Two-layer slotted-waveguide antenna array with broad reflection/gain bandwidth at millimetre-wave frequencies

Transcription

1 Two-lyer slotted-wveguide ntenn rry with rod reflection/gin ndwidth t millimetre-wve frequencies S.-S. Oh, J.-W. Lee, M.-S. Song nd Y.-S. Kim Astrct: A slotted-wveguide rry ntenn is presented in the pper. The surry concept is introduced to provide rod reflection nd gin ndwidth. A wveguide feed network is proposed to feed equl mplitudes nd equl phses to the surrys; it is composed of two lyers, nd is thus more compct nd simpler thn conventionl feed networks. The surry is mde up of the feeding wveguide coupling slot, rditing wveguide nd rditing slot. The mesured reflection ndwidth is 5.5% (VSWR r2.) nd 9.5% (VSWR r2.7). The ntenn gin vries within 2.1 db over 4 GHz (9.5%). The mximum gin is 33.8 dbi t 41.5 nd 42.5 GHz. 1 Introduction Slotted-wveguide ntenn rrys re ttrctive for mny millimetre-wve rdr nd communiction pplictions ecuse of their low loss, high efficiency nd fltness. These ntenns my e either stnding-wve or trvelling-wve rrys of vrious rditing slots. Stnding-wve rrys hve rodside em t the centre frequency ut nrrow reflection nd gin ndwidth, while trvelling rrys produce rod reflection/gin ndwidth ut hve tilted em from the rodside t the off-centre frequency. In oth rrys, the em directions re frequency dependent. The surry concept ws presented in [1, 2] to otin rod reflection/gin ndwidth while keeping rodside em direction. In [1], only the guidelines for the expected ndwidth improvements were descried. More detiled geometries were provided in [2]. However, only theoreticl exmintion ws conducted; experimentl considertions were not included. Furthermore, the descried rry size in [2] wsssmlls8 8. To design lrge rry using the rry scheme shown in [2] or 32 32, for exmple the feed network will require four or more lyers. The coupling slot used in [2] ws series centre-inclined slot, which required folded short circuit ttched to the end of the feeding wveguide. Therefore, the rry cn ecome very complicted nd the scheme descried in [2] is not pproprite for lrger rrys. In this pper, compct two-lyer feed network is proposed to design lrge rry ntenn which provides rod reflection nd gin ndwidth for r IEE, 24 IEE Proceedings online no doi:1.149/ip-mp:24813 Pper first received 17th Septemer 23 nd in revised form 24th My 24. Originlly pulished online: 27th July 24 S.-S. Oh is with the Deprtment of Electricl nd Computer Engineering, University of Mnito, 15 Gillson Street, Winnipeg, MB R3T 5V6, Cnd J.-W. Lee nd M.-S. Song re with the Rdio nd Brodcsting Lortory, Electronics nd Telecommunictions Reserch Institute (ETRI), 161 Gjeongdong, Yuseong-gu, Dejeon 35-35, Kore Y.-S. Kim is with the Deprtment of Rdio Sciences nd Engineering, Kore University, 1 5-g, Anm-dong Sunguk-gu, Seoul , Kore rodnd multimedi wireless service (BMWS) pplictions over GHz. The rry consists of 4 4 surrys, which hve feeding wveguides, rditing wveguides, coupling slots nd rdition slots. The feeding wveguides re milled in the ottom lyer nd the rditing wveguides re stcked ove them. Longitudinl shunt slots re used for the coupling nd rdition slots so tht folded short circuit is unnecessry. Therefore, the rry scheme cn e implemented with only two lyers. 2 Surry A longitudinl slot in the rod wll of rectngulr wveguide is dopted s the coupling slot, s shown in Fig. 1. The wve incident from port 1 on the feeding wveguide is coupled into the rditing wveguide through the coupling slot nd propgtes into ports 2 nd 3. Figure 1 shows the geometry of the rdition slot; it is lso longitudinl shunt slot so tht folded short circuit is not required. A longitudinl slot is usully modelled s shunt element, for which the equivlent normlised slot dmittnce Y cn e otined s follows [3]: Y ¼ 1 G ð1þ Y 1 þ G where Y is the wveguide dmittnce nd G is the reflection coefficient, which is otined from simultion with the id of the finite element method tool, Ansoft s HFSS [4].Inthis study, the slot is round-ended, 1. mm in width, 1. mm in thickness, nd plced t qurter guided wvelength from the shorted wll. A correction is usully pplied for the round-end effects of the slot fter the rectngulr slot hs een modelled [1], ut in this study they re included in the simultion. Dt for the self-dmittnce, resonnt conductnce, nd resonnt length ginst slot offset re otined t severl points from the HFSS simultion. Then, in the rry design procedure, curve fits with polynomil expressions re used to extrct more dt. Figure 2 shows the geometry of the surry, which consists of T-junction, two feeding wveguides, six rditing wveguides, four coupling slots, nd 6 6 rditing slots. The width of the rod wll of the feeding wveguide is 4.7 mm, which is reduced from the width of IEE Proc.-Microw. Antenns Propg., Vol. 151, No. 5, Octoer Authorized licensed use limited to: Kore Aerospce University. Downloded on April 14, 29 t :55 from IEEE Xplore. Restrictions pply.

