Gain and Bandwidth Limitations of Reflectarrays

Transcription

1 7 ACES JOURNAL VOL. 6 NO. FEBRUARY Gai ad Badwidth Limitatios of Reflectarrays Bhavai Devireddy Ag Yu Fa Yag ad Atef Z. Elsherbei Departmet of Electrical Egieerig The Uiversity of Mississippi Uiversity MS USA bdevired@olemiss.edu ayu@olemiss.edu fyag@olemiss.edu atef@olemiss.edu Abstract - I reflectarray atea desigs it is importat to fid the gai ad badwidth for a desired applicatio. I this paper two aalysis methods are illustrated which ca provide quick estimatios o the reflectarray gai ad badwidth. A quatitative compariso o these two differet approaches is made i terms of accuracy ad computatio time. Parametric studies are performed to provide desig guidelies for selectig appropriate f/d ratio ad feed patter of a ceter-fed reflectarray i order to optimize the atea gai ad badwidth. A gai ad badwidth compariso betwee the broadside ad offset fed reflectarray ateas is preseted. Furthermore the effect of elemet badwidth o the performace of a X-bad reflectarray is give both umerically ad experimetally. Idex Terms Badwidth directivity efficiecy gai reflectarray. I. INTRODUCTION Reflectarray atea combies the advatages of both traditioal reflectors ad covetioal phased array ateas. It has a high gai like parabolic reflectors. But ulike the reflector that has a theoretically ifiite badwidth due to its curved surface the reflectarray has a arrow badwidth due to its phase compesatio mechaism. I the last decades it has bee show that there are maily two factors which limit the badwidth performace of a reflectarray atea [-]. Oe is the arrow badwidth of the microstrip patch elemet [3] ad the other is the differetial spatial path delay. The secod badwidth limitatio factor depeds o system parameters like aperture diameter (D) focal legth to diameter ratio (f/d) ad power factor (q) of the feed patter. I this paper the gai ad badwidth of reflectarrays are studied i details ad the focus is o the effects of the system parameters. Note that the frequecy badwidth i this paper if ot explicitly defied is calculated at - db from the maximum gai. Sectio II of this paper describes two differet methods to quickly estimate the reflectarray gai ad badwidth. A compariso is made i terms of accuracy ad computatio time. Focusig o the differetial spatial delay effect Sectio III presets the badwidth study of a broadside ceter-fed reflectarray atea. Parametric studies are performed i order to optimize the atea gai ad badwidth. I Sectio IV a compariso betwee broadside ad offset reflectarray atea i terms of gai ad badwidth is give. I Sectio V a X-bad reflectarray with idetical circularly polarized elemets but differet rotatio agles is ivestigated. Both the effect of differetial spatial path delay ad the effect of elemet badwidth o the performace of reflectarray are studied. The simulated gai of this reflectarray atea is compared with the measured result. II. GAIN COMPUTATION METHODS To aalyze the radiatio performace of reflectarray ateas several approaches have bee developed with differet levels of accuracy ad complexity. The most accurate method is to perform a full wave simulatio o the etire reflectarray aperture ad the feed hor. However this method requires prohibitively large memory storage ad computatioal time especially for large-size reflectarrays. A ifiite array approach is widely used by assumig local periodicity where each reflectarray elemet is aalyzed withi ACES

2 DEVIREDDY YU YANG ELSHERBENI: GAIN AND BANDWIDTH LIMITATIONS OF REFLECTARRAYS 7 a periodic eviroet to obtai its reflectio magitude ad phase. The frequecy variatio polarizatio status ad the actual icidet agle ca be cosidered i the simulatio. Oce the elemet property is determied the aperture field distributio ca be calculated ad the radiatio performace of the reflectarray ca be obtaied. This method is proved to be accurate; however the algorithm is relatively complex ad simulatio time is relatively log. I some egieerig desigs it is ecessary to provide quick estimatios o the reflectarray performace such as the gai ad badwidth. I light of this two simple ad quick approaches are preseted here for such estimatios which are based o the array theory ad the aperture efficiecy. Their accuracy ad computatioal time are compared quatitatively i this paper. Combied with specific