MM-Wave Phased Array Quasi-Yagi Antenna for the Upcoming 5G Cellular Communications

applied sciences

Article MM-Wave Phased Array Quasi-Yagi Antenna for the Upcoming 5G Cellular Communications

Naser Ojaroudi Parchin 1,* , Mohammad Alibakhshikenari 2 , Haleh Jahanbakhsh Basherlou 3 , Raed A. Abd-Alhameed 1 , Jonathan Rodriguez 4,5 and Ernesto Limiti 2

1 Faculty of Engineering and Informatics, School of Electrical Engineering and Computer Science, University of Bradford, Bradford BD7 1DP, UK; [email protected] 2 Electronic Engineering Department, University of Rome Tor Vergata, Via del Politecnico 1, 00133 Rome, Italy; [email protected] (M.A.); [email protected] (E.L.) 3 Bradford College, West Yorkshire, Bradford BD7 1AY, UK; [email protected] 4 Instituto de Telecomunicações-Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal; [email protected] 5 Mobile and Satellite Communications Research Group, University of South Wales, Treforest CF37 1DL, UK * Correspondence: [email protected]; Tel.: +44-734-143-6156

Received: 21 January 2019; Accepted: 5 March 2019; Published: 8 March 2019

Abstract: The focus of this manuscript was to propose a new phased array antenna design for the fifth generation (5G) mobile platforms. Eight elements of compact Quasi-Yagi antennas were placed on the top portion of smartphone printed circuits board (PCB) to form a beam-steerable phased array design. The −10 dB impedance-bandwidth of proposed 5G smartphone antenna spans from 25 GHz to 27 GHz providing 2 GHz bandwidth with less than −16 dB mutual coupling function. A coax-to-microstripline with a truncated crown of vias around the coaxial cable was used as a feeding mechanism for each radiation element. An Arlon Ad 350 substance with properties of ε = 3.5, δ = 0.003, and h = 0.8 mm was chosen as the antenna substrate. The proposed phased array antenna provides wide-angle scanning of 0◦~75◦ with more than 10 dB realized gain levels. For the scanning angle of 0◦~60◦, the antenna array provides more than 90% (−0.5 dB) radiation and total efficiencies. In addition, the specific absorption rate (SAR) function and radiation performance of the design in the presence of the user-hand/user-hand have been studied. The results validate the feasibility of the proposed design for use in the 5G handheld devices. Furthermore, using the presented Quasi-Yagi elements, the radiation properties of 2 × 2, 4 × 4, and 8 × 8 planar arrays were studied and more than 8.3, 13.5, and 19.3 dBi directivities have been achieved for the designed planar arrays. The results show that the designed arrays (linear & planar) satisfy the general requirements for use in 5G platforms.

Keywords: 5G systems; end-ﬁre radiation beam; cellular communications; phased array; mm-Wave applications; Quasi-Yagi antenna

1. Introduction One of the issues expected for the ﬁfth generation (5G) cellular communications is the move to the millimeter-Wave (mm-Wave) bands [1], which has received great attention from many researchers and industry. There has been a lot of reported research efforts on mm-Wave-based 5G communication systems [2]. The 5G mm-Wave communication technology can handle over a thousand times more mobile trafﬁc than previous mobile communication networks such as 4G LTE [3]. Moving to mm-Wave bands would bring new challenges and certainly will require careful consideration on the antenna design for the 5G handheld devices. The 26 GHz is one of the promising frequency bands for mm-Wave 5G communications, which has been proposed by Ofcom, UK [4]. Compact antennas arranged as

Appl. Sci. 2019, 9, 978; doi:10.3390/app9050978 www.mdpi.com/journal/applsci Appl. Sci. 2019, 9, x 2 of 14 consideration on the antenna design for the 5G handheld devices. The 26 GHz is one of the promising frequency bands for mm-Wave 5G communications, which has been proposed by Ofcom, UK [4]. Appl. Sci. 2019, 9, 978 2 of 14 Compact antennas arranged as an array can be employed at different portions of a smartphone PCB to form linear phased arrays with high gain and directional radiation beams. Different from conventionalan array can antennas, be employed such at as different patch, slot, portions or monopole of a smartphone antennas, PCB to cover to form the linear required phased coverage- arrays spacewith highof 5G gain cellular and directional communications, radiation the beams. end-fire Different antennas, from such conventional as horn, antennas,Yagi-Uda, such Quasi-Yagi, as patch, LTSA,slot, or Dipole, monopole and antennas,Vivaldi, are to covermore thesuitable required [5–11]. coverage-space Among them, of the 5G cellularQuasi-Yagi communications, antenna is a promisingthe end-ﬁre candidate antennas, due such to asits horn, attractive Yagi-Uda, features, Quasi-Yagi, such as LTSA,compact Dipole, size, andhigh Vivaldi, gain, and are moreeasy integration.suitable [5– 11 ]. Among them, the Quasi-Yagi antenna is a promising candidate due to its attractive features,The Quasi-Yagi such as compact antenna size, is higha widely gain, used and easyantenna integration. with high gain end-fire radiation patterns. Its configurationThe Quasi-Yagi consists antenna of a reflector is a widelyand a driven used antennaelement withalong highwith gainone or end-fire multiple radiation directors. patterns. It can provideIts configuration excellent consists directional of a reflectorpropagation and a at driven the hi elementgher frequencies along with oneand orcould multiple be used directors. for radar, It can detecting,provide excellent and phased directional array propagation applications at the [12]. higher This frequencies study investigates and could be the used configuration for radar, detecting, and characteristicsand phased array of the applications mm-Wave [12 phased]. This array study antenna investigates with the Quasi-Yagi configuration radiation and characteristicselements for use of the in 5Gmm-Wave cellular phased platforms. array Eight antenna Quasi-Yagi with Quasi-Yagi antenna radiation elements elements are placed for use on in 5Gthe cellulartop side platforms. of the smartphoneEight Quasi-Yagi PCB antenna and fed elements by 50-Ohm are placed coax-to-micros on the top sidetriplines of the [13]. smartphone Each element PCB and is fedcomposed by 50-Ohm of drivingcoax-to-microstriplines dipole arms with [13 a pair]. Each of director element elements is composed on the of top driving layer dipole of the substrate. arms with For a pair the ofhandheld director devices,elements the on measurement the top layer of of end-fire the substrate. microstrip-fe For thed antennas handheld (such devices, as Bow-tie, the measurement Dipole, Yagi, of Vivaldi, end-fire etc.)microstrip-fed can only be antennas performed (such using as Bow-tie, cable due Dipole, to th Yagi,e ground Vivaldi, plane etc.) of can smartphone only be performed PCBs [14–17]. using cable We proposedue to the here ground a new plane coax-to-microstripline of smartphone PCBs feedin [14–17g]. technique We propose to hereachieve a new a better coax-to-microstripline transition. The designedfeeding technique 5G smartphone to achieve antenna a better has transition. 2 GHz (below The designed −10 dB Snn 5G) in smartphone the frequency antenna range has of 25 2 GHz to 27 (below GHz. Good−10 dB radiation Snn) in theproperties frequency in terms range of of the 25 toantenna’s 27 GHz. fundamental Good radiation properties properties have in termsbeen obtained of the antenna’s for the antenna.fundamental In addition, properties the designed have been 5G obtained antenna forprovides the antenna. sufficient In SAR addition, levels with the designed good behavior 5G antenna in the vicinityprovides of sufficient the user’s SAR hand. levels The with planar good phased behavior array in configurations the vicinity of theof the user’s Quasi-Yagi hand. The antenna planar with phased 2 × 2,array 4 × 4, configurations and 8 × 8 radiation of the elements Quasi-Yagi were antenna also desi withgned 2 × and2, 4 high× 4, anddirectivity 8 × 8 radiation radiation elements beams have were been also obtained.designed Simulations and high directivity were carried radiation out using beams comp haveuter been simulation obtained. technology Simulations (CST) were software carried out [18]. using computer simulation technology (CST) software [18]. 2. Quasi-Yagi Antenna 2. Quasi-Yagi Antenna In recent years, printed Quasi-Yagi antennas have been exhaustively analyzed and experimentallyIn recent years, researched. printed According Quasi-Yagi to antennas the driven have element been exhaustively form, the existing analyzed Quasi-Yagi and experimentally antenna canresearched. be divided According into a tomicrostrip the driven patch, element double-sided form, the existing dipole, Quasi-Yagi or single-sided antenna dipole can be form divided [19]. into A schematica microstrip of patch,the designed double-sided Quasi-Ya dipole,gi antenna or single-sided is displayed dipole in Figure form [1.19 The]. A antenna schematic was of thedesigned designed on aQuasi-Yagi 0.8 mm Arlon antenna Ad 350 is displayed(ε = 3.5 and in δ Figure = 0.003)1. Thedielectric antenna to operate was designed at 26 GHz. on a 0.8 mm Arlon Ad 350 (ε = 3.5 and δ = 0.003) dielectric to operate at 26 GHz.

