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Novel Wideband MIMO Antennas That Can Cover the Whole LTE Spectrum in Handsets and Portable Computers

Novel Wideband MIMO Antennas That Can Cover the Whole LTE Spectrum in Handsets and Portable... Hindawi Publishing Corporation e Scientific World Journal Volume 2014, Article ID 694805, 9 pages http://dx.doi.org/10.1155/2014/694805 Research Article Novel Wideband MIMO Antennas That Can Cover the Whole LTE Spectrum in Handsets and Portable Computers 1 2 Mohamed Sanad and Noha Hassan AmantAntennas, Lot13/C, Second Industrial Zone,6October City,Giza12451,Egypt Faculty of Engineering, Cairo University, Giza, Egypt Correspondence should be addressed to Mohamed Sanad; msanad@amantantennas.com Received 25 August 2013; Accepted 24 October 2013; Published 16 January 2014 Academic Editors: Y. C. Chiang and J. Dauwels Copyright © 2014 M. Sanad and N. Hassan. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A dual resonant antenna configuration is developed for multistandard multifunction mobile handsets and portable computers. Only two wideband resonant antennas can cover most of the LTE spectrums in portable communication equipment. The bandwidth that can be covered by each antenna exceeds 70% without using any matching or tuning circuits, with efficiencies that reach 80%. u Th s, a dual configuration of them is capable of covering up to 39 LTE (4G) bands besides the existing 2G and 3G bands. 2×2 MIMO configurations have been also developed for the two wideband antennas with a maximum isolation and a minimum correlation coefficient between the primary and the diversity antennas. 1. Introduction 1.1. Conventional Antenna Challenges in LTE. The antenna is becoming an increasingly critical component for LTE Customers’ increasing expectations for speed, bandwidth, device vendors. It is possible that future terminal devices and global access are driving the evolution of wireless broad- will have more than 20 antennas to cover all the important band technology. Customers want more information such as wireless applications [4]. In addition, the industry is painfully business, consumer applications, and entertainment available aware of the issues that surround implementing LTE in small through their mobile devices, but with greater speeds [1]. mobile devices with already limited space and extremely LTE represents the next big step towards the 4th generation high performance expectations. Due to this trend, wideband (4G) of radio technologies which is expected to increase the antenna coverage is a hot issue that has to be addressed [5]. capacity and the speed of mobile telephone networks. These Device makers are ndin fi g it difficult to decide which bands to expectations put a significant burden on device performance. prioritize as chipsets and handsets are developed. The priority eTh lack of spectrum harmonization represents a key chal- wouldbefor the800MHzband. Most of theinvestments lenge for the emerging LTE ecosystem, potentially preventing has been directed towards that band because it is the band vendors from delivering globally compatible LTE products that two-thirds of current LTE users occupy, largely driven such as devices and chipsets [2]. Spectrum fragmentation by the U.S. network roll outs of Verizon Wireless and AT&T has the potential to hinder global LTE roaming if device [3]. This low frequency band means larger antennas in terms manufacturers are required to include support for many of size, which is a challenging issue, keeping in mind the disparate frequencies in their devices. Yet, in fragmented limited size of LTE devices. The urgent demand for wideband regional markets such as Europe, LTE roaming is some way LTE coverage represents a serious challenge facing antenna off as operators will be providing LTE in different bands and designers. Adapting the conventional antenna technology to the devices will need to be able to seamlessly switch between serve the wideband demand was not a much of a success, thefrequency bandsusedfor LTEinaddition to the2Gand leading to a definitive belief that passive antennas have 3G networks [3]. reached their limits [6]. uTh s, theactivetuneableantenna 2 The Scientific World Journal L band numbers5,6,8,11, 12,13, 14,17, 18,19, 20,21, 26, D D D D 27, 28, 29, and 44. eTh second one is covering the high D D 2 3 4 7 1 8 band portion of the LTE spectrum starting from 1.52 GHz to 3.8 GHz corresponding to LTE band numbers 1, 2, 3, 4, 7, 9, 10,22, 23,24, 25,33, 34,35, 36,37, 38,39, 40,41, 42, W 2 and 43. This means that a total number of 39 LTE bands can be covered beside the 2G and 3G frequency bands. eTh D D 5 6 new antenna can be implemented in smart phone handsets, tablets, laptops, and notebooks. It consists of two narrow printed metallic arms connected together by a shorting Short arm metallic strip. eTh two arms may be parallel to each other or may have any angle between them. eTh two arms can be shaped in different ways in order to optimize the antenna Shorting strip performance. As shown in Figure 1, each arm has a set of slots Long arm Slots having different configurations. These slots can be circular, rectangular, square, triangular, or other shapes. eTh arm Figure 1: Geometry of the new wideband antenna. lengths of the new antenna, especially the length of the short arm, are the main parameters that determine the operating frequency of the antenna. The bandwidth, the peak gain, and approach has been adopted to fulfil the market need for the efficiency of the antenna are mainly determined by the world LTE devices, trading the passive antenna simplicity widths of the two arms, the angle between them, the thickness with active antenna complexity. of the antenna, and the