elemet phasig techiques these approaches ca be used to calculate the gai ad badwidth of reflectarray ateas. The gai (G) calculatio of a reflectarray atea is defied as a product of the directivity (D a ) ad aperture efficiecy (η a ) [4] such that G = Da η a () where D a of the aperture with a area A is 4πA Da =. () λ The η a is the product of spillover efficiecy (η s ) illumiatio efficiecy (η i ) ad other efficiecy (η o ) factors. Other efficiecies iclude the feed loss feed blockage reflectarray elemet loss polarizatio loss mismatch loss etc. Thus η a = η s ηi η o. (3) I some gai computatio methods the directivity is calculated from the aperture field distributio [5-7]. Thus the gai already icludes the illumiatio efficiecy which ca the be represeted by the followig equatio G = D η η. (4) A. Directivity Calculatios: Method The directivity of a array with isotropic elemets whose mai beam is poitig i the θ = θ ad φ=φ directio is give as AF( θ ϕ ). (5) D = ππ AF( θ ϕ) si θdθdϕ 4π s o where N = jφ j rˆ. r AF( ) A. e β θ ϕ. e. (6) Here A ad φ are the amplitude ad phase of the th array elemet ad rˆ. r = p siθ cosϕ + p siθ siϕ. x y (7) The positio of the th elemet i a N-elemet plaar array i the xy-plae is deoted by ( p p ). x y The array ca have arbitrary cofiguratio i the xy-plae ad each elemet is idexed with a sigle idex. Note that N is the total umber of elemets ad would equal to the product of the umber of elemets i x ad y directios (N x N y ) for a rectagular array. The deomiator i Eq. (5) referred to as DEN ca be writte as = DEN π π [ AF( θ ϕ) ][ AF( θ ϕ) ]* siθdθdϕ. 4π (8) Whe substitutig equatio (6) ito equatio (8) oe obtais N π * DEN = w wm siθdθ m π π exp j x π λ where = (9) p p ( p siθ cosϕ + p siθ si ϕ) dϕ y w = p x = p y jφ = A.e () x y p p xm ym = ρ cosϕ = ρ siϕ ( p ) + ( p y ) ) x () ρ = = p () p y = arcta ϕ. px Usig Eqs. () ad () i the ier itegral i Eq. (9) gives π π exp j ρ siθ ( cos( ϕ ϕ ) ) dϕ π λ (3) π = J ρ siθ λ where J (.) is a Bessel fuctio of order zero. Substitutig Eq. (3) ito Eq. (9) gives

3 7 ACES JOURNAL VOL. 6 NO. FEBRUARY π * π DEN = w wm siθ. J ρ siθ dθ m= λ (4) * π = w wmsic ρ. m= λ Thus the directivity i Eq. (5) ca be calculated aalytically ad the computatioal time of equatio (4) is i the order of N. B. Directivity Calculatios: Method Aother simple approximatio formula to calculate the directivity of a large plaar array is D = Da η i. (5) The illumiatio efficiecy (η i ) due to the ouiform amplitude ad phase distributio o the aperture plae [8] is give as ηi = ηt η ph (6) where η t ad η ph are the taper ad phase efficiecies. The η t accouts for the aperture illumiatio taper due to the feed ad the reflector geometry ad is give by E x y = = η. (7) t A E x y The η ph accouts for the phase-error over the aperture due to various causes such as frequecy chage displacemet of the feed-hor from the o-axis focus distortio of the optical surfaces or it may be caused by phase-error i the field of the feed-hor. This η ph is give by E x y η ph =. cosθ (8) N E = x y Fially the illumiatio efficiecy is give as where E x y η i = cosθ A E x y E (9) jφ jβ r... r = A e e. () The term β( r. r ) is the phase due to the chage i the mai beam directio. For a broadside beam this term will disappear. The parameters Δx ad Δy represet the spacig betwee the elemets alog x ad y axes respectively. It is worthwhile to poit out that the computatioal time i the deomiator of Eq. (9) is oly a order of N. I summary from Method to Method the computatioal time of the directivity is reduced from a O(N ) to O(N). C. Spillover Efficiecy The spillover efficiecy (η s ) is defied as the ratio of the power itercepted by the reflectig elemets to the total power [9] p. ds A η s =. () p. ds Σ Both itegrals are the fluxes of the Poytig vector p through some certai surface areas. The itegral of the deomiator is performed over the etire spherical surface cetered at the feed deoted by Σ. The itegral i the umerator is evaluated o the array aperture A. Oce the spillover efficiecy is determied the reflectarray gai ca be calculated usig equatio (4). D. Compariso of Results By assumig the efficiecy factor η o = i equatio (4) a compariso betwee Method ad Method for gai calculatios was performed for a rectagular aperture reflectarray atea which has a ceter feed ad a broadside mai beam (frequecy = 3 GHz; spacig