This is a repository copy of Four-port diplexer for high Tx/Rx isolation for integrated transceivers.

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1 This is repository copy of Four-port diplexer for high Tx/Rx isoltion for integrted trnsceivers. White Rose Reserch Online URL for this pper: Version: Accepted Version Article: Konpng, J orcid.org/ , Sndhu, M, Somjit, N orcid.org/ et l. (1 more uthor) (2018) Four-port diplexer for high Tx/Rx isoltion for integrted trnsceivers. IET Microwves, Antenns nd Propgtion, 12 (6). pp ISSN Institution of Engineering nd Technology. This pper is postprint of pper sumitted to nd ccepted for puliction in IET Microwves, Antenns nd Propgtion nd is suject to Institution of Engineering nd Technology Copyright. The copy of record is ville t the IET Digitl Lirry. Reuse Items deposited in White Rose Reserch Online re protected y copyright, with ll rights reserved unless indicted otherwise. They my e downloded nd/or printed for privte study, or other cts s permitted y ntionl copyright lws. The pulisher or other rights holders my llow further reproduction nd re-use of the full text version. This is indicted y the licence informtion on the White Rose Reserch Online record for the item. Tkedown If you consider content in White Rose Reserch Online to e in rech of UK lw, plese notify us y emiling eprints@whiterose.c.uk including the URL of the record nd the reson for the withdrwl request. eprints@whiterose.c.uk

2 A four-port diplexer for high Tx/Rx isoltion for integrted trnsceivers Jessd Konpng*, Muhmmd Sndhu, Nutpong Somjit nd In C. Hunter School of Electronic nd Electricl Engineering, Institute of Microwves nd Photonics, University of Leeds, Leeds LS2 9JT, U.K. * eljk@leeds.c.uk Astrct: A four-port diplexer consisting of two ck-to-ck three-port diplexers comined with 180 phse shifter in one rnch is presented. The technique chieves high Tx/Rx isoltion with reltively low degree filters. Two experimentl diplexers re demonstrted, one with equl Q resontors in ll filters nd the other with dissimilr Q fctors, enling minituriztion nd cost reduction. Mesured results of Tx/Rx diplexer devices t 2.13/1.73GHz re presented nd 40dB Tx/Rx isoltion is chieved with only second-order filters. 1. Introduction Diplexer, which re usully set in the form of filters, re three-port networks nd commonly used to comine or seprte different signl frequencies. RF front-ends in rdio cellulr network uses ndpss filters to discriminte two different frequency nds for trnsmitting (Tx) nd receiving (Rx) chnnels when single ntenn is shred in the se sttion. Generlly, reltive high-power signls, with n order of 30W, re generted nd flow in the Tx chnnel. These high-power signls generted in the Tx rnch cn esily interfere the Rx chnnel nd cn even destroy some Rx components, e.g. low-noise mplifiers nd etc., if the signl isoltion etween Tx nd Rx chnnels re not sufficiently high [1]. Therefore, design technique to increse signl isoltion while offering ese of design nd superior figure-of-merit, e.g. low signl losses s well s low cost nd smll size, is required. Normlly, the most common diplexer structure is to comine ndpss filters through three-port impednce mtching network. Most diplexer designs with high Tx/Rx isoltion require high degree filters, resulting in very complicted filter design nd friction. Consequently, these complicted higher-order filter rchitectures increse overll signl losses s well s high friction cost nd lrge diplexer size. Diplexer designs sed on microstrip structure cn chieve low cost, smll filter size nd ese of integrtion ut provide low power hndling nd high signl losses due to dielectric nd ohmic losses [2-5]. An lterntive technology to reduce overll signl