Dissertation in the field of Circuit Theory, Anu Lehtovuori
The title of thesis is On wideband matching circuits in handset antenna design
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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.
Opponent: Professor Max Ammann, Dublin Institute of Technology
Supervisor: Professor Keijo Nikoskinen, Aalto University School of Electrical Engineering, Department of Radio Science and Engineering