0 dB -2 dB -4 dB -6 dB -8 dB -10 dB -12 dB -14 dB

-16 dB

-18 dB (a) Unbalanced-fed

-20 dB -22 dB -24 dB -26 dB -28 dB -30 dB -32 dB -34 dB -36 dB -38 dB -40 dB

(b) Balanced-fed

Figure 10.13 Current distribution of a folded loop antenna in the vicinity of a spherical head model (f0 = 1860 MHz): (a) unbalanced feed and (b) balanced feed.

and the boundary of the handset, because the antenna is assumed to be surrounded by a housing for avoiding direct contact between the user’s hand and the interior elements.

In the MoM simulator, the number of cells per wavelength is 10 and the numbers of total cells of unbalanced-fed and balanced-fed models are 2864 and 2918, respectively. In the FDTD simulator, models are divided into non-uniform meshing of 0.5 to 4 mm and the numbers of total cells of unbalanced-fed and balanced-fed models are 367 275 and 313 880, respectively. In the FEM simulator, the numbers of total cells of unbalanced-fed and balanced-fed models are 18 345 and 12 253, respectively. In the FIM simulator, the total number of cells of unbalanced-fed and balanced-fed models are 9 660 189.

Figure 10.13 shows the simulated current distribution on the GP in the vicinity of the head model by using the MoM simulator, where (a) and (b) are the currents of unbalanced and balanced-fed models. As in the case of free space, the current on the GP is reduced even in the vicinity of the head model. Moreover, the result of an unbalanced-fed model agrees very well with that of a balanced-fed model. This shows that the self-balance effect is still maintained even though a folded loop is located in the vicinity of the human head.

10.3.4.2Analytical results

Figure 10.14 shows the radiation patterns in the vicinity of the head model, where (a) and (b) are the radiation patterns of unbalanced and balanced-fed models. In the figure, the difference of about 4 dB between the simulated and measured results is seen in the vicinity of a head model, while they are almost the same in the free space. It is considered that the calculated gains by each simulator include the different loss of the impedance mismatch and are different from each other, because the radiation patterns by each simulator are calculated at the center frequency of 1860 MHz. Furthermore, users need

References 407

Figure 10.15 Radiation pattern of an unbalanced-fed model in the vicinity of head and hand models (f0 = 1860 MHz).

in the vicinity of a head model. There is almost no difference between the results of unbalanced and balanced-fed models.

Figure 10.15 shows the radiation pattern of a folded loop antenna in the vicinity of head and hand models at 1860 MHz. By the presence of a hand model, the maximum gain was reduced in the y–z plane.

References

[1]A. Vasylchenko, Y. Schols, W. De Raedt, and G. A. E. Vandenbosch, Quality Assessment of Computational Techniques and Software Tools for Planar-Antenna Analysis, IEEE Antennas and Propagation Magazine, vol. 51, February 2009, no. 1, pp. 23–38.

[2]M. Taguchi, On Electromagnetic Simulators for Antenna Analysis, Proceedings IEICE General Conference, 1998, C1 TB-1–1, p. 736.

[3]K. Sato, K. Nishikawa, N. Suzuki, and A. Ogawa, Analysis of Antennas Mounted on Portable Equipment Near Human Body, IEICE Transactions (Japan), vol. J79-B-II, November 1996, no. 11, pp. 892–900.

408Electromagnetic simulation

[4]K. Hirasawa and K. Fujimoto, Characteristics of Wire antenna on a Rectangular Conducting Body, IECE Transactions (Japan), vol. J65-B, April 1982, pp. 382–389.

[5]K. Sato, K. Matsumoto, K. Fujimoto, and K. Hirasawa, Characteristics of a Planar Inverted- F Antenna on a Rectangular Conducting Body, IECE Transactions (Japan), vol. J71-B, November 1988, pp. 1237–1243.

[6]K. D. Katsibas, C. A. Balanis, P. A. Tirkas, and C. R. Birtcher, Folded Loop Antenna for Mobile Hand-held Units, IEEE Transactions on Antennas and Propagation, vol. 46, 1998, no. 2, pp. 260–266.

[7]Y. Kim, H. Morishita, Y. Koyanagi, and K. Fujimoto, A Folded Loop Antenna System for Handset Development and Based on the Advanced Design Concept, IEICE Transactions on Communications, vol. E84-B, September 2001, no. 9, pp. 2468–2475.

[8]Zeland Software, Inc., IE3D User’s Manual, Release 8.0, Fremont, 2001.

[9]T. Uno, FDTD for Electromagnetic Field and Antenna Analyses, Corona Publishing Co., Ltd., 1998, p. 2.

[10]Zeland Software, Inc., FIDELITY User’s Manual, release 1.5.

[11]K. Fujimoto and J. R. James, Mobile Antenna Systems Handbook, Artech House, 1994.

[12]J. D. Kraus, Antennas, 2nd edn., McGraw-Hill, 1988.

[13]H. Morishita, Y. Kim, and K. Fujimoto, Design Concept of Antennas for Small Mobile Terminals and the Future Perspective, IEEE Antennas and Propagation Magazine, vol. 44, October 2002, no. 5, pp. 30–43.

[14]H. Morishita, H. Furuuchi, and K. Fujimoto, Performance of Balance-fed Antenna System for Handsets in the Vicinity of a Human Head or Hand, IEE Proceedings: Microwaves, Antennas and Propagation, vol. 149, April 2002, no. 2, pp. 85–91.

[15]Y. Kim, H. Furuuchi, H. Morishita, and K. Fujimoto, Characteristics of Balance-fed L- type Loop Antenna System for Handsets in Vicinity of Human Head, Proceedings 2000 International Symposium on Antennas and Propagation, vol. 3, August 2000, pp. 1203– 1206.

[16]H. Morishita, Y. Kim, and K. Fujimoto, Analysis of Handset Antennas in the Vicinity of the Human body by the Electromagnetic Simulator, IEICE Transactions on Electronics, vol. E84-C, July 2001, no. 7, pp. 937–947.

[17]T. Taga and K. Tsunekawa, Performance Analysis of a Built-in Planar Inverted F Antenna for 800 MHz Band Portable Radio Units, IEEE Journal on Selected Areas in Communications, vol. SAC-5, June 1987, no. 5, pp. 921–929.

[18]K. Hirasawa and K. Fujimoto, Characteristics of Wire Antenna on a Rectangular Conducting Body, IEICE Transactions on Communications (Japanese), vol. J65-B, April 1982, pp. 382–389.

[19]K. Fujimoto, A. Henderson, K. Hirasawa, and J. R. James, Small Antennas, Research Studies Press, UK, 1987.

[20]C. A. Balanis, Antenna Theory: Analysis and Design, 2nd edn., John Wiley and Sons, 1997.

[21]H. Uchida and Y. Mushiake, VHF-Antenna, Corona Publishing (in Japanese), 1961.

[22]R. C. Johnson, Antenna Engineering Handbook, 3rd edn., McGraw-Hill. Inc., 1961, Chapter 4.

[23]Zeland Software, Inc., IE3D ver. 7.0: www.zeland.com/IE3D.htm

[24]Zeland Software, Inc., Fidelity ver. 3.0: www.zeland.com/Fidelity.htm

[25]Ansoft, HFSS 8.0, The Maxwell Online Help System, 2001.

[26]Computer Simulation Technology AG, CST Microwave Studio ver. 2006: www.cst.com

[27]Schmid & Partner Engineering AG, www.speag.com/