RADIOENGINEERING, VOL. 27, NO. 1, APRIL 2018 207 Design of Miniturized 10 db Widend Brnh Line Coupler Using Dul Feed nd T-Shpe Trnsmission Lines Mukesh KUMAR, SK. Nurul ISLAM, Goind SEN, Susnt Kumr PARUI, Sntnu DAS Dept. of Eletronis & Teleommunition Engineering, Indin Inst. of Engineering Siene & Tehnology, Shipur-711103, Indi {mukeshnitd415, dshys, goind.dets}@gmil.om, {rkpv, sntnumds}@yhoo.om Sumitted April 3, 2017 / Aepted Novemer 13, 2017 Astrt. This pper presents design mehnism of miniturized widend rnh line oupler (BLC) with loose oupling of 10 db. Dul trnsmission lines re used s feed network whih provides size redution of 32% with frtionl ndwidth (FBW) of 60% for 10±0.5 db oupling ut return loss performne is found to e poor in the operting nd. For further improvement of return loss performne s well s for size redution of the BLC, T- shpe trnsmission lines re used insted of series qurter wvelength trnsmission lines, nd hene the overll size redution of round 44% with FBW of 50.4% is hieved. The return loss nd isoltion performne is found to e < 15 db in the entire operting nd (2.5 4.1 GHz) with respet to design frequeny 3G Hz. The proposed BLC is nlyzed, frited nd tested. Keywords Brnh line oupler, dul line, minituriztion, T-shpe trnsmission line (TL), widend 1. Introdution Mirowve ouplers re ruil devies nd re used in mny mirowve susystems, suh s power mplifiers, phse shifter, modultors nd power divider nd so on [1 4]. In modern mirowve iruits there is n inresing demnd for wide ndwidth nd ost-effetive omponents. Some of the mirowve systems require low power to drive su iruits suh s mixers nd ntenn rrys. Therefore, the ility of ouplers to produe ritrry oupling level is of reent interest. The rnh line oupler (BLC) is the most ommon mong different types of plnr ouplers, due to its simple design nd esy integrtion with other iruits. The BLC is ommonly used for designing tight (3dB) oupler. The mjor drwks of designing BLC re lrge iruit size nd nrrow ndwidth. The iruit re eomes lrge, s it hs λ/4 series nd shunt trnsmission lines. Reserhers hve proposed severl tehniques to redue the size nd the prie of the ouplers [5], [6]. Vrious minituriztion tehniques suh s defeted ground struture [7], vrying dieletri onstnt ner the side wll [8], left-hnded trnsmission lines [9], lumped element [10] nd dul trnsmission lines in single lyered sustrte [11] re presented in litertures. However, the trde off in the size redution is ndwidth, s the minituriztion ours ndwidth eomes nrrower. Due to the struturl dependene of the BLC on the qurter wvelength (λ/4) nd hrteristis impednes of trnsmission line, its pplition is limited to tight oupling nd nrrow-nd iruits. Design of loose oupled BLC requires high impedne line (nrrow line width) whih is some extent imprtil for design of ny mirowve iruits. Therefore, the designs of loose BLC s re mere hllenges nowdys. Reserhers hve proposed vrious design methodology for widening the ndwidth s well s to hieve loose oupling of the BLC s simultneously, suh s series stu [12], symmetrilly oupled port feeding network [13], λ/4 open iruited oupled lines [14], nd λ/4 single line trnsformer s feeding network [15]. In the forementioned methodologies, extr λ/4 trnsmission lines re inserted s feed network to hieve wide ndwidth, s result of whih the size of the oupler is inresed y hlf of wvelength. In this mnusript, the design nd implementtion of miniturized widend loose BLC (10dB) is demonstrted. For designing suh BLC extr qurter wve length trnsmission line