betwee elemets = λ/; f/d =.5; feed patter power factor q = 3). Ideal phasig elemets are used i these comparisos. These comparisos are performed usig Matlab o a Itel duo-core 3. GHz CPU ad GB of RAM ad the results are reported i Table. Note that Method always gives accurate results for ay aperture size whereas the approximatio error i Method decreases whe the aperture size icreases. Figure illustrates the percetage error of Method with respect to Method. The error is calculated usig the followig equatio: G( M ) G( M) Error (%) = %. () G( M) Of the two methods the time take for gai calculatio is much less usig Method. From Fig. a clear agreemet of the two methods at off-ceter frequecies ca be see for a broadside reflectarray. For frequecy poits the Method

4 DEVIREDDY YU YANG ELSHERBENI: GAIN AND BANDWIDTH LIMITATIONS OF REFLECTARRAYS 73 takes about 8 miutes whereas the Method oly takes aroud 3 secods. The badwidth obtaied usig either of the methods is about 5 %. Table : Gai ad CPU time compariso Array size Gai (db) Method Method Time (s) Method Method Fig.. Gai error of Method vs. umber of elemets. Fig.. Gai compariso of two methods for a 8 8 elemet reflectarray. III. BANDWIDTH OF BROADSIDE FED REFLECTARRAY Badwidth of reflectarrays is determied by two factors: the system cofiguratio ad the elemet performace. I Sectios III ad IV we focus o the effects of the system cofiguratio amely the aperture size the feed property ad the feed locatio. Durig this ivestigatio a ideal elemet phase is used that is as frequecy varies the relative elemet reflectio phase does ot chage. The reaso for this assumptio is to study oly the effects of the system parameters. This assumptio is valid also because i the elemet rotatio techique to be discussed i Sectio V the relative reflectio phase of the copolarized CP wave (ormalized to a referece elemet e.g. the elemet located at the ceter of the aperture) oly depeds o the rotatio agle ad is therefore a costat over the frequecy rage of iterest. Cosiderig the accuracy ad computatio time Method is used here to coduct a parametric study o the reflectarray gai ad badwidth performace. A. Gai ad Badwidth vs. (f/d q) First a parametric study has bee doe for a circular aperture (frequecy = 3 GHz; spacig betwee elemets = λ/; diameter =.5 m (D/λ = 53.4); umber of elemets = 8937) with a gai aroud 43 db. As the gai ad badwidth of a reflectarray varies with q ad f/d ratio a appropriate selectio of these parameters is required. For a give q value the gai versus f/d icreases to a certai value ad the decreases as show i Fig. 3. The larger the q value the arrower the hor beam. Thus we eed to choose a larger f/d i such cases i order to have a more uiform field distributio o the array. It has bee oticed that for a particular f/d ad q value where we get maximum gai the badwidth may ot be maximum. I Fig. 4 a gai of 43 db is obtaied for differet combiatios of f/d ad q but the badwidth is wider for larger f/d ad q values. The phase efficiecies at f/d =.5 ad.75 are show i Fig. 5 with q = 3. At off-ceter frequecies the phase efficiecy is high for large f/d ratio. This phase efficiecy cotributes to the icreased badwidth whe we icrease the f/d ratio. The badwidth icreases

5 74 ACES JOURNAL VOL. 6 NO. FEBRUARY with a icrease i the two parameters f/d ad q as show i Fig. 6. Fig. 3. Gai (db) vs. (f/d q) for a ceter-fed reflectarray at 3 GHz. Fig. 6. Percetage badwidth vs. (f/d q) for a ceter-fed reflectarray. B. Gai ad Badwidth Relatio A relatio betwee gai ad badwidth of a large size (43 db; D/λ = 53.4) ad middle size (3 db; D/λ = 6) reflectarray is show i Figs. 7 ad 8 respectively. It ca be observed that for a fixed q value the variatio i gai is small (<.4 db) whe the f/d is icreased. Meawhile the icrease i badwidth is high for a middle size reflectarray whe compared to that of a large size reflectarray. At q = 3 ad f/d from the badwidth of a large size reflectarray is varyig from 4.9 % to 6.5 % whereas the badwidth of middle size reflectarray is varyig from 6.37 % to. %. Figures 7 ad 8 also illustrate that the gai ad badwidth are high for large f/d ad q. Fig. 4. Gai of ceter-fed reflectarrays with differet q ad f/d. Fig. 7. Gai vs. badwidth for a large size ceterfed reflectarray with D/λ = Fig. 5. Phase efficiecy vs. frequecy for a ceterfed reflectarray with q = 3.

