No Frequency Reuse: Wearable Steerable MIMO Microstrip Antenna Array for Mobile Ad Hoc Applications

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1 British Jurnal f Applied Science & Technlgy 4(17): , 014 SCIENCEDOMAIN internatinal N Frequency Reuse: Wearable Steerable MIMO Micrstrip Antenna Array fr Mbile Ad Hc Applicatins Taha A. Elwi1,,3*, Sa ad Al-Frieh1, Mhammed Al-Bawi1 and Mhammed Nri1 1 Department f Cmmunicatin, Al-Mammn University Cllage, Baghdad, Iraq. Department f Electrnics and Cmmunicatin, University f Baghdad, Baghdad, Iraq. 3 Institute f Mathematical Research INSPEM, University Putra Malaysia UPM, Serdang , Selangr, Malaysia. Authrs cntributins: This wrk was carried ut in cllabratin between all authrs. Authr Taha designed the antenna design and supervised the numerical simulatins. The first draft f the manuscript wrte by the secnd and the third authrs. Authr Nri managed literature searches. All authrs cllabrated t finalize the manuscript. All authrs read and apprved the final manuscript. th Original Research Article Received 8 December 013 th Accepted 17 February 014 th Published 8 April 014 ABSTRACT Aim: The principle f eliminating the frequency reuse in the mbile Ad Hc system amng the sectrs f the unit cell using Multi Inputs Multi Outputs (MIMO) antenna array is investigated in this paper. Antenna Design: The size f the prpsed antenna array is cm t btain a bandwidth arund 1 GHz. The single antenna element is cnstructed frm sub-patches that are cnnected with feeding netwrk thrugh pin dides, as switches, that are munted n an FR-4 substrate. Antenna Perfrmance: The antenna elements are characterized frm 0.8 GHz t GHz in terms f S-parameters and radiatin patterns with different switching OFF/ON categries. Methdlgy: A numerical investigatin based n Finite Integral Techniques (FIT) f Time Dmain (TD) frmulatins is cnducted using CST MWS t evaluate the antenna perfrmance. A Frequency Dmain (FD) slver based n CST frmulatins is cnducted fr validatin. *Crrespnding authr: taelwi@ualr.edu;

2 British Jurnal f Applied Science & Technlgy, 4(17): , 014 Results: It is fund the antenna shws insignificant cupling arund 1. GHz and 1.6 GHz. Furthermre, the radiatin patters f the antenna are fund t be in the end fir directin with phase change f abut 10 amng antenna sectrs. The antenna prvides abslute gain f dbi at 1. GHz and.9 dbi at 1.6 GHz. It is fund that the prpsed antenna behaves like highly directive end fire antenna at the main lbe directin arund 1.6 GHz. Mrever, it is fund that the antenna array exhibits insignificant cupling amng each ther arund this frequency. Cnclusin: The perfrmance and structure f the prpsed design allws the use with wearable Ad Hc mbile systems withut the need fr frequency reuse by steering the radiatin patterns f the antenna sectrs thrugh switching antenna branches. Finally, an excellent agreement has been achieved between the regarded results frm TD and FD slvers. Keywrds: Ad Hc; Array; Wearable devices; FIT; TD; FD. 1. INTRODUCTION Decreasing the crrelatin between cnventinal antennas munted n physically miniaturized arrays is ne f the mst substantial demands in MIMO systems [1]. Hwever, cnvent antennas face a severe cupling in their arrays at the near-field due t the diffractin frm finite-grund planes and exterirs surface waves []. Therefre, mutual cupling reductin has becme a very demand feature in the design f antenna structure. On the ther hand, antenna array based n different patch cnfiguratins were perfrmed fr high gain, beam frming, and high diversity applicatins [3-6], hwever, the mutual cupling resulted frm mutual cupling was addressed as an imprtant issue in mst MIMO applicatins. This is due t the fact f the surface wave prpagatin amng patches elements leading t sever effects n the antennas perfrmance in their arrays [7-8]. Mrever, the mutual cupling depends n the separatin distance between the adjacent elements and their feed rientatin [9-11]. In the literature, t vercme the negative effects f the mutual cupling, several traditinal appraches were intrduced in [1-15] such as cavity backing and substrate remval in the miniaturized antenna arrays. In [1], a pure reactance was intrduced between antennas at the resnance frequency t realize a separated netwrk frm cnnecting a lssless netwrk between the input prts and the antenna prts. While in [13], transmissin lines as antenna decuplers were invlved t reduce the mutual cupling effects, hwever; such kinds f the decuplers are narrwband and restricted with the antenna bandwidth. The mutual cupling between antenna elements was mitigated in [14] thrugh sharing a defected grund plane with resnant slits. A different strategy was presented in [15] by intrducing split-ring resnatr magnetic inclusins between clsely-separated mnple t increase the islatin. Electrmagnetic Band Gap (EBG) defects n the grund planes f the micrstrip antennas were intrduced as nncnventinal appraches fr mutual cupling reductin as in [16-1]. Hwever, the mst manufacturing prcesses that assciated with such appraches are cmplicated [16]. Nevertheless, the EBG structures in the grund plane increases the back radiatin frm antenna array that limits their use in wearable devices in clse t the human bdy []. In additin t that, the EBG defects n the grund plans blcking the surface waves in a particular frequency band as presented in [16-30]. All these attempts shw narrw bandwidth ver the frequency f interest such as a frk-like planar EBG in [6] at 5.4 GHz, a mushrm-ebg matrix at 5.8 GHz in [17], a dumbbell-shape structure [9] at 5.6 GHz, and a C-shaped EBG array [30] at 5.5 GHz. Anther reprted 478