(a) (b) (c)

FigureFigure 1. Quasi-Yagi 1. Quasi-Yagi antenna antenna schematic; schematic; (a (a)) transparent transparent view, view, (b ()b top,) top, and and (c) ( bottomc) bottom layers. layers.

AsAs shown shown in in Figure Figure 11,, thethe antennaantenna isis fedfed byby aa coax-to-microstripline.coax-to-microstripline. TheThe feedingfeeding pointpoint ofof thethe coaxialcoaxial cable cable has has been been surrounded surrounded by a cylindrical metal vias. It It is is seen seen that that the the inner inner connector connector of of the probe is connected to the feed line of the Yagi’s arm while the outer connector has been connected to the ground plane. The final dimensions of the proposed Quasi-Yagi antenna and its linear array parameters are specified in Table1. Figure2 depicts the frequency response (S 11) of the Quasi-Yagi Appl. Sci. 2019, 9, x 3 of 14 the probe is connected to the feed line of the Yagi’s arm while the outer connector has been connected Appl.to the Sci. ground2019, 9, 978plane. The final dimensions of the proposed Quasi-Yagi antenna and its linear array3 of 14 parameters are specified in Table 1. Figure 2 depicts the frequency response (S11) of the Quasi-Yagi antenna. For comparison purposes, the antenna element was also designed using Ansoft high antenna. For comparison purposes, the antenna element was also designed using Ansoft high frequency frequency structure simulator (HFSS) software [20], and its S11 result has been added to Figure 2. As structure simulator (HFSS) software [20], and its S result has been added to Figure2. As shown, more shown, more than 2 GHz bandwidth with good impe11 dance-matching function in the frequency range than 2 GHz bandwidth with good impedance-matching function in the frequency range of 25 to 27 GHz of 25 to 27 GHz has been achieved. has been achieved. Table 1. Parameter values of the Quasi-Yagi antenna and its array design. Table 1. Parameter values of the Quasi-Yagi antenna and its array design. Parameter Value (mm) Parameter Value (mm) Parameter Value (mm) Parameter Value (mm) Parameter Value (mm) Parameter Value (mm) Wsub 60 Lsub 120 hS 0.8 Wsub 60 Lsub 120 hS 0.8 WS 4.5 Lg 2.5 Wf 0.5 WS 4.5 Lg 2.5 Wf 0.5 Lf 3.15 LC 3 W 1.95 Lf 3.15 LC 3 W 1.95 L L0.1 0.1Wa Wa 40 40LS L=S L=a La 99 W1 W1 1.8 1.8L1 L1 1.251.25 r1 r1 0.50.5 r2 0.87 r3 0.15 R 0.25 r2 0.87 r3 0.15 R 0.25

FigureFigure 2. 2. SS1111 functionfunction of thethe antenna. antenna.