congfi urations of the slots, which are all optimized together in order to enhance the antenna 1.2. Disadvantages of Active Antennas and Extended Grounds performance, especially the bandwidth. This geometry can be Planes. Passive antennas have various advantages over the scaled and optimized for any application to successfully cover active tuneable antennas.First of all, thepassive antennadoes any frequency band [7, 8]. nothavetobesupported with RF controllingcircuit to do thejob as theactiveone,soitwillsavealargespace required 2. Numerical and Experimental Results of inside the handset to tfi both the antenna and the RF circuit. This is not the only problem of the RF circuit, as additional the New Antenna circuit components are connected to the antenna; it will suffer Two versions of the new LTE antenna have been designed, from impedance mismatch. In this situation a severe decrease manufactured, and tested. Calculated and measured return in the efficiency of the antenna will lead to a lower speed losses will be presented in addition to the calculated gain, of data transfer and a higher number of dropped calls. Also, efficiency, and radiation patterns. The first antenna version theactiveantenna is powerconsuming,causing asignicfi ant can cover a frequency band from 698 MHz up to 1.51 GHz and decrease in the battery lifetime. us, Th it will be a problem it will be referred to as “the low band antenna.” To cover the for power hungry, smart handheld devices. Last but not least, high band portion of the LTE spectrum, a second version of theactiveantenna seemstohavebandlimitations too, as the antenna has been designed and manufactured by scaling the maximum number of bands that commercial LTE active and optimizing the geometry shown in Figure 1.Theantenna antennas can support is 13 bands only out of 39 potential is operating all over the high frequency band 1.52–3.8 GHz LTE bands [6]. On the other hand, current handset antenna anditwillbereferredtoas“thehighbandantenna.” A technologies are still tied with the extended ground plane’s reduced size version of these wideband antennas can be dilemma. As the antenna is not just the module that tfi s under developed and customized for smaller LTE devices. Together, the speaker, however, it includes a large PCB ground plane. thetwo reducedsizeantennasare capableofcovering38LTE A minimum limit size of the ground plane is required for bands with slightly lower but still acceptable efficiencies. eTh the antenna to have an acceptable performance. u Th s, adding reducedsizeversionsofthe lowbandand high band antennas an extravolume counted on the total size of the antenna. As will be also demonstrated. the ground plane is a part of the antenna structure, then, the hand grip on the phone will cause detuning of the antenna operating frequency causing a poor efficiency. 2.1. eTh Low Band and High Band Antennas. The low band antenna has a volume of1.3×0.4×14.5 =7.54 cm .Itshould be noted that the proposed volume is the total volume of 1.3. A Novel Resonant Wideband Passive Antenna. Anovel the antenna because it does not require an additional ground antenna technology has been developed to solve the problem plane or matching circuits. The high band antenna has a of the urgent need for universal LTE devices. eTh new technology can cover all the possible LTE spectrum bands volume of 1.2 × 0.4 × 5.9 = 2.832 cm .Likethe lowband using only two antennas with bandwidths of 73% and 85%, antenna, theproposedvolumeofthe high band antennais respectively, without using any matching or tuning circuits. the total volume of the antenna. As Figure 2(a) shows, the eTh rfi st antennaiscoveringthe lowbandLTE spectrum return loss of the low band antenna is lower than−8dB over starting from 698 MHz up to 1.51 GHz which includes LTE most of thebands having amaximum valueof −5.5 dB. For The Scientific World Journal 3 −2 −5 −4 −6 −10 −8 −15 −10 −12 −20 −14 −25 −16 1.52 1.98 2.43 2.89 3.34 3.80 0.70 0.90 1.10 1.31 1.51 Frequency (GHz) Frequency (GHz) Calculated Calculated Measured Measured (a) (b) Figure 2: Return loss (S11) of (a) the low band antenna and (b) the high band antenna. 100 100 90 90 80 80 70 70 60 60 50 50 40 40 0.70 0.90 1.10 1.31 1.51 1.52 1.98 2.43 2.89 3.34 3.80 Frequency (GHz) Frequency (GHz) (a) (b) Figure 3: Efficiency of (a) the low band antenna and (b) the high band antenna. thehighbandantenna, Figure 2(b) shows that the return the frequency band from 1.71 GHz to 3.8 GHz which is loss is also lower than −8 dB all over the band. eTh total 75.8%. The total efficiencies shown in Figures 7(a) and efficiency shown in Figures 3(a) and 3(b) demonstrates 80% 7(b) demonstrate almost 70% and 80% average efficiencies and 90% average efficiencies of the low band and high band of the reduced size versions of low band and high band antennas, respectively. The gain of the low band antenna is antennas,respectively. eTh gain of thereduced size version shown in Figure 4(a) as a function of the frequency, while of the low band antenna is higher than 1 dBi over most thehighbandantenna’s gain is shownin Figure 4(b).The of thebands as shownin Figure 8(a), while the high band Radiation patterns of the low band and high band antennas antenna’s gain is more than 2 dBi as shown in Figure 8(b).The are demonstrated in Figure 5(a) at 900 MHz and Figure 5(b) radiation patterns of the low band and high band antennas at 2.3 GHz, respectively, at phi= 0and phi= 90. are presented in Figure 9(a) at 750 MHz and Figure 9(b) at 2.7 GHz, respectively. 