2 rditing wveguide port 2 rditing slot coupling slot port 3 feeding wveguide port 1 over the desired frequencies nd 3-dB power splitting rtio. Coupling slots re plced to provide n equl offset from the centreline of the feeding wveguide, s shown in Fig. 2, so tht lternting-phse wves re fed into the rditing wveguides [8]. The surfce currents on oth sides of the nrrow wll flow in opposite directions so tht the totl current cross the contct vnishes. Therefore, perfect electricl contct etween the wveguide nd slot plte is unnecessry compred to in-phse feed schemes [9]. However, the ntenn gin decreses ecuse the nonuniformity of the rditing slot increses. The surry shown in Fig. 3 hs een modelled using the HFSS simultor [4]. The mgnitude of the return loss is shown, which hs rod reflection ndwidth of 4 GHz (9.5%) sed on VSWR r2.. The simulted gin ptterns of the E-plne round the rodside t 4.5, 42. nd 43.5 GHz re plotted in Fig. 4. The pek gin t ll three frequencies is B22 dbi, nd the lrgest difference etween the vlues is only.4 dbi. Therefore, surrying chieves lmost the sme pek gin over rod frequencies. This surry is comined with the feed network in the following Section. port 1 rditing wveguide Fig. 1 Geometry of slot Coupling slot Rditing slot 5 feeding wveguide coupling slot S 11, db port 1 Fig Simulted mgnitude of return loss (S 11 ) of surry rditing wveguide rditing slot GHz 42. GHz 43.5 GHz Fig. 2 Geometry of surry 22 stndrd WR-22, 5.7 mm, since the thickness etween the nrrow wlls of djcent rditing wveguides must e 41. mm for the friction process. The height of the nrrow wll of the feeding wveguide is 3. mm. The feeding wveguide is 4.7 mm in width nd 2.85 mm in height. The length nd offset of ech rditing slot is determined using Elliott s design procedure [5, 6] nd the dt otined from the simultions descried in Figs. 1 nd 1. The centre-feed configurtion is used, which increses the reflection ndwidth [7]. The designed T-junction hs low reflection coefficient elow 25 db gin, dbi ngle, deg. Fig. 4 Simulted gin ptterns round rodside of E-plne of surry 394 IEE Proc.-Microw. Antenns Propg., Vol. 151, No. 5, Octoer 24 Authorized licensed use limited to: Kore Aerospce University. Downloded on April 14, 29 t :55 from IEEE Xplore. Restrictions pply.