6 DEVIREDDY YU YANG ELSHERBENI: GAIN AND BANDWIDTH LIMITATIONS OF REFLECTARRAYS 75 q = 3 ad f/d = for a broadside fed reflectarray the maximum gai of 43.5 db is achieved whe f/d =.56 while the largest badwidth of 6.5% is obtaied whe f/d =.74. Yet for a offset reflectarray atea the maximum gai of 4.5 db is achieved whe f/d =.5 while the largest badwidth of 7.5% is obtaied whe f/d =.74. Fig. 8. Gai vs. badwidth for a middle size ceter-fed reflectarray with D/λ = 6. IV. BROADSIDE AND OFFSET FED REFLECTARRAY For a circular aperture (frequecy = 3 GHz; spacig betwee elemets = λ/; diameter =.5 m; umber of elemets = 8937) a compariso is doe betwee broadside ad offset reflectarrays. Here the icidet ad mai beam of the offset reflectarray is makig a agle of 5 with respect to the broadside directio. I doig so the reflected eergy ad the reradiated eergy of each reflectarray elemet ca be collocated i the same directio ad ot wasted []. At fixed f/d ad q values a offset reflectarray has lower gai but wider badwidth (gai = 4.48 db badwidth = 5.3%) whe compared to that of a broadside reflectarray (gai = 43.8 db badwidth = 4.95%) as show i Fig. 9. Fig. 9. Gai vs. frequecy for broadside ad offset reflectarrays at q = 3 ad f/d =.5. The gai ad badwidth characteristics of both reflectarray ateas are show i Fig.. At Fig.. Gai vs. badwidth for broadside ad offset reflectarrays at q = 3 ad f/d = V. ELEMENT BANDWIDTH EFFECT I this sectio the effect of the elemet badwidth is icluded to ivestigate the performace of a X bad reflectarray operatig at 8.4 GHz. A split square loop is desiged to reflect the CP wave with the same polarizatio state at X- bad (8.4 GHz). A modified elemet rotatio techique is used to compesate the spatial phase delay []. The full wave solver Asoft Desiger is applied i the elemet desigs. Periodic boudary coditios (PBC) are placed aroud a sigle elemet to model a ifiite array eviroet ad a plae wave is lauched to illumiate the uit cell. It is worthwhile to poit out that the mutual couplig effects betwee elemets are cosidered i this aalysis. The array grid is uiform ad square shaped with a period p = 8.75 mm betwee adjacet cells as show i Fig.. Figure shows the magitudes of the reflected co-polarized (right had circularly polarized RHCP) ad the cross-polarized (left had circularly polarized LHCP) compoets uder ormal icidece. The elemet badwidth obtaied at - db is about 4.9% ( GHz) cetered at 8.4 GHz. By rotatig the slots aroud the perimeter of the square loop differet reflectio phases ca be obtaied to compesate

7 76 ACES JOURNAL VOL. 6 NO. FEBRUARY the spatial phase delay of elemets at differet locatios o the reflectig surface. Fig.. Elemet geometry []: a =.375 mm w = mm s = 7. mm ad P = 8.75 mm (substrate thickess =.57 mm ad ε r =.33). The atea elemets are aliged o a circular aperture with the diameter D = 5 mm (D/λ = 4) f/d =.68 q = 6 ad a offset feed structure is used with a agle of 5 aside from the ormal directio of the reflector plae. Usig these cofiguratio parameters the effect of differetial spatial phase delay is studied first ad the results are show i Fig. 3. Here the gai is calculated usig Method. As the aperture directivity (D a ) liearly icreases with frequecy it ca be observed that the maximum gai is obtaied at 9 GHz istead of the desig frequecy 8.4 GHz. Figure 3 also shows the aperture efficiecy over a frequecy rage of 7.8 GHz 9 GHz. Note that the spillover ad taper efficiecies are costat with frequecy but the phase efficiecy varies with frequecy. The gai badwidth due to differetial spatial phase delay is 5.83%. Fig. 3. Reflectarray performace due to spatial phase delay effect. To iclude the elemet effect the values of RHCP show i Fig. are cosidered as polarizatio mismatch i the code while doig frequecy sca. The effect of elemet badwidth o the performace of the reflectarray is show i Fig. 4. The badwidth with elemet effect is about 4.9% ( GHz). The badwidth obtaied is equal to that of the elemet badwidth but ote that the frequecy rage is slightly higher. It was observed that the badwidth from elemet is much arrower tha the badwidth from differetial spatial phase delay. Therefore the elemet performace has a domiat effect o the reflectarray badwidth compared to the spatial phase delay. Fig. 4. Effects of spatial phase delay ad elemet badwidth o the reflectarray gai. Fig.. Performace of the CP elemet usig Asoft Desiger. The gai of the reflectarray atea obtaied from simulatios is compared with the measured result i Fig. 5. The gai of the prototype was obtaied from ear field measuremets [].

