• No results found

Wideband printed MIMO/diversity monopole antenna for WiFi/WiMAX applications

N/A
N/A
Protected

Academic year: 2020

Share "Wideband printed MIMO/diversity monopole antenna for WiFi/WiMAX applications"

Copied!
8
0
0

Loading.... (view fulltext now)

Full text

(1)

Wideband Printed MIMO/Diversity Monopole

Antenna for WiFi/WiMAX Applications

Chan Hwang See, Raed A. Abd-Alhameed, Zuhairiah Z. Abidin, Neil J. McEwan, and

Peter S. Excell

, Senior Member, IEEE

Abstract—A novel printed diversity monopole antenna is pre-sented for WiFi/WiMAX applications. The antenna comprises two crescent shaped radiators placed symmetrically with respect to a defected ground plane and a neutralization lines is connected be-tween them to achieve good impedance matching and low mutual coupling. Theoretical and experimental characteristics are illus-trated for this antenna, which achieves an impedance bandwidth of 54.5% (over 2.4–4.2 GHz), with a reflection coefficient 10 dB

and mutual coupling 17 dB. An acceptable agreement is

ob-tained for the computed and measured gain, radiation patterns, envelope correlation coefficient, and channel capacity loss. These characteristics demonstrate that the proposed antenna is an attrac-tive candidate for multiple-input multiple-output portable or mo-bile devices.

Index Terms—Impedance bandwidth, monopole antenna, mul-tiple-input multiple-output (MIMO), WiFi/WiMAX.

I. INTRODUCTION

T

HE unprecedented growth in the use of wireless commu-nication technologies internationally has opened an im-mense commercial opportunity for the mobile industry. Over recent years, due to the rapid evolution of wireless service ap-plications including live HDTV broadcast, online game, and real-time video streaming, mobile electronic devices that are capable of handling these high data rate applications are in bur-geoning demand.

Multiple-input multiple-output (MIMO) communication technology implements multiple antenna elements on the trans-mitting and receiving ends of the MIMO system to achieve the aim of maximizing the channel capacity for delivering high data rate traffic in a rich scattering environment [1]–[3]. Theoretical and experimental published research articles [3], [4] confirm the superior data rate enhancement, multipath fading reduction and co-channel interference suppression capabilities [1], [2] when deploying MIMO technology. Due to the competitive market pressures, mobile device manufacturers have to im-prove their products to enable MIMO radio within the existing low-profile handheld devices. When implementing a single

Manuscript received April 11, 2011; revised September 12, 2011; accepted November 05, 2011. Date of publication January 31, 2012; date of current ver-sion April 06, 2012.

C. H. See, R. A. Abd-Alhameed, Z. Z. Abidin, and N. J. McEwan are with Mobile and Satellite Communications Research Center, Bradford Uni-versity, West Yorkshire BD7 1DP, U.K. (e-mail: c.h.see2@bradford.ac.uk; r.a.a.abd@bradford.ac.uk).

P.S. Excell is with Glyndwr University, Wrexham LL11 2AW, U.K. (e-mail: p.excell@glyndwr.ac.uk).

Color versions of one or more of thefigures in this paper are available online at http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TAP.2012.2186247

antenna element on a portable wireless device, bandwidth enhancement, and size reduction are critical criteria, so that the antenna can operate over as many existing wireless com-munication standards as possible. Nevertheless, when multiple antenna elements are closelyfitted into a confined space within the standard commercial enclosure, mutual coupling/isolation between these antennas becomes another crucial parameter that has to be taken into consideration. Hence, it is a challenging task to design a compact MIMO/diversity antenna with low mutual coupling among its elements while preserving the performance of a single element antenna, when these antennas are forced to be installed within a small area enclosure.