hve een inserted s feeding network t ll the ports of the onventionl BLC. To redue the oupler size, ll λ/4 setions re repled y dul trnsmission lines. Therefore size redution of 32% with FBW of 60% for 10±0.5 db oupling nd return loss performne < 10 db is hieved. Further minituriztion of the proposed oupler with improved return loss performne is otined y repling series λ/4 trnsmission lines y T-shpe trnsmission lines. As result the overll size redution of 44% nd return loss performne < 15 db in the operting nd is otined without ffeting oupler performne. DOI: 10.13164/re.2018.0207 CIRCUITS
208 M. KUMAR, S.K. NURUL ISLAM, G. SEN, ET AL., DESIGN OF MINIATURIED 10 DB WIDEBAND BRANCH LINE COUPLER 2. Widend Loose Brnh Line Coupler nd Its Minituriztion 2.1 Design of Widend 10d BLC The mjor issue relted to onventionl BLC is nrrow ndwidth due to ll λ/4 trnsmission lines (series nd shunt) whih resontes t prtiulr frequeny. In order to inrese the ndwidth of the BLC the extr λ/4 trnsmission line is used s feed network. Figure 1 shows the shemti digrm of 10dB BLC with qurter wve length extr feed network. All the setions re of qurter wvelength mintined s per the design vlues of BLC [15]. The vlues of the hrteristi impednes ( 1, 2 nd 3 ) re lulted from the referene [15]. The mirostrip widths nd lengths orresponding to the hrteristi impednes for the Arlon sustrte with dieletri onstnt ε r = 3.2, thikness h = 0.787 mm nd loss tngent of 0.002 is shown in T. 1. Figure 2 shows the simulted S-prmeters response of the BLC. Figure 2 depits 46.7% FBW with oupling level of 10±0.5 db t the operting frequeny of 3 GHz. The return loss is found to e 18.3 db t the lower (2.3 GHz) nd 17.2 db t the upper (3.8 GHz) edges of the frequeny nd; similrly t those frequenies the isoltion is 17.8 db nd 15 db, respetively. 2.2 Minituriztion of Widend 10dB BLC using Dul Trnsmission Line As mentioned in the prtiulr setion the ndwidth of BLC is inresed y introduing extr λ/4 TL s feeding network resulting in the size inrement of BLC. By introduing extr element t ll ports, the size of the oupler is inresed y hlf of the wve length. In order to redue the overll size, dul TL is used in ple of single λ/4-long TL t eh port. In dul TL, λ/4 TL of initil design is split into prllel TL s struture s shown in Fig. 3. Impedne (Ω) Width (mm), Length (mm) 0 (50) 1.89, 5 1 (36) 3.07, 15.4 2 (24.6) 5, 15.1 T. 1. Dimensions of 10dB referene BLC. Fig. 1. BLC with λ/4 feeding network. 3 (77.76) 0.8, 16.1 () Fig. 2. () S-prmeters response of BLC. Phse differene (<S21 - <S31). Fig. 3. Equivlent iruit of single TL with dul TL. Here,,,, nd re defined s the hrteristi impednes nd the eletril lengths of dul TL s, respetively, nd < = 90 <. Here (90 ) is the eletril length of the single TL nd the trnsmission mtrix (ABCD prmeter) is written in (1). Similrly ABCD mtrixes re written for oth lines 1 nd 2 in (2), (3). The expression for the hrteristi impednes nd the eletril lengths re otined from relting (1 3) nd giving in (4 6). The hrteristi impednes ( nd ) of these dul-lines re lulted from (4 6) y properly seleting the vlue of their eletril lengths ( nd ). In order to redue the iruit size, the ondition < = 90 < nd + = 180 must e stisfied. Therefore this dul trnsmission lines re omposed of two high impedne lines with high impedne nd different eletril lengths. Out of these two lines, longer one ( ) is mender in shpe to redue the iruit re. The lyout of the proposed BLC nd simulted S- prmeters response re shown in Fig. 4 nd 5 respetively.
