Tuning techniques for the planar inverted-F antenna

The rapid growth of mobile communications since the introduction of GSM has challenged the industry for designing terminals of reduced size, cost and power consumption. The efficiency and size trade-offs of the antenna on such terminals become an important issue. On the other hand, multi-band operation covering the existing GSM900/DCS1800 and the future UMTS bands is another significant subject of investigation in the mobile phone industry. In this paper, different methods for tuning the planar inverted-F antenna (PIFA) are discussed, in particular with regard to the positioning of the short pins and the introduction of tuning capacitors. A reduced size dual band fine tuned PIFA for the GSM900/DCS1800 bands is introduced and its performance demonstrated. Finally, a technique employing reversed biased varactors for electronically tuning the PIFA is presented.