Experimental Characterization of UWB Antennas for On-Body Communications

866 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 57, NO. 4, APRIL 2009

Experimental Characterization of UWBAntennas for On-Body Communications

Terence S. P. See and Zhi Ning Chen, Fellow, IEEE

Abstract—In this paper, the radiation of three types of ultra-wideband (UWB) antennas is experimentally characterized fornear/on human body scenarios. The transmission performancefor vertical and horizontal polarizations is measured at differentbody orientations. The received pulses are analyzed in the timedomain by selecting Dirac impulse and sine-modulated Gaussianmonocycle as source pulses. The peak-to-peak amplitudes, fidelity,and stretch ratio of the waveforms of the received pulses arecomputed based on the measured results. In measurements, threetypes of UWB antennas are studied, namely an omnidirectionalmonopole antenna, directional suspended plate antenna, andprinted diversity antenna. From the study, it is found that the om-nidirectional antenna experiences an increase in the transmissiondue to the reflections from the body but suffers from narrowerhorizontal coverage due to a higher attenuation as the body turnsaway from the transmit antenna compared to the directionalantenna. However, the directional antenna is less sensitive tothe distance of the antenna away from the body in vertical andhorizontal polarizations. The diversity antenna is able to maintainhigh peak-to-peak amplitudes in the waveforms of received pulsesfor both polarizations and the high fidelity when it is placed nearthe body. Therefore, the printed diversity antenna is suitable foron-body-centric communications with improved quality of theoverall radio-frequency link.

Index Terms—Body-area networks (BANs), on-body communi-cations, RF transmission, ultrawideband (UWB) antennas.

I. INTRODUCTION

I N recent years, much attention has been paid to employingultrawideband (UWB) devices with the human body [1].

With a low effective isotropic radiated power of less than41.3 dBm/MHz, longer battery life for wearable units can

be achieved. Furthermore, its potential high-data-rate trans-mission makes UWB technology a promising candidate forbody-centric networks. Much research effort on body-areanetworks (BANs), especially in the area of large-scale fadingcharacteristics and human body channel modeling, has beendevoted [2]–[5]. In such wearable computing applications, theantenna design is a critical issue since it can affect the trans-mission range, reliability, and quality significantly. Besideshaving the requirements of light weight, low profile, unobtru-siveness to the user, high electrical, and mechanical tolerances,UWB-based systems often require that the antennas featureacceptable impedance and radiation performances over a broad

Manuscript received March 01, 2008; revised December 14, 2008. Currentversion published April 08, 2009.

The authors are with the Institute for Infocomm Research, Singapore 138632(e-mail: [email protected]; [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TAP.2009.2014595

frequency range, typically of 3.1–4.8 GHz, which correspondsto the lower UWB band.

In UWB applications, planar antennas instead of conventionalnarrowband designs, such as thin wire dipoles or microstrippatch antennas, are popular candidates due to their broad band-widths, small size, low cost, and can be made to conform withthe human body. The radiated and received pulses by planar an-tennas have been experimentally investigated in free space [6],[7] as well as on the inhomogeneous and lossy human body[8], [9]. It is evident that the presence of the human body hasa considerable effect on the antenna system performance in thefrequency domain in terms of transmission, gain, radiation pat-terns, and impedance matching. In the time domain, the wave-forms of the received pulses are affected when the antennas areplaced on/near the human body.

In this paper, the human body effects on the transmissionand the received pulse characteristics of three types of typ-ical antennas, namely an omnidirectional printed monopoleantenna, a directional suspended plate antenna backed by afinite-size ground plane, and a printed diversity antenna will beanalyzed experimentally. The UWB antennas that were chosenin this paper are compact and low profile which will be suitablefor on-body communications. The waveforms of the receivedpulses are derived from the measured transmission re-sponses of the antenna system by using the Dirac impulse andthe sine-modulated Gaussian monocycle as the source pulses.The waveforms are analyzed in terms of the peak-to-peakamplitude, fidelity, and stretch ratio of waveforms of receivedpulses. In the measurements, the antenna system consists of astandard horn antenna in free space as the transmit antenna,and an antenna under test as the receive antenna placed near/onthe human body.