3 British Jurnal f Applied Science & Technlgy, 4(17): , 014 studies shwed mutual cupling reductin at 4.18 GHz [16] and 1. GHz with tw different EBG defects [31] and [3]. We are investigated in this paper the use f directive sectrs based n three patches t act as radiatin directrs t decrease the mutual cupling effects between the array sectrs within a miniaturized prfile. The prpsed array perfrmance is investigated using CST MWS numerical frmulatins [33]. The rganizatin f this paper is stated as: In Sectin II, the prpsed antenna array features are discussed. The perfrmance f the antenna array is presented in Sectin III. Lastly, in Sectin IV, the accmplishments f the prpsed paper are cncluded.. ANTENNA DESIGN AND METHODOLOGY The prpsed antenna array is based n three main sectrs munted n a circular substrate and fed by cplanar transmissin line netwrk with three prts as seen in Fig. 1(a). The individual sectr is cnstructed frm three patches fed with a transmissin line netwrk as presented in Fig. 1(b). Generally, the micrstrip antenna array is shaped circularly; see Fig. 1(c), t achieve high diversity in the radiatin patterns f the antenna elements. The patches and the grund planes are cnsidered as PEC layer munted n a lssy dielectric, εr=4.3 and tanδ=0.05, FR-4 substrate. The three patches are separated with 10 rtatinally arund the z-axis at the rigin. The dimensins and lcatins f the patches are listed in Table 1 accrding t Fig. 1(b). The lcatin f the feeding psitin t the patch is listed in Table 1 frm the center f the array. Three sectrs are used fr full spatial cnverge, where, each sectr cvers 10. Fig. 1. Antenna dimensins and features in (mm): (a) Frnt panel, (b) Single antenna sectr, and (c) Back panel 479