2.2. Reduced Size Version of the Low Band and High Band Antennas. eTh reducedsizeversion of thelow band antenna 3. MIMO Diversity Configuration has a total volume of 0.4 × 0.4 × 15.6 = 2.496 cm , while Multiples of low band and high band antennas can be used for that of the high band antenna has a total volume of 0.4 × LTE MIMO diversity coverage in laptops, tablets, and smart 0.4 × 5.9 = 0.944 cm .As Figure 6(a) shows, the return phones. Each of these different situations has been studied loss of the low band antenna is lower than −5dB almost all and will be presented. over the frequency band from 698 MHz to 1.51 GHz which is 73% bandwidth. For the reduced size version of the high band antenna, Figure 6(b) showsthatmostofthe calculated 3.1. MIMO Configurations for Smart Phones. The new wide- andmeasuredreturnlossesislower than −5dB all over band antenna can be customized for implementation in smart Return loss (S11 dB) Efficiency (%) Efficiency (%) Return loss (S11 dB) 4 The Scientific World Journal 4 5 4.5 3.5 3.5 2.5 2.5 1.5 1.5 0.5 0.5 0 0 0.70 0.90 1.10 1.31 1.51 1.52 1.98 2.43 2.89 3.34 3.80 Frequency (GHz) Frequency (GHz) (a) (b) Figure 4: Gain of (a) the low band antenna and (b) the high band antenna. 0 0 ∘ ∘ ∘ ∘ −30 30 −30 30 −10 −10 ∘ ∘ ∘ ∘ −20 60 −20 60 −60 −60 −30 −30 ∘ ∘ ∘ 90 90 −90 −90 −30 −30 −20 −20 ∘ 120 ∘ 120 −120 −120 −10 −10 ∘ ∘ 150 150 −150 −150 ∘ ∘ 180 180 E total @ 𝜙= 0 E total @ 𝜙= 0 E total @ 𝜙= 90 E total @ 𝜙= 90 (a) (b) Figure 5: Radiation patterns of (a) the low band antenna at 900 MHz and (b) the high band antenna at 2.3 GHz. −5 −10 −5 −15 −20 −10 −25 −30 −15 −35 −40 −45 −20 1.71 2.13 2.55 2.96 3.38 3.80 0.70 0.80 0.90 1.00 1.10 1.21 1.31 1.41 1.51 Frequency (GHz) Frequency (GHz) Calculated Calculated Measured Measured (a) (b) Figure 6: Return loss of (a) the reduced size version of the low band antenna and (b) the reduced size version of the high band antenna. Gain (dB) S11 (dB) Gain (dB) S11 (dB) The Scientific World Journal 5 40 40 20 20 10 10 0.70 0.80 0.90 1.00 1.10 1.21 1.31 1.41 1.51 1.71 2.13 2.55 2.96 3.38 3.80 Frequency (GHz) Frequency (GHz) (a) (b) Figure 7: Efficiency of (a) the reduced size version of the low band antenna and (b) the reduced size version of the high band antenna. −1 −1 −2 −2 −3 −3 0.70 0.80 0.90 1.00 1.10 1.21 1.31 1.41 1.51 1.71 2.13 2.55 2.96 3.38 3.80 Frequency (GHz) Frequency (GHz) (a) (b) Figure 8: Gain of (a) the reduced size version of the low band antenna and (b) the reduced size version of the high band antenna. phones. It can be bent or wrapped as an “L” shape to tfi in the thefactthatthe phoneisactingasanisolating medium which void around the chassis of the handset. This customization guarantees lower coupling between the primary and diversity has been studied numerically and experimentally for 2× antennas. eTh correlation coefficient between primary and 2 MIMO of the reduced size low band and high band diversity low band antennas was lower than 0.55 as shown antennas. As shown in the schematic in Figure 10,theprimary in Figure 11(b). On the other hand, the measured isolation reducedsizelow band antennaismarkedasnumber“1” between the primary and diversity high band antennas was and the diversity antenna is marked as number “2.” The lower than −30 dB as shown in Figure 12(a). This is an primary and diversity antennas are wrapped in “L-” shaped expected isolation result due to the perpendicular position configurations. A 2×2 MIMO congfi uration of the reduced of theprimary antennarelativetothe diversityantenna size high band antenna has been also tested numerically and which have been proved to be the best isolation technique experimentally and their relative positions to each other have in such a small available space inside handsets [9]. The been optimized for the implementation in smart phones. eTh perpendicular relative position also has a positive eeff ct on relative positions of the primary and diversity antennas are the correlation coecffi ient. As shown in Figure 12(b),the shown in Figure 10. eTh primary reduced size high band maximum correlation value does not exceed 0.1 and most of antenna is marked as number “3” and the diversity antenna thevaluesare lowerthan0.01. is marked as number “4.” The urgent demand for universal LTE smart phones The measured isolation between the primary and diver- requires an antenna solution that is able to cover most of the sity low band antennas has been investigated. As shown in LTEbands forglobalroaming.Bycombining thetwo new Figure 11(a), acceptable isolation values, lower than −10 dB, wideband antennas together in one device, it will fulfill that are obtained from isolation measurements (S21) in free space. need as demonstrated in Figure 10.Thehighbandantennas The measured isolation on the chassis of smart phone was marked as numbers 3 and 4 are located in a higher plane much better than the isolation in free space, as it has an above the low band antennas by 1 mm. The biggest concern average of −15 dB over most of the bands. This is due to in this case is the isolation values between the low band and Efficiency (%) Gain (dB) Efficiency (%) Gain (dB) 6 The Scientific World Journal ∘ ∘ −30 30 −10 −20 60 −60 −30 ∘ 4 −90 −30 −20 −120 −10 −150 E total @ 𝜙= 0 Figure 10: eTh schematic diagram of MIMO wideband antenna E total @ 𝜙= 90 solution for LTE smart phones. (a) ∘ ∘ −30 30 −10 the same time, the coupling eeff ct is significantly reduced as a result of antennas perpendicular relative positions [9]. −20 60 −60 u Th s, this position will have a positive eeff ct on the calculated −30 correlation coefficient between the two of the reduced size low band antennas, as shown in Figure 14(a).Themaximum correlation coefficient value is lower than 0.025. The isolation ∘ ∘ −90 between the primary and the diversity antennas has been measured on a laptop and in free space keeping the same −30 relative positions and distance between them. The measured −20 ∘ isolation on the laptop gets