RADIOENGINEERING, VOL. 27, NO. 1, APRIL 2018 209 A B 0 j 0, (1) A B os j0sin, (2) sin os line1 A B os j0sin, sin os line2 (3) os os, (4) sin os os os, (5) sin os tn. (6) tn 14.9 db nd 12.54 db, respetively. To improve the performne nd for further redution of the oupler size, T- shpe TL is used in ple of series qurter wvelength line. 2.3 Minituriztion nd Performne Improvement of Widend 10dB BLC using T-shpe Trnsmission Line To improve the performne s well s the size redution of the BLC, series qurter wvelength TL is repled y two series lines nd one open stu in the middle whih looks like letter T s shown in Fig. 6. The ABCD mtrix of series λ/4 TL is given y (1) nd open stu is given in (7) where dmittne of the stu Y = j tn d / d. Furthermore, the ABCD mtrix for eh of the two TL tht hs hrteristi impedne of nd eletril length of is given y (8). The overll trnsmission mtrix of T shpe TL is equted with λ/4 TL mtrix in order to otin the hrteristi impednes nd eletril lengths of the proposed T-shpe model s shown in (9). A B A B 1 0, Y 1 S os j sin, L sin os (7) (8) A B 0 j A B A B A B, (9) 0 L S L Fig. 4. Lyout of BLC with dul TL s feeding network. sin os tn A D 0 os sin, (10) 2 2 d d 2 2 d j sin tn B j jsin2, (11) 2 d jsin 2 jos tn C, (12) d d, (13) tn Fig. 5. Simulted S-prmeters of 10dB BLC with dul TL. From Fig. 5 it is ler tht y inorporting the dul trnsmission line in ple of λ/4 TLs s feed network the return loss (S 11 ) performne drstilly hnges in the operting frequeny nd. The return loss performne is degrded due to the step hnges (use prsiti effets) t the line joint etween the dul TL, series nd shunt qurter wvelength line. The S11 performnes re found to e 12.2 db t the lower edge (2.5 GHz) nd 10.3 db t upper edge (4.3 GHz) of the frequeny nd with isoltion of tnd tn 2 d. (14) 2 The ABCD prmeters re written in (10 12). Solving (10 11), the hrteristi impednes nd d of stu loded T-shpe TL in terms of eletril length re otined s desried in (13 14). The vlues of nd in Fig. 7 re evluted y properly hoosing the eletril lengths ( nd d ) of series line nd open stu in order to hieve minituriztion. For this = 20 nd d = 40 re hosen. Therefore vlue of is otined from d = 40 nd the vlue of is otined from d y using (14). The lyout of the proposed BLC is shown in Fig. 7. The simulted S- prmeters responses of the proposed oupler re shown in Fig. 8.
210 M. KUMAR, S.K. NURUL ISLAM, G. SEN, ET AL., DESIGN OF MINIATURIED 10 DB WIDEBAND BRANCH LINE COUPLER Fig. 6. Equivlent model of single TL s T-shpe TL. Fig. 7. Lyout of the proposed BLC. size redution of round 44% is hieved in design B. The other prmeters remin unhnged. The proposed ouplers hve een frited on Arlon sustrte of dieletri onstnt ε r = 3.2, thikness h = 0.787 mm nd loss tngent of 0.002. The hrteristi impednes nd optimized design prmeters of BLC s for design A nd B re tulted in T. 2. The photogrphs of the frited prototype for oth design A nd B re shown in Fig. 9. An Agilent vetor network nlyzer is used to test the performne of the frited BLC s nd ompred with the simulted results to ensure tht the oupler design exhiits good performne in the rel time environment. Figure 10 nd 11 show the simulted (Sim) nd mesured (Me) S-prmeter responses for oth designs A nd B, respetively. Tle 3 illustrtes the simulted nd mesured S-prmeters detils, FBW nd size of proposed ouplers (design A nd B). FBW is found to e 60% for the oupling level of 10±0.5 db, phse imlne 90 ±10 nd return loss nd isoltion re < 10 db nd < 15 db for design A, respetively. Similrly for design B, FBW is 50.04% for the oupling (C) level of 10±0.5 db, phse imlne 90 ±10 with return loss nd isoltion performne etter thn round 15 db. Design A Impedne (Ω) 1 = 36 = = 102 2 = 24.6 3 = 77.76 Width(mm), length(mm) W 1 = 0.4, L 1 =L =8, L =24 W 2 = 4.5, L 2 = 14.6 W 3 = 0.5, L 3 = 16.3 Fig. 8. Simulted S-prmeters response of proposed oupler. From Fig. 8 it is evident the return loss (S11) performne is improved due to inorporting the T-shpe trnsmission line in ple of series λ/4-long TL. The return loss (S11) performne is improved y minimum 8 db in the whole frequeny nd. The isoltion (S41) performne is improved y 7 db t the operting frequeny. Design B Impedne (Ω) Width(mm), length(mm) 1 = 36 2 = 24.6 = = 102 W 1 = 0.4, L 1 =L =8, L =24 = 67.57, d = 23.79 =9, =5.6, =4, d=1.2 T. 2. Dimensions of the proposed BLC s. 3 = 77.76 W 3 = 0.5, L 3 = 16.3 3. Experimentl Results The proposed 10-dB BLC s re designed nd frited t operting frequeny of 3 GHz: Design A onsists of dul TL s feed network nd Design B onsists of dul TL long with T-shpe TL for minituriztion of widend BLCs. In design A, eletril lengths of feed network, 1 nd 2 re hosen s 45 (L 1 = L ) nd 135 (L = 4l 1 + 2l 2 + 3l 3 ) respetively nd the orresponding hrteristi impednes ( nd ) re lulted from (4 6), where is 36 Ω, therefore = = 102 Ω. Therefore size redution of 32% is hieved in design A. In design B, the hrteristi impednes ( nd d ) nd eletril lengths ( nd d ) re evluted from (13 14) where is tken s 24.6 Ω nd the eletril lengths (, nd d ) re seleted s 20 nd 40, respetively. Therefore the overll () Fig. 9. Photogrph of frited prototype of the proposed BLC s: () design A, design B.