losses nd increse power hndling with the sme or etter isoltion compred to the microstrip technology is comline coxil resontor structures [6-7]. However, the min drwck of this design technique is tht the degree of the filters increses linerly when higher signl isoltion is required ecuse this conventionl diplexer structure design is still sed on three-port networks. To chieve higher signl isoltion, higher-order conventionl diplexer design technique cn e used ut t the costs of higher signl losses, complexity, cost nd igger size. In this pper, new design technique of nonconventionl four-port diplexer for high Tx/Rx isoltion with reltively low-order filter topology for integrted highpower trnsceivers is introduced. The new design technique is sed on two ck-to-ck second-degree diplexers, Fig. 1. Schemtic digrm of four-port diplexer using two ck-to-ck three-port diplexers with mplitude nd 180 phse cncelltion technique etween Rx nd Tx chnnel which re comined to form four-port diplexer s shown in Figure 1. The design frequencies of the four-port diplexer re 1.73GHz nd 2.13GHz for Rx nd Tx module, respectively. Two different designs of four-port diplexer prototypes, sed on filter designs with similr nd dissimilr Q-fctors, re fricted nd mesured to verify the new design technique. High signl isoltion etween Tx nd Rx module is chievle y only using second-order filter topology nd the design technique is sed on mplitude nd phse cncelltion etween two diplexer rnches of the four-port diplexer. This pper is extended from the pulished conference pper y the uthors [8]. In the conference pper, the mthemticl model ws developed nd some nlyticl nd simultion results were otined to verify the model. In this pper, we show complete diplexer designs nd fricted diplexer prototypes with extensive mesurement results to verify the designs. Moreover, in this pper, we lso introduced n dditionl design technique sed on dissimilr Q-fctors for ech three-port diplexer rnch, which is verified y mesurement results, to decrese the overll size nd cost of the diplexer system, while still offering superior figure-of-merits, e.g. high Tx/Rx isoltion. 1

3 2. Four-port diplexer nlysis nd synthesis For lossless nd reciprocl network, the unitry condition of network cn e shown s [1]: [S][S*]=[1] (1) The solution for four-port diplexer from [8] cn replce conventionl diplexer. Hence, we exmine fourport network s shown in Fig. 1. Let Let we consider Tx frequency, By setting nd, which re ritrry numers, then we define sine wves with the sme mplitude, A, ut different phses etween point 2 nd 4 cn e expressed s sin sin, where is the phse of sinusoidl signls nd is the phse difference etween these two signls. Then, the reltionship etween signl phses of these two sinusoidl signls nd Tx/Rx signl isoltion re simulted nd plotted, s shown in Fig. 2. To otin the est Tx/Rx isoltion, the two sinusoidl signls in Pths 1 nd 2 must hve the sme mplitude nd the signl phses etween Ports 2 nd 4 must e out of phse, 180 difference. To fulfill these requirements we, therefore, use two resontors with equl Q-fctors (Q 1=Q 2) nd dd n dditionl 180 phse shifter in our diplexer designs, which is shown in Fig. 1. To decrese the overll size of the four-port diplexer, resontors with dissimilr Q-fctors etween Pths 1 nd 2 = 1,, = 1, =0 (2) In order to determine S24, we consider from four-port S-prmeters = (3) A solution from [8] is For rel quntities nd (4) =, (5) When 1 Therefore, the scttering prmeters of four-port network t Tx frequency cn e given s Fig. 2. Simulted Tx/Rx isoltion versus phse differences etween port 2 nd 4 of two-diplexers (Pth 1 nd Pth 2) with the sme Q-fctors. The est Tx/Rx signl isoltion is chievle t 180 phse shift (6) And t Rx