IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 55, NO. 5, MAY 2007 1457 Internal Compact Dual-Band Printed Loop Antenna for Mobile Phone Application Yun-Wen Chi and Kin-Lu Wong Abstract—A novel dual-band printed loop antenna very promising for application in mobile phones as an internal antenna is presented. The an- tenna comprises an outer loop strip and an inner inverted-L strip connected to and enclosed by the outer loop strip. The antenna occupies a compact area of 15 × 50 mm² only, yet generating three resonant modes to form two wide bands at about 900 and 1800 MHz for the Global System for Mobile Communication/Digital Communication System operation. Detailed design considerations of the three excited modes are described in the paper. When a shielding metal case is placed close to the antenna, small effects on the an- tenna’s impedance matching are seen, allowing compact integration of the antenna with nearby conducting elements or electronic components. The antenna is also found to result in small excited surface current distributions on the system ground plane of the mobile phone. This behavior is expected to lead to reduced user’s hand effects on the radiation efficiency of the an- tenna. Index Terms—Dual-band antennas, mobile phone antennas, printed an- tennas, printed loop antennas. I. INTRODUCTION Conventional internal antennas for mobile phone applications are generally in the forms of the planar inverted-F patch antenna, very- low-profile printed or metal-plate monopole antenna, and so on [1]. Such internal mobile phone antennas usually excite large surface cur- rents on the system ground plane of the mobile phone, which functions as an effective radiation portion, especially for the lower frequency operation in the Global System for Mobile Communication (GSM, ) band. Owing to the large excited surface currents on the system ground plane, especially in the region near the internal antenna, an isolation distance of about 7 mm or larger between the an- tenna and the nearby conducting elements or electronic components in the mobile phone is usually required to avoid large degradation effects on the performances of the internal antenna [2], [3]. To decrease or eliminate the system ground plane effects on the an- tenna performances, the modified one-wavelength loop antenna has been proposed [4]. This kind of modified loop antenna is expected to operate as a self-balanced structure, thus resulting in small excited surface currents on the system ground plane. However, owing to its one-wavelength resonant structure, such a modified loop antenna is usually bulky in volume, causing a limitation in its practical appli- cation for mobile phones. In this paper, we present a novel printed loop antenna for mobile phone applications. The antenna has a planar configuration and is easy to implement with a low cost by printing on the system circuit board of the mobile phone. In addition, the an- tenna occupies a compact area of 15 50 only, yet providing two wide bands for GSM and Digital Communication System (DCS, ) operation. The antenna comprises an outer loop strip and an inner inverted-L strip, and provides two resonant loop paths. The first loop path is con- trolled by the outer loop strip, while the second loop path is formed by the inner inverted-L strip and part of the outer loop strip. The two loop paths support three resonant modes for the antenna. The first and second modes are formed into a wide band at about 1 GHz to easily Manuscript received August 6, 2006; revised November 14, 2006. The authors are with the Department of Electrical Engineering, National Sun Yat-Sen University, Kaohsiung 804, Taiwan, R.O.C. Digital Object Identifier 10.1109/TAP.2007.895641 Fig. 1. (a) Geometry of the printed loop antenna enclosed by the housing of the mobile phone. (b) Side view of (a). (c) Detailed dimensions of the antenna. cover the GSM operation, and the third mode provides a wide band at about 1800 MHz to cover the DCS operation. The antenna can lead to small excited surface current distributions on the system ground plane. This behavior is expected to result in a small isolation distance required between the antenna and the nearby conducting elements or electronic components in the mobile phone. For this verification, effects of a shielding metal case placed close to the antenna are studied. In addition, it may also be expected that the user’s hand effects will become small, when the excited surface current distributions on the system ground plane are small. For this analysis, the study of the antenna with the user’s hand is conducted. II. DESIGN CONSIDERATIONS OF PROPOSED ANTENNA Fig. 1(a) shows the geometry of the antenna enclosed by the housing of the mobile phone, and the side view of the geometry is shown in Fig. 1(b). The mobile phone housing is fabricated using a 1-mm thick acrylonitrile butadiene styrene (ABS) plate with relative permittivity 0018-926X/$25.00 © 2007 IEEE