improved over most of the bands ∘ 120 −120 as demonstrated in Figure 14(b). eTh previous experiments −10 are repeated for2×2 MIMO of the reduced size high band ∘ antennas perpendicular to each other and 10 cm apart. In −150 terms of wavelength, the distance between the primary and the diversity antennas is larger in the high frequency band than in the low frequency band. This is reflected in a positive E total @ 𝜙= 0 way on the correlation coefficient values which are lower E total @ 𝜙= 90 than 0.001 as shown in Figure 15(a).Alsoalowerisolation (b) than −30 dB in free space and on the laptop is shown in Figure 15(b). Figure 9: Radiation patterns of (a) the reduced size version of the low band antenna at 750 MHz and (b) the reduced size version of the high band antenna at 2.7 MHz. 4. Conclusion A novel very wideband MIMO antenna solution was devel- high band antennas. eTh isolation is calculated for this case oped, capable of covering 39 LTE bands besides 2G and and the results are mostly lower than−20 dB for low band and 3G. This provided device manufacturers with a new antenna high band frequency spectrums as shown in Figures 13(a) and technology to fulfill the urgent need for universal LTE smart 13(b),respectively. phones, tablet computers, laptops, and notebooks. 3.2. MIMO Configurations on Laptops and Tablets. For2× 2 MIMO diversity, a primary antenna and a diversity antenna Conflict of Interests canbeplaced10cmapart andperpendicular to each other inside laptops and tablets. Although primary and diversity eTh authors declare that there is no conflict of interests antennas are operating over the same frequency band at regarding the publication of this paper. The Scientific World Journal 7 1.0 0.9 −5 0.8 −10 0.7 −15 0.6 −20 0.5 0.4 −25 0.3 −30 0.2 −35 0.1 −40 0.0 0.70 0.80 0.90 1.00 1.10 1.21 1.31 1.41 1.51 0.70 0.80 0.90 1.00 1.10 1.21 1.31 1.41 1.51 Frequency (GHz) Frequency (GHz) Free space Smart phone (b) (a) Figure 11: (a) Measured isolation (S21) and (b) correlation coefficient between primary and diversity MIMO low band antennas. 0 0.10 0.09 −10 0.08 0.07 −20 0.06 −30 0.05 0.04 −40 0.03 0.02 −50 0.01 −60 0.00 1.71 2.13 2.55 2.96 3.38 3.80 1.71 2.13 2.55 2.96 3.38 3.80 Frequency (GHz) Frequency (GHz) Free space Smart phone (a) (b) Figure 12: (a) Measured isolation (S21) and (b) correlation coefficient between primary and diversity MIMO high band antennas. −5 −10 −10 −15 −20 −20 −30 −25 −30 −40 −35 −50 −40 −60 −45 1.7 2.1 2.5 3.0 3.4 3.8 0.70 0.80 0.90 1.00 1.10 1.21 1.31 1.41 1.51 Frequency (GHz) Frequency (GHz) S13 S23 S13 S23 S14 S24 S14 S24 (a) (b) Figure 13: Isolation between each of low band and high band antennas in (a) the low frequency band and (b) the high frequency band on smart phones. S21 (dB) Isolation (dB) S21 (dB) Correlation coefficient Correlation coefficient Isolation (dB) 8 The Scientific World Journal 0.025 0 −5 0.020 −10 −15 0.015 −20 −25 0.010 −30 −35 0.005 −40 −45 0.000 0.70 0.80 0.90 1.00 1.10 1.21 1.31 1.41 1.51 0.70 0.80 0.90 1.00 1.10 1.21 1.31 1.41 1.51 Frequency (GHz) Frequency (GHz) Free space Laptop (a) (b) Figure 14: (a) Correlation coefficient and (b) measured isolation between primary and diversity MIMO low band antennas perpendicular to each other and 10 cm apart. 0.0020 −10 0.0015 −20 0.0010 −30 −40 0.0005 −50 0.0000 −60 1.71 2.13 2.55 2.96 3.38 3.80 1.71 2.13 2.55 2.96 3.38 3.80 Frequency (GHz) Frequency (GHz) Free space Laptop (a) (b) Figure 15: (a) Correlation coefficient and (b) measured isolation between primary and diversity MIMO high band antennas perpendicular to each other and 10 cm apart. Acknowledgments 196/38-fragmented-frequencies-confuse-scale-benefits-of-LTE -terminals.html. eTh authors would like to thank Mahetab Salama and Lamiaa [4] P. Vainikainen, J. Holopainen, C. Icheln et al., “More than 20 Nail for their great eo ff rt in preparing this paper. antenna elements in future mobile phones, threat or oppor- tunity?” in Proceedings of the 3rd European Conference on Antennas and Propagation (EuCAP ’09), pp. 2940–2943, Berlin, References Germany, March 2009. [1] “LTE: the future of mobile broadband technology,” Verizon [5] B.-N. Kim, S.-O. Park, J.-K. Oh, and G.-Y. Koo, “Wideband Wireless. built-in antenna with new crossed C-shaped coupling feed for future mobile phone application,” IEEE Antennas and Wireless [2] “The wireless intelligence website,” 2012, http://www.wireless- Propagation Letters, vol. 9, pp. 572–575, 2010. intelligence.com/analysis/2011/12/global-lte-network-forecasts -and-assumptions-one-year-on/. [6] “Mobile development & design website,” 2012, http://mobile- [3] “The global telecommunications business website,” 2012, http:// devdesign.com/tutorials/4g-devices-demand-active-antenna- www.globaltelecomsbusiness.com/Article/2948514/Sectors/25- solutions-0216/?cid=ed. Correlation coefficient Correlation coefficient S21 (dB) S21 (dB) The Scientific World Journal 9 [7] M. Sanad and N. Hassan, “A 470 to 960 MHz resonant antenna: covering uhf mobile TV and CDMA/GSM without tuning circuits,” Microwave Journal,vol.53, no.11, pp.56–73,2010. [8] M. Sanad and N. Hassan, “Dual antenna configuration for multi-standard multifunction handsets and portable comput- ers,” in Proceedings of the 3rd European Wireless Technology Conference (EuWiT ’10), pp. 173–176, September 2010. [9] M. Sanad and N. Hassan, “Low-interference dual resonant antenna configurations for multistandard multifunction hand- sets and portable computers,” International Journal of Antennas and Propagation,vol.2012, ArticleID407973, 8pages,2012. 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Novel Wideband MIMO Antennas That Can Cover the Whole LTE Spectrum in Handsets and Portable Computers

The Scientific World Journal , Volume 2014 – Jan 16, 2014