In general, the mutual coupling between two closely placed antennas is mainly caused by induced currents due to the sharing of common ground and near field coupling [5]. This adverse impact can degrade the radiation performance of the antenna. Significant research efforts to reduce the mutual coupling or achieve good isolation between closely placed antenna elements have been made [6]–[16]. For example, by modifying the geom-etry of the defected ground plane of the printed antenna array [6]–[9], port-to-port isolation as good as 20 dB can be real-ized, where the minimal distance between two antennas can be kept between 0.0147 to 0.08 . These studies include inserting tree-like structure in the defected ground plane [7], embedding T-shaped and dual inverted-L-shaped ground branches in the ground plane [8] and cutting a resonant slot in the center of the ground plane [9]. It is also interesting to observe that by adding a lumped-element decoupling network after the two cou-pled antenna, the inter-port isolation better than 15 dB can be obtained for two planar radiators separated by 0.069 [10]. However, this method will increase the cost of manufacture and lumped elements will impair the radiation efficiency of the an-tenna. Moreover, many efforts have been made using electro-magnetic band gap (EBG) structures [11]–[13] to suppress the unwanted surface propagation wave at a specific frequency, and thus minimize the mutual coupling between antenna elements. These EBG structures provide a substantial decoupling effect, but suffer from large size, high cost of manufacture and com-plicated design. In order to avoid increasing the volume and weight of the antenna, authors in [14]–[16] propose a neutraliza-tion technique to cancel out the reactive coupling between two closely placed radiators. This is done by physically connecting the multiple antenna elements with a transmission line. This method has been initially used on a suspended PIFA antenna structure as in [14], [15]. Then, this work was further adopted on a printed microstrip antenna array for mobile applications [16]. The results in [14]–[16] reveal that this technique provides an isolation of about 18 dB between two antenna elements for

(2)
[image:2.592.41.288.62.271.2]

Fig. 1. Geometry of the proposed antenna.

which the center to center inter-element spacing ranges from 0.027 to 0.12 .

By examining all these methods as in [6]–[16], it is noticed that they are only capable of offering narrow band isolation be-tween two antennas and very few techniques such as in [7] can handle wide band isolation. In order tofill this need, the present paper introduces a novel wideband isolation technique for two closely spaced printed monopole antennas. This has been real-ized by connecting the two antenna elements with a new neu-tralization lines configuration that is able to suppress the mutual coupling between closely packed monopole antennas operating in the same frequency band. In comparison with neutraliza-tion line methods used in [14]–[16], this present method offers enhanced performance in terms of good impedance matching across the desired operating frequency bands combined with high inter-port isolation between the antenna elements. Each antenna is designed to operate over a bandwidth from 2.4 to 4.2 GHz and is intended to meet the demands of the existing wireless communication standards, i.e., Wifiand Wimax. The overall dimensions of this antenna, including the ground size (i.e., equivalent terminal size) are 90 40 0.79 mm . Using a composite neutralization line etched on the substrate between the two antennas, it is found that an isolation better than 17 dB over the whole frequency band can be achieved when the two antennas are separated by .

II. ANTENNADESIGNCONCEPTS ANDSTRUCTURE

The proposed antenna geometry is illustrated in Fig. 1. A crescent shaped radiator which is similar to that in [17] is adopted. The radiator is fed by an 10.86 1 mm 83 microstrip line which improves impedance matching. The radiators are separated by 23.9 mm, approximately (where is the free space wavelength) at 2.4 GHz (i.e., the lowest resonant frequency) for the optimal mutual coupling suppression. These radiators are printed on one side of a Duroid 5870 substrate material with a thickness of 0.79 mm, dielectric constant of 2.33 and a loss tangent of 0.0012, while a 67.5 40 mm