8 DEVIREDDY YU YANG ELSHERBENI: GAIN AND BANDWIDTH LIMITATIONS OF REFLECTARRAYS 77 Table summarizes the gai ad badwidth values. Sice the measured result icludes other efficiecy factors such as the feed loss which is lower tha the simulated results. A major reaso for the discrepacy betwee the simulated ad measured results is due to the feed hor atea effect. The q value the purity of the RHCP beam ad the retur loss of the hor all vary with frequecy which causes gai reductio. I particular at 8.8 GHz the retur loss of the hor is poor resultig i a low gai. Sice we do ot have the complete data for the hor this effect is ot calculated i the simulatio. Fig. 5. Measured ad simulated results of a offset reflectarray with D = 5 mm f/d =.68 ad q = 6. Table : Gai ad badwidth from the measured ad simulated results Gai at 8.4 GHz (db) db Badwidth (%) 3 db Badwidth (%) Measured Simulated VI. CONCLUSION Two methods of gai computatio have bee described ad it is observed that Method has acceptable accuracy ad takes less time for calculatio. Based o the coducted parametric studies it was observed that the selectio of f/d ad q will affect both the gai ad badwidth performace of a reflectarray atea. The tradeoff betwee gai ad badwidth is revealed to obtai a optimum performace of reflectarrays ad it was observed that a reflectarray with large f/d ad q ca give a high gai ad large badwidth. At a fixed f/d ad q value a offset reflectarray has low gai but large badwidth whe compared to that of a broadside reflectarray. The gai ad badwidth of a X-bad reflectarray has bee calculated ad the results are proved to be i good agreemet with the measured results. For reflectarray with small D/λ the spatial phase delay effect is smaller tha the elemet effect o the performace of reflectarray. ACKNOWLEDGEMENT This work was supported by NASA/MS Space Grat Cosortium uder the cotract umber NNG5GJ7H ad by NASA Steis Space Ceter uder the cotract umber NNX9AP8A. REFERENCES [] J. Huag Badwidth Study of Microstrip Reflectarray ad a Novel Phased Reflectarray Cocept IEEE APS/URSI Symp. Dig. Newport Beach CA USA pp Jue 995. [] D. M. Pozar Badwidth of Reflectarrays Electroic Letters vol. 39 o. pp Oct. 3. [3] S. Gulteki K. Guey ad S. Sagiroglu Neural Networks for the Calculatio of Badwidth of Rectagular Microstrip Ateas ACES Joural vol. 8 o. pp [4] A. W. Rudge K. Mile A. D. Olver ad P. Kight The Hadbook of Atea Desig vols. ad Chap. 3 pp [5] C. A. Balais Atea Theory Third ed. Joh Wiley & Sos New Jersey 5. [6] H. L. Va Trees Detectio Estimatio ad Modulatio Theory Optimum Array Processig Part IV Joh Wiley & Sos. [7] W. L. Stutzma ad G. A. Thiele Atea theory ad Desig ed. Joh Wiley & Sos 998. [8] W. V. Cappelle Efficiecy ad Sesitivity Defiitios for Reflector Ateas i Radio- Astroomy SKADS MCCT Workshop 6-3 Nov. 7. [9] A. Yu F. Yag A. Z. Elsherbei J. Huag ad Y. Rahmat-Samii Aperture Efficiecy Aalysis of Reflectarray Ateas Microwave ad Optical Techology Letters vol. 5 o. pp Feb..