3 3 Feed network configurtion A corporte feed is n optimum method for feeding equl mplitudes nd equl phses into surrys over ll frequencies. Three types of corporte feed networks re showninfig.5,inwhichsmllsolidcirclerepresentsthe coupling slot of the surry shown in Fig. 3 nd solid line indictes the wveguide. The first cse, illustrted in Fig. 5, is mostly used when implementing corporte feed network with the microstrip line. It requires the smllest whole feeding pths of the three cses. However, s shown in the dotted circle A, the distnce etween the coupling slots within the circle is greter thn one wvelength. Assuming tht thewidthoftherodwllofthewveguideis4.7mm, this distnce is 1.74 l or 12.4 mm ( ¼ mm), where 2.85 is the qurter guided wvelength nd 1. is the mrginl thickness etween djcent wveguides. A centrl spcing roder thn one wvelength increses the side loe level (SLL) [1] nd thus decreses the ntenn gin. The second cse, illustrted in Fig. 5, does not hve the ove descried prolem. However, s shown in circle B, the spcing etween djcent feeding wveguides is so smll tht milling friction my e impossile. Furthermore, it is desirle tht chokes re mde to suppress lekge etween djcent wveguides [9], ut spcing inside circle B does not llow it. In this study, the third cse, shown in Fig. 5c, hs een used. The centrl spcing in circle A is not ny roder thn in the other cses. In circle B, the feeding wveguide is not dense nd thus the milling process is possile nd chokes cn e plced etween djcent wveguides. Figure 5d illustrtes the simultion geometry for the corporte feed given in Fig. 5c. The numers shown from 1 to 17 indicte the ports. The surry of Fig. 3 will e ttched to ech port when the entire rry is ssemled. The WG-22 stndrd hs een used for the input port 1. The T-junction used in the surry of Fig. 3 hs een dopted. The lengths d 1 nd d 2 differ y qurter guided wvelength to cncel the reflected wves from the T-junctions nd the 9-degree H-plne ends ecuse of A B A B d 1 d 2 1 Fig. 5 Three types of corporte feed networks, Filed schemes c Proposed scheme d Simulted geometry of Fig. 5c c d IEE Proc.-Microw. Antenns Propg., Vol. 151, No. 5, Octoer Authorized licensed use limited to: Kore Aerospce University. Downloded on April 14, 29 t :55 from IEEE Xplore. Restrictions pply.

4 the hlf-wvelength difference of the pth. The simultion hs een performed using the HFSS softwre, nd the results re plotted in Figs. 6 nd 7. The return losses in the desired frequencies re mostly elow 15 db, s shown in Fig. 6. The mgnitude nd phse of the trnsmission coefficients from input port 1 to the other 16 ports re S 11, db Fig. 6 mgnitude, db phse, deg Simulted mgnitude of return loss (S 11 )offeednetwork Fig. 7 Simulted trnsmission coefficient Mgnitude Phse depicted in Figs. 7 nd, respectively. The vrition of mgnitude is within.3 db, which is tolerle in lrge rry. The phses of the trnsmission coefficients re lmost identicl. 4 Mesured results The ntenn rry hs een configured y comining the surry of Fig. 3 nd the feed network of Fig. 9, nd hs een fricted using milling process. Figure 8 shows photogrphs of the fricted ntenn. The rditing slot re is cm 2.Figure8 shows the feeding wveguides. Chokes [9] re grooved long nd eside the feed network. They ct s short circuits long the wveguide upper corner nd therefore suppress lekge. Figures 8 nd 8c show the rditing wveguides nd the entire ssemled ntenn, respectively. Figure 8d is the entire ssemled ntenn with the top-mounted rditing slots. Metllic screws hve een used to join the wveguide pltes nd the slot pltes. The mesured mgnitude of the return loss is shown in Fig. 9. The ndwidth of return loss sed on VSWR r2. is B2.3 GHz (5.5%), nd tht sed on VSWR r2.7 is 44. GHz (9.5%). Around the centre frequencies, very good return losses of db re shown, especilly 28 db t 41.6 GHz, which comes from the qurter guided-wvelength difference etween d 1 nd d 2 illustrted in Fig. 5d. The deteriortion round 43 GHz might e due to the friction tolernce, especilly, t the T-junctions nd slots. An overdesigned T-junction with return loss of B 4 db my overcome the friction tolernce. Even if the chokes were used, imperfect contcts etween the wveguides nd the slot pltes might lso ffect the return loss chrcteristics. It must e noted tht the thickness of the coupling nd rditing slot pltes is 1. mm ecuse of the limit of our friction, ut if the thinner pltes re used, the Q- fctor of the slot decreses, nd the ndwidth of the return loss could roden. The mesured rdition ptterns t 4.5, 42. nd 43.5 GHz re shown in Fig. 1. The SLLs re B 12 db t three frequencies, which stisfies the SLL of the equlmplitude feeding rry. However, s the frequency keeps wy from the centre frequency, there re severl high sideloes etween 11 nd 81. The reson my e due to surry scheme shown in Fig. 2 where three rditing slots re plced in oth sides. In the centre frequency, the rditing wves re in-phse, while t off-centre frequencies, phse differences mong three slots exist. The second reson my e the Q-fctor of the slot, nd the reltively thick slot pltes further increse the Q-fctor. The E-plne hs lrger SLL thn tht of the H-plne, which is cused y the displced slot position in the E-plne, s shown in Fig. 8d. The emwidths re B2.21 with mximum vrition of.71 mong three frequencies. The mesured ntenn gin nd perture efficiency re shown in Fig. 11. The mximum gin is 33.8 dbi t 41.5 GHz nd 42.5 GHz, which gives very high perture efficiency of 51%. The minimum gin is 31.7 dbi t oth 41. GHz nd 43. GHz. The gin vrition over 4 GHz (9.5%) is within 2.1 db, which is very rod gin ndwidth. 5 Conclusions A slotted-wveguide rry ntenn ws produced to provide rod reflection nd gin ndwidth. The surry concept ws introduced nd the two-lyer compct producile feed network ws proposed. Our mesurement results indicte rod gin ndwidth of 396 IEE Proc.-Microw. Antenns Propg., Vol. 151, No. 5, Octoer 24 Authorized licensed use limited to: Kore Aerospce University. Downloded on April 14, 29 t :55 from IEEE Xplore. Restrictions pply.

