11. Compact Wideband Balanced Antenna Structure for 3G Mobile Handsets

In most of the antenna designs for mobile handsets, unbalanced antennas like IFA (inverted F antenna) and PIFA (planar inverted F antenna) type designs have been widely used. Such types of designs usually offer wide impedance bandwidth and compact design; however, the characteristics of the antenna property vary a lot when the phone is held by the user in talk position, causing performance degradation. On the contrary, balanced type of antennas for the mobile handsets unlike unbalanced antennas can offer promising performance in both free space (FS) and in handheld scenarios. This is mainly because the balanced types of antenna radiate by the antenna element itself and less coupled the antenna ground plane associated to the antennas, such as printed circuit boards (PCB). Dipoles and loops are the most commonly encountered balanced antennas. In order to achieve a compact size, folded structures of balanced type of antenna radiators have been introduced. Comparing to the unbalanced antennas, their low levels of induced current on the ground plane, stable radiation performance, and relatively low specific absorption rate (SAR) beside to human head have been observed with balanced antenna design concept. However, a drawback of such antennas is a lack of impedance bandwidth to cover the frequency bands required for modern wireless mobile communications. This chapter demonstrates some novel techniques to enhance of impedance bandwidth for balanced antennas. Design examples are mainly focused on the frequency bands at 2G and 3G and 2.4 GHz bands.