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Publisher
Hindawi Publishing Corporation
Copyright
Copyright © 2014 Mohamed Sanad and Noha Hassan. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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2356-6140
eISSN
1537-744X
DOI
10.1155/2014/694805
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Abstract

Hindawi Publishing Corporation e Scientific World Journal Volume 2014, Article ID 694805, 9 pages http://dx.doi.org/10.1155/2014/694805 Research Article Novel Wideband MIMO Antennas That Can Cover the Whole LTE Spectrum in Handsets and Portable Computers 1 2 Mohamed Sanad and Noha Hassan AmantAntennas, Lot13/C, Second Industrial Zone,6October City,Giza12451,Egypt Faculty of Engineering, Cairo University, Giza, Egypt Correspondence should be addressed to Mohamed Sanad; msanad@amantantennas.com Received 25 August 2013; Accepted 24 October 2013; Published 16 January 2014 Academic Editors: Y. C. Chiang and J. Dauwels Copyright © 2014 M. Sanad and N. Hassan. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A dual resonant antenna configuration is developed for multistandard multifunction mobile handsets and portable computers. Only two wideband resonant antennas can cover most of the LTE spectrums in portable communication equipment. The bandwidth that can be covered by each antenna exceeds 70% without using any matching or tuning circuits, with efficiencies that reach 80%. u Th s, a dual configuration of them is capable of covering up to 39 LTE (4G) bands besides the existing 2G and 3G bands. 2×2 MIMO configurations have been also developed for the two wideband antennas with a maximum isolation and a minimum correlation coefficient between the primary and the diversity antennas. 1. Introduction 1.1. Conventional Antenna Challenges in LTE. The antenna is becoming an increasingly critical component for LTE Customers’ increasing expectations for speed, bandwidth, device vendors. It is possible that future terminal devices and global access are driving the evolution of wireless broad- will have more than 20 antennas to cover all the important band technology. Customers want more information such as wireless applications [4]. In addition, the industry is painfully business, consumer applications, and entertainment available aware of the issues that surround implementing LTE in small through their mobile devices, but with greater speeds [1]. mobile devices with already limited space and extremely LTE represents the next big step towards the 4th generation high performance expectations. Due to this trend, wideband (4G) of radio technologies which is expected to increase the antenna coverage is a hot issue that has to be addressed [5]. capacity and the speed of mobile telephone networks. These Device makers are ndin fi g it difficult to decide which bands to expectations put a significant burden on device performance. prioritize as chipsets and handsets are developed. The priority eTh lack of spectrum harmonization represents a key chal- wouldbefor the800MHzband. Most of theinvestments lenge for the emerging LTE ecosystem, potentially preventing has been directed towards that band because it is the band vendors from delivering globally compatible LTE products that two-thirds of current LTE users occupy, largely driven such as devices and chipsets [2]. Spectrum fragmentation by the U.S. network roll outs of Verizon Wireless and AT&T has the potential to hinder global LTE roaming if device [3]. This low frequency band means larger antennas in terms manufacturers are required to include support for many of size, which is a challenging issue, keeping in mind the disparate frequencies in their devices. Yet, in fragmented limited size of LTE devices. The urgent demand for wideband regional markets such as Europe, LTE roaming is some way LTE coverage represents a serious challenge facing antenna off as operators will be providing LTE in different bands and designers. Adapting the conventional antenna technology to the devices will need to be able to seamlessly switch between serve the wideband demand was not a much of a success, thefrequency bandsusedfor LTEinaddition to the2Gand leading to a definitive belief that passive antennas have 3G networks [3]. reached their limits [6]. uTh s, theactivetuneableantenna 2 The Scientific World Journal L band numbers5,6,8,11, 12,13, 14,17, 18,19, 20,21, 26, D D D D 27, 28, 29, and 44. eTh second one is covering the high D D 2 3 4 7 1 8 band portion of the LTE spectrum starting from 1.52 GHz to 3.8 GHz corresponding to LTE band numbers 1, 2, 3, 4, 7, 9, 10,22, 23,24, 25,33, 34,35, 36,37, 38,39, 40,41, 42, W 2 and 43. This means that a total number of 39 LTE bands can be covered beside the 2G and 3G frequency bands. eTh D D 5 6 new antenna can be implemented in smart phone handsets, tablets, laptops, and notebooks. It consists of two narrow printed metallic arms connected together by a shorting Short arm metallic strip. eTh two arms may be parallel to each other or may have any angle between them. eTh two arms can be shaped in different ways in order to optimize the antenna Shorting strip performance. As shown in Figure 1, each arm has a set of slots Long arm Slots having different configurations. These slots can be circular, rectangular, square, triangular, or other shapes. eTh arm Figure 1: Geometry of the new wideband antenna. lengths of the new antenna, especially the length of the short arm, are the main parameters that determine the operating frequency of the antenna. The bandwidth, the peak gain, and approach has been adopted to fulfil the market need for the efficiency of the antenna are mainly determined by the world LTE devices, trading the passive