IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 55, NO. 4, APRIL 2007 1155 Low SAR Ferrite Handset Antenna Design Maria I. Kitra, Member, IEEE, Chinthana J. Panagamuwa, Patrick McEvoy, Member, IEEE, J. (Yiannis) C. Vardaxoglou, Member, IEEE, and Jim R. James Abstract—The beneﬁts resulting from the inclusion of ferrite in material loaded antennas are investigated, initially through the use of a spherical analytic model and then through a transmission line matrix simulation tool applied to a rectangular slab geometry. It is observed that a material with equality of relative permittivity and permeability in combination with speciﬁc positioning of the antenna in relation to the head, can result in the deﬁnitive small- size, high efﬁciency and bandwidth, low speciﬁc absorption rate (SAR) antenna. The accuracy of the simulations is validated both through efﬁciency and SAR measurements of three material coated monopole samples. Further research into optimizing the above at- tributes and translating them into a handset antenna leads to a multiband antenna design covering the GSM 1800, 1900, UMTS and Bluetooth bands, with a SAR value reduced by 88% compared to conventional phones and an efﬁciency of 38% at 1.8 GHz. A tri-band antenna design is also presented, utilizing currently avail- able lossy ferrite material and it is considered as the ﬁrst step to- wards the feasibility of the ultimate low SAR multiband ferrite handset antenna, until further material development speciﬁcally for antenna applications takes place. Index Terms—Ferrite loaded antennas, multiband, speciﬁc ab- sorption rate (SAR), wireless handset. It is with sadness we report Prof. James (73) passed away on July 24, 2006, following an illness. He was a force to be reckoned with, he was world renowned for his academic work and had great respect for and from the scientiﬁc establishment. He will remain an important ﬁgure in his scientiﬁc ﬁeld of work for years to come, a ﬁne scientist of the old school who will be very sadly missed by colleagues and not least of all by his family. Devoted husband, family man, father, and grandfather, Prof. James was an immense contributor to the engineering community and a highly valued colleague at Loughborough University. He will be greatly missed. I. INTRODUCTION T HE use of material loading to reduce the electrical size of wire monopoles and other antennas is well known [1], [2] and was previously regarded as a technique reserved for a few specialized applications. The antenna size constraints imposed Manuscript received August 3, 2005; revised May 28, 2006. This work was supported by the U.K. EPSRC under Grant GR/R94596/01. M. I. Kitra, C. J. Panagamuwa, P. McEvoy, and J. C. Vardaxoglou are with Loughborough University, Loughborough, Leicestershire, LE11 3TU, U.K. (e-mail: m.kitra@lboro.ac.uk; j.c.vardaxoglou@lboro.ac.uk). J. R. James (deceased) was with Loughborough University, Loughborough, Leicestershire, LE11 3TU, U.K. on leave from Cranﬁeld University, RMCS, Shrivenham, Swindon, Wilts., SN6 8LA, U.K. Color versions of one or more of the ﬁgures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identiﬁer 10.1109/TAP.2007.893370 by mobile handset requirements and the availability of new di- electric materials has created much interest in dielectric loaded antennas [3], [4]. Tuning stability and good isolation from the handset and the human operator are cited as important features of dielectric loading which may enable a stand-alone ceramic chip antenna to be ﬁnally realized in practice over all the oper- ating bands. There is also some expectation that somewhat less power is dissipated in the operator’s head but the orientation of the dielectric antenna with respect to the head and the position of the antenna inside the handset in relation to the electronics is likely to remain the major inﬂuence on the speciﬁc absorption rate (SAR). The use of ferrite material loading has previously been inves- tigated [5], [6] but it is only recently that the merits of equalizing the material relative permittivity and permeability values have been reported [7]–[9]. The beneﬁts include increased bandwidth (BW) and radiation efﬁciency . The inﬂuence of magnetic material on dielectric resonator antennas has also been investi- gated [10]. A previous study [11] used a very lossy ferrite sheet attachment on the handset case to reduce SAR. Realizing fer- rite material as a metamaterial has been considered [12]. How- ever for handset compacted antenna applications the metama- terial heterogeneity and obtaining a small enough cell size are apparent difﬁculties with this concept. In this present research the above-established material loading techniques were brought together to create a multiband low SAR handset antenna. The continued reduction in the SAR is of interest to both manufacturers and users and is the central theme in this present research. The present paper commences with the analysis of generic spherical shaped loaded monopoles and their extension to more realistic shapes. Optimal bandwidth, radiation efﬁciency and SAR properties are demonstrated by simulation using Flomerics’ microstripes transmission line matrix (TLM) method and measurements. In particular, the inﬂuence of the choice of materials and the antenna excitation process on the near-ﬁelds and hence SAR, are considered. Retention of the antenna performance when embedded in a typical handset ground plane has received much attention in the present research and simulated results are included making available many design options to achieve the multiband low SAR operation. These are described in detail and ﬁnal design recommendations are presented. II. FUNDAMENTAL DESIGN ASPECTS A. Generic Spherical Model The antenna performance advantages of using a ferrite loading material are shown analytically by the following spherical model with inﬁnitesimally small Hertzian excitation 0018-926X/$25.00 © 2007 IEEE