II. UWB ANTENNA DESIGNS

Fig. 1(a) shows the geometry of the omnidirectional printedUWB antenna (Antenna A) [9]. The overall size of the antennais 25 mm 35 mm. The radiator and ground plane are etchedon the opposite sides of a printed-circuit board (PCB) (RO4003,

3.38 and 0.8 mm in thickness). The radiator consists of anopen-ended vertical rectangular notch of 1 mm 16 mm locatedat the center of the radiator so that it is symmetrical around theaxis. Two horizontal strips of 2 mm 4 mm are extended fromthe top left and right corners of the radiator, respectively. Theradiator is fed by a microstrip line of 1.86-mm width locatedat the center with a 1.5-mm feed gap. The ground plane has avertical length of 13.5 mm.

The UWB directional antenna design (Antenna B) in Fig. 1(b)is a suspended plate antenna which is backed by a ground planeof size similar to Antenna A [10]. The antenna consists of an

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SEE AND CHEN: EXPERIMENTAL CHARACTERIZATION OF UWB ANTENNAS 867

Fig. 1. Geometry of (a) Antenna A omnidirectional antenna. (b) Antenna Bdirectional antenna. (c) Antenna C diversity antenna.

L-shaped radiator, with its vertical section shorted at a distanceof 9 mm from the top of the ground plane of size 25 35 mm.The antenna is fed by a microstrip line of 1.86 mm width be-neath the ground plane and is connected to a Z-shaped feedingplate. The ground plane and the microstrip line are printed onthe top and bottom surfaces of the FR4 substrate, respectively.The feeding plate is suspended at a height of 3.5 mm above theground plane and positioned in a way such that the antenna issymmetrical about the axis. The vertical top section of thefeeding plate is separated from the shorting wall and the hori-zontal section of the radiator.

Fig. 1(c) shows the geometry of the UWB diversity an-tenna (Antenna C) [11]. The antenna was printed on a37 45 0.8-mm PCB slab. The dielectric substrate (Rogers4003) has a relative dielectric constant of 3.38. The two radia-tors are separated 3 mm from each other and are symmetricallypositioned with respect to the axis. The radiators are excitedvia two 50- microstrip lines of 1.86-mm width in and135 configurations. Each radiator has a 1.5-mm-wide notchetched in a direction parallel to the feeding strip. A stub mea-suring 4 mm 3 mm on the feeding strip close to the radiator isused for impedance matching. There is a gap of 1 mm betweenthe ground plane on the reverse side of the PCB and the bottomside of the radiators. A central strip extends vertically from theground in order to reduce the mutual coupling between the twoantenna elements.

Fig. 2. Radiation patterns of the antennas at 4 GHz (a)� (horizontal). (b)�(vertical).

All three antennas have a good impedance matching responseacross the lower UWB band of 3.1–4.8 GHz. Antenna A hasomnidirectional radiation in the - plane similar to a monopoleantenna, Antenna B has the patch-like radiation patterns withthe main beam directed along the axis, and Antenna C hastwo different coverage regions that are symmetrical to the –plane when Ports 1 and 2 are excited, respectively. The radiationpatterns in the plane of rotation of the body (i.e., – plane)for the three antennas are shown in Fig. 2. For brevity, only theradiation patterns at 4 GHz are given since the patterns at otherfrequencies between 3 and 5 GHz demonstrate similar trends.