frequency (7) In (6) nd (7), S 13 is equl to -S 24, i.e. the sme vlue ut different sign or 180 out of phse. Therefore, it is noticele tht, etween Port 2 nd 4, exctly 180 phse shift must e introduced while keeping the signl mplitudes equl in order to otin n infinite Tx/Rx signl isoltion. To investigte the signl from Tx to Rx, we consider two sinusoidl signls propgting in two pths: Pth 1 nd Pth 2, s shown in Fig. 1. The superposition of these two Fig. 3. Simulted Tx/Rx signl isoltion versus ttenution of two diplexers with different Q-fctors. The resonle Tx/Rx signl isoltion of etter thn 40 db is otined when the ttenution difference etween the two diplexers is less thn 0.1 db 2

4 my e used. For the resontors with dissimilr Q-fctors, Q 1 Q 2, we lso consider the superposition of two sinusoidl signls with different mplitudes nd phse different of 180 s sin sin 180 ), where A nd B re the signl mplitudes in oth signl pths nd we ssume A<B (Q 1<Q 2). The reltionship etween signl ttenution, differences etween B nd A, nd the Tx/Rx signl isoltion is clculted nd plotted in Fig. 3. To mintin resonle Tx/Rx signl isoltion, e.g. etter thn 40 db, the mplitude ttenution etween the two diplexers must e kept smller thn 0.1dB. Fig. 4. Four-port diplexer topology nd its equivlent circuit sed on second-order filter consisting of externl coupling, internl coupling coefficients nd element vlues of resontors with 180 phse shifter etween Port 2 nd 4 Fig. 5. Simultion results () S-prmeters of the four-port diplexer design t Tx=2.13 GHz, Rx=1.73 GHz, () Phses of S 13 nd S 24 with 180 phse difference t 2.13 GHz 3. Lumped element model The key design prmeters of lumped-element Cheyshev four-port diplexer re specified s the centre frequency, pssnd ndwidth, stopnd ttenution, pssnd insertion loss nd pssnd return loss. Both fourport diplexers with the equl Q (Q 1=Q 2=1800) nd dissimilr Q-fctors (Q 1=1800, Q 2=3600) re designed t the centre frequency of 1.73 GHz nd 2.13 GHz for Rx nd Tx module, respectively, with 20-dB ndwidth of 50 MHz. The equivlent circuit of the four-port diplexer, for oth equl nd dissimilr Q-fctors is shown in Fig. 4. The loded normlized lowpss prototype filter element vlues (g i) cn e clculted s in [9]. The clculted design element vlues of the equl Q nd dissimilr Q-fctors with db ripple re given s g 0=1, g 1=0.6682, g 2= nd g 3= The impednce inverter for externl coupling coefficients re K T1= nd K R1= The impednce inverter for internl coupling coefficients re K T12= 0.084, K R12= Therefore, K T nd K R refer to the impednce converters t the input nd output port of ech filter. The element vlues of shunt resontor re L 11= nh, L 22= nh, C 11= pf, C 22= pf. Both equl Q nd dissimilr Q fctor diplexer designs hve exctly the sme prmeters s the key design prmeters nd the only difference etween these two designs re the Q fctors. From Fig.4, two diplexers, which cn hve either similr or dissimilr Q-fctors, with phse difference of 180 re comined together y using ck-to-ck technique to chieve n optimum Tx/Rx signl isoltion. The simultion results of the four-port diplexer circuit nlysis simulted y AWR Microwve Office is plotted in Fig. 5(). For the similr Q-fctor diplexer design, Diplexer 1 nd 2 re designed with the sme Q-fctors of The simultion results show tht the pssnd insertion loss (IL) in Tx nd is less thn 0.25 db while, in Rx nd, it is less thn 0.32 db. For dissimilr Q-fctor diplexer design, Diplexer 1, is designed with Q fctor of 1800 while the second diplexer, Diplexer 2, is designed with Q fctor of From the simultion results, the pssnd IL in Tx nd is less thn 0.19 db nd the pssnd IL in Rx nd is less thn 0.23 db. The return loss (RL) of the diplexer design for oth similr nd dissimilr Q-fctors in oth Tx nd Rx chnnels re etter thn 20 db in the pssnd. According to (6) nd (7), the phse responses of S 12 nd S 34 hve the sme phse ut, for S 13 nd S 24, phse difference etween these prmeters re 180 or out of phse. Fig. 5() depicts the phse responses of S 13 nd S 24. To chieve n optimum Tx/Rx isoltion, the phse of S 13 nd S 24 re designed to e nd , respectively, 3