4 British Jurnal f Applied Science & Technlgy, 4(17): , 014 Table 1. Patch dimensins, lcatins, and feeding psitin in (mm) Patch I II III Dimensins (Majr Minr) Lcatin (x, y) (, 13) (, -19) (40, -3) Feed (Xffset, Yffset) (0, 7) (0, -6) (30, 0) 3. ANTENNA PERFOMANCE AND DISCUSSION T study the perfrmance f the prpsed antenna array, in terms f S-parameters, gain, and radiatin patterns, a full wave simulatin based n FIT frmulatins are invked using CST MWS [7] as fllw: 3.1 Antenna Perfrmance based n Single Sectr Element A numerical study is perfrmed n a single sectr element t evaluate the S11 and radiatin patterns in this sectin. It is fund when all branches are ON; the sectr exhibits three resnance mdes as seen in the S11 as seen in Fig.. Hwever, when the secnd patch is switched OFF nly, tw mdes appear at 1.3 GHz and 1.83 GHz. By switching the first and the secnd patch OFF, the antenna shws a mde at 1.3 GHz, while the secnd mde is appeared due t the harmnic generatin. Fig.. The S11 spectra f the three patches f a single sectr. The radiatin patterns f the antenna elements at the three scenaris are presented in Fig. 3 in the E- and H-planes at 1. GHz and 1.6 GHz. The radiatin patterns f the antenna array are studied at these frequencies fr MIMO applicatins systems [15]. 3. Antenna Perfrmance based n Array Structure In this sectin, the antenna array perfrmance is investigated by switching the patches f the single sectr elements sequentially in their array structure. As seen in Fig. 4, the Sparameters in terms f S11, S1, and S13 are displayed by switching the antenna branches. It is fund frm switching the all patches n, the antenna shws three mdes at 1.18 GHz, 1.6 GHz, and 1.8 GHz as seen in Fig. 4(a). Hwever, by switching OFF patch II, tw 480

5 British Jurnal f Applied Science & Technlgy, 4(17): , 014 mdes appear at 1.3 GHz and 1.83 GHz. After switching nly the third patch ON, the antenna shws a mde at 1.3 GHz and the secnd mde is appeared due t the secnd harmnic generatin. In Fig. 4(b), the cupling effects between the sectr 1 and sectr is presented. When three antenna branches are switched n, the antenna array shws the minimum cupling at 1.18 GHz, while, it shws higher cupling at 1.3 GHz and 1.8 GHz. By switching n the big and small branches n, the antenna prvides -10 db at 1.3 and 1.83 GHz. Nw, after switching the big branch n, the antenna presents abut -9 db at 1.3 GHz. The cupling effects between the sectr 1 and sectr 3 is perfrmed in Fig. 4(c). A higher cupling is fund t be when three antenna branches are n at 1.18 GHz, 1.3 GHz, and 1.8 GHz. When the big and small branches are switched n, abut the same cupling effect is btained between sectr 1 and sectr in Fig. 4(b). The lwer cupling effect is achieved by switching nly the big branch n at 1.3 GHz. Fig. 3. Far field radiatin patterns: (a) E-plane at Theta = 90 and (b) H-plane at Phi = 90 fr 1. GHz. (c) E-plane at Theta = 90 and (d) H-plane at Phi = 90 fr 1.6 GHz. 481

6 British Jurnal f Applied Science & Technlgy, 4(17): , 014 Fig. 4. S-parameters spectra: (a) S11, (b) S1, and (c) S13. Fr a MIMO system, the tw adjacent antenna elements, the envelpe crrelatin between the antenna elements is given by [6] e Sii* Sij S *ji S jj [1 ( Sii S ji )][1 ( S jj Sij )] (1) where i and j are fr the first and the secnd antenna elements, respectively. The crrelatin envelp is evaluated between the first element with the secnd element and the first element with third element in terms f S1 and S13, respectively as seen in Fig

7 British Jurnal f Applied Science & Technlgy, 4(17): , 014 Fig. 5. Crrelatin prfile amng 1,, and 3 sectrs In Fig. 6, the radiatin patterns in the E- (Theta=90) and H- (Phi=90) planes are displayed at 1. GHz and 1.6 GHz when the three switches are ON. The values f the antenna gain, beam width, main lbe directin are listed in Table. Table. Antenna array perfrmance Sectr Sectr Sectr 3 Perfrmance 1.6 GHz Sectr 1 Sectr 3 1. GHz Sectr 1 Values Main lbe magnitude 1.8 db Main lbe directin 14.0 Beam Width 86.5 Main lbe magnitude 1.8 db Main lbe directin Beam Width 86.4 Main lbe magnitude Main lbe directin.0 db 95.0 Beam Width 85.0 Main lbe magnitude Main lbe directin.9 db 14.0 Beam Width 87.5 Main lbe magnitude.9 db Main lbe directin Beam Width 87.4 Main lbe magnitude.8 db Main lbe directin 96.0 Beam Width