In addition, for the dual antenna shown in Fig. 1, to achieve suf-ficient isolation between the two identical elements maintain a good impedance matching over the desired frequency band, a new neutralization lines (0.5 mm widths) structure was intro-duced between the two radiators. In principle, its function is to provide an anti-phase coupling current to eliminate the original coupling current. Hence, the existing electromagnetic coupling between two antenna elements can be weakened. Tofind op-timal locations of lines, several simulations were performed to check the isolation, return loss and radiation characteristics of the antenna. It was interesting to find that these lines had to be linked to a low impedance area of the radiators where the currents have the highest intensity, for optimal performance of the antenna. Thesefindings were in agreement with published works [14], [15]. Notably, in the present case study, two max-imum current locations were selected, i.e., one is on the center of the crescent radiator and the other is on the end of the transmis-sion line. In general, the neutralization lines transfer some cur-rents from thefirst antenna and re-inject it in the second antenna with a suitable magnitude and phase to cancel out the existing coupling current between two antenna elements. The additional network does not remove the inherent coupling between the an-tennas, but enhances the inter-port isolation. The coupling net-work does not have attributes of afilter or resonator, and most resembles a branch line coupler introducing several paths be-tween its nodes.

To evaluate the effectiveness of the neutralization lines, the simulated reflection coefficient and mutual coupling of the proposed antenna with and without the lines are shown in Fig. 2. As can be seen, by implementing the lines, can be improved from 8 dB to below 10 dB, while values vary between 12 and 20 dB without the neutralization lines, and 17 and 34 dB with the lines, across the operating frequency band.

(3)
[image:3.592.42.287.62.228.2] [image:3.592.307.550.63.233.2]

Fig. 2. Simulated -parameters of the proposed antenna with and without the neutralization lines.

Fig. 3. Four possible decoupling current paths on the neutralization lines. Port 1 (left) is excited and port 2 is terminated in 50 .

[image:3.592.42.288.272.533.2]

This current path contributes to enhance isolation at the highest edge of the frequency band. At cases (b) and (c), both of the continuous decoupling current paths are 64.39 mm which is ap-proximately 0.5 at 2.35 GHz. These two current paths have the pivotal role in improving the inter-port isolation at the lowest edge of the operating band. This explanation can be validated by the parameters curve of the antenna with the neutralization lines on Fig. 2. As can be seen, the antenna with neutralization lines show a 33-dB-deep null at 2.35 GHz. At case (d), the full length of the longest current path of the neutralization lines is 82.09 mm, which is around 0.5 at 1.8 GHz. Since the op-eration frequency of this current path is 600 MHz away from the lowest operating frequency (2.4 GHz) of the proposed an-tenna, therefore, it has no significant influences on the antenna performance.

Fig. 4. Simulated -parameters of the proposed antenna different sections of the neutralization lines.

Fig. 5. Contour plot surface current distributions without (top) and with (bottom) the neutralization lines at (i) 2.4 GHz, (ii) 3 GHz, and (iii) 3.5 GHz. Port 1 (left) is excited and port 2 is terminated in 50 .

[image:3.592.316.539.278.574.2]
(4)
[image:4.592.309.546.62.394.2]

Fig. 7. Simulated and measured -parameters of the proposed antenna.

the injection via CE but modified in amplitude and phase by the changed voltage transfer function between AC (and JE) pro-duced by the paths ADC and JGE.

Moreover, to further understand the contribution of the neu-tralization lines, the simulated surface current distributions of the antenna with and without the lines are illustrated in Fig. 5. As can be seen, when the port 1 is excited and port 2 is termi-nated in 50 , without the lines, the surface currentsflow in the excited radiator induces current in the feed line of the port 2 radiator at all frequencies. This introduces a strong mutual cou-pling between the two antenna elements. By inserting the lines, it can be noticed that the surface currents on both radiators are transferred to the neutralization lines and a current of similar magnitude in the top of the neutralization line is clearly seen to cancel this feed line current. This tends to decouple the cur-rents on the port 2 radiator and hence it enhances the isolation between the two radiator elements efficiently.

III. RESULTS ANDDISCUSSION

To validate the simulated results, a prototype of the proposed antenna was fabricated and tested, as shown in Fig. 6. The mea-sured and simulated values of and are plotted in Fig. 7: these results exhibit reasonable agreement although there is a frequency shift that can be attributed to reflections from the SMA connector and some uncertainty in the electrical proper-ties of the substrate material. As can be seen, the impedance

[image:4.592.73.258.64.201.2]

Fig. 8. Simulated and measured MIMO characteristics of the proposed an-tenna. (a) Correlation coefficient. (b) Capacity loss.