5 Fig. 6. Geometricl structure of comline filters () Positive coupling introduced vi n iris/window, () Negtive coupling (phse shifter) chieved y n opening in the upper prt of the wll nd metllic wire suspended in the iris etween the resontors Fig. 8. Geometricl structure of four-port comline filters () The geometric structure of four-port diplexer with the similr Q-fctors (Q 1=Q 2=1800), () Top view without lid of the fricted four-port diplexer prototype with the similr Q-fctors Fig. 7. Simultion results () S-prmeters of comline filter designed y positive nd negtive coupling structures t Tx nd of 2.13 GHz, () Phse responses of S 13 nd S 24 nd, thus the phse difference etween them is 180 t f 0 =2.13 GHz, which fulfil the requirements s stted in (6) nd (7). The phse of S 13 nd S 24 re not fixed y these vlues. The comintion of phse should e 180. Idelly, when the filter is designed with 180 phse shift nd equl mplitudes, the resulting isoltion ecomes infinity. However, it is not necessry to chieve exct 180 phse shift. If the required isoltion of the diplexer is etter thn 40 db, the phse etween S 13 nd S 24 does not require to e exctly 180 difference. The phse shift cn esily e tuned using single phse shifter in second diplexer rnch without introducing further complexity. 4. Diplexer designs nd friction Bsed on the mthemticl synthesis nd lumpedelement model, the individul filter rnches consist of second-order Cheyshev diplexer design re fricted y using comline resontors. To chieve the filter design with 180 phse shift etween two diplexer rnches, the 90 positive inverter nd -90 negtive inverter coupled filter re required. The positive nd negtively coupled comline filters re designed y using Ansys HFSS with the physicl structure presented in Fig. 6. The negtive coupling in Fig. 6() cn e designed with n opening in the upper prt of the wll, y which the electric field coupling is strongest, 4

6 Tle 1 Prmeters of geometric structure of four-port diplexer ccording to Fig. 8(), 9() nd 12 Prmeters Vlues Vlues Prmeters (mm) (mm) 50.6 d c h 24.2 r t 4.00 d r d r d w 3.00 d g s1 s2 s3 s4 s5 z d5 d6 j k p q for ech filter pir while Fig. 9() shows the fricted prototype of the dissimilr-q-fctor for-port diplexer. The optimized prmeters for oth four-port diplexers, with equl nd dissimilr Q-fctors, re listed in tle 1. The prototypes of oth four-port diplexers re fricted y using computer numericlly controlled (CNC) mchine nd Aluminum nd Copper re used s structurl mterils. Tuning screws re implemented etween ech resontor to compenste mnufcturing errors s well s to optimize the resonnt frequencies nd inter-resontors couplings. Fig. 9. Geometricl structure of four-port comline filters () The geometric structure of four-port diplexer with dissimilr Q-fctors (Q 1=1800, Q 2=3600), () Top view without lid of the fricted four-port diplexer prototype with dissimilr Q-fctors while the positive coupling cn e implemented y using n iris/window, s shown in Fig. 6(). To increse the efficiency of the negtive coupling, n inversed U-shpe metllic wire is suspended ove the iris etween the resontors s shown in Fig. 6(). In prctice, the metllic wire is supported y Teflon with dielectric constnt 2.1 or ny other dielectric mterils, which hve dielectric property close to ir. Simultion results of second-order comline filters with positive nd