The operation frequency frequency of of the the Quasi-Yagi Quasi-Yagi antenna antenna can can be be controlled controlled by bychanging changing the thesize size of the of thecritical critical parameters. parameters. Based Based on onthe the obtained obtained results results in inFigure Figure 3a,b,3a,b, the the resonance frequency ofof thethe antenna cancan bebe tuned tuned by by changing changing the the values valu ofes W of (width W (width of antenna of antenna arm) andarm) L gand(length Lg (length of the ground of the plane).ground Furthermore,plane). Furthermore, as evident as from evident Figure from3c, the Figure length 3c, of the the directors length (Wof the1) has directors a significant (W1) impacthas a onsignificant the matching impact function on the matching of the designed function Quasi-Yagiof the designed antenna. Quasi-Yagi Figure antenna.4a represents Figure the 4a simulatedrepresents surfacethe simulated current surface densities current of the densities Quasi-Yagi of antennathe Quasi-Yagi at its resonance antenna frequency at its resonance (26 GHz): frequency the current (26 flowsGHz): are the opposite current aroundflows are the opposite antenna around driving armsthe antenna and directors. driving The arms radiation and directors. pattern ofThe the radiation antenna atpattern 26 GHz of isthe displayed antenna inat Figure26 GHz4b: is thedisplayed Quasi-Yagi in Figure antenna 4b: exhibits the Quasi-Yagi an end-fire antenna radiation exhibits pattern an end- and providesfire radiation 4.4 dB pattern realized and gain provides level at 4.4 its dB frequency realized resonance. gain level Theat its realized frequenc gainy resonance. is the power The gain realized of the antennagain is the including power mismatchgain of the losses antenna [21]. including It should bemismatch noted that losses the [21]. directors It should of the be antenna noted improvethat the thedirectors radiation of the behavior antenna and improve impedance-matching the radiation be ofhavior the designed and impedance-matc Quasi-Yagi antennahing of [the22]. designed Figure5 illustratesQuasi-Yagi the antenna Quasi-Yagi [22]. Figure radiation 5 illustrates and total the efficiencies Quasi-Yagi versus radiation its impedance and total bandwidth.efficiencies versus It can beits observedimpedance that bandwidth. high-efficiency It can be characteristics observed that (radiation high-efficiency efficiency characteristics > 95% and total(radiationefficiency efficiency > 85% >) have95% and been total achieved efficiency over > the 85%) antenna have been operation achieved bandwidth. over the antenna operation bandwidth. Using thethe directors, directors, the the antenna antenna can can provide provide a well-defined a well-defined and more and directional more directional end-fire radiationend-fire pattern.radiation It pattern. can also It improve can also the improve gain level the ofgain the level antenna of the at antenna the operation at the frequency. operation Figurefrequency.6 illustrates Figure a6 comparisonillustrates a comparison of the antenna of the radiation antenna behavior radiation with/without behavior with/without the directors. the Asdirectors. seen in As Figure seen6 a,in theFigure antenna 6a, the with antenna directors with can directors provide can a goodprovide radiation a good patternradiation with pattern higher with gain higher and efficiencygain and propertiesefficiency properties at 26 GHz comparedat 26 GHz withcompared the antenna with the without antenna the directors.without the In addition,directors. asIn illustratedaddition, as in Figureillustrated6b, using in Figure the directors, 6b, using the the realized directors, gain the function realized of the gain antenna function over of the the operation antenna bandover hasthe beenoperation increased band significantly.has been increased significantly. Appl. Sci. 2019, 9, x 4 of 14 Appl. Sci. 2019, 9, x 4 of 14 Appl. Sci. 2019, 9, x 4 of 14 Appl. Sci. 2019, 9, 978 4 of 14

(a) (b) (b) (a) (a) (b)

(c) (c) Figure 3. S11 results of the Quasi-Yagi antenna for different values of (a) W (width of the (c) antennaFigure 3. arm), S11 results (b) Lg (lengthof the Quasi-Yagi of the ground antenna plane), for and different (c) W1 (lengthvalues ofof (a)the Wdirectors). (width of the

g 1 antennaFigure 3. 3. arm),S 11S11results results (b) L of (length theof the Quasi-Yagi Quasi-Yagi of the antennaground antenna for plane), different for and different values (c) W of (lengthvalues (a) W (width ofof (a)the of Wdirectors). the (width antenna of arm), the (antennab)Lg (length arm), of (b) the L groundg (length plane), of the and ground (c)W1 (lengthplane), of and the (c) directors). W1 (length of the directors).

(a) (b)

(a) (b) Figure 4. (a) Current densities and (b) 3D radiation pattern at 26 GHz. FigureFigure 4. ( 4.a) (Currenta)) Current densities densities and and ( (b) 3D radiationradiation(b) pattern pattern at 26at GHz.26 GHz. Figure 4. (a) Current densities and (b) 3D radiation pattern at 26 GHz.

FigureFigure 5. 5. SimulatedSimulated efficiencies. efﬁciencies. Figure 5. Simulated efficiencies. Figure 5. Simulated efficiencies. Appl. Sci. 2019, 9, x 5 of 14 Appl.Appl. Sci. Sci. 20192019,, 99,, x 978 5 5of of 14 14

(a) (b) (a) (b) Figure 6. Comparison of the antenna performance with/without directors: (a) radiation patternFigureFigure 6. 6.andComparison Comparison (b) gain. of theof antennathe antenna performance performance with/without with/without directors: directors: (a) radiation (a) pattern radiation and pattern(b) gain. and (b) gain. In order to investigate the performance of the Quasi-Yagi antenna as a transmitter/receiver in a In order to investigate the performance of the Quasi-Yagi antenna as a transmitter/receiver in mobileIn orderterminal, to investigate the fidelity the factor performance of the ofprop theosed Quasi-Yagi design antennahas been as calculated.a transmitter/receiver Two identical in a a mobile terminal, the fidelity factor of the proposed design has been calculated. Two identical antennas antennasmobile terminal, as transmitter the fidelity (TX) and factor receiver of (RtheX ) propare placedosed designwith 100 has mm been shift calculated.of their center Two points. identical The as transmitter (T ) and receiver (R ) are placed with 100 mm shift of their center points. The antenna antennaantennas orientations as transmitterX are (T arrangedX) and receiver Xin side (R byX) side are placedand face with to face100 mmconfigurations. shift of their Figure center 7 points. illustrates The theantennaorientations transmitted orientations are signal arranged are in arrangedfree in space side in byand side side received by and side face pu andlses. to face face The to configurations. calculatedface configurations. fidelity Figure factor Figure7 illustratesof the7 illustrates antenna the forthetransmitted thetransmitted face signalto facesignal in and free in free spaceside spaceby and side receivedand configurat received pulses. puions Thelses. are calculated The equal calculated to fidelity 0.90 fidelityand factor 0.98, factor of therespectively. antennaof the antenna for The the achievedforface the to faceface fidelity and to sideface results byand side confirm side configurations by that side the configurat designed are equalions Quasi-Yagi to 0.90are andequal 0.98,antenna to respectively.0.90 imposes and 0.98, negligible The respectively. achieved effects fidelity The on theachievedresults transmitted confirm fidelity pulses that results the [23]. confirm designed that Quasi-Yagi the designed antenna Quasi-Yagi imposes antenna negligible imposes effects negligible on the transmitted effects on thepulses transmitted [23]. pulses [23].