Fig. 9. Simulated and measured gains of the proposed antenna.

bandwidth of the antenna encompasses the operating frequency spectra from 2.4 to 4.2 GHz for a reflection coefficient

10 dB, which corresponds to 1.8 GHz bandwidth or about 54.6% relative bandwidth with respect to the center frequency of 3.3 GHz. The bandwidth achieved fully covers the require-ments of WiFi (2.4 to 2.485 GHz) and WiMAX (2.5 to 2.69 GHz and 3.3 to 3.7 GHz).

[image:4.592.46.281.237.398.2] [image:4.592.311.545.433.591.2]
(5)
[image:5.592.109.499.80.470.2]

Fig. 10. Simulated and measured normalised radiation patterns of the proposed antenna for three planes [(left) - plane, (center) - plane, and (right) -plane] at (a) 2.45 GHz, (b) 3 GHz, and (c) 3.5 GHz. Port 1 (left) is terminated in 50 and port 2 (right) is excited. “xxxx” simulated cross-polarization, “oooo” simulated co-polarization “- - - -” measured cross-polarization, “—” measured co-polarization.

performance of a MIMO system [1], [2]. In general, the enve-lope correlation coefficient of an antenna array can be computed by using either the far-field radiation pattern [2], [18] or scat-tering parameters from the antenna system [19]. Due to the com-plication of the 3D farfield measurement and calculation, the -parameters method of computing the correlation coefficient of the two antennas is used. According to [19], the envelope correlation coefficient of a two antennas system can be de-termined using the following equation:

(1)

Fig. 8(a) shows the variation of the envelope correlation coef-ficient across the desired operating frequency band. Both sim-ulated and measured are less than 0.005, which is compa-rable to the results obtained from [14], [18]. However, there is a slight discrepancy between the simulated and measured results that can be attributed to truncating the entire structure (including measurement cables) in the simulation.

Theoretically, increasing the number of antennas of the MIMO system can improve the channel capacity. However, the presence of uncorrelated Rayleigh-fading MIMO channels will induce loss of channel capacity. This loss can be computed from the correlation matrices given in [3], [20], [21]. In the case of 2 2 MIMO system, taking the consideration of only the receiving antennas are correlated and assuming the worst scenario where high SNR is occurred, the capacity loss can be evaluated by using the equation as follows [20], [21]:

(2)

where is the receiving antenna correlation matrix that given

by: , and

, For or 2.

(6)
[image:6.592.98.496.61.444.2]

Fig. 11. Simulated normalised radiation patterns of the single antenna, and proposed antenna without neutralization lines, for three planes [(left) - plane, (center) - plane, and (right) - plane) at (a) 2.45 GHz (b) 3 GHz, and (c) 3.5 GHz. Port 1 (left) is terminated in 50 and port 2 (right) is excited. “xxxx” (single antenna alone) cross-polarization, “oooo” (single antenna alone) co-polarization “——” (without neutralization lines) cross-polarization, “——” (without neutralization lines) co-polarization.

and simulated radiation efficiencies of this antenna confi gura-tion were above 90% across the whole bandwidth. These results confirm that good impedance matching and isolation between two antenna elements lead to low capacity loss.

Fig. 9 plots the simulated and measured maximum gains of the MIMO antenna over the interval from 2.35 to 4 GHz. At low frequency band from 2.4 to 2.7 GHz, the results showfl uctua-tion can be reached as high as 1.2 dBi. As at higher frequency band above 2.7 GHz, both disagreement of results reduce to as low as 0.5 dBi. This is due to the cable loss, misalignment of the antenna and presence of SMA connector in the measure-ment which is not taken into consideration in the simulated mod-eling processes. It should be noted that the measured maximum gain of proposed antenna at 2.45, 3.0, and 3.5 GHz are 1, 2, and 2.5 dBi, respectively, and the variation of the gains is about

0.75 dBi.