5 5 1 S 11, db Fig. 9 Mesured mgnitude of return loss (S 11 )ofthe24 24 rry reltive mplitude, db ngle, deg. reltive mplitude, db ngle, deg. Fig. 8 Photogrphs of fricted rry Feeding wveguide Coupling slot c Rditing wveguide d Assemled rry B9.5% with vrition within 2.1 db. The mesured mximum gin is 33.8 dbi t oth 41.5 nd 42.5 GHz. The reflection ndwidth is B2.3 GHz sed on VSWR r2., nd 44. GHz sed on VSWR r2.7. Fig. 1 Mesured rdition ptterns E-plne H-plne FF 4.5 GHz GHz 43.5 GHz The SLLs re B 12 db, nd the 3-dB emwidths re lmost the sme, t the desired frequencies. These results demonstrte tht the slotted-wveguide ntenn rry with proposed two-lyer feed network hs rod reflection/gin ndwidth, nd it cn e successfully pplied to rodnd millimetre-wve communictions systems. IEE Proc.-Microw. Antenns Propg., Vol. 151, No. 5, Octoer Authorized licensed use limited to: Kore Aerospce University. Downloded on April 14, 29 t :55 from IEEE Xplore. Restrictions pply.

6 gin, dbi Fig. 11 Mesured ntenn gin nd perture efficiency perture efficiency, % 2 Coetzee, J.C., Jouert, J., nd Tn, W.L.: Frequency performnce enhncement of resonnt slotted wveguide rrys through the use of widend rditors or surrying, Microw. Opt. Technol. Lett., 1999, 22, pp Josefsson, L.G.: Anlysis of longitudinl slots in rectngulr wveguides, IEEE Trns. Antenns Propg., 1987, 35, pp HFSS Relese 8., Ansoft Corp., USA, 21 5 Elliott, R.S., nd Kurtz, L.A.: The design of smll slot rrys, IEEE Trns. Antenns Propg., 1976, 26, pp Elliott, R.S.: Antenn theory nd design: revised edition (Wiley/ IEEE, New York, 23) 7 M.uller, M., Theron, I.P., nd Dvidson, D.B.: Improving the ndwidth of slotted wveguide rry y using centre-feed configurtion. Proc. IEEE AFRICON, Cpe Town, South Afric, Sept. 1999, pp Skkir, K., Kimur, Y., Akiym, A., Hirokw, J., Ando, M., nd Goto, N.: Alternting phse-fed wveguide slot rrys with single-lyer multiple-wy power divider, IEE Proc., Microw. Antenns Propg., 1997, 144, pp Kimur, Y., Hirno, T., Hirokw, J., nd Ando, M.: Alterntingphse fed single-lyer slotted wveguide rrys with chokes dispensing with nrrow wll contcts, IEE Proc., Microw. Antenns Propg., 21, 148, pp Oh, S.-S., Seo, S.H., Yoon, M.K., Oh, C.Y., Kim, E.B., nd Kim, Y.-S.: A rodnd microstrip ntenn rry for LMDS pplictions, Microw. Opt. Technol. Lett., 22, 32, pp References 1 Richrdson, P.N., nd Yee, H.Y.: Design nd nlysis of slotted wveguide ntenn rrys, Microw. J., 1988, 31, (6), pp IEE Proc.-Microw. Antenns Propg., Vol. 151, No. 5, Octoer 24 Authorized licensed use limited to: Kore Aerospce University. Downloded on April 14, 29 t :55 from IEEE Xplore. Restrictions pply.