RADIOENGINEERING, VOL. 27, NO. 1, APRIL 2018 211 () () () () Fig. 10. Simulted nd mesured S-prmeters response of design A: () S21, S31, S41, S11, () S21 nd S31 phse. Prmeters λ/4-long FN Sim Design A Sim/Me Design B Sim/Me S21 2.4-4.21 2.3-4.1/2.1-4.1 2.41-4.1/2.5-4.1 S31 2.35-3.75 2.4-4.35/2.2-4 2.4-4/2.4-3.9 S41 2.14-3.81 2.4-4.0/2.2-3.7 2.4-3.8/2.4-3.7 S11 1.8-4.31 1.63-4.03/1.7-4 2.1-4.02/2-4 FBW 46.7% 65%/60% 53%/50.4% Are (mm 2 ) 45.9 16.1 31 16.2 25.5 16.2 T. 3. Simulted nd mesured S-prmeter performne of the proposed BLCs. (d) Fig. 11. Simulted nd mesured S-prmeters response of design B: () S21, S31, S41, S11, () S21 nd S31 phse, (d) phse differene (<S21 - <S31).
212 M. KUMAR, S.K. NURUL ISLAM, G. SEN, ET AL., DESIGN OF MINIATURIED 10 DB WIDEBAND BRANCH LINE COUPLER Ref. f o (GHz) S 11 (db) S21 (db) C ± r (db) S 41 (db) FBW (%) Are (mm 2 ) [12] 2.9 20 4 3±0.5 20 30 0.75 λ g 0.25λ g [13] 1 10 3.1 3.4±0.6 10 52 0.75 λ g 0.25λ g [14] 5.9 20 3.6 3.6±0.5 20 49 0.85 λ g 0.24λ g [15] 3 15 1 10.1±0.3 19.8 50.9 0.72 λ g 0.26λ g Design A 3 14 1.02 10.1±0.5 22 60.4 0.50 λ g 0.25λ g Design B 3 21 0.95 10.5±0.5 29 55.4 0.40λ g 0.25λ g The proposed design is imed t minimiztion of the referene (existing) BLC [15] with proposed tehnique y giving sustntilly minituriztion of 44%. It is to e further noted tht despite the minituriztion, no other performne ftors re degrded. Herein lies the dvntge of the proposed design over the existing design sine the proposed struture is very ompt thus mking it suitle to e used in ompt nd sophistited mirowve systems. The wide nd property long with other hrteristis of the proposed design is lso ompred with some other works nd the omprison is tulted in T. 4. It is found tht the BLC in Ref. [14] is lrger in size in omprison with tht in Ref. [12], [13]. The proposed oupler is smller in size, whih is 52% nd 47% smller ompred to the BLC in Ref. [14] nd Ref. [12], [13], respetively. Also the FBW of the proposed design is more ompred with the Ref. [12 14]. 4. Conlusion A miniturized widend BLC is designed using T- shpe TL setion nd dul TL s feed network in ple of λ/4-long series TL. The proposed design provides n overll size redution of 44% ompred to the BLC with single qurter wvelength setion s feed network t ll the ports. The mesured results re ompletely ompiled with the simulted frequeny response for 50.4% FBW with isoltion nd return loss etter thn 15 db. The proposed struture is frited with stndrd printed iruit ord whih is ost effetive in terms of mss prodution, s result of whih it hs gret demnd in mirowve iruits. Aknowledgments This work is supported y the Ministry of Eletronis nd Informtion Tehnology (MeitY) for providing finnil support under Visvesvry PhD sheme. Referenes [1] LI, Y., SUN, S., YANG, F. Dul-nd hyrid pth oupler with emedded spirl open stus. In Proeedings of Asi Pifi Mirowve Conferene. Kohsiung (Tiwn), 2012, p. 169 171. DOI: 10.1109/APMC.2012.6421535 T. 4. Comprisons of widend BLC with the proposed