antenna simplicity widths of the two arms, the angle between them, the thickness with active antenna complexity. of the antenna, and the congfi urations of the slots, which are all optimized together in order to enhance the antenna 1.2. Disadvantages of Active Antennas and Extended Grounds performance, especially the bandwidth. This geometry can be Planes. Passive antennas have various advantages over the scaled and optimized for any application to successfully cover active tuneable antennas.First of all, thepassive antennadoes any frequency band [7, 8]. nothavetobesupported with RF controllingcircuit to do thejob as theactiveone,soitwillsavealargespace required 2. Numerical and Experimental Results of inside the handset to tfi both the antenna and the RF circuit. This is not the only problem of the RF circuit, as additional the New Antenna circuit components are connected to the antenna; it will suffer Two versions of the new LTE antenna have been designed, from impedance mismatch. In this situation a severe decrease manufactured, and tested. Calculated and measured return in the efficiency of the antenna will lead to a lower speed losses will be presented in addition to the calculated gain, of data transfer and a higher number of dropped calls. Also, efficiency, and radiation patterns. The first antenna version theactiveantenna is powerconsuming,causing asignicfi ant can cover a frequency band from 698 MHz up to 1.51 GHz and decrease in the battery lifetime. us, Th it will be a problem it will be referred to as “the low band antenna.” To cover the for power hungry, smart handheld devices. Last but not least, high band portion of the LTE spectrum, a second version of theactiveantenna seemstohavebandlimitations too, as the antenna has been designed and manufactured by scaling the maximum number of bands that commercial LTE active and optimizing the geometry shown in Figure 1.Theantenna antennas can support is 13 bands only out of 39 potential is operating all over the high frequency band 1.52–3.8 GHz LTE bands [6]. On the other hand, current handset antenna anditwillbereferredtoas“thehighbandantenna.” A technologies are still tied with the extended ground plane’s reduced size version of these wideband antennas can be dilemma. As the antenna is not just the module that tfi s under developed and customized for smaller LTE devices. Together, the speaker, however, it includes a large PCB ground plane. thetwo reducedsizeantennasare capableofcovering38LTE A minimum limit size of the ground plane is required for bands with slightly lower but still acceptable efficiencies. eTh the antenna to have an acceptable performance. u Th s, adding reducedsizeversionsofthe lowbandand high band antennas an extravolume counted on the total size of the antenna. As will be also demonstrated. the ground plane is a part of the antenna structure, then, the hand grip on the phone will cause detuning of the antenna operating frequency causing a poor efficiency. 2.1. eTh Low Band and High Band Antennas. The low band antenna has a volume of1.3×0.4×14.5 =7.54 cm .Itshould be noted that the proposed volume is the total volume of 1.3. A Novel Resonant Wideband Passive Antenna. Anovel the antenna because it does not require an additional ground antenna technology has been developed to solve the problem plane or matching circuits. The high band antenna has a of the urgent need for universal LTE devices. eTh new technology can cover all the possible LTE spectrum bands volume of 1.2 × 0.4 × 5.9 = 2.832 cm .Likethe lowband using only two antennas with bandwidths of 73% and 85%, antenna, theproposedvolumeofthe high band antennais respectively, without using any matching or tuning circuits. the total volume of the antenna. As Figure 2(a) shows, the eTh rfi st antennaiscoveringthe lowbandLTE spectrum return loss of the low band antenna is lower than−8dB over starting from 698 MHz up to 1.51 GHz which includes LTE most of thebands having amaximum valueof −5.5 dB. For The Scientific World Journal 3 −2 −5 −4 −6 −10 −8 −15 −10 −12 −20 −14 −25 −16 1.52 1.98 2.43 2.89 3.34 3.80 0.70 0.90 1.10 1.31 1.51 Frequency (GHz) Frequency (GHz) Calculated Calculated Measured Measured (a) (b) Figure 2: Return loss (S11) of (a) the low band antenna and (b) the high band antenna. 100 100 90 90 80 80 70 70 60 60 50 50 40 40 0.70 0.90 1.10 1.31 1.51 1.52 1.98 2.43 2.89 3.34 3.80 Frequency (GHz) Frequency (GHz) (a) (b) Figure 3: Efficiency of (a) the low band antenna and (b) the high band antenna. thehighbandantenna, Figure 2(b) shows that the return the frequency band from 1.71 GHz to 3.8 GHz which is loss is also lower than −8 dB all over the band. eTh total 75.8%. The total efficiencies shown in Figures 7(a) and efficiency shown in Figures 3(a) and 3(b) demonstrates 80% 7(b) demonstrate almost 70% and 80% average efficiencies and 90% average efficiencies of the low band and high band of the reduced size versions of low band and high band antennas, respectively. The gain of the low band antenna is antennas,respectively. eTh gain of thereduced size version shown in Figure 4(a) as a function of the frequency, while of the low band antenna is higher than 1 dBi over most thehighbandantenna’s gain is shownin Figure 4(b).The of thebands as shownin Figure 8(a), while the high band Radiation patterns of the low band and high band antennas antenna’s gain is more than 2 dBi as shown in Figure 8(b).The are demonstrated in Figure 5(a) at 900 MHz and Figure 5(b) radiation patterns of the low band and high band antennas at 2.3 GHz, respectively, at phi= 0and phi= 90. are presented in Figure 9(a) at 750 MHz and Figure 9(b) at 2.7 GHz, respectively. 