Evaluation of Adaptive Impedance Tuning for Reducing the Form Factor of Handset Antennas

In this paper, we evaluate adaptive impedance tuning in combination with intrinsically unmatched antennas in order to reduce the form factor of handset antennas. Thereby, we are able to shrink the size of an antenna element by a factor of four compared to an intrinsically broadband matched antenna while maintaining a similar total efficiency in usage scenarios. The antenna concept is based on an unmatched coupling element in order to obtain a flat impedance behavior, which is relatively insensitive to the user interaction. It enables a broadband adaptive matching by a tunable Π-section network using varactors. The network takes into account the parasitic effects of the impedance detector and the ESD protection circuit.