one. [2] SUN, S., HU, L. Miniturized pth hyrid ouplers using symmetrilly loded ross slots. IET Mirowves, Antenns nd Propgtion, 2010, vol. 4, no. 9, p. 1427 1433. DOI: 10.1049/IET-MAP.2009.0293 [3] TSAI, K. Y., YANG, H. S., CHEN, J. H., CHEN, Y. J. E. A miniturized 3 db rnh-line hyrid oupler with hrmonis suppression. IEEE Mirowve nd Wireless Components Letters, 2011, vol. 21, no. 10, p. 537 539. DOI: 10.1109/LMWC.2011.2164901 [4] GHALI, H., MOSELHY. T. A. Miniturized frtl rt-re, rnh-line, nd oupled-line hyrids. IEEE Trnstions on Mirowve Theory nd Tehniques, 2004, vol. 52, no. 11, p. 2513 to 2520. DOI: 10.1109/TMTT.2004.837154 [5] TANAKA, H., BANBA, N., ARI, S., NISHIKAWA, T. 2 GHz one otve-nd 90 degree hyrid oupler using oupled mender line optimized y 3-D FEM. In IEEE MTT-S Interntionl Mirowve Symposium Digest. Sn Diego (CA, USA), 1994, vol. 2, p. 903 to 906. DOI: 10.1109/MWSYM.1994.335211 [6] VOGEL, R. W. Anlysis nd design of lumped- nd lumpeddistriuted-element diretionl ouplers for MIC nd MMIC pplitions. IEEE Trnstions on Mirowve Theory nd Tehniques, 1992, vol. 40, no. 2, p. 253 262. DOI: 10.1109/22.120097 [7] MOHRA, A. S., ALKANHAL, M. A., ABDULLAH, E. A. Sizeredued defeted ground mirostrip diretionl oupler. Mirowve nd Optil Tehnology Letters, 2010, vol. 52, p. 1933 1937. DOI: 10.1002/mop.25410 [8] YAMAMOTO, S., HIROKAWA, J., ANDO, M. Length redution of short-slot diretionl oupler in single-lyer dieletri sustrte wveguide y removing dieletri ner the side wlls of the oupler. In IEEE Antenns nd Propgtion Soiety Symposium. Monterey (CA, USA), 2004, vol. 3 p. 2353 2356. DOI: 10.1109/APS.2004.1331844 [9] XINHUA REN, QI HU, SHANJIA XU. Design of diretionl oupler with left-hnded trnsmission line. In IEEE Antenns nd Propgtion Soiety Interntionl Symposium, 2006, p. 4157 to 4160. [10] ABDALLA, M. A. Y., PHANG, K., ELEFTHERIADES, G. V. A ompt highly reonfigurle CMOS MMIC diretionl oupler. IEEE Trnstions on Mirowve Theory nd Tehniques, 2008, vol. 56, no. 2, p. 305 319. DOI: 10.1109/TMTT.2007.913360 [11] TANG, C. W., CHEN, M. G., TSAI, C. H. Minituriztion of mirostrip rnh-line oupler with dul trnsmission lines. IEEE Mirowve nd Wireless Components Letters, 2008, vol. 18, no. 3, p. 185 187. DOI: 10.1109/LMWC.2008.916798 [12] KAWAI, T., TANIGUCHI, H., OHTA, I., ENOKIHARA, A. Brodnd rnh-line oupler with ritrry power split rtio utilizing mirostrip series stus. In40th Europen Mirowve Conferene. Pris (Frne), 2010, p. 1170 1173. DOI: 10.23919/EUMC.2010.5616093 [13] WONG, Y. S., HENG, S. Y., CHAN, W. S. Multifold ndwidth rnh line oupler with filtering hrteristi using oupled port
