A study of the effects of human proximity on the polarization purity of two types of circularly-polarized handset antennas for personal satellite communications was investigated using the hybrid method of moments (MoM)/finite-difference time-domain technique. Associated with this, assessments of specific absorption rate in the head were made. The method gave stable results, in accordance with physical expectations; good agreement with the pureMethod of Moments was shown in simplified cases omitting the head. The quadrifilar spiral antenna (QSA) was shown to be a propitious design for personal satellite communications

Abd-Alhameed, R A

Excell, Peter S

Khalil, K

Mangoud, M A

English

Glyndŵr University Research Online

Glyndŵr UniversityGlyndŵr University Research OnlineComputing Computer Science1-1-2005Investigations of polarization purity and specificabsorption rate for two dual-band antennas forsatellite-mobile handsetsR A. Abd-AlhameedM A. MangoudPeter S. ExcellGlyndwr University, p.excell@glyndwr.ac.ukK KhalilFollow this and additional works at: http://epubs.glyndwr.ac.uk/cairPart of the Computer Engineering Commons, and the Computer Sciences CommonsThis Article is brought to you for free and open access by the Computer Science at Glyndŵr University Research Online. It has been accepted forinclusion in Computing by an authorized administrator of Glyndŵr University Research Online. For more information, please contactd.jepson@glyndwr.ac.uk.Recommended CitationAbd-Alhameed, R. A., Mangoud, M. A., Excell, P. S., & Khalil, K. (2005) 'Investigations of polarization purity and specific absorptionrate for two dual-band antennas for satellite-mobile handsets'. IEEE Transactions on Antennas and Propagation, 53(6), 2108-2110.Investigations of polarization purity and specific absorption rate for twodual-band antennas for satellite-mobile handsetsAbstractA study of the effects of human proximity on the polarization purity of two types of circularly-polarizedhandset antennas for personal satellite communications was investigated using the hybrid method ofmoments (MoM)/finite-difference time-domain technique. Associated with this, assessments of specificabsorption rate in the head were made. The method gave stable results, in accordance with physicalexpectations; good agreement with the pureMethod of Moments was shown in simplified cases omitting thehead. The quadrifilar spiral antenna (QSA) was shown to be a propitious design for personal satellitecommunications.KeywordsCircular polarization, finite-difference time-domain (FDTD), hybrid method, method of moments (MoM),satellite mobileDisciplinesComputer Engineering | Computer SciencesComments©2005 IEEE. Personal use of this material is permitted. However, permission to reprint/republish thismaterial for advertising or promotional purposes or for creating new collective works for resale orredistribution to servers or lists, or to reuse any copyrighted component of this work in other works must beobtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technicalwork. Copyright and all rights therein are retained by authors or by other copyright holders. All personscopying this information are expected to adhere to the terms and constraints invoked by each author'scopyright. In most cases, these works may not be reposted without the explicit permission of the copyrightholder. This paper was published in IEEE Transactions on Antennas and Propagation in June 2005 sponsoredby IEEE Antennas and Propagation Society. The definitive version is available at http://ieeexplore.ieee.orgThis article is available at Glyndŵr University Research Online: http://epubs.glyndwr.ac.uk/cair/182108 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 53, NO. 6, JUNE 2005Communications______________________________________________________________________Investigations of Polarization Purity and SpeciﬁcAbsorption Rate for Two Dual-Band Antennas forSatellite-Mobile HandsetsRead A. Abd-Alhameed, M. Mangoud, P. S. Excell, and K. KhalilAbstract—A study of the effects of human proximity on the polariza-tion purity of two types of circularly-polarized handset antennas for per-sonal satellite communications was investigated