(a) (a)

(b) (c) (b) (c) FigureFigure 7.7.( a(a)) Transmitted Transmitted signal signal in free in space free space and received and received pulses for pulses (b) side for by side(b) side and (byc) face side to and face. (Figurec) face 7.to (face.a) Transmitted signal in free space and received pulses for (b) side by side and 3. The(c) Phased face to face. Array 5G Smartphone Antenna 3. TheTransparent Phased Array and 5G top Smartphone views of a linear Antenna phased array design with the Quasi-Yagi antenna elements 3. The Phased Array 5G Smartphone Antenna 2 are shownTransparent in Figure and8 top. It views has a of low a linear proﬁle phased of W arraa ×yL designa = 9 × with40 mmthe Quasi-Yagi. The antenna antenna elements elements are arranged with a distance of d = 5 mm. As it can be observed, it is composed of eight 26 GHz Quasi-Yagi are shownTransp inarent Figure and 8. top It has views a low of aprofile linear of phased Wa × L arraa = 9y × design 40 mm with2. The the antenna Quasi-Yagi elements antenna are arrangedelements withareantenna shown a distance elements in Figure of d and = 8. 5 It couldmm. has As a be low it used can profile be on observed, the of top/bottomWa × L ita is= 9composed × portions40 mm2 .of ofThe eight the antenna smartphone 26 GHz elements Quasi-Yagi PCB are to arranged form antenna two with a distance of d = 5 mm. As it can be observed, it is composed of eight 26 GHz Quasi-Yagi antenna Appl. Sci. 2019, 9, x 6 of 14

Appl. Sci. 2019,, 9,, 978x 66 of of 14 elements and could be used on the top/bottom portions of the smartphone PCB to form two sets of linearelements phased and couldarrays be [24,25]. used on Figure the top/bottom 9 shows a portions phased ofarray the smartphonesystem architecture PCB to formwith twoa feeding sets of networksetslinear of linearphased that phasedcould arrays be arrays used[24,25]. for [24 Figure,the25]. linear Figure 9 shows phased9 shows a arrayphased a phased Quasi-Yagi array array system system antenna architecture architecture and can be with with demonstrated aa feedingfeeding usingnetwork phase that shifters could be for used beam for theswitching. linear phased Various array techniques Quasi-Yagi of antennafeeding andnetwork can be design demonstrated such as parallelusing phasephase and shiftersseries shifters can for for be beam employedbeam switching. switching. for this Various Variouspurpose. techniques techniques of feeding of feeding network network design design such as such parallel as andparallel series and can series be employed can be employed for this purpose.for this purpose.

Figure 8. (a) 3D transparent and (b) top views of the linear phased array antenna. FigureFigure 8. (a 8.) (3Da) 3Dtransparent transparent and and ( (bb)) top top views of of the the linear linear phased phased array array antenna. antenna.

. Figure 9. Phased array system architecture. Figure 9. Phased array system architecture. . In array designing, the spacingFigure 9. between Phased the array adjacent system elements architecture. must be determined carefully due In array designing, the spacing between the adjacent elements must be determined carefully due to its impact on the fundamental characteristics of the array [26]. The properties of the Quasi-Yagi array to its impact on the fundamental characteristics of the array [26]. The properties of the Quasi-Yagi withIn various array distancesdesigning, of the the spacing adjacent between radiation the elementsadjacent elements have been must studied be determined in Figure 10 carefully. Its various due array with various distances of the adjacent radiation elements have been studied in Figure 10. Its conﬁgurationsto its impact on are the illustrated fundamental in Figure characteristics 10a. Mutual of couplingthe arraycharacteristics [26]. The properties of the middleof the Quasi-Yagi element of various configurations are illustrated in Figure 10a. Mutual coupling characteristics of the middle thearray array with (S 21various) for various distances distances of the areadjacent plotted radiat in Figureion elements 10b. As seen,have forbeen different studied values in Figure of d (3.510. Its to element of the array (S21) for various distances are plotted in Figure 10b. As seen, for different values of 6.5various mm), configurations the mutual coupling are illustrated function variesin Figure from 10a.−8 toMutual−20 dB. coupling Figure 10 characteristicsc illustrates the of 3D the radiation middle d (3.5 to 6.5 mm), the mutual coupling function varies from −8 to −20 dB. Figure 10c illustrates the 3D beamselement of of the the Quasi-Yagi array (S21) for antenna various array distances with are directivity plotted in values Figure for 10b. different As seen, values for different of d at values 0◦ angle. of radiation beams of the Quasi-Yagi antenna array with directivity values for different values of d at 0° Asd (3.5 seen, to 6.5 by increasingmm), the mutual the distance coupling between function the varies elements, from the −8 antenna to −20 dB. radiation Figure characteristics10c illustrates the can 3D be angle. As seen, by increasing the distance between the elements, the antenna radiation characteristics improved.radiation beams However, of the on Quasi-Yagi the other hand,antenna the array scanning with directivity angle of the values array for will different be limited values signiﬁcantly. of d at 0° can be improved. However, on the other hand, the scanning angle of the array will be limited So,angle. a trade-off As seen, between by increasing wide scanningthe distance and between high radiation the elements, characteristics the antenna is needed. radiation characteristics significantly. So, a trade-off between wide scanning and high radiation characteristics is needed. can beFigure improved. 11 illustrates However, the proposed on the other mm-Wave hand, phased the scanning array 5G angle smartphone of the antenna.array will The be antennalimited significantly.Figure 11 So, illustrates a trade-off the betw proposedeen wide mm-Wave scanning ph andased high array radiation 5G3 smartphone characteristics antenna. is needed. The antenna has an overall dimension of Wsub × Lsub = 60 × 120 × 0.8 mm and has been constructed on the has an overall dimension of Wsub × Lsub = 60 × 120 × 0.8 mm3 and has been constructed on the Arlon ArlonFigure Ad 350 11 dielectric.illustrates the The proposed designed mm-Wave linear array phased is placed array on 5G the smartphone top side of antenna. the PCB The to provideantenna Ad 350 dielectric. The designed linear array is placed on the3 top side of the PCB to provide beam- beam-steeringhas an overall dimension function at of different Wsub × L scanningsub = 60 × angles.120 × 0.8 In mm order and to has acquire been a constructed wide-scanning on the function Arlon steering function at different scanning angles. In order to acquire a wide-scanning function (0 to ±75 (Ad0 to 350±75 dielectric. degree), theThe antenna designed elements linear arearray placed is pl withaced aon bit the less top than sideλ/2 of (d the = 5 mm)PCB distance.to provide Another beam- degree), the antenna elements are placed with a bit less than λ/2 (d = 5 mm) distance. Another set of setsteering of the function design could at different be deployed scanni atng the angles. bottom In sideorder of to the acquire smartphone a wide-scanning PCB. The S function parameter (0 resultsto ±75 the design could be deployed at the bottom side of the smartphone PCB. The S parameter results of ofdegree), the Quasi-Yagi the antenna 5G elements antenna are array placed are shown with a inbit Figure less than 12: λ Good/2 (d = impedance-matching 5 mm) distance. Another and sameset of the Quasi-Yagi 5G antenna array are shown in Figure 12: Good impedance-matching and same bandwidththe design could of the be single deployed element at the (25 bottom to 27 side GHz) of havethe smartphone been achieved PCB. for The the S parameter proposed structure.results of bandwidth of the single element (25 to 27 GHz) have been achieved for the proposed structure. In Inthe addition, Quasi-Yagi a low 5G mutual antenna coupling array functionare shown between in Figure the adjacent 12: Good antenna impedance-matching elements has been and achieved. same addition,bandwidth a low of the mutual single coupling element function (25 to 27 between GHz) have the adjacent been achieved antenna for elements the proposed has been structure. achieved. In addition, a low mutual coupling function between the adjacent antenna elements has been achieved. Appl. Sci. 2019, 9, x 7 of 14 Appl.Appl. Sci. Sci. 20192019,, 99,, x 978 7 7of of 14 14