RADIOENGINEERING, VOL. 27, NO. 1, APRIL 2018 213 feeding. Progress In Eletromgneti Reserh, 2011, vol. 118, p. 17 35. DOI: 10.2528/PIER11041401 [14] ARRIOLA, W. A., LEE, J. Y., KIM, D. I. S. Widend 3 db rnh line oupler sed on λ/4- open iruited oupled lines. IEEE Mirowve nd Wireless Components Letters, 2011, vol. 21, no. 9, p. 486 488. DOI: 10.1109/LMWC.2011.2138687 [15] LEE, L., LEE, Y. Widend rnh-line ouplers with singlesetion qurter-wve trnsformers for ritrry oupling levels. IEEE Mirowve nd Wireless Components Letters, 2012, vol. 22, no. 1, p. 19 21. DOI: 10.1109/LMWC.2011.2176723 Aout the Authors... Mukesh KUMAR (1989) reeived the B.Teh. degree in Eletroni nd Tele-omm. Engineering from the Biju Ptnik University of Tehnology, Rourkel, Oriss in 2011, nd the M.Teh degree in Eletronis nd Communition Engineering from the Ntionl Institute of Tehnology, Durgpur in 2015. He is urrently pursuing the Ph.D. degree in Mirowve Engineering with the Eletronis nd Teleommunition Engineering Dept., Indin Inst. of Engineering Siene nd Tehnology, Shipur, Howrh, Indi. His urrent reserh interests inlude mirowve plnr iruits, power divider, ouplers. SK. Nurul ISLAM (1989) reeived the B.Teh. degree in 2011 nd the M.Teh degree in 2013, oth in Eletroni nd Comm. Engineering from the West Bengl University of Tehnology, Kolkt. He is urrently pursuing the Ph.D. degree in Mirowve Engineering with the Eletronis nd Teleommunition Engineering Dept., Indin Inst. of Engineering Siene nd Tehnology, Shipur, Howrh, Indi. His urrent reserh interests inlude mirowve plnr ntenn, metmteril. Goind SEN (1988) reeived the B.Teh. degree in Eletroni nd Comm. Engineering from the West Bengl University of Tehnology in 2010, nd the M.Teh degree in Communition Engineering from the University of Klyni, Klyni in 2013. He is urrently pursuing the Ph.D. degree in Mirowve Engineering with the Eletronis nd Teleommunition Engineering Dept., Indin Inst. of Engineering Siene nd Tehnology, Shipur, Howrh, Indi. His urrent reserh interests inlude metmteril inspired struture for performne improvement of ntenn, sorers. Susnt Kumr PARUI (1965) reeived the B.S degree in Physis, nd the B.Teh. degree in Rdio Physis nd Eletronis from the University of Clutt in 1987 nd 1990, respetively. He hs done the Mster degree in Mirowve Communition Engineering from the Bengl Engineering College, Indi in 1993. From 1993 to 2000, he worked s n Instrument Engineer. Sine 2000, he is ssoited with the Dept. of Eletronis nd Teleommunition Engineering, Bengl Engineering nd Siene University, Indi nd presently holds the post of Senior Leturer. His urrent reserh interests inlude the plnr iruits, filters, ntenn elements nd eletromgneti ndgp strutures. Sntnu DAS (1968) reeived the B.E. degree in Eletroni nd Teleom. Engineering from the Bengl Engineering College in 1989, nd the M.E degree in Mirowve Engineering from the Jdvpur University, Clutt in 1992. He otined the Ph.D (Engineering) degree in the yer 1998 from the Jdvpur University. As Leturer in Eletronis nd Teleommunition Engineering, he joined the deprtment of the Bengl Engineering nd Siene University in 1998 nd presently holds the post Professor t the sme deprtment. His urrent reserh interests inlude the mirostrip iruits, ntenn elements nd rrys, FSS nd defeted ground strutures. He is life memer of the Institution of Engineers, Indi.