using the hybrid method ofmoments (MoM)/ﬁnite-difference time-domain technique. Associated withthis, assessments of speciﬁc absorption rate in the head were made. Themethod gave stable results, in accordance with physical expectations; goodagreement with the pureMethod ofMoments was shown in simpliﬁed casesomitting the head. The quadriﬁlar spiral antenna (QSA) was shown to bea propitious design for personal satellite communications.Index Terms—Circular polarization, ﬁnite-difference time-domain(FDTD), hybrid method, method of moments (MoM), satellite mobilecommunications, speciﬁc absorption rate (SAR).I. INTRODUCTIONDegradation of circular polarization purity (equivalent to degradationof axial ratio performance) of radiatedﬁelds from satellite-mobile hand-sets in the proximity of the human head has been addressed in the past[1]. Further, speciﬁc absorption rate (SAR) assessments in comparisonwith terrestrial mobile handset antennas have been presented in [2] and[3]. In [1] it was found that the presence of the head degraded the av-erage axial ratio within a 50 cone by between 2.9 and 9.1 dB, whichcan have a signiﬁcant effect on system performance. The antenna wasrather larger thanwould be realistic, but the intentionwas to characterizethe polarization issue only. Concerning the SAR in the user’s head, in [2]and [3] the authors compared a quadriﬁlar helix antenna (QHA) with amonopole antenna. It was shown that, when operating in satellite mode,the QHA allowed input power to be increased by 27% for the same peakSAR level. Recently, novel satellite antennadesigns have beenproposedthat use complex curved geometries to improve on the QHA [4]–[6].It is concluded in [7] that the hybrid MoM/FDTD technique suitsinvestigations of all of these types very well. In this paper, the polar-ization purity and SAR of two dual-band antennas for satellite-mobilehandsets adjacent to the human head are investigated (see Fig. 1), usingthe hybrid computational method. These antennas are the quadriﬁlarspiral antenna (QSA) [8] and quadriﬁlar helical antenna (QHA) [6]. Asmall distance between the head and the handset was chosen to high-light the effects of the relatively high radiated power needed for satellitesystems. The results for two operating frequency bands were studied:1.61–1.6214 GHz (L-band) and 2.4835–2.5 GHz (S-band).II. SATELLITE ANTENNAS ON HANDSET ADJACENT TOREALISTIC HEAD MODELThe QSA and QHA are very attractive candidate antennas for satel-lite mobile handsets due to the symmetry of their geometry, propertiesof balanced feeding and their ability to provide circular polarizationManuscript received December 13, 2002; revised October 10, 2004.The authors are with the Mobile and Satellite Communication ResearchCentre, Bradford University, Bradford BD7 1DP, U.K. (e-mail: r.a.a.abd@bradford.ac.uk).Digital Object Identiﬁer 10.1109/TAP.2005.848516Fig. 1. Geometry for the dual band QHA (left) and QSA (right).Fig. 2. E and E with and without the human head versus  at  = 0 forQSA (L-band).over a broad angular region. As seen in Fig. 1, the maximum dimen-sion of the QSA is signiﬁcantly smaller than that of the QHA, thus it isworthwhile to investigate both antenna performances in the vicinity ofthe human head, since the QHA is a well-established benchmark designagainst which the QSA can be compared, although the concentration ofthe near ﬁeld distribution in their vicinities will be very different. TheQSA consists of four spirals equally spaced circumferentially (placedat 90 to each other) whereas the QHA has four helices placed at 90to each other. Both antennas are fed with equal amplitude signals with90 phase difference between feeding sources (i.e., 0, 90, 180, and270). The handset dimensions were selected to be 56 56 140 mm:this is rather larger than modern handsets, but was a convenient choicefor prototype studies, including future experimental tests. It should benoted that the QSA here is fed from its inner perimeter rather than theouter ends of the arms since this is more convenient. Problems can arise0018-926X/$20.00 © 2005 IEEEIEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 53, NO. 6, JUNE 2005 2109Fig. 3. Axial ratio in dB versus  for two