(a) (b) (a) (b)

valesFigureFigure of 10.10. d. ((aa)) Conﬁgurations, Configurations, (b)S (b21) ,S and21, and (c) radiation(c) radiation beams beams of the of linear the arraylinear for array different for different vales of d. vales of d.

(a) (a)

(b) (c)

FigureFigure 11. 11.TheThe mm-Wave mm-Wave smartphonesmartphone(b) antenna, antenna, (a ) transparent,( a ) (transparent,c) (b) top, (b and) top, (c) bottomand (c) views. bottom views.Figure 11. The mm-Wave smartphone antenna, (a) transparent, (b) top, and (c) bottom views. Appl.Appl. Sci.Sci. 20192019,, 99,, xx 88 ofof 1414 Appl.Appl. Sci. Sci. 20192019, ,99, ,x 978 8 8of of 14 14

FigureFigure 12.12. SS parameterparameter resultsresults ofof thethe mm-Wavemm-Wave 5G5G smartphonesmartphone antenna.antenna. FigureFigure 12. S 12. parameterS parameter results results of of the the mm-Wave mm-Wave 5G5G smartphone smartphone antenna. antenna. TheThe simulatedsimulated surfacesurface currentcurrent densitiesdensities atat 2626 GHzGHz forfor thethe phasedphased arrayarray 5G5G smartphonesmartphone antennaantenna hashas beenbeenTheThe simulated illustrated simulatedillustrated surface surfaceinin FigureFigure current current 13.13. It Itdensities densities cancan bebe seenseenat at 26 26 thatGHzthat GHz the thefor for currentcurrentthe the phased phased flowsflows array array areare 5G 5Gdistributeddistributed smartphone smartphone aroundaround antenna antenna thethe radiationhasradiationhas been been armsillustratedarms illustrated ofof thethe in in Quasi-YagiQuasi-Yagi Figure Figure 13.13 . antennaItantenna It can can be be elements elementsseen seen that that onon the the thethe current current toptop sideside flows ﬂows ofof thetheare are smartphonedistributedsmartphone distributed around PCB. aroundPCB. EachEach the the single-elementradiationsingle-elementradiation arms arms Quasi-YagiofQuasi-Yagi of the the Quasi-Yagi Quasi-Yagi radiatorradiator antenna antenna hashas aa elements elementshighhigh currentcurrent on on the the densitydensity top top side side andand of of appearsappearsthe the smartphone smartphone veryvery activeactive PCB. PCB. atat Each Each thethe resonancesingle-elementresonancesingle-element frequencyfrequency Quasi-YagiQuasi-Yagi (26(26 GHz)GHz) radiator radiator [27].[27]. has has a higha high current current density density and appears and appears very active very at active the resonance at the resonancefrequency frequency (26 GHz) [(2627]. GHz) [27].

FigureFigureFigure 13.13. 13. TheTheThe currentcurrent current distributiondistribution distribution at atat 26 2626 GHz. GHz.GHz. Figure 13. The current distribution at 26 GHz. InInIn orderorder order toto to demonstratedemonstrate demonstrate thatthat that thethe the groundground ground planeplane plane (G(G (GND)ND)ND) ofof of thethe the smartphonesmartphone smartphone PCBPCB PCB hashas has anan an insignificantinsignificant insignificant effecteffecteffectIn onon order thethe radiation radiation to demonstrate behavior behavior that ofof the thethe ground phasedphased plane arrayarrayarray (G Quasi-Yagi Quasi-YagiQuasi-YagiND) of the antenna, antenna,smartphoneantenna, the thethe radiation PCB radiationradiation has performancesan performancesperformances insignificant of ofeffectofthe thethe 5G 5Gon5G smartphone thesmartphonesmartphone radiation antenna antenna antennabehavior with withwith of differentthe differentdifferent phased lengths lengthlength arrayss ofQuasi-Yagi ofof the thethe PCBPCBPCB groundgroundantenna, plane plane the radiation have have beenbeen performances investigated investigated inofinin FiguretheFigure Figure 5G smartphone14. 14.14 . AsAs As illustrated,illustrated, illustrated, antenna thethe the with sizesize size different ofof of thethe the PCBPCB PCB length groundground grounds of the planeplane plane PCB doesdoes doesground notnot not planehavehave have a ahave a significantsignificant significant been investigated impactimpact impact onon on theinthethe Figure radiationradiation radiation 14. Aspropertiesproperties properties illustrated, ofof of thethe thethe array,array, array,size of suchsuch such the asPCBas as thethe the ground antennaantenna antenna plane gaingain gain does andand and notitsits its efficiency. efficiency. efficiency.have a significant LessLess Less thanthan than impact aa a 0.30.3 0.3 dBondB dB variationthevariationvariation radiation hashas has beenpropertiesbeen been obtainedobtained obtained of the inin in array,thethe the realizedrealized realized such as gaingain gain the level level levelantenna ofof of thethe thegain smartphonesmartphone and its efficiency. antennaantenna antenna Less arrayarray array than inin in the the thea 0.3 mainmain main dB ◦ radiationvariationradiationradiation beamhasbeam beam been (0°)(0°) (0 )obtained forfor for differentdifferent different in the lengthslengths lengths realized ofof of thethe thegain PCBPCB PCB level groundground ground of the plane.plane. plane. smartphone antenna array in the main radiation beam (0°) for different lengths of the PCB ground plane.

