efficient procedure for determining the available bandwidth with a certain matching topology, i.e., the bandwidth estimator, enable accounting for the matching circuit from the beginning of the antenna design process. Furthermore, evaluating the potential of different radiating structures becomes feasible. In mobile systems, the desired frequency band consists of two passbands, and therefore finding methods for dual-band matching is reasonable. This work presents how any two matching circuits designed separately for frequencies f1 and f2 can be converted into a dualband matching circuit operating both at f1 and f2. In addition, simple design equations for dualband matching are given. A dual-band matching can be realized also with two radiating elements. This widens the study to illustrate how bandwidth estimators can be used to design matching circuits for multiple ports. Moreover, it is shown that bandwidth estimator analysis offers a suitable starting point for practical design — the simulations and measurements are in good agreement. Finally, the work introduces other ways to improve antenna performance with aid of circuit elements and bandwidth estimators.Transferring the growing amount of data calls for wider bandwidths in new wireless standards. For the mobile antennas, which have to be squeezed to a very limited space, this poses quite a challenge for impedance matching, if efficiency is not to be sacrificed. Earlier, wideband matching was studied as a rather theoretical problem, but this work takes a practical viewpoint to produce readily applicable results. The goal is to utilize circuit elements to improve the performance of handset antennas. Because the number of matching elements is to minimized in practical designs, this work focuses particularly on three-element matching circuits. The presented efficient procedure for determining the available bandwidth with a certain matching topology, i.e., the bandwidth estimator, enable accounting for the matching circuit from the beginning of the antenna design process. Furthermore, evaluating the potential of different radiating structures becomes feasible. In mobile systems, the desired frequency band consists of two passbands, and therefore finding methods for dual-band matching is reasonable. This work presents how any two matching circuits designed separately for frequencies f1 and f2 can be converted into a dualband matching circuit operating both at f1 and f2. In addition, simple design equations for dualband matching are given. A dual-band matching can be realized also with two radiating elements. This widens the study to illustrate how bandwidth estimators can be used to design matching circuits for multiple ports. Moreover, it is shown that bandwidth estimator analysis offers a suitable starting point for practical design — the simulations and measurements are in good agreement. Finally, the work introduces other ways to improve antenna performance with aid of circuit elements and bandwidth estimators.