2.2. Reduced Size Version of the Low Band and High Band Antennas. eTh reducedsizeversion of thelow band antenna 3. MIMO Diversity Configuration has a total volume of 0.4 × 0.4 × 15.6 = 2.496 cm , while Multiples of low band and high band antennas can be used for that of the high band antenna has a total volume of 0.4 × LTE MIMO diversity coverage in laptops, tablets, and smart 0.4 × 5.9 = 0.944 cm .As Figure 6(a) shows, the return phones. Each of these different situations has been studied loss of the low band antenna is lower than −5dB almost all and will be presented. over the frequency band from 698 MHz to 1.51 GHz which is 73% bandwidth. For the reduced size version of the high band antenna, Figure 6(b) showsthatmostofthe calculated 3.1. MIMO Configurations for Smart Phones. The new wide- andmeasuredreturnlossesislower than −5dB all over band antenna can be customized for implementation in smart Return loss (S11 dB) Efficiency (%) Efficiency (%) Return loss (S11 dB) 4 The Scientific World Journal 4 5 4.5 3.5 3.5 2.5 2.5 1.5 1.5 0.5 0.5 0 0 0.70 0.90 1.10 1.31 1.51 1.52 1.98 2.43 2.89 3.34 3.80 Frequency (GHz) Frequency (GHz) (a) (b) Figure 4: Gain of (a) the low band antenna and (b) the high band antenna. 0 0 ∘ ∘ ∘ ∘ −30 30 −30 30 −10 −10 ∘ ∘ ∘ ∘ −20 60 −20 60 −60 −60 −30 −30 ∘ ∘ ∘ 90 90 −90 −90 −30 −30 −20 −20 ∘ 120 ∘ 120 −120 −120 −10 −10 ∘ ∘ 150 150 −150 −150 ∘ ∘ 180 180 E total @ 𝜙= 0 E total @ 𝜙= 0 E total @ 𝜙= 90 E total @ 𝜙= 90 (a) (b) Figure 5: Radiation patterns of (a) the low band antenna at 900 MHz and (b) the high band antenna at 2.3 GHz. −5 −10 −5 −15 −20 −10 −25 −30 −15 −35 −40 −45 −20 1.71 2.13 2.55 2.96 3.38 3.80 0.70 0.80 0.90 1.00 1.10 1.21 1.31 1.41 1.51 Frequency (GHz) Frequency (GHz) Calculated Calculated Measured Measured (a) (b) Figure 6: Return loss of (a) the reduced size version of the low band antenna and (b) the reduced size version of the high band antenna. Gain (dB) S11 (dB) Gain (dB) S11 (dB) The Scientific World Journal 5 40 40 20 20 10 10 0.70 0.80 0.90 1.00 1.10 1.21 1.31 1.41 1.51 1.71 2.13 2.55 2.96 3.38 3.80 Frequency (GHz) Frequency (GHz) (a) (b) Figure 7: Efficiency of (a) the reduced size version of the low band antenna and (b) the reduced size version of the high band antenna. −1 −1 −2 −2 −3 −3 0.70 0.80 0.90 1.00 1.10 1.21 1.31 1.41 1.51 1.71 2.13 2.55 2.96 3.38 3.80 Frequency (GHz) Frequency (GHz) (a) (b) Figure 8: Gain of (a) the reduced size version of the low band antenna and (b) the reduced size version of the high band antenna. phones. It can be bent or wrapped as an “L” shape to tfi in the thefactthatthe phoneisactingasanisolating medium which void around the chassis of the handset. This customization guarantees lower coupling between the primary and diversity has been studied numerically and experimentally for 2× antennas. eTh correlation coefficient between primary and 2 MIMO of the reduced size low band and high band diversity low band antennas was lower than 0.55 as shown antennas. As shown in the schematic in Figure 10,theprimary in Figure 11(b). On the other hand, the measured isolation reducedsizelow band antennaismarkedasnumber“1” between the primary and diversity high band antennas was and the diversity antenna is marked as number “2.” The lower than −30 dB as shown in Figure 12(a). This is an primary and diversity antennas are wrapped in “L-” shaped expected isolation result due to the perpendicular position configurations. A 2×2 MIMO congfi uration of the reduced of theprimary antennarelativetothe diversityantenna size high band antenna has been also tested numerically and which have been proved to be the best isolation technique experimentally and their relative positions to each other have in such a small available space inside handsets [9]. The been optimized for the implementation in smart phones. eTh perpendicular relative position also has a positive eeff ct on relative positions of the primary and diversity antennas are the correlation coecffi ient. As shown in Figure 12(b),the shown in Figure 10. eTh primary reduced size high band maximum correlation value does not exceed 0.1 and most of antenna is marked as number “3” and the diversity antenna thevaluesare lowerthan0.01. is marked as number “4.” The urgent demand for universal LTE smart phones The measured isolation between the primary and diver- requires an antenna solution that is able to cover most of the sity low band antennas has been investigated. As shown in LTEbands forglobalroaming.Bycombining thetwo new Figure 11(a), acceptable isolation values, lower than −10 dB, wideband antennas together in one device, it will fulfill that are obtained from isolation measurements (S21) in free space. need as demonstrated in Figure 10.Thehighbandantennas The measured isolation on the chassis of smart phone was marked as numbers 3 and 4 are located in a higher plane much better than the isolation in free space, as it has an above the low band antennas by 1 mm. The biggest concern average of −15 dB over most of the bands. This is due to in this case is the isolation values between the low band and Efficiency (%) Gain (dB) Efficiency (%) Gain (dB) 6 The Scientific World Journal ∘ ∘ −30 30 −10 −20 60 −60 −30 ∘ 4 −90 −30 −20 −120 −10 −150 E total @ 𝜙= 0 Figure 10: eTh schematic diagram of MIMO wideband antenna E total @ 𝜙= 90 solution for LTE smart phones. (a) ∘ ∘ −30 30 −10 the same time, the coupling eeff ct is significantly reduced as a result of antennas perpendicular relative positions [9]. −20 60 −60 u Th s, this position will have a positive eeff ct on the calculated −30 correlation coefficient between the two of the reduced size low band antennas, as shown in Figure 14(a).Themaximum correlation coefficient value is lower than 0.025. The isolation ∘ ∘ −90 between the primary and the diversity antennas has been measured on a