different  angles; (a) QSA at L-band; (b) QSA at S-band; (c) QHA at L-band; (d) QHA at S-band.with inner feeding when the distance between the feed lines is small,causing signiﬁcant mutual coupling effects.The size of the equivalent Huygens surface that surrounds theantenna and handset (the MoM region) inside the FDTD grid wasselected to be 36 36 72 FDTD cells for the QSA antenna and36 36 117 cells for the QHA antenna. This closed surface wasplaced adjacent to a realistic 3D head image. The FDTD details forboth frequency bands were as follows: the FDTD cell size was 2.5mm; the sizes of the problem spaces were 127 96 127 cells (QSA)and 127 91 137 cells (QHA). The time steps at L-band and S-bandwere 3.375 ps and 2.75 ps respectively. The total number of cyclessimulated for both operating frequencies was 25. The tissue-classiﬁedhead used in this work is given in [10]: it uses 16 different tissuedielectric properties. The handset body was placed 7.5 mm from thenearest point of the head tissue. These parameters are signiﬁcantlymore realistic than those used in the earlier pilot study [9], whichused 5 mm cell size, handset dimensions 80 80 133.3 mm and aminimum separation distance from the head of 2 cm, with a QHA only.III. NUMERICAL RESULTS WITH AND WITHOUT THE HEADThe relative bandwidth (for VSWR 3) at the input ports of the an-tennas shown in Fig. 1, without the head present, are 5% at L-bandand 8.2% at S-band (for the QSA), and 3% at L-band and 6.5% atS-band (for the QHA). Good axial ratios for both antennas in the twobands were observed with the following power gains: 5 dB (L-band)and 6.5 dB (S-band) for the QSA; 6 dB (L-band) and 8 dB (S-band) forthe QHA. Reasonable circular polarization elevation angle coveragesof approximately50 (QSA) and45 (QHA) were obtained, theseangles being similar for both the L- and S-bands. The ﬁeld patterns(for 1 W input power to lossless antennas) with and without the headfor the QSA antenna at 1.6 GHz are shown in Fig. 2. As shown, theﬁeld patterns, without the head, obtained using the hybrid method [7]and the pure Method of Moments (MoM) were in good agreement: theworst-case disagreement is about 0.5 dB (relative to 8 dB, at 120 in theE curves), corresponding to 5.6% variation in the ﬁeld strength. Thisonly occurs in a relatively weak-ﬁeld zone which is more susceptibleto numerical noise: the majority of the curves are in much better agree-ment. It is considered that this adequately veriﬁes the validity of thehybrid method. When the head is added to the model, the ﬁeld patternsobtained show that, over the useful range of elevation angles, the ﬁeldsare not greatly changed, but the E component in directions close tothe head is attenuated by around 5 dB, which will cause some deterio-ration of the axial ratio.The axial ratio results were computed for the x-z plane ( = 0)and y-z plane ( = 90) in the presence of the head. Fig. 3(a) and (b)2110 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 53, NO. 6, JUNE 2005TABLE ICOMPUTED SAR AND POWER ABSORBED FOR BOTH QSA AND QHA ANTENNASpresent these ratios for the QSA at L-band and S-band respectively, andFig. 3(c) and (d) show it for theQHAat L-band and S-band respectively.The distance between the handset and the head was kept at 7.5 mm forall cases. Reasonably good circular polarization coverage is observedover the elevation angle range of 40 for both bands of interest. Thecircular polarization purity for both bands decreases in the presence ofthe head by 2 to 5 dB, which is much better than for the single axialmode helix [1].The calculated peak SAR in the head, the maximum averaged SARovermassesof10gand1gand thepowerabsorbedfordifferentdistancesbetween the head and the handset for both antennas shown in Fig. 1 aresummarized in Table I for an input power of 1 W. The computationsindicate that approximately 24% (L-band) and 14% (S-band) of the totaldelivered power was absorbed by the head when using the QSA, while13%(L-band)and8%(S-band)of the totaldeliveredpowerwasabsorbedbytheheadwhenusingtheQHA.Theseresultsaremuchlower thanthosereported in [7] foraGSM1800 terrestrialhandset, forwhichpeakSARinthe head was between 10 and 21W/kg/W for a head-handset separationof 