III. MEASUREMENT SETUP

Fig. 3 shows the measurement setup for a transmit-receive an-tenna system by using a standard double-ridged horn (MDRH-1018-S) as the transmit antenna. The gain is around 10 dBifrom 3–5 GHz, and the half power beamwidth is 45 in theH-plane and 50 in the E-plane. The measurements were con-ducted in an anechoic chamber. Since it would not be prac-tical to provide the radiation patterns across the UWB band forthe different body orientations, the was measured since thetransmission performance is related to the radiation characteris-tics of the antenna. By comparing the transmission performance


TABLE ITISSUE PARAMETERS AT 3, 4, AND 5 GHZ

Fig. 3. Measurement setup.

of the antenna on the body to that in free space, the attenua-tion due to the presence of the body can be obtained. Also, thetransmission performance of the antennas for the different bodyorientations can be analyzed. The readings were recordedacross a frequency sweep from 10 MHz–12 GHz using an Ag-ilent N5230A vector network analyzer. In the measurements,the transmit horn and receive (AUT) antennas were separatedat a distance of 1.1 m from each other so that two antennaswere in the far-field zone of each other at 3 GHz and above.The receive antenna was placed directly on the body around thechest area ( 0 mm) and at a distance of 5 and 10 mmaway from the body. The person wearing the AUT was standingabove a rectangular absorber where the horn antenna was in-stalled. Both the AUT and horn antenna were placed at a heightof about 1.2 m. Table I shows the relative permittivity and con-ductivity of the skin, muscle, and fat tissues at 3, 4, and 5 GHz[12]. The orientation of the body is defined such thatcorresponds to the case where the AUT and horn antenna werealigned face-to-face at the boresight, and andcorrespond to the and directions of the AUT, respec-tively. The human body (where the receive antenna was placed)was standing on an absorber and rotated at an angle ofto in steps of 15 in the horizontal plane. It is noted thatdue to the antenna symmetry about the axis for Antennas A

Fig. 4. Effects of the human body on the return loss.

and B, only the values of from 0 to 90 were taken. For An-tenna C, when Port 1 was excited and Port 2 was terminatedwith a 50- load, the measurements were performed with thehuman body rotating from 90 to 90 in steps of 15 . Inthe measurements, the AUTs were placed (vertically) such thatthe -direction is directed toward the head.

IV. MEASURED RESULTS

The effect of the human body on the impedance matching ofthe antennas is shown in Fig. 4. It can be seen that the impedancematching for antennas A and C is very sensitive to the humanbody. When the antenna is directly in contact with the lossyhuman body, namely 0 mm, the return loss is lowered dueto the significant absorption by the body. However, the effect ofthe body on the impedance matching of Antenna B is limitedsince the ground plane is not in direct contact with the body.When Antennas A and C are placed in close proximity to thehuman body, the lower edge frequency is reduced, which leadsto an increase in the bandwidth.

Figs. 5–10 show the measured for the different at thevertical and horizontal polarizations when Antennas A–C areplaced in free space and near/on the body. It can be observedfrom Fig. 5 that when Antenna A is placed near the body, theradiation for the vertical polarization is increased by as much as5 dB due to the reflections from the body, especially at higherfrequencies. The increase in transmission is observed for


Fig. 5. Measured �� with Antenna A for the vertical polarization.

Fig. 6. Measured �� with Antenna A for the horizontal polarization.

– . Comparing the transmission responses of the antennain free space and on the body, it can be observed that when theantenna is placed on the body, there is an additional attenuationof more than 5 dB due to the absorption by the human body.Below 4 GHz, the attenuation is greater than 10 dB. Also, itcan be observed that as the human body is turned away from thehorn antenna, the transmission declines rapidly after asthe radiation of Antenna A has become more directional due tothe presence of the human body. For the horizontal polarizationscenario in Fig. 6, when the antenna is placed close to the body,there is an increase in the transmission when . Thetransmission for the horizontal polarization is generally lowerthan that of the vertical polarization since the antenna is linearly(vertically) polarized.

