Phased Array Antennas and their Localisation Capability

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1 Ja 2016 Vol 3, No.1

2 Phased Array Ateas ad their Localisatio Capability Aboyi D.O Eugu State Uiversity of Sciece ad Techology Offor K. J Chukwuemeka Odumegwu Ojukwu Uiversity ke.offor@asu.edu.g Abstract Localisatio is a uavoidable practise i the world because aturally ma keeps searchig for oe thig or the other i his daily life. With the growth i techology, these aturally occurrig search is advacig rapidly to accommodate more search objects like aircrafts, mobile phoes, movig vehicles, tags i shops etc. Localizatio is therefore the process of tryig to electroically locate the positio of objects i space. These electroic search has bee implemeted i differet ways like i Radio Frequecy Idetificatio (RFID), RADAR, GPS, Remote sesig ad also i our popular cellular mobile commuicatio where BTS must locate the MS for commuicatio to occur. This paper x-rays the theory of phased array ateas ad with simulatio of uiform liear atea array radiatio patters, showed how localisatio ca be achieved usig RSS algorithm. Pre-determied patters were obtaied by simulatio of 2-elemet ateas i space. The two atea array system was located at the cetre of a x-y-plae ad te radomly scattered poits were displayed radomly withi the plae to represet the radio uits which are at this poit of this research statioary. Applyig the theory which says that a directioal atea will have its maximum trasmissio or receptio i the directio of its maximum gai, it was show that the patter with highest received sigal stregth for a particular ode will have that ode located at its regio. Key words: Localisatio, Phased array ateas, Received sigal stregth (RSS), Atea patter INTRODUCTION Searchig is a everyday affair, so log as ma lives, search will cotiue to exist. I our everyday life, somethig is always beig beig searched. Techology has tried tremedously to make this search a lot easier ad more sophisticated ad iterestig. Serious techological applied search ca be traced to the ivetio of RADAR- Radio Detectio ad Ragig system which was a helpful tool to Eglad durig the world war 11. They used a defece Radar which was based o keepig the volume of sky uder surveillace literally floodlit with RF eergy, the back scattered echoes from all aircraft withi this volume are received at the groud statio by a set of crossed-dipole coected to a low-oise, high-gai receiver ad displayed as a Y-deflectio alog the time base of a CRT. The aircraft rage is a precise measuremet of the time betwee pulse trasmissio ad the echo receptio ad the bearig is a measure of the ratio of echo stregths of the X- ad Y-compoets of the crossed-dipoles. Researchers have worked hard i this area for a improved target detectio ad localisatio i geeral. A improved phased array radar has bee developed (Tei-Wei, Yug-Sheg, Chi-Fu, & Cheg, 2005). A MIMO radar has also bee developed (Hassaie & Vorobyov, 2010a, 2010b) ad a combiatio of both Phased array ad MIMO was proposed (Guag & Abeysekera, 2013) ad proved to have the best performace (Hassaie & Vorobyov, 2010b). Radio Frequecy Idetificatio (RFID) is aother area that has draw a lot of iterest i recet times, the fudametal of this techology is that a spectrum of radio frequecy is used to trasfer the idetificatio iformatio betwee two commuicatio devices: RFID tags ad RFID readers (Po, Weya, Moiri, & Chibelushi, 2013). I other to save memory space i the tag, a etwork RFID has bee developed which tries to remove data from the tag ad maipulates the data o the etwork (Doggeo, Seogyu, Howo, & Namje, 2010). Phased array RFID has bee widely applied i areas like retail item maagemet, access cotrol system, electroic toll collectio, ad etc (Tzyh-Ghuag, Chao-Wei, Re- Chig, & Cheg-Fa, 2008). Phased arrays has bee used i Global positioig systems (GPS) for more precise measuremets ad to provide ati-jammig effect (Kai, Lig, Zhogxiag, & Boyu, 2006). Localisatio ca be classified ito rage-based or rage-free localisatio. Rage-based localizatios achieve high locatio accuracy by usig specific hardware or usig absolute received sigal stregth idicator (RSSI) values, whereas rage-free approaches obtai locatio estimates with lower accuracy. Because of the hardware ad eergy costraits i sesor etworks, RSSI offers a coveiet method to fid the positio of sesor odes (Mistry & Mistry, 2015). Africa Joural of Educatio, Sciece ad Techology, Jauary, 2016 Vol 3, No

