A tunable planar inverted-F antenna with an RF MEMS switch for the correction of impedance mismatch due to human hand effects

Abstract

In this work we demonstrated a tunable planar inverted-F antenna (PIFA) for the correction of impedance mismatch resulting from the resonant frequency shift in the usage of mobile phones due to human hand effects. The tunable PIFA has a tuning line with electrical path to the ground plate through an RF MEMS switch and loading capacitor. By changing the switch status, the resonant frequency of the PIFA can be tuned with the loading capacitance value. The characteristics of the tunable PIFA with different positions of tuning line and value of loading capacitance have been evaluated. A metal-to-metal direct-contact-type RF MEMS switch has been used for tuning the resonant frequency of the capacitor-loaded PIFA, which is piezoelectrically actuated with low actuation voltage. The insertion loss of the RF MEMS switch was measured to be -0.23 dB at 2 GHz with an applied DC bias of 2.5 V. The isolation of the switch was -42.5 dB at 2 GHz. The resonant frequency of the PIFA shifted from 842 to 762 MHz by turning the switch on. The characteristics of the tunable PIFA were measured in the presence of a phantom hand, to show the feasibility of correcting the resonant frequency shift by human hand effects. When the switch was on, the resonant frequency of the PIFA shifted from 762 to 690 MHz, and this was attributed to the phantom hand effect. Turning the switch off caused the PIFA to recover its original resonant frequency with the phantom hand. The measured resonant frequency of the PIFA with the switch off was 760 MHz with the phantom hand and the return loss at the resonant frequency was -22 dB. © 2009 IOP Publishing Ltd.