negtive couplings re shown in Fig.7. From the simultion results, the positive nd negtively coupled comline-filter designs hve the sme resonnt frequency ut with the phse difference of 177.4, which is only 2.6 phse error from the mthemticl model. However, the phse error of comline filters cn e vried due to friction ccurcy ut cn e compensted y tuning coupling-screws s shown in Fig. 6. The comintion of four-filters is used to complete the four-port diplexer design. The 3D geometricl structure nd the fricted prototype of the four-port diplexer with ll filters designed with equl Q-fctors re show in Fig. 8() nd (), respectively. Likewise, Fig. 9() represents the 3D structure of the four-port diplexer with dissimilr Q-fctors 5. Mesurement results nd result comprisons 5.1. Mesurement results of for-port diplexer with equl Q-fctors The S-prmeter mesurement is chieved y using Agilent E5071C Network Anlyzer. Four-port clirtion is performed using Agilent N Electronic Clirtion Module prior to the mesurement. The mesured S-prmeters of four-port diplexer with the sme Q-fctors in ll rnches re shown in Fig. 10. From Fig. 10(), the pssnd ILs of oth Tx nd Rx nds re less thn 0.46 db nd 0.48 db, respectively. The RLs of oth Tx nd Rx chnnels re etter thn 20 db in the pssnd with the 20- db ndwidth of 50 MHz. Fig. 10() represents the comprison of mesured Tx/Rx isoltion of conventionl 3-port diplexer nd the new four-port diplexer design. At the centre frequency of 1.73 GHz nd 2.13 GHz for Rx nd Tx module, the mesured Tx/Rx isoltion of the conventionl three-port diplexer is db nd it is db for the four-port diplexer. Fig. 10(c) depicts the mesured phse response of Tx filter rnches, S 13 nd S 24, t the centre frequency of 2.13 GHz. From the mesurement results, the phses of S 13 nd S 24 re nd , respectively. Therefore, the phse difference etween the Tx nd Rx rnches is , which is only 2.35 error compred to the nlyticl model Mesurement results of four-port diplexer with different Q-fctors 5

7 The mesurement results of the second-order fourport diplexer with unequl Q-fctors for ech diplexer rnch is shown in Fig. 11. From Fig. 11(), the pssnd ILs of the Tx nd Rx nds re less thn 0.42 db. The RLs in oth chnnels re etter thn 20 db in the pssnd with the 20-dB ndwidth of 50 MHz. From Fig. 11(), the c Fig. 10. Mesurement results: () S-prmeters of four-port diplexer with the similr Q-fctors where Q 1= Q 2=1800 t Tx=2.13 GHz, Rx=1.73 GHz, () Signl isoltion, S 23, of four-port diplexer with the similr Q 1-fctors (35.15 db) nd three-port diplexer (26.28 db), (c) Phses of S 13 nd S 24 with phse difference t 2.13 GHz c Fig. 11. Mesurement results: () S-prmeters of four-port diplexer with dissimilr Q-fctors where Q 1= 1800, Q 2=3600 t Tx=2.13 GHz, Rx=1.73 GHz, () Signl isoltion, S 23, of four-port diplexer with dissimilr Q 1-fctors (40.11 db) nd three-port diplexer (26.28 db), (c) Phses of S 13 nd S 24 with phse difference t 2.13 GHz 6

8 Tle 2 Comprison of four-port diplexer with the stte-of-the rts diplexer Ref. Architecture Degree Insertion Loss (db) Tx/Rx 1 st /2 nd Pssnd (GHz) [5] 3-port / /1.3 [10] 3-port 3 1.6/ /10.5 Types Dul-mode Microstrip ring resontor Sustrte integrted surfce (SIW) Power Hndling [11] 3-port 5 0.6/ /2.67 Coxil resontors High [12] 3-port / /2.67 Three-port diplexer (This work) Four-port with the sme Q s (This work) Fourport with dissimilr Qs (This work) 3-port / / port / / port / /2.13 Triple-Mode Dielectric Loded resontors Comline resontors Comline resontors Comline resontors Low Low High High High High Size 0.82 g 0.82 g ( g 2 ) (mm 2 ) Isoltion (db) >26 >35 >55 >50 >26.28 >35 >40 Prcticlly, the mplitude nd phse errors result from friction nd tuning screws s well s negtive