3 THEORY OF PHASED ARRAY ANTENNA Phased array atea is a collectio of two or more atea elemets i a array with the relative phases of the respective sigals feedig the elemets or beig received by the elemets set i such a way that the radiatio patter of the array is reiforced i a wated directio ad suppressed i a uwated directio. The atea elemets ca be dipoles, helices, spirals, micro-strip ateas, ope-eded waveguides, slotted waveguides etc. Atea elemets are arraged i differet cofiguratios to achieve a desired radiatio patter. These cofiguratios ca be liear if arraged i a straight lie, plaar if arraged i a 2D plae which ca be circular, square or rectagular aperture ad the coformal if arraged i a o-plaar surface, for example if arraged to coform to a existig surface of differet shapes. Phased array ateas has bee applied for groud based multi-fuctio radar for military use, airbore radar for surveillace (RBE2), space bore SAR ad commuicatios for remote sesig ad also i radio astroomy. Uiform Liear Array (ULA) Uiform Liear array cosists of idetical atea elemets that are equally spaced, excited with uiform curret with progressive phase shift ad arraged i a lie called the axis of the array. The array beam is formed by coheret additio of the idividual radiatio i space. Figure 1 illustrates a ULA. Figure 1: Uiform phases array atea structure Mathematical Backgroud From figure 1, assumig the output from ith atea at a specific time is x i, ad this output is weighted by w i, the Array output, S is give by; S (θ) = i=1 w i x i 1 A sigal is described by its amplitude ad phase, therefore the sigal received or trasmitted by each atea at a specific time is give by; X(z, t) = x(t)e jkz 2 where z is a positio vector k is the wave vector which describes the phase variatio of the plae wave. Africa Joural of Educatio, Sciece ad Techology, Jauary, 2016 Vol 3, No

4 k = (k x, k x, k x ) = 2π λ (si θ cos φ, si θ si φ, cos θ) 3 The wave vector is a property of the plae wave ad will always be equal to the magitude for a plae wave. Therefore; k = 2π λ (radias sec. ) 4 Writig the ormalised field patter for each atea as a fuctio of k, array output of equatio I ca be writte as; S (θ) = i=1 w i x(t)e jkz if(k) 6 For idetical elemets; S (θ) = x(t)f(k)[ i=1 w i e jkz i] 7 where; Z i is the positio of the ith elemet i the array The term i square bracket is kow as the Array Factor. Equatio 5 is the patter multiplicatio equatio which says that the array output is give by the received sigal multiplied by the elemet factor ad the Array Factor. This is valid for arrays with idetical elemets ad orieted i the same directio. For a oe-dimesioal array with elemets arraged i z-axis, cosiderig equatio (3) Array Factor, AF = i=1 w i e jkz i cos θ 8 AF is a fuctio of oly the elevatio agle for a oe-dimesioal array ad so ca oly filter sigal based o their polar agle, θ but caot differetiate arrivig sigal based o their azimuth agle, ϕ. Array Factor ca be used to examie the effect of a array o the received sigal as a fuctio of the agle of arrival. This is a plot of the radiatio patter. Beam Steerig The simplest way of steerig a beam is by applyig a liear phase taper to the weight. This ca be achieved my applyig a phase shifter to eforce a phase delay o the sigals arrivig o the differet elemets of the atea. I other to steer the array to a directio θ, w will be; w i = e jkz i cos θ 9 Substitutig equatio (9) ito (8); AF = e jkz i cos θ i=1 e jkz i cos θ 10 I more compact form; AF = e jkz i(cos θ cos θ) i=1 11 For a ULA, with distace d betwee adjacet ateas. The positio of ith atea for i=1,2 will be; Z i = d(i 1) ( d( 1) ) 12 2 Cosiderig a progressive phase values, β for each elemet, equatio 10 becomes; S (θ) = e j(kz icosθ +β) e jkz icosθ i=1 13 Where; θ is the agle of arraival of plae wave θ is the focusig or steerig agle Z i is the positio of ith elemet i the array β is the phase of each elemet k is the wave costace give by 2π/λ I this paper, a broadside array is cosidered ad so θ = 90 degrees where array axis is alog z-axis of a spherical coordiate system. Africa Joural of Educatio, Sciece ad Techology, Jauary, 2016 Vol 3, No

5 Simulatio of radiatio patter of 2-elemet uiform liear atea array (ULA) for selected phases. Matlab code was used to produce differet patters for differet phases of atea 1 ad atea 2 after which the followig phases of table 1 were selected. Cartesia plots achieved by idividual phases ad showig a coverage over 360 degrees from these patters are show i Figure 2. Table 1: Selected Phases Phase of Atea 1, β 1 Phase of Atea 2, β 2 Patters 0 0 P P P P4 SIMULATION RESULTS Figure 2: 360 degrees coverage of selected phases Africa Joural of Educatio, Sciece ad Techology, Jauary, 2016 Vol 3, No