For Antenna B, the variation in the transmission for the ver-tical polarization when the antenna is placed on/near the humanbody becomes greater with an increase in the as shown in

Fig. 7. Measured �� with Antenna B for the vertical polarization.

Fig. 8. Measured �� with Antenna B for the horizontal polarization.

Fig. 7. When , the transmission is relatively insen-sitive to the body movements. The attenuation increases rapidlydue to the weaker radiation from the antenna as . It canbe observed that unlike Antenna A, Antenna B does not expe-rience significant attenuation even when the antenna is placeddirectly on the body ( 0 mm). This is due to the weakercurrent on the ground plane as well as its directional radiationcharacteristics. From Fig. 8, it can be seen that the transmissionfor the horizontal polarization is relatively unresponsive to thechanges in the distance . The presence of the human body isable to increase the transmission when due to the re-flections from the body. However, when , a significantattenuation in the transmission is observed due to the blockageby the human body.

Antenna C has the characteristics of pattern and polariza-tion diversity so that the radiation is mainly concentrated onthe plane when Port 1 is excited, and the


Fig. 9. Measured �� with Antenna C for the vertical polarization for (a) � �

� to �� (b) � � �� to � .

plane when Port 2 is excited. Due to theblockage of the human body, the measurements were conductedfrom . Fig. 9 shows the transmission responseof Antenna C when Port 1 is excited for the vertical polariza-tion. It can be observed that the variation in the transmissionfrom – is within 10 dB for 5 and 10 mm. How-ever, there is significant attenuation when the antenna is placeddirectly on the body that is due to the increased radiation absorp-tion and impedance mismatching at the antenna input. Satisfac-tory transmission can be achieved when but a largervariation in the transmission can be observed when .By switching the excitation between the two ports, the patterndiversity antenna enables a greater degree of body movementfrom with less attenuation as compared to thedirectional antenna. The dip in transmission at 5 GHz is due tothe reduction in the gain of Antenna C at that frequency. Thereis a larger variation in transmission with body movement for the

Fig. 10. Measured �� with Antenna C for the horizontal polarization for(a) � � � to �� . (b) � � �� to � .

horizontal polarization as shown in Fig. 10. In addition, the at-tenuation with respect to free space is limited when the antennais placed near the body. Compared to Antenna A, Antenna Chas a much stronger transmission for the horizontal polariza-tion, which is desirable in order to increase the link quality foron-body communication systems.

The transmit and receive antennas can be treated as a singlelinear time-invariant system. The time-domain impulse re-sponse of the antenna system can be obtained by takingthe inverse Fourier transform in (1), and the output of thereceiving antenna for an arbitrary source pulse can be obtained

(1)


(2)

where is the incident voltage at Port 1 and is the sourcevoltage. The conjugate relationship in (3) can be used to obtain

for , assuming that is real for all physicallyrealized electrical systems, which include the antenna systemin this paper.

is a real function.(3)

In order to predict the pulse waveforms at the receive antennasas well as to study the effect of the source pulse, two types ofsource pulses were selected in this study. The first type is a Diracimpulse with an amplitude of V. The Dirac impulsewas selected so that the received waveforms will be independentof the pulse spectrum that is constant across all frequencies.The second type is a sine-modulated Gaussian pulse centeredat 4 GHz, with the source-pulse parameter , and400 ps.

Figs. 11(a)–(f) show the peak-to-peak amplitudes of the re-ceived pulse waveforms for the vertical and horizontal polariza-tions at 0, 5, and 10 mm, and in free space for AntennasA, B, and C when the Dirac impulse was chosen as the sourcepulse.