(a) (b) (c) (a) (b) (c) (a) (b) ◦ (c) FigureFigureFigure 14. 14. RadiationRadiation beams beamsbeams of ofof the thethe 5G 5G5G smartphone smartphonesmartphone antenna antennaantenna at 0 atat,( a0°,0°,) without ((aa)) withoutwithout GND, GND,GND, (b) half, ((bb) and) half,half, (c ) andFigureandfull GND.((cc)) 14.fullfull Radiation GND.GND. beams of the 5G smartphone antenna at 0°, (a) without GND, (b) half, and (c) full GND. Appl. Sci. 2019, 9, x 9 of 14

Appl. Sci. Sci. 20192019,, 99,, x 978 9 9of of 14 14 3D radiation beams of the 5G smartphone antenna are displayed in Figure 15. The direction and scanning3D radiation angle of beams the phased of the 5Garray smartphone radiation antenna beams arecan displayed be assessed in Figure by applying 15. The direction the relative and amplitudesscanning3D radiation angle and phasesof beams the tophased ofthe the radiators. 5Garray smartphone radiationIt can be antenna seenbeams that arecan the displayed bepresented assessed in 5G Figure by smartphone applying 15. The directionantennathe relative has and well-definedamplitudesscanning angle and directional of phases the phased to beams the array radiators. with radiation wide-scanning It can beams be seen canproperty that be assessed the and presented high by applying directivity 5G smartphone the values. relative antennaIn amplitudes addition, has thewell-definedand values phases of to directionalthe the antenna radiators. beams realized It can with be gains wide-scanning seen at that differ theent presented property angles, 5G andwhich smartphone high are directivity specified antenna values. in hasFigure well-definedIn addition, 16a. As shown,thedirectional values the of5G beams the smartphone antenna with wide-scanning realizedantenna gainsdesign property at exhibits differ andent sufficient highangles, directivity realizedwhich are values. gain specified levels In addition, (morein Figure than the 16a. 10 values dB) As inshown,of the the scanning antenna the 5G realizedsmartphone range of gains 0° antennato at 75°, different which design angles, makes exhibitswhich it suitablesufficient are specified for realized future in gaincellular Figure levels 16 applications.a. (more As shown, than The 10 the dB)5G 5G smartphoneinsmartphone the scanning antenna range designalso of provides0° exhibits to 75°, good sufficientwhich efficiencies makes realized it atsuitable gain different levels for (morescanning future than cellular beams. 10 dB) applications. inAs the can scanning be observed The range 5G ◦ ◦ fromsmartphoneof 0 Figureto 75 , 16b, whichantenna more makes also than provides it − suitable0.5 dB (90%)good for future efficiencies cellular haveat applications.different been obtained scanning The in 5G beams. the smartphone scanning As can range antennabe observed of 0–60 also degrees.fromprovides Figure Furthermore, good 16b, efficiencies more thana high at −0.5 different directivitydB (90%) scanning efficiencies characteristic beams. have As (11–12.5 canbeen be obtained observed dBi) inhas fromthe been scanning Figure achieved 16 rangeb, more for of 0–60 thanthe presenteddegrees.−0.5 dB (90%)Furthermore, design. efficiencies a havehigh beendirectivity obtained characteristic in the scanning (11–12.5 range of dBi) 0–60 has degrees. been Furthermore, achieved for a highthe presenteddirectivity design. characteristic (11–12.5 dBi) has been achieved for the presented design.

Figure 15. 3D radiation beams of the 5G smartphone design at (a) 0°, (b) 15°, (c) 30°, (d) 45°, (FigureFiguree) 60°, 15.and15.3D 3D (d radiation )radiation 75°. beams beams of of the the 5G 5G smartphone smartphone design design at (a) at 0◦ (,(ab) )0°, 15 (◦b,()c 15°,) 30◦ (,(c)d 30°,) 45◦ (,(de) )45°, 60◦ , ◦ (ande) 60°, (f) 75and. (d) 75°.

(a) (b)

FigureFigure 16. 16. (a(a)) Realized Realized gaingain(a (Cartesian),) (Cartesian), (b )( b efﬁciency ) efficiency and and directivity directivit ( propertiesb) y properties at different at different angles. angles.Figure 16. (a) Realized gain (Cartesian), (b) efficiency and directivity properties at different Table2 provides a comparative summary of the fundamental characteristics for the proposed angles. phased array with the recently reported 5G antenna array available in the literature. As can be observed Appl.Appl. Sci. 2019 Sci. ,20199, 978, 9, x 10 of10 14 of 14

Table 2 provides a comparative summary of the fundamental characteristics for the proposed fromphased the table, array the with proposed the recently phased reported array Quasi-Yagi 5G antenna antenna array available can support in the wide literature. scanning As angles can be with highobserved gain and from efficiencies. the table, Different the proposed from phased the reported array Quasi-Yagi designs, theantenna gain ca andn support efficiency wide characteristics scanning of theangles design with are high almost gain constantand efficiencies. over the Different scanning from range the reported of 0–75 degrees.designs, the In addition,gain and efficiency the antenna elementscharacteristics have more of the than design 18 dBare isolation.almost constant Furthermore, over the scanning the Quasi-Yagi range of 0–75 antenna degrees. elements In addition, are also suitablethe antenna for use elements in planar have phased more array than designs18 dB isolatio for basen. Furthermore, station applications. the Quasi-Yagi antenna elements are also suitable for use in planar phased array designs for base station applications. Table 2. Comparison between the proposed and the reported mobile handset antennas. Table 2. Comparison between the proposed and the reported mobile handset antennas. Bandwidth Efficiency Element Isolation Scanning Reference Bandwidth Efficiency GainGain (dB) Element Size 2 Isolation Scanning Reference (GHz) (%) Size (mm ) (dB) Range (GHz) (%) (dB) (mm2) (dB) Range [7] 21–22 - 8–12 - 14 0◦~75◦ [8][7] 27.5–28.521–22 70 - 7–11 8–12 - 7 × 5.5 14 110°~75° 0◦~60 ◦ [9][8] 27–2927.5–28.5 80 70 8–11 7–11 7 × 5.5 5.5 × 5.5 11 140°~60° 0◦~60 ◦ [10[9]] 16–1827–29 - 80 7–11.5 8–11 5.5 × 95.5× 9 14 170°~60° 0◦~60 ◦ [11[10]] 21–2316–18 85 - 9–12 7–11.5 9 × 9 12 × 6 17 120°~60° 0◦~75 ◦ ◦ ◦ [14[11]] 27.4–28.821–23 - 85 7–11 9–12 12 × 6 9 × 6 12 160°~75° 0 ~60 ◦ ◦ [16[14]] 27–2927.4–28.8 80 - 5–9.5 7–11 9 × 6 5 × 4 16 130°~60° 0 ~75 ◦ ◦ [17[16]] 27.5–28.527–29 - 80 8–11.5 5–9.5 5 × 4 - 13 150°~75° 0 ~60 Proposed 25–27 90 10.5–12 9 × 4.5 16 0◦~75◦ [17] 27.5–28.5 - 8–11.5 - 15 0°~60° Proposed 25–27 90 10.5–12 9 × 4.5 16 0°~75° 4. User-Impact on the Proposed Smartphone Antenna 4. User-Impact on the Proposed Smartphone Antenna One of the human body parts that most frequently touch the smartphone is the user’s hands, which usually hasOne a of negative the human impact body on parts the that smartphone most frequent antennaly touch performance the smartphone [28– 30is ].the The user’s fundamental hands, radiationwhich characteristics usually has a of negative the 5G smartphoneimpact on the antenna smartphone in the presenceantenna ofperformance the user’s hands[28–30]. is studiedThe in thisfundamental section. The radiation radiation characteristics beams of of the the presented 5G smartphone phased antenna array designin the presence for a scanning of the user’s range of hands is studied in this section. The radiation beams of the presented phased array design for a 0–75 degrees in the vicinity of the user’s hand are represented in Figure 17. As seen, it provides good scanning range of 0–75 degrees in the vicinity of the user’s hand are represented in Figure 17. As seen, radiation beams with high directivity values at different angles. Table3 summarizes the effect of the it provides good radiation beams with high directivity values at different angles. Table 3 summarizes user’s hands on the antenna performance. Compared with the antenna in free space, the overall losses the effect of the user’s hands on the antenna performance. Compared with the antenna in free space, of thethe smartphone overall losses antenna of the smartphone characteristics antenna in terms characteristics of antenna in gain, terms radiation, of antenna and gain, total radiation, efficiencies and are less thantotal efficiencies 3 dB, −2 dB, are and less −than2.5 3 dB, dB, respectively. −2 dB, and −2.5 dB, respectively.