6 Figure 3: Atea array radiatio patter i space for P1, P2, P3, ad P4 respectively Figure 4: Patter compariso for te sample odes Africa Joural of Educatio, Sciece ad Techology, Jauary, 2016 Vol 3, No

7 DISCUSSION Followig the fact that the patter with highest gai will receive highest RSS from a radio uit i frot of the patter, the followig ca be derived from the results of figures 2, 3 ad 4 above. Node 1: P2 will receive the highest RSS from ode 1 meaig that ode 1 is located o the regio of patter 2 Node 2: P1 will receive highest RSS at this poit meaig ode 2 is located i patter 1 regio. Node 3: P2 will receive highest RSS. Therefore this ode must be located i the regio of patter 2 Node 4: P4 will receive highest RSS. Therefore this ode must be located i the regio of patter 4 Node 5: P1 will receive highest RSS. Therefore this ode must be located i the regio of patter 1 Node 6: P4 will receive highest RSS. Therefore this ode must be located i the regio of patter 4 Node 7: P3 will receive highest RSS. Therefore this ode must be located i the regio of patter 3 Node 8: P3 will receive highest RSS. Therefore this ode must be located i the regio of patter 3 Node 9: P4 will receive highest RSS. Therefore this ode must be located i the regio of patter 4 Node 10: P4 will receive highest RSS. Therefore this ode must be located i the regio of patter 4 CONCLUSION This is a o-goig research ad i this paper we have demostrated a ovel ad simple approach to localisatio usig 2-elemet phased array ateas. It was show that usig pre-determied array radiatio patters, the agle of arrival (AOA) of the sigal from a ode ca be determied by cosiderig the patter with highest RSS as compared with all other patters ad a coclusio ca be draw that the ode is located i the regio of maximum radiatio of that patter. This ca be applied to directio fidig system desig. It ca be a very useful tool for mobile etwork plaers to determie regios of high mobile users for deploymet of smaller cells. REFERENCES Doggeo, L., Seogyu, K., Howo, K., & Namje, P. (2010, April 2010). Mobile Platform for Networked RFID Applicatios. Paper preseted at the Iformatio Techology: New Geeratios (ITNG), 2010 Seveth Iteratioal Coferece o. Guag, H., & Abeysekera, S. S. (2013). Receiver Desig for Rage ad Doppler Sidelobe Suppressio Usig MIMO ad Phased- Array Radar. Sigal Processig, IEEE Trasactios o, 61(6), doi: /TSP Hassaie, A., & Vorobyov, S. A. (2010a). Phased-MIMO Radar: A Tradeoff Betwee Phased-Array ad MIMO Radars. Sigal Processig, IEEE Trasactios o, 58(6), doi: /TSP Hassaie, A., & Vorobyov, S. A. (2010b, Aug. 2010). Why the phased-mimo radar outperforms the phased-array ad MIMO radars. Paper preseted at the Sigal Processig Coferece, th Europea. Kai, W., Lig, Z., Zhogxiag, S., & Boyu, Z. (2006, Jue 2006). A Ati-Jammig 5-Elemet GPS Atea Array Usig Phase- Oly Nullig. Paper preseted at the ITS Telecommuicatios Proceedigs, th Iteratioal Coferece o. Mistry, H. P., & Mistry, N. H. (2015, Feb. 2015). RSSI Based Localizatio Scheme i Wireless Sesor Networks: A Survey. Paper preseted at the Advaced Computig & Commuicatio Techologies (ACCT), 2015 Fifth Iteratioal Coferece o. Po, Y., Weya, W., Moiri, M., & Chibelushi, C. C. (2013). Efficiet Object Localizatio Usig Sparsely Distributed Passive RFID Tags. Idustrial Electroics, IEEE Trasactios o, 60(12), doi: /TIE Tei-Wei, K., Yug-Sheg, C., Chi-Fu, K., & Cheg, C. (2005). Real-time dwell schedulig of compoet-orieted phased array radars. Computers, IEEE Trasactios o, 54(1), doi: /TC Tzyh-Ghuag, M., Chao-Wei, W., Re-Chig, H., & Cheg-Fa, Y. (2008, 4-6 March 2008). Phased Array Atea for UHF RFID applicatios Usig Artificial Trasmissio Lies. Paper preseted at the Atea Techology: Small Ateas ad Novel Metamaterials, iwat Iteratioal Workshop o. Africa Joural of Educatio, Sciece ad Techology, Jauary, 2016 Vol 3, No

Performances Evaluation of Reflectarray Antenna using Different Unit Cell Structures at 12GHz

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