It can be observed from Fig. 11(a) that the amplitude is in-creased compared to that free space when when An-tenna A is placed near the body which is due to the reflec-tions from the body. On the other hand, the amplitude decreasesrapidly when . When the antenna is placed on the body,the amplitude decreases by more than 50%, which is due to thesignificant absorption by the human body. For Antenna B, theincrease in amplitude arising from the reflections from the bodyis less than that of Antenna A as shown in Fig. 11(c). Due tothe directional radiation property of Antenna B, the amplitudeis seen to decrease steadily as the body turns away from thehorn antenna. From Fig. 11(e), the amplitude of the receivedwaveforms for Antenna C is still high when .Therefore, Antenna C is able to increase the overall link qualityby switching between the two ports. Antenna B is relatively in-sensitive to the changes in the distance for the horizontal po-larization as observed in Fig. 11(d). Also, compared to AntennaA, the amplitude when for Antenna C is muchhigher. In general, when Antenna C is placed near the body,the waveform amplitudes corresponding to the vertical and hor-izontal polarizations are almost the same, while those of An-tennas A and B experience greater variation. Here, it should benoted that due to the extremely wide spectrum of the Dirac im-pulse, the significant ringings in the received waveforms are dueto the narrower system bandwidth of the antennas and/or thenonlinearity in the phase response.

In order to preserve the fidelity of the received pulse wave-forms by having the majority of the energy of the source pulse

Fig. 11. Peak-to-peak amplitudes of the received pulse waveforms for(a) Antenna A, vertical polarization; (b) Antenna A, horizontal polarization;(c) Antenna B, vertical polarization; (d) Antenna B, horizontal polarization;(e) Antenna C, vertical polarization; and (f) Antenna C, horizontal polarization.

concentrated within the bandwidth of interest (3–5 GHz), a sine-modulated Gaussian monocycle centered at 4 GHz was chosenas the source pulse. The fidelity of the pulses of an antennasystem can be calculated to assess the quality of the receivedpulse and select a proper detection template. The definition ofthe fidelity can be written as

(4)

where refers to the waveform of the received pulse andis the template pulse, which was taken to be the source pulse inthis case.

Figs. 12–14 show the fidelity and stretch ratio of the receivedpulse waveforms with respect to the source pulse. The sourcepulses with 100, 200, and 400 ps were chosen. The


Fig. 12. Fidelity and stretch ratio for Antenna A. (a) Vertical polarizationof 100 ps. (b) Horizontal polarization of 100 ps. (c) Vertical polarizationof 200 ps. (d) Horizontal polarization of 200 ps. (e) Vertical polarization of400 ps. (f) Horizontal polarization of 400 ps.

fidelity parameter is useful in assessing the capability of a co-herent receiver to detect the received UWB signals. The stretchratio is defined in (5) as the ratio of the width of the receivedwaveform to the width of the source waveform . Thepulse width for the 90% energy capture is defined as the width ofthe signal after removing the first and last 5% energy portionsin the time axis [13]. Through the comparison of the fidelityand stretch ratio performance in free space to that on the body,a better understanding of the effects of the human body on thequality of the pulse can be achieved

(5)It can be seen from Fig. 12 that Antenna A is able to achieve ahigh fidelity for the vertical polarization with the different bodyorientations. The stretch ratio is also low when and400 ps. However, when 100 ps, the stretch ratio is in-creased when the body is rotated away from the transmitter, andthe antenna is placed close to the body. Also, for the horizontalpolarization, the presence of the human body is able to increasethe fidelity and reduce the stretch ratio.

Fig. 13. Fidelity and stretch ratio for Antenna B. (a) Vertical polarizationof 100 ps. (b) Horizontal polarization of 100 ps. (c) Vertical polarizationof 200 ps. (d) Horizontal polarization of 200 ps. (e) Vertical polarization of400 ps. (f) Horizontal polarization of 400 ps.

In the case of Antenna B, the fidelity in free space is low butincreases when the antenna is placed on/near the human body asshown in Fig. 13. The human body provides a more significantimprovement to the stretch ratio for the horizontal polarization.The improvement is more apparent for the vertical polarizationwhen , but with lower fidelity compared to that in freespace. Generally, high fidelity and low stretch ratio are achievedfor the vertical and horizontal polarizations. Also, compared toAntenna A, Antenna B is less sensitive to the presence of thebody when it is placed on the body.