Figure 17. 3D radiation beams of the 5G smartphone antenna in the vicinity of the user’s hands at (a) 0◦,(b) 15◦,(c) 30◦,(d) 45◦,(e) 60◦, and (f) 75◦. Appl. Sci. 2019, 9, x 11 of 14

Appl. FigureSci. 2019 ,17. 9, x 3D radiation beams of the 5G smartphone antenna in the vicinity of the user’s11 of 14 hands at (a) 0°, (b) 15°, (c) 30°, (d) 45°, (e) 60°, and (d) 75°. Figure 17. 3D radiation beams of the 5G smartphone antenna in the vicinity of the user’s Appl. Sci. 2019, 9, 978 11 of 14 Tablehands 3. at The (a) properties0°, (b) 15°, of(c )the 30°, 5G (d antenna) 45°, (e )with 60°, theand user’s (d) 75°. hands at different scanning angles. Param./Angle 0° 15° 30° 45° 60° 75° TableTable 3. The 3. The properties properties of ofthe the 5G 5G antenna antenna with with the user’s handshands at at different different scanning scanning angles. angles. Rad. Effic. (dB) −1.52 −1.56 −1.78 −2.11 −2.56 −2.83 Param./AngleTot.Param./Angle Effic. (dB) 0◦−2.03 0° −152.08 15°◦ −2.2530°30◦ −2.7845°45 ◦ −2.6460° 60◦−75°4.5 75◦ Rad.Directivity Effic.Rad. (dB)Effic. (dBi) (dB)− 1.5211.8−1.52 − 12.1−1.561.56 −− 121.781.78 11.92−2.11−2.11 11.6−2.56 − 2.56 10.8−2.83 −2.83 Tot. Effic.Rlzd.Tot. (dB) Effic.Gain (dB)− 2.03− 9.82.03 −−2.08 102.08 9.77−−2.252.25 9.14−2.78− 2.78 8.12−2.64 − 2.64 6.4−4.5 −4.5 DirectivityDirectivity (dBi) (dBi) 11.8 11.8 12.1 12.1 12 12 11.92 11.92 11.6 11.6 10.8 10.8 The SAR functionRlzd. GainRlzd. of (dB) Gainthe proposed (dB) 9.8 9.8phased 10 10 array 9.77smartphone 9.77 9.14 9.14 antenna 8.12 8.12 is 6.4 studied 6.4 in Figure 18. SAR, one of the most critical issues of mobile terminal systems, is a measurement function for absorbedTheThe electromagnetic SAR functionfunction ofof thewaves the proposed proposed by the phasedhuman phased arraybody, array smartphonewhich smartphone should antenna beantenna as low is studied isas studiedpossible in Figure in [31,32]. Figure 18. The SAR, 18. distanceSAR,one of one the between of most the criticalthemost 5G critical issuessmartphone ofissues mobile antennaof terminalmobile and terminal systems,the user’s systems, is hand a measurement in is the a measurementz-axis function is less than forfunction absorbed 15 mm. for Asabsorbedelectromagnetic illustrated electromagnetic in Figure waves 18, by wavesthe the antenna human by the body,has human sufficient which body, should SAR which values be should as lowfor bedifferent as as possible low placements.as [possible31,32]. The [31,32]. There distance isThe a bitdistancebetween of a difference thebetween 5G smartphone inthe the 5G SAR smartphone antenna values andfor antenna top the user’san andd bottom handthe user’s inplacements the hand z-axis in isof lessthe the z-axis than 5G antenna, 15 is mm. less Asthan which illustrated 15 wasmm. predictableAsin Figureillustrated 18 due, the in to antennaFigure different 18, has thedistances. sufficient antenna SAR has valuessufficient for differentSAR values placements. for different There placements. is a bit of a There difference is a bitin theof a SAR difference values in for the top SAR and values bottom for placements top and bottom of the 5Gplacements antenna, of which the 5G was antenna, predictable which due was to predictabledifferent distances. due to different distances.

(a) (b) Figure 18. SAR analysis: (a) top and (b) bottom placements of the 5G smartphone phased (a) (b) array antenna. FigureFigure 18.18.SAR SAR analysis: analysis: (a) top(a) andtop (andb) bottom (b) bottom placements placements of the 5G smartphoneof the 5G smartphone phased array antenna.phased 5. Planararray Phased antenna. Array Design of the 26 GHz Quasi-Yagi Antenna 5. Planar Phased Array Design of the 26 GHz Quasi-Yagi Antenna The designed 26 GHz Quasi-Yagi antenna can also be used in a planar array form for 5G base 5. Planar Phased Array Design of the 26 GHz Quasi-Yagi Antenna stationThe or designedchannel measurement 26 GHz Quasi-Yagi applications antenna [33,34]. can also Figure be used 19 inillustrates a planar the array structures form for and 5G basethe directionalstationThe or designed radiation channel 26 measurementbeams GHz ofQuasi-Yagi the designed applications antenna planar [can33 phased,34 also]. Figurebe array. used 19 in illustrates a planar array the structures form for 5G and base the stationdirectional or channel radiation measurement beams of the applications designed planar [33,34]. phased Figure array. 19 illustrates the structures and the directional radiation beams of the designed planar phased array.