7.5 mm. Additionally, the head absorbed between 48 and 68% of thepower delivered to the antenna. The decrease in the absorption levels forsatellite terminals ispartlyduetothedirectionofradiationbeingdifferentfor the two cases and partly to the inherently somewhat greater distancebetween the head and the antenna.IV. CONCLUSIONThe effect of the presence of a head model on the axial ratio and thecircular polarization radiation purity for two dual-band satellite-mobilehandset antennas was investigated in detail using a hybridMoM/FDTDtechnique. The computations indicated that approximately 14% to 24%of the total delivered power was absorbed by the head for the QSAantenna and 8% to 17% for the QHA antenna, compared with 48 to68% for a canonical GSM terrestrial handset. The results also show theimpact of the presence of the head on the circular polarization purityof the satellite antennas, indicated by the axial ratio: for both bands,this varied between 2 and 5 dB over the required elevation angle range,which is acceptable, given the presence of the head. Because of its smallsize and acceptable performance, the QSA has been shown to be a pro-pitious design for personal satellite communications.The nature of satellite-mobile services demands somewhat higherradiated powers and power gains than with terrestrial systems, leadingto public concerns about the levels of SAR in the head. These resultsshow that such concerns are groundless, at least in comparison withterrestrial systems: they also demonstrate the power and utility of thehybrid ﬁeld computation method for such complex geometries in thepresence of human tissue or other lossy dielectrics.REFERENCES[1] J. S. Colburn and Y. Rahmat-Samii, “Human proximity effects on cir-cular polarized handset antennas in personal satellite communications,”IEEE Trans. Antennas Propag., vol. 46, no. 6, pp. 813–820, Jun. 1998.[2] P. Suvannapattana and S. R. Saunders, “Satellite and terrestrial mobilehandheld antenna interactions with the human head,” Proc. Inst. Elect.Eng. Microwaves Antennas and Propagation, vol. 146, no. 5, pp.305–310, 1999.[3] A. A. Agius, S. M. Leach, P. Suvannapattana, and A. R. Saunders, “Ef-fects of the human head on the radiation pattern performance of thequadriﬁlar helix antenna,” in Proc. IEEE Int. Symp. Antennas Propa-gation, vol. 2, 1999, pp. 1114–1117.[4] J. S. Colburn and Y. Rahmat Samii, “Quadriﬁlar-curl antenna for the“Big-LEO” mobile satellite service system,” in IEEE Int. Symp. An-tennas Propag., vol. 2, 1996, pp. 1088–1091.[5] M. E. Ermutlu, “Modiﬁed quadriﬁlar helix antennas for mobile satellitecommunication,” in Proc. IEEE Conf. Antennas and Propagation forWireless Communications, 1998, pp. 141–144.[6] S. M. Daddish, R. A. Abd-Alhameed, and P. S. Excell, “New designsfor dual band antennas for satellite-mobile communications handsets,”Appl. Comput. Electromagn. Soc. J., vol. 15, no. 3, pp. 248–258, 2000.[7] M. A. Mangoud, R. A. Abd-Alhameed, and P. S. Excell, “Simulation ofhuman interaction with mobile telephones using hybrid techniques overcoupled domains,” IEEE Trans. Microw. Theory Tech., vol. 48, no. 11,pp. 2014–2021, 2000.[8] K. Alazhari, R. A. Abd-Alhameed, P. S. Excell, and K. Khalil, “Newdesign for single and dual band quadriﬁlar spiral antennas (QSA) forsatellite-mobile handsets,” in Proc. Inst. Elect. Eng. Int. Conf. Antennasand Propagation, vol. 2, Apr. 2001, pp. 750–753.[9] M. A. Mangoud, R. A. Abd-Alhameed, and P. S. Excell, “Investigationof polarization purity and SAR for personal satellite communicationsantennas using a hybrid computational method,” Electron. Lett., vol. 37,no. 21, pp. 1272–1274, Oct. 2001.[10] P. S. Excell, “Computer modeling of high frequency electromagneticﬁeld penetration into the human head,” Meas. Contr., vol. 31, no. 6, pp.170–175, 1998.

Investigations of polarization purity and specific absorption rate for two dual-band antennas for satellite-mobile handsets

https://glyndwr.repository.guildhe.ac.uk/193/1/fulltext.pdf

Investigations of polarization purity and specific absorption rate for two dual-band antennas for satellite-mobile handsets

Abstract

Similar works

Full text

Available Versions

Glyndŵr University Research Online