In Fig. 14, with the Port 1 of Antenna C being excited, highfidelity for the vertical polarization can be obtained generallywhen . When the antenna is placed on thebody, the fidelity is reduced for the horizontal polarization butincreased for the vertical polarization. From the results, it canbe seen that by switching between the two ports, the high fi-delity can be achieved for when AntennaC is placed on or in close proximity to the body. Similarly, thestretch ratio is also maintained low when 200 and 400 ps.Due to the narrower transmission bandwidth of Antenna C com-pared to Antennas A and B, the pulse fidelity and stretch ratioperformance when 100 ps are correspondingly degraded.

V. CONCLUSION

In this paper, the transmission of UWB antennas with omni-directional, directional, and pattern diversity radiation charac-teristics has been experimentally characterized by placing themon or in close proximity to the human body. The transmission


Fig. 14. Fidelity and stretch ratio for Antenna C. (a) Vertical polarizationof 100 ps. (b) Horizontal polarization of 100 ps. (c) Vertical polarizationof 200 ps. (d) Horizontal polarization of 200 ps. (e) Vertical polarization of400 ps. (f) Horizontal polarization of 400 ps.

response at the vertical and horizontal polarizations have beenmeasured and used to obtain the received pulse waveforms.Using the Dirac impulse as the source pulse, the peak-to-peakamplitudes of the received pulse waveforms have suggestedthat the omnidirectional antenna is more sensitive to the bodyorientation as well as the distance of the antenna from the bodythan the directional antenna. However, the directional antennais less sensitive to the distance of the antenna from the bodyfor the vertical and horizontal polarizations. Generally, the fi-delity performance has been improved when the antennas wereplaced near the body compared to free space by selecting thesine-modulated Gaussian monocycle as the source pulse. Thestudy has shown that the diversity antenna is able to maintainhigh peak-to-peak amplitudes in the received pulse waveformsfor the vertical and horizontal polarizations as well as the highfidelity and low stretch ratio when it is placed near the body.Therefore, the diversity antenna can be used in on-body-centricUWB communications to improve the overall link quality.

REFERENCES

[1] J. A. Ruiz and S. Shimamoto, “A study on the transmission characteris-tics of the human body towards broadband intrabody communications,”in Proc. 9th Int. Symp. Consumer Electron., 2005, pp. 99–104.

[2] A. Alomainy, Y. Hao, C. G. Parini, and P. S. Hall, “On-body prop-agation channel characterization for UWB wireless body centric net-works,” in Proc. IEEE Antennas Propag. Symp., 2005, vol. 1B, pp.694–697.

[3] A. Alomainy, Y. Hao, C. G. Parini, and P. S. Hall, “Comparison be-tween two different antennas for UWB on-body propagation measure-ments,” IEEE Antennas Wireless Propag. Lett., vol. 4, pp. 31–34, 2005.

[4] T. Zasowski, F. Althaus, M. Stager, A. Wittneben, and G. Troster,“UWB for noninvasive wireless body area networks: Channel mea-surement and results,” in Proc. IEEE Conf. Ultra Wideband Syst. andTechnol., 2003, pp. 285–289.

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[6] X. H. Wu, Z. N. Chen, and N. Yang, “Optimization of planar diamondantenna for single/multi-band UWB wireless communications,” Mi-crow. Opt. Technol. Lett., vol. 42, no. 6, pp. 451–455, 2004.

[7] X. H. Wu and Z. N. Chen, “Comparison of planar dipoles in UWBapplications,” IEEE Trans. Antennas Propag., vol. 53, no. 6, pp.1973–1983, Jun. 2005.

