Planar meander sleeve monopole antenna for DVB-H/GSM mobile handsets
can be easily manufactured with thin and inexpensive printed circuit board or copper strips.
B.H. Sun, J.F. Li, T. Zhou and Q.Z. Liu A novel planar meander sleeve monopole antenna for digital video broadcasting-hand held (DVB-H) and GSM mobile handsets is presented. By using the planar sleeve monopole type radiating element constructed with meander strips, the antenna provides a degree of miniaturisation while retaining a wide bandwidth covering the DVB-H and GSM-900 bands. A prototype is constructed and tested, which shows that an impedance bandwidth of 498 MHz (463– 961 MHz) within 2.5:1 VSWR is achieved.
Introduction: Recently, the rapid progress of integrated circuit technology has made it possible for a multimedia mobile handset to deal with both the global system for mobile communication (GSM) services and the digital video broadcasting-handheld (DVB-H) services. The DVBH standard uses the frequency range of 470 – 706 MHz in the UHF bands [1] and the GSM-900 standard uses the frequency range of 880 – 960 MHz. Owing to the wide operating bandwidth (470– 960 MHz) and the long wavelength at the lower end of the band (about 640 mm), it is a challenging task to design a practical antenna suitable for the application of the multimedia mobile handset capable of GSM and DVB-H functions. Several promising antenna designs for DVB-H applications have been studied and reported [2– 4], in which impedance matching circuits [2, 3] or frequency tuning circuits [4] have been utilised to realise the wide impedance bandwidths to cover the DVB-H band. In general, these circuits can also lead to a degree of insertion loss and system complexity. A modified monopole antenna, without additional matching circuits, has been proposed by Choi et al. [5]. The antenna has compact size and wide impedance bandwidth, but the VSWR of the antenna is relatively large (6:1 VSWR). A larger VSWR corresponds to a larger mismatch [6]. The sleeve monopole antenna is an attractive candidate for its wide impedance bandwidth, but the antenna height is roughly fixed at a quarter of a wavelength at the desired frequency [6, 7]. For the lower end of the DVB-H band, it can be assumed that the conventional sleeve monopole antenna is difficult to implement in a practical mobile handset directly. In this Letter, a novel planar meander sleeve monopole antenna for DVB-H and GSM mobile handsets is presented. By using a planar sleeve monopole type radiating element constructed with meander strips, the antenna provides a degree of miniaturisation while retaining a wide bandwidth covering the DVB-H and GSM-900 bands. A prototype is constructed and tested. The measured and simulated data, along with the antenna structure, are presented and discussed.
Antenna design: The geometry of the proposed planar sleeve monopole antenna along with its design parameters and co-ordinate system is shown in Fig. 1. The antenna is a planar structure of size 97 44 mm2 and is located above a metal box. The metal box is treated in this study as the body (i.e. the system circuit board and its shielding box) of a practical mobile handset, and is selected to have reasonable dimensions of 97 44 6 mm3. The antenna is connected to the metal box at the bottom corners using two metal hinges. By such a configuration, the antenna can also act as a flip cover of the mobile handset. A similar configuration has been used in [3]. By the way, one example of utilising the antenna is that: when the flip cover is open, the mobile handset is in operating condition for both the GSM and the DVB-H services. When the flip cover is closed, the DVB-H service is off and the GSM service is switched to another internal antenna built in the mobile handset. Notice that by this switching approach the effects of the DVB-H antenna (in operating condition) on the internal GSM antenna are avoided. As illustrated in Fig. 1b, the radiating element of the antenna is basically composed of three meander strips, i.e. that a monopole strip is located at the centre and two parasitic strips are displaced beside the monopole strip with close spaces. Both the monopole strip and parasitic strips are meander structures, which form a modified open sleeve monopole antenna. There is also a small parasitic strip located between the monopole strip and one of the parasitic strips, which can be used to improve the impedance performance slightly, especially at the higher end of the band. Because of its simple structure, the proposed antenna
Fig. 1 Geometry of proposed design a 3D view b Front view
It is worth noting that two significant techniques are used to improve the performances of the proposed antenna. First, by using meander structures, the antenna height is reduced effectively. A similar principle has been investigated and reported in [8, 9]. Secondly, by using sleeve type radiators, the antenna exhibits relatively wide impedance bandwidth. Consequently, by properly adjusting the geometrical parameters illustrated in Fig. 1, the proposed design can provide a degree of miniaturisation while retaining a wide bandwidth covering the DVB-H and GSM-900 bands, which will be demonstrated in the following Section. Results: An antenna prototype, with dimensions as shown in Fig. 1b, is fabricated and tested. The meander sleeve radiating element is printed on an FR4 substrate (thickness of 0.5 mm, relative permittivity of 4.4), and a copper box of size 97 44 6 mm3 is selected as the metal box of the mobile handset. The measurement of the VSWR for the prototype was performed using a HP8753D network analyser, and the simulation was implemented by the HFSS simulation software. The simulated and measured VSWR results are shown in Fig. 2. As can be seen, experimental data are in good agreement with simulated results. A wide impedance bandwidth, determined by 2.5:1 VSWR, reaches 498 MHz (463– 961 MHz), which covers both the DVB-H and the GSM bands.
Fig. 2 Simulated and measured VSWR against frequency
Fig. 3 gives the measured radiation patterns in the horizontal and vertical planes at 500, 700 and 900 MHz. Other frequencies in the DVB-H and GSM bands have also been investigated and show similar radiation performances. For the DVB-H band, omnidirectional radiations in the
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x-y plane are observed, which are almost as good as for a conventional dipole antenna. The measured peak gain of the prototype is 1.13, 1.58 and 2.07 dBi in the DVB-H and GSM bands, respectively.
omnidirectional radiation patterns across the two bands. It is reasonable to assume that the configuration discussed in this Letter can also be used to develop antennas for other potential applications. # The Institution of Engineering and Technology 2008 2 March 2008 Electronics Letters online no: 20080598 doi: 10.1049/el:20080598 B.H. Sun, J.F. Li, T. Zhou and Q.Z. Liu (National Laboratory of Antennas and Microwave Technology, Xidian University, No. 2 South TaiBai Road, Xi’an, Shaanxi 710071, People’s Republic of China) E-mail:
[email protected] References
Fig. 3 Measured radiation patterns for proposed antenna —*— 500 MHz —W— 700 MHz —— 900 MHz
Conclusion: By using a planar sleeve monopole type radiating element constructed with meander strips, a novel planar meander sleeve monopole antenna for multimedia mobile handsets capable of DVB-H and GSM services has been proposed and implemented. The antenna provides a degree of miniaturisation whilst retaining a wide bandwidth covering both the DVB-H and the GSM-900 bands, and exhibits nearly
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