coupling. Therefore, the four-port diplexer with different Q-fctors hs slightly etter isoltion thn the design with the sme Q- fctors Comprisons to three-port diplexer To compre the isoltion of the proposed four port diplexer, conventionl three-port diplexer is implemented y shorting out ll the tuning screws in the diplexer 2 s shown in Fig.12. The mesured isoltion of three-port diplexer is db s compred in Fig. 10() nd 11(). Fig. 12. Geometricl structure of three-port comline filters mesured isoltion of the conventionl three-port diplexer is db nd it is 40.11dB for the four-port diplexer. The phse responses of S 13 nd S 24 t the centre frequency of 2.13 GHz re plotted in Fig.11(c). The mesured phses of S 13 nd S 24 re nd S , respectively, resulting in phse difference of which is only 1.67 phse error compred to the mthemticl model. Tle 2. represents the figure-of-merits nd extensive comprisons etween the novel four-port diplexer designs nd the pulished reserch works with different diplexer rchitectures. Theoreticlly, infinite signl cncelltion is chievle if the signls propgting through oth rnches hve the sme mplitude nd 180 phse difference. 6. Conclusions A new method for chieving high Tx/Rx isoltion using four-port diplexer is proved in here. The technique chieves high isoltion with two ck-to-ck low degree diplexers. However, one diplexer cn hve significntly lower Q thn the other. The four-port diplexer is designed t the centre frequency of Tx t 2.13 GHz, Rx t 1.73 GHz with BW=50MHz. The new technique design cn enhnce the isoltion (S 23) more thn 14 db from the conventionl diplexer. Finlly, this RF interference rejection technique cn e used in wireless communiction systems where smll size, low losses nd low complexity re required. Currently, work is progressing on investigting the effects of mismtched ntenn port. Clerly, if the ntenn port impednce is not 50 Ω, then the isoltion reduces. However, methods for compensting for this utomticlly djusting the isolted port lod impednce re eing investigted. 7

9 7. Acknowledgments The uthors would like to thnk Rdio Design Ltd. for supporting technicl technique. The dt ssocited with this pper re openly ville from the University of Leeds dt repository ( 8. References [1] Hunter, I.C.: Theory nd design of microwve filters (IEE Electromgnetic wves series, 2001) [2] Peng, H.-S. nd Ching, Y.-C.: Microstrip Diplexer Constructed With New Types of Dul-Mode Ring Filters, IEEE Microw. Wireless Compon. Lett., 2015, 25, (1), pp. 7-9 [3] Xue, Q. nd Chen, J.-X.: Compct diplexer sed on doule-sided prllel-strip line, Electron. Lett., 2008, 44, (2), pp [4] Zhou, Y., Deng, H.-W. nd Zho, Y.: Compct Blnced-to-Blnced Microstrip Diplexer with High Isoltion nd Common-Mode Suppression, IEEE Microw. Wireless Compon. Lett., 2014, 24, (3), pp [5] Chen, D., Zhu, L., Bu, H., et l.: A Novel Plnr Diplexer Using Slotline-Loded Microstrip Ring Resontor, IEEE Microw. Wireless Compon. Lett, 2015, 25, (11), pp [6] Shmsifr, K., Rodriguez, T. nd Hs, J.: High-power comline diplexer for spce, IEEE Trns. Microw. Theory Techn., 2013, 61, (5), pp [7] Surmnym, A. V. G., Sivreddy, D., Srinivsn, V. V., et l.: Multipction-free comline diplexer for deep spce pplictions, in 2014 IEEE Int. Microw. RF Conf. (IMRC)., Bnglore, Decemer 2014, pp [8] Konpng, J., Sndhu, M., Somjit, N., et l.: Novel RF interference rejection technique using four-port diplexer, th Europen Microw. Conf. (EuMC)., London, Octoer 2016, pp [9] Hong, J.-S. G. nd Lncster, M.J.: Microstrip filters for RF/microwve pplictions (Wiley, New York, 2001, 1st edn.) [10] Mrtínez, S. Sirci, J. D., Vgue, J. nd Bori, V. E.: Sustrte integrted wveguide diplexer sed on circulr triplet comline filters, IEEE Microw. Wireless Compon. Lