Frequency-tunable Internal Antenna for Mobile Phones

New approaches are needed for improving the performance of small antennas to fulfill the multiband operation requirements of future wireless mobile communications terminals. In this paper, a novel low-loss frequencytuning circuit for mobile handset antennas is proposed. The presented design takes into account several factors that affect the practical mobile handset antenna design, such as the biasing limitations and distortion of the switching component as well as the effect of the mobile handset -sized ground plane. An antenna prototype that is capable of switching between the US cellular and GSM systems at 800-900 MHz frequency range was designed and measured. The antenna was positioned on a metallized printed circuit board (PCB) having size equal to that of a typical mobile phone. The tuning circuit, consisting of transmission line sections and an SPDT (single-pole, double-throw) FET switch, was fabricated directly on the substrate of the PCB. The designed antenna has high radiation efficiency and low distortion in both system bands.