The prototype’s radiation patterns were measured at the three frequencies 2.45, 3.0, and 3.5 GHz covering the designated bandwidth were measured, and the corresponding results cross validated with the simulation data are depicted in Fig. 10. In the measurement, three pattern cuts (i.e., , and -planes) were recorded at three selected operating frequencies

(2.45, 3.0, and 3.5 GHz), covering the whole of the designated bandwidth in this study. The results are presented in Fig. 10, which show that the radiation patterns are stable and consistent at all of the designated frequencies.

To check the direct contribution of the neutralization lines to the radiationfield, characteristic of the antenna, the simulated radiation patterns of the single element of the antenna and two element antennas without the neutralization lines are presented in Fig. 11. As can be seen, these radiation patterns are very sim-ilar to those in Fig. 10, with only insignificant distortions.

IV. CONCLUSION

(7)

has confirmed that it is capable of overcoming multipath fading propagation problem through offering pattern diversity.

REFERENCES

[1] G. J. Foschini and M. J. Gans, “On limits of wireless communications in a fading environment when using multiple antennas,”Wireless Per-sonal Commun., vol. 6, pp. 311–335, 1998.

[2] R. G. Vaughnan and J. B. Andersen, “Antenna diversity in mobile communication,”IEEE Trans. Veh. Technol., vol. VT-36, no. 4, pp. 149–172, 1987.

[3] H. Shin and J. H. Lee, “Capacity of multiple-antenna fading chan-nels: Spatial fading correlation, double scattering, and keyhole,”IEEE Trans. Inform. Theory, vol. 49, no. 10, pp. 2636–2647, Oct. 2003. [4] J. Wallace, M. Jensen, A. Swindlehurst, and B. Jeffs, “Experimental

characterization of the MIMO wireless channel: Data acquisition and analysis,”IEEE Trans. Wireless Commun., vol. 2, no. 2, pp. 335–343, Mar. 2003.

[5] D. Pozar, “Input impedance and mutual coupling of rectangular mi-crostrip antennas,”IEEE Trans. Antennas Propag., vol. AP–30, pp. 1191–1196, Nov. 1982.

[6] D. Ahn, J.-S. Park, C.-S. Kim, J. Kim, Y. Qian, and T. Itoh, “A design of the low-passfilter using the novel microstrip defected ground struc-ture,”IEEE Trans. Microw. Theory Tech., vol. 49, no. 1, pp. 86–93, Jan. 2001.

[7] S. Zhang, Z. Ying, J. Xiong, and S. He, “Ultrawideband MIMO/diver-sity antennas with a tree-like structure to enhance wideband isolation,”

IEEE Antennas Wireless Propag. Lett., vol. 8, pp. 1279–1282, 2009. [8] Y. Ding, Z. Du, K. Gong, and Z. Feng, “A novel dual-band printed

di-versity antenna for mobile terminals,”IEEE Trans. Antennas Propag., vol. 55, no. 7, pp. 2088–2096, Jul. 2007.

[9] S. Zhang, S. N. Khan, and S. He, “Reducing mutual coupling for an extremely closely-packed tunable dual-element PIFA array through a resonant slot antenna formed in-between,”IEEE Trans. Antennas Propag., vol. 58, no. 8, pp. 2771–2776, Aug. 2010.

[10] S.-C. Chen, Y.-S. Wang, and S.-J. Chung, “A decoupling technique for increasing the port isolation between two strongly coupled antennas,”

IEEE Trans. Antennas Propag., vol. 56, no. 12, pp. 3650–3658, Dec. 2008.

[11] D. Sievenpiper, L. Zhang, R. F. J. Broas, N. G. Alexopolus, and E. Yablonovitch, “High-impedance electromagnetic surfaces with a for-bidden frequency band,”IEEE Trans. Microw. Theory Tech., vol. 47, pp. 2059–2074, 1999.