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[9] T. S. P. See and Z. N. Chen, “Characterization of received pulses byantennas in proximity of human body,” presented at the 2nd Eur. Conf.on Antennas and Propag., Edinburgh, U.K., Nov. 11–16, 2007.

[10] T. S. P. See and Z. N. Chen, “An electromagnetically coupled UWBplate antenna,” IEEE Trans. Antennas Propag., vol. 56, no. 5, pp.1476–1479, May 2008.

[11] T. S. P. See and Z. N. Chen, “A miniaturized ultra-wideband diversityantenna,” IEEE Trans. Antennas Propag., to be published.

[12] Dielectric Properties of Body Tissues in the Frequency Range10 Hz–100 GHz., [Online]. Available: http://niremf.ifac.cnr.it/tis-sprop/#refs., Italian Nat. Res. Council, Inst. Appl. Phys.

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Terence S. P. See received the B.Eng. and M.Eng.degrees in electrical engineering from the NationalUniversity of Singapore, Singapore, in 2002 and2004, respectively.

In 2004, he joined the Institute for Infocomm Re-search, Singapore. Currently, he is Senior ResearchEngineer in the Antenna Lab under the RF and Op-tical Systems Department. His main research inter-ests include antenna design and theory, particularlyin small and broadband antennas and arrays, diversityantennas, antennas for portable devices, and antennas

for on-body communications.

Zhi Ning Chen (F’08) received the B.Eng., M.Eng.,Ph.D., and Do.E. degrees in electrical engineeringfrom Southeast University of China, Nanjing, China,and the University of Tsukuba, Japan.

Since 1988, he has been with the Institute forCommunications Engineering, Southeast Univer-sity, City University of Hong Kong, Hong Kong,China, with teaching and research appointments.From 1997 to 1999, he conducted research at theUniversity of Tsukuba, Japan, as a Research Fellowawarded by the Japanese Society for Promotion of

Science (JSPS). In 2001 and 2004, he visited the University of Tsukuba, againsponsored by Invitation Fellowship Program (senior level) of JSPS. In 2004,he worked in the Thomas J. Watson Research Center, International BusinessMachines Corporation (IBM), Yorktown, NY, as Academic Visitor. In 1999, he


joined the Institute for Infocomm Research as a Member of the Technical Staff(MTS) and was then promoted to Principal of MTS. He is now working asPrincipal Scientist and Department Head for RF & Optical. He is concurrentlyholding Adjunct/Guest Professor Appointments at the National University ofSingapore and Nanyang Technologies University, Nanjing University, South-east University, and Shanghai Jiao Tong University. He has been TechnicalAdvisor in Compex since 2005. He founded the IEEE International Workshopon Antenna Technology (iWAT), one of most important international antennaevents, and as General Chair, organized the IEEE iWAT: Small Antennasand Novel Metamaterials, 2005, Singapore. He is chairing iWAT SteeringCommittee and managing future iWAT. He has played the important rolesin many international events as chairs for the Technical Program Committeeand International Advisory Committee as well as keynote/invited speakers.His research areas cover applied electromagnetics and antenna theory, designwireless communication, and imaging systems. In particular, he is interested in

the R&D of small and broadband antennas and arrays for wireless local-areanetworks, worldwide interoperability for microwave access (WiMAX), wirelesspersonal-area network (WPAN), radio-frequency identification, multiple inputmultiple output, ultrawideband, millimeter wave (mmW), submmW, tetrahertz,and implanted systems. He has authored and co-authored more than 230 tech-nical papers published in international journals and presented at internationalconferences. He has been published in the following books Broadband PlanarAntennas, UWB Communications, and Antennas for Portable Devices (Wiley).In addition, he has contributed to multiple chapters in three books about antennadesigns. He also has five granted patents and 11 filed patent applications. Someof them have been licensed to industry for production.

Dr. Chen is the Antennas and Propagation Society Distinguished Lecturer(2008–2010).

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Experimental Characterization of UWB Antennas for On-Body Communications