Analysis of SAR Caused by PIFA Mounted on Folder type Mobile Phones

In recent years, planar inverted F antennas (PIFAs) are attractive candidates for using in mobile phones due to its ability to reduce SAR induced in the human head and its compact size. In this research, the PIFA is designed to apply for a folder type mobile phone with small size enough to be inserted in a folder case and SAR on human head is calculated. In the simulation, the case of the phone is composed of plastic materials (εr = 2.2). Apertures (LCD, microphones, key pad, etc.) of the phone are also considered. The operating frequency is about 1.8 GHz. The performances of the folder type mobile phones such as impedance bandwidth, gain and radiation patterns were simulated using CST based upon FIT method. 1g-averaged peak SAR was simulated using SEMCAD based upon FDTD method. From the results, SAR caused by PIFA mounted on the folder type handset is less than that caused by helix of same condition. Introduction (a) composition of PIFA (b) parameters Fig. 1 Simulation parameters of PIFA with Rectangular patch Analysis of SAR Caused by PIFA Mounted on Folder type Mobile Phones 899 PIFA with rectangular patch is shown in Figure 1. It is composed with shorting strip, rectangular patch, cutting plate, feeding wire and ground metal. The design details on the antenna in the figure1 is used as beginning deigns for engineers interested in the simple resonant structures. [1] To analyze the effect of design parameters of handset, various parameters are considered. [2] As variety of parameters, reflection loses (s11) are calculated by using FDTD method. The results are shown in Figure 2. Tuning of frequencies is done as varying the parameters, length of shorting strip(dl), position of feeding point(dx, dy), cutting dimension(a). Operating frequency is targeted in 1800 MHz, PCS band. (a) length of shorting strip (b) y-position of feeding (c) x-position of feeding (d) dimension of cutting plate Fig2. S11 parameter as variation of parameters J.D. Park, B.C.Kim, H.D. Choi 900 (a) PIFA mounted on the phone (b) Helix mounted on the phone Fig.3 composition of folder type handheld transceiver and head phantom The designed PIFA inserted in the case of the folder is shown in figure 3(a). Helix shown in figure 3(b) is also considered in this simulation. The simulation has done by CST program based upon FIT(Finite Integral Technology) method. Figure 4 shows the conditions of SAR calculation using SAMCAD based upon FDTD(Finite Difference .Time Domain)[3] method. In this simulation, the performances of the folder type mobile phones such as impedance bandwidths, gain and radiation patterns were calculated. Fig.4 head phantom for FDTD calculation Table 1 shows the part of results of the simulation briefly. It is shown that bandwidth of the PIFA is narrower than that of helix, SAR caused by PIFA is less than that caused by helix. Because radiation characteristic of the PIFA is directive, SAR caused by PIFA mounted on the folder type handset is less than that caused by helix. Table 1.results of simulation Antenna Gain Efficiency -10[dB] bandwidth 1g-avg. peak SAR Helix 2.3[dB] 0.87 11.8% (212 MHz) 1.23 [W/Kg] PIFA 2.7[dB] 0.92 9.2% (166MHz) 0.92 [W/Kg] Analysis of SAR Caused by PIFA Mounted on Folder type Mobile Phones 901 Summary The PIFA with rectangular patch is designed to apply for a folder type mobile phone and SAR on human head is calculated. In the simulation, various antenna parameters are considered The operating frequency is about 1.8 GHz. From the results of FDTD simulation, if bandwidth of the PIFA could be improved, the proposed structure of a PIFA gives the better choice of phone antenna by producing the lower SAR in human head as well as reasonable performance for wireless communication of phone antenna. References [1] Virga, K.L. ; Rahmat-Samii, Y. , “Low-profile enhanced-bandwidth PIFA antennas for wireless communications packaging”, Microwave Theory and Techniques, IEEE Transactions on , Vol.45, pp.1879 – 1888, Oct. 1997. [2] Rowell, C.R. ; Murch, R.D. , “A Capacitively loaded PIFA for compact mobile telephone handsets”, Antennas and Propagation, IEEE Trans. on , Vol.45, pp. 837-842, May 1997. [3] Amos, S.V. ; Smith, M.S., Kitchener, D. , “Modelling of handset antenna interactions with the user and SAR reduction techniques” Antennas and Propagation, 1999. IEE National Conference on. , pp. 12-15,1999.