[12] F. Yang and Y. Rahmat-Samii, “Microstrip antennas integrated with electromagnetic band-gap (EBG) structures: A low mutual coupling design for array applications,”IEEE Trans. Antennas Propag., vol. 51, no. 10, pp. 2936–2946, Oct. 2003.

[13] G. Dadashzadeh, A. Dadgarpour, F. Jolani, and B. S. Virdee, “Mutual coupling suppression in closely spaced antennas,”IET Microw. An-tennas Propag., vol. 5, no. 1, pp. 113–125, Jan. 12, 2011.

[14] A. Diallo, C. Luxey, P. L. Thuc, R. Staraj, and G. Kossiavas, “En-hanced two-antenna structures for universal mobile telecommunica-tions system diversity terminals,”IET Microw. Antennas Propag., vol. 2, no. 1, pp. 93–101, Feb. 2008.

[15] A. Chebihi, C. Luxey, A. Diallo, P. L. Thuc, and R. Staraj, “A novel iso-lation technique for closely spaced PIFAs for UMTS mobile phones,”

IEEE Antennas Wireless Propag. Lett., vol. 7, pp. 665–668, 2008. [16] Z. Li, K. Ito, Z. Du, and K. Gong, “Compact wideband printed

diver-sity antenna for mobile handsets,” inProc. Asia–Pac. Radio Sci. Conf., Toyama, Japan, Oct. 2010, pp. 1–4.

[17] C. H. See, R. A. Abd-Alhameed, D. Zhou, and P. S. Excell, “A crescent-shaped multiband planar monopole antenna for mobile wire-less applications,”IEEE Antenna Wireless Propag. Lett., vol. 9, pp. 152–155, 2010.

[18] R. A. Bhatti, J.-H. Choi, and S.-O. Park, “Quad-band MIMO antenna array for portable wireless communications terminals,”IEEE Antennas Wireless Propag. Lett., vol. 8, pp. 129–132, 2009.

[19] S. Blanch, J. Romeu, and I. Corbella, “Exact representation of antenna system diversity performance from input parameter description,” Elec-tron. Lett., vol. 39, pp. 705–707, 2003.

[20] S. H. Chae, S.-K. Oh, and S.-O. Park, “Analysis of mutual coupling, correlations, and TARC in WiBro MIMO array antenna,”IEEE An-tenna Propag. Lett., vol. 6, pp. 122–125, 2007.

[21] D. Valderas, P. Crespo, and C. Ling, “UWB portable printed monopole array design for MIMO communications,”Microw. Opt. Technol. Lett., vol. 52, no. 4, pp. 889–895, 2010.

Chan Hwang Seewas born in Selangor, Malaysia. He received the B.Eng. (Hons.) degree in electronic, telecommunication, and computer engineering, and the Ph.D. degree from the University of Bradford, West Yorkshire, U.K., in 2002 and 2007, respec-tively.

While working toward the Ph.D. degree, he was also working on a number of government/industry projects, concentrating on antenna design and com-putational electromagnetics within the Antennas and Applied Electromagnetic Research Group, Mobile Satellite Communications Research Center (MSCRC), University of Bradford. From November 2006 to February 2009, he was appointed as a Knowledge Transfer Partnership (KTP) Associate sponsored by Yorkshire Water Services (YWS), Yorkshire, U.K. His work focused on the development of wireless low cost communication system to monitor the sewerage infrastructure owned by YWS. Currently, he is working as a postdoctoral Research Assistant to support various projects related to sensors for the water industry. He has published over 100 refereed journal and conference papers and is coauthor of one book and one book chapter. His overarching research interests are multidisciplinary and have a number of cross-cutting themes that include research in computational electromagnetics, acoustic sensor technologies, wireless sensor network, and antenna design with the application of theoretical, computational, and analytical approaches.