9 78 ACES JOURNAL VOL. 6 NO. FEBRUARY [] J. Huag ad J. A. Eciar Reflectarray Ateas Joh Wiley & Sos New Jersey 7. [] F. Yag A. Yu A. Z. Elsherbei ad J. Huag A X-Bad Circularly Polarized Reflectarray Usig Split Square Rig Elemets ad the Modified Elemet Rotatio Techique The 8 IEEE Iteratioal Symposium o Ateas ad Propagatio pp July 8. Bhavai Devireddy received her Bachelor of Techology degree from Jawaharlal Nehru Techological Uiversity Hyderabad Idia i Electroics ad Commuicatios Egieerig i 7. She received her M.S. degree from the Uiversity of Mississippi i. Her research iterests are focused o reflectarray ateas. Ag Yu was bor i Beijig Chia i 978. He received the B.S. ad M.S. degrees from Tsighua Uiversity Beijig Chia both i Electrical Egieerig i ad 3 respectively ad received his Ph.D. degree from the Uiversity of Mississippi i. From to 3 he was a Research Assistat with the State Key Laboratory of Microwave ad Digital Commuicatios Tsighua Uiversity Beijig Chia. From 3 to 5 he was a egieer i Beijig Zhogjiaxu Atea Techology Corporatio. His research iterests iclude microstrip atea ad array desig electromagetic bad gap structures ad metamaterials. Fa Yag received the B.S. ad M.S. degrees from Tsighua Uiversity i 997 ad 999 ad the Ph.D. degree from Uiversity of Califoria Los Ageles (UCLA) i. He is a Associate Professor at the Electrical Egieerig Departmet The Uiversity of Mississippi. Dr. Yag s research iterests iclude atea theory desigs ad measuremets electromagetic bad gap (EBG) structures ad their applicatios computatioal electromagetics ad optimizatio techiques ad applied electromagetic systems such as the radio frequecy idetificatio (RFID) system ad cocetratig solar eergy system. He has published over 5 techical joural articles ad coferece papers five book chapters ad two books etitled Electromagetic Bad Gap Structures i Atea Egieerig ad Electromagetics ad Atea Optimizatio Usig Taguchi s Method. Dr. Yag serves as a Associate Editor of the ACES Joural ad the IEEE Tras. Ateas Propagatio. He is also a frequet reviewer for over twety scietific jourals ad book publishers ad has chaired umerous techical sessios i various iteratioal symposiums. Atef Elsherbei is a Professor of Electrical Egieerig ad Associate Dea of Egieerig for Research ad Graduate Programs the Director of The School of Egieerig CAD Lab ad the Associate Director of The Ceter for Applied Electromagetic Systems Systems Research (CAESR) at The Uiversity of Mississippi. I 4 he was appoited as a adjuct Professor at The Departmet of Electrical Egieerig ad Computer Sciece of the L.C. Smith College of Egieerig ad Computer Sciece at Syracuse Uiversity. I 9 he was selected as Filad Distiguished Professor by the Academy of Filad ad TEKES. Dr. Elsherbei is the co-author of the followig books: The Fiite Differece Time Domai Method for Electromagetics With MATLAB Simulatios SciTech 9; the book Atea Desig ad Visualizatio Usig Matlab SciTech 6; MATLAB Simulatios for Radar Systems Desig CRC Press 3; Electromagetic ScatterigUsig the Iterative Multiregio Techique Morga & Claypool 7; Electromagetics ad Atea Optimizatio usig Taguchi's Method Morga & Claypool 7; ad the mai author of the chapters Hadheld Ateas ad The Fiite Differece Time Domai Techique for Microstrip Ateas i Hadbook of Ateas i Wireless Commuicatios CRC Press. Dr. Elsherbei is a Fellow member of the Istitute of Electrical ad Electroics Egieers (IEEE) ad a Fellow member of The Applied Computatioal Electromagetic Society (ACES). He is the Editor-i- Chief for ACES Joural.