8 British Jurnal f Applied Science & Technlgy, 4(17): , 014 O Fig. 6. Far field radiatin patterns: (a) E-plane at Theta = 90 and (b) H-plane at Phi = O O O 90 fr 1. GHz. (c) E-plane at Theta = 90 and (D) H-plane at Phi = 90 fr 1.6 GHz The validatin is attempted using anther slver based n FD frmulatins t study the antenna array perfrmance. An excellent agreement is achieved in terms f S-parameters and radiatin patterns as can be seen in Fig

9 British Jurnal f Applied Science & Technlgy, 4(17): , 014 Fig. 7. Antenna perfrmance validatin using TD and FD frmulatins based n CST MWS 3 patches ON: (a) S11, (b) Radiatin patterns at 1. GHz, (c) Radiatin Patterns at 1.6 GHz 485

10 British Jurnal f Applied Science & Technlgy, 4(17): , CONCLUSION The eliminating f frequency reuse principle in the mbile Ad Hc system using MIMO antenna array amng the sectrs f the unit cell is inspected in this paper. T realize this achievement, an antenna array f size f cm is cnsidered with using high diversity amng antenna sectrs. The single antenna sectr is cnstructed frm three patches that are cnnected t feeding transmissin netwrk thrugh pin dides, as switches, that are erected n an FR-4 substrate. Each single element f the antenna differentiated in the space with 10 rtatinally. The antenna perfrmance is characterized frm 0.8 GHz t GHz in terms f S-parameters and radiatin patterns with different switching OFF/ON strategies. It is fund that the antenna lw crrelatin factr and end fire radiatin at the main lbe directin arund 1. GHz and 1.5 GHz. A numerical investigatin based n FIT is cnducted using CST MWS t evaluate the antenna perfrmance. Finally, tw different numerical slutins based n TD and FD slvers fr CST MWS frmulatins are cnducted t perfrm a validatin fr the achieved results. ACKNOWLEDGEMENTS The authrs wuld like t thank the Engineering Cllage/ Department f Electrical Engineering at UPM fr their valuable supprt during the numerical simulatins. COMPETING INTERESTS Authrs declare that there are n cmpeting interests. REFERENCES Fschini GJ, Gans MJ. On limits f wireless cmmunicatins in a fading envirnment when using multiple antennas, Wireless Persnal Cmmunicatins. 1998;6(3): Vaughan, Andersen J. Antenna diversity in mbile cmmunicatins, IEEE Transactins n Vehicular Technlgy. 1987;36(4): Quan XL, Li R-L, Wang JY, Cui YH. Develpment f a bradband hrizntally plarized mnidirectinal planar antenna and its array fr base statins," Prgress In Electrmagnetics Research. 01;18: Wei K, Zhang Z, Feng Z. Design f a dualband mnidirectinal planar micrstrip antenna array. Prgress In Electrmagnetics Research. 01;16: Csta F, Genvesi S, Mnrchi A. A frequency selective absrbing grund plane fr lw-rcs micrstrip antenna arrays. Prgress in Electrmagnetics Research. 01;16: Elwi TA, Al-Rizz HM, Buaynaya N, Hammd MM, Al-Naiemy Y. Thery f gain enhancement f UC-PBG antenna structures withut invking Maxwell's equatins: An array signal prcessing apprach. Prgress in Electrmagnetics Research. 011;34: Wang M, Wu W, Fang D. Uniplanar single crner-fed dual-band dual-plarizatin patch antenna array. Prgress in Electrmagnetics Research Letters. 01;30: Abedin MF, M Ali. Effects f a smaller unit cell planar EBG structure n the mutual cupling f a printed diple array. IEEE Antennas and Wireless Prpagatin Letters. 005;4:

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