Dr. See is a Chartered Engineer and Member of the Institution of Engineering and Technology (MIET) in the U.K. He has a National Vocational Qualification (NVQ) level 4 in Management from the Chartered Management Institute, U.K. He was the recipient of the Radio Frequency Engineering Education Initiative (RFEEI) RF Project Prize in 2002, and of two Young Scientist Awards from the International Union of Radio Science (URSI) and Asia–Pacific Radio Science Conference (AP–RASC) in 2008 and 2010, respectively. The completed KTP project previously described has been recognized by the British Technology Strategy Board as outstanding and awarded the project a Grade A, which is a highest grade achieved by only 4% of completed U.K. KTP projects.

Raed A. Abd-Alhameed received the B.Sc. and M.Sc. degrees from Basrah University, Basrah, Iraq, in 1982 and 1985, respectively, and the Ph.D. degree from the University of Bradford, West Yorkshire, U.K., in 1997, all in electrical engineering.

(8)

and is currently working toward the Ph.D. degree from the School of Engineering, Design and Tech-nology, Bradford University, West Yorkshire, U.K.

She was a Lecturer at Tun Hussein Onn University of Malaysia since 2004. She has authored or coauthored several refereed journal articles and international conference papers. Her current research interests in-clude MIMO antenna design, electromagnetic bandgap (EBG), defected ground structures (DGS), and neutralizations techniques for wireless and mobile sys-tems using genetic algorithm optimization.

Neil J. McEwanreceived the M.A. degree in math-ematics from Cambridge University, Cambridge, U.K., and the Ph.D. degree in radio astronomy from Manchester University, Manchester, U.K., in 1975.

He has held the title of Reader in Electromagnetics at the University of Bradford, West Yorkshire, U.K., since 1986. He was a visiting Research Scientist with Millitech Corporation, South Deerfield, MA, from 1987 to 1989, working on 98 GHz quasi-optical antennas. He was a Principal Research Engineer with Filtronic, Shipley, U.K., from 1998 to 2007 where he

applications and computation of high-frequency electromagneticfields. His principal recent work has been in the computation and measurement of electromagneticfields due to mobile communications ter-minals. This led to significant advances in the development of the hybridfield computation method and novel designs for mobile communications antennas. His current work includes studies of advanced methods for electromagnetic

field computation (including the use of high-performance computing), the effect of electromagneticfields on biological cells, advanced antenna designs for mobile communications, and consideration of usage scenarios for future mobile communications devices. There has been fruitful new collaborative work on design of content for mobile screens and on integration of mobile devices with garments.

Figure

Fig. 1. Geometry of the proposed antenna.
Fig. 4. Simulated-parameters of the proposed antenna different sections ofthe neutralization lines.
Fig. 8. Simulated and measured MIMO characteristics of the proposed an-
Fig. 10. Simulated and measured normalised radiation patterns of the proposed antenna for three planes [(left)-plane, (center)-plane, and (right)-plane] at (a) 2.45 GHz, (b) 3 GHz, and (c) 3.5 GHz
+2

References

Related documents

It proves that the multicloud implementation of a computing cluster is viable from the point of view of measurability, and doesn’t introduce vital overheads, that may cause

This work focuses on developing a framework for calculating hydrogen solubility based on environmental conditions and the formation energies of its point defects, and then applying

In our studies storage server stored data in encrypted format with codeword symbol and with using key storage server massage can decrypt and when user want to forward massage

To eliminate the security challenges in cloud computing we have explainedkey policy advanced encryption standard associated with user authorization period (KP-AESAP)

We use the North Atlantic tropical cyclone (TC) count series from 1950 to 2009 from the seasonal (July through November) Atlantic hurricane database (HURDAT) at the National

In cipher text-policy attribute-based encryption, cipher text involves some access policies and only the users with those attribute values in the access policy can decrypt the

Heart is muscle that works continuously much like pump. Each beat of heart is set in motion by an electrical signal from within heart muscle. The electrical activity is indicated by

So all the operating characteristics shows that antenna is best suited for surveillance applications due its high gain and wide operating bandwidth.. C