laptop and in free space keeping the same −30 relative positions and distance between them. The measured −20 ∘ isolation on the laptop gets improved over most of the bands ∘ 120 −120 as demonstrated in Figure 14(b). eTh previous experiments −10 are repeated for2×2 MIMO of the reduced size high band ∘ antennas perpendicular to each other and 10 cm apart. In −150 terms of wavelength, the distance between the primary and the diversity antennas is larger in the high frequency band than in the low frequency band. This is reflected in a positive E total @ 𝜙= 0 way on the correlation coefficient values which are lower E total @ 𝜙= 90 than 0.001 as shown in Figure 15(a).Alsoalowerisolation (b) than −30 dB in free space and on the laptop is shown in Figure 15(b). Figure 9: Radiation patterns of (a) the reduced size version of the low band antenna at 750 MHz and (b) the reduced size version of the high band antenna at 2.7 MHz. 4. Conclusion A novel very wideband MIMO antenna solution was devel- high band antennas. eTh isolation is calculated for this case oped, capable of covering 39 LTE bands besides 2G and and the results are mostly lower than−20 dB for low band and 3G. This provided device manufacturers with a new antenna high band frequency spectrums as shown in Figures 13(a) and technology to fulfill the urgent need for universal LTE smart 13(b),respectively. phones, tablet computers, laptops, and notebooks. 3.2. MIMO Configurations on Laptops and Tablets. For2× 2 MIMO diversity, a primary antenna and a diversity antenna Conflict of Interests canbeplaced10cmapart andperpendicular to each other inside laptops and tablets. Although primary and diversity eTh authors declare that there is no conflict of interests antennas are operating over the same frequency band at regarding the publication of this paper. The Scientific World Journal 7 1.0 0.9 −5 0.8 −10 0.7 −15 0.6 −20 0.5 0.4 −25 0.3 −30 0.2 −35 0.1 −40 0.0 0.70 0.80 0.90 1.00 1.10 1.21 1.31 1.41 1.51 0.70 0.80 0.90 1.00 1.10 1.21 1.31 1.41 1.51 Frequency (GHz) Frequency (GHz) Free space Smart phone (b) (a) Figure 11: (a) Measured isolation (S21) and (b) correlation coefficient between primary and diversity MIMO low band antennas. 0 0.10 0.09 −10 0.08 0.07 −20 0.06 −30 0.05 0.04 −40 0.03 0.02 −50 0.01 −60 0.00 1.71 2.13 2.55 2.96 3.38 3.80 1.71 2.13 2.55 2.96 3.38 3.80 Frequency (GHz) Frequency (GHz) Free space Smart phone (a) (b) Figure 12: (a) Measured isolation (S21) and (b) correlation coefficient between primary and diversity MIMO high band antennas. −5 −10 −10 −15 −20 −20 −30 −25 −30 −40 −35 −50 −40 −60 −45 1.7 2.1 2.5 3.0 3.4 3.8 0.70 0.80 0.90 1.00 1.10 1.21 1.31 1.41 1.51 Frequency (GHz) Frequency (GHz) S13 S23 S13 S23 S14 S24 S14 S24 (a) (b) Figure 13: Isolation between each of low band and high band antennas in (a) the low frequency band and (b) the high frequency band on smart phones. S21 (dB) Isolation (dB) S21 (dB) Correlation coefficient Correlation coefficient Isolation (dB) 8 The Scientific World Journal 0.025 0 −5 0.020 −10 −15 0.015 −20 −25 0.010 −30 −35 0.005 −40 −45 0.000 0.70 0.80 0.90 1.00 1.10 1.21 1.31 1.41 1.51 0.70 0.80 0.90 1.00 1.10 1.21 1.31 1.41 1.51 Frequency (GHz) Frequency (GHz) Free space Laptop (a) (b) Figure 14: (a) Correlation coefficient and (b) measured isolation between primary and diversity MIMO low band antennas perpendicular to each other and 10 cm apart. 0.0020 −10 0.0015 −20 0.0010 −30 −40 0.0005 −50 0.0000 −60 1.71 2.13 2.55 2.96 3.38 3.80 1.71 2.13 2.55 2.96 3.38 3.80 Frequency (GHz) Frequency (GHz) Free space Laptop (a) (b) Figure 15: (a) Correlation coefficient and (b) measured isolation between primary and diversity MIMO high band antennas perpendicular to each other and 10 cm apart. Acknowledgments 196/38-fragmented-frequencies-confuse-scale-benefits-of-LTE -terminals.html. eTh authors would like to thank Mahetab Salama and Lamiaa [4] P. Vainikainen, J. Holopainen, C. Icheln et al., “More than 20 Nail for their great eo ff rt in preparing this paper. antenna elements in future mobile phones, threat or oppor- tunity?” in Proceedings of the 3rd European Conference on Antennas and Propagation (EuCAP ’09), pp. 2940–2943, Berlin, References Germany, March 2009. [1] “LTE: the future of mobile broadband technology,” Verizon [5] B.-N. Kim, S.-O. Park, J.-K. Oh, and G.-Y. Koo, “Wideband Wireless. built-in antenna with new crossed C-shaped coupling feed for future mobile phone application,” IEEE Antennas and Wireless [2] “The wireless intelligence website,” 2012, http://www.wireless- Propagation Letters, vol. 9, pp. 572–575, 2010. intelligence.com/analysis/2011/12/global-lte-network-forecasts -and-assumptions-one-year-on/. [6] “Mobile development & design website,” 2012, http://mobile- [3] “The global telecommunications business website,” 2012, http:// devdesign.com/tutorials/4g-devices-demand-active-antenna- www.globaltelecomsbusiness.com/Article/2948514/Sectors/25- solutions-0216/?cid=ed. Correlation coefficient Correlation coefficient S21 (dB) S21 (dB) The Scientific World Journal 9 [7] M. Sanad and N. Hassan, “A 470 to 960 MHz resonant antenna: covering uhf mobile TV and CDMA/GSM without tuning circuits,” Microwave Journal,vol.53, no.11, pp.56–73,2010. [8] M. Sanad and N. Hassan, “Dual antenna configuration for multi-standard multifunction handsets and portable comput- ers,” in Proceedings of the 3rd European Wireless Technology Conference (EuWiT ’10), pp. 173–176, September 2010. [9] M. Sanad and N. Hassan, “Low-interference dual resonant antenna configurations for multistandard multifunction hand- sets and portable computers,” International Journal of Antennas and Propagation,vol.2012, ArticleID407973, 8pages,2012. 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