FigureFigure 19. Configuration 19. Conﬁguration and and 3D 3Dbeams beams of of the the Quasi-Yagi Quasi-Yagi phasedphased array array at at different different angles. angles.

× AsFigureAs shown, shown, 19. 64Configuration 64 elements elements of of and26 26 GHz GHz3D beamsQuasi-Yagi Quasi-Yagi of the ra radiatorsQuasi-Yagidiators are are phasedemployed employed array to to atform form different the the proposed proposed angles. 8×8 8 8 planarplanar antenna antenna array array design. design. In In other other words, words, the the planar planar array array has has been been designed designed using using eight eight rows rows of of thethe linear linearAs shown, phased phased 64 array array elements described described of 26 in GHz in Section Section Quasi-Yagi 3.3. The The proposed proposedradiators planar planarare employed array array antenna antenna to form works works the proposed in in the the same same 8×8 operationplanaroperation antenna band band of ofarray the the design.single elementelemen In othert Quasi-YagiQuasi-Yagi words, the (frequency (frequency planar array range range has from beenfrom 25 designed25 to to 27 27 GHz). GHz). using It isIt eight seenis seen rows that that the of thedesigned linear planarphased array array has described a compact in Section size, high 3. The gain, proposed sufﬁcient planar efﬁciency, array and antenna beam-steering works in properties. the same operationIn addition, band of thethe characteristicssingle element ofQuasi-Yagi the 26 GHz (frequency planar Quasi-Yagi range from antenna25 to 27 arrayGHz). withIt is seen different that numbers of the radiators (2 × 2, 4 × 4, and 8 × 8) are studied in Figure 20. As shown in Figure 20a, Appl. Sci. 2019, 9, x 12 of 14 the designed planar array has a compact size, high gain, sufficient efficiency, and beam-steering properties.Appl. Sci. 2019 , 9, 978 12 of 14 In addition, the characteristics of the 26 GHz planar Quasi-Yagi antenna array with different numbers of the radiators (2 × 2, 4 × 4, and 8 × 8) are studied in Figure 20. As shown in Figure 20a, the designedthe designed planar planar arrays arrays exhibit exhibit directional directional radiat radiationion beams beams with with high high gain gain levels. levels. Figure Figure 20b,c 20b,c illustratesillustrates the the reflection reflection coefficient coefficient and and mutual mutual coupling coupling (S (Snnnn andand Snm Snm) characteristics) characteristics of of the the middle middle elementselements for for the planarplanar arrays.arrays. As As shown, shown, similar simila performancesr performances of the of S the parameters S parameters with high with isolation high − − isolationand low and mutual low mutual coupling coupling have been have obtained been obtained for them. for them. Reflection Reflection coefficients coefficients (Snn) (S ofnn) 35,of −35,48, −48,and and−43 −43 dB dB have have been been achieved achieved for for 2 ×2 ×2, 2, 4 4× × 4, and 8 8 ×× 88 planar planar arrays. arrays. Furthermore, Furthermore, the the designed designed Quasi-YagiQuasi-Yagi antenna antenna arrays arrays provide provide a a low low mutual mutual coupling coupling characteristic characteristic (less (less than than −−1313 dB dB at at 26 26 GHz). GHz).

(a)

(b) (c)

FigureFigure 20. (a 20.) Radiation(a) Radiation beams, beams, (b ()b S)Snn,nn and, and (c ()c )SSnmnm characteristicscharacteristics ofof thethe planar planar arrays. arrays.

5.6. Conclusions Conclusions AA phased phased arrayarray 5G 5G smartphone smartphone antenna antenna with Quasi-Yagiwith Quasi-Yagi radiators radiators was designed was anddesigned investigated and investigatedin this manuscript. in this manuscript. The antenna The array antenna has array well-defined/wide-scan has well-defined/wide-scan radiation radiation beams withbeams end-fire with end-firemodes modes at the 26at GHzthe 26 5G GHz band. 5G Fundamental band. Fundamental characteristics characteristics of the presentedof the presented smartphone smartphone antenna antennaarray and array its and elements its elements (Quasi-Yagi (Quasi-Yagi radiators) radiators) have been have studied. been studied. SAR and SAR user-impact and user-impact on the on 5G × × thesmartphone 5G smartphone were alsowere investigated. also investigated. In addition, In addi usingtion, using the Quasi-Yagi the Quasi-Yagi antenna antenna elements, elements, 2 2, 2 4 × 2, 4, × 4 and× 4, 8and8 8 planar × 8 planar phased phased array designs array designs were designed, were designed, and their and characteristics their characteristics have been investigated.have been investigated.Based on the Based obtained on the result, obtained the Quasi-Yagi result, the antenna Quasi-Yagi element, antenna itslinear element, and its planar linear phased and planar arrays, phasedis promising arrays, foris promising use in 5G cellularfor use in communications. 5G cellular communications. Author Contributions: Writing—original draft preparation, N.O.P., M.A., H.J.B., R.A.A.-A., J.R., and E.L.; Authorwriting—review Contributions: and editing, Writing—original N.O.P., H.J.B., draft J.R., andpreparation, R.A.A.-A.; N.O.P. investigation,, M.A., H.J.B., N.O.P., R.A.A.-A., M.A., and H.J.B.;J.R., and resources, E.L.; writing—reviewN.O.P., J.R., and and R.A.A.-A.; editing, For N.O.P., other cases, H.J.B., all J.R., authors and have R.A.A.-A.; participated. investigation, N.O.P., M.A., and H.J.B.; resources,Funding: N.O.P.,This project J.R., and has R.A.A.-A.; received funding For other from cases, the all European authors Union’shave participated. Horizon 2020 Research and Innovation Programme under grant agreement H2020-MSCA-ITN-2016 SECRET-722424. Funding: This project has received funding from the European Union’s Horizon 2020 Research and Innovation ProgrammeAcknowledgments: under grantAuthors agreement wish H to2020-MSCA-ITN-2016 express their thanks for SECRET-722424. the support provided by the innovation programme under grant agreement H2020-MSCA-ITN-2016 SECRET-722424. Acknowledgments: Authors wish to express their thanks for the support provided by the innovation Conflicts of Interest: The authors declare no conflict of interest. programme under grant agreement H2020-MSCA-ITN-2016 SECRET-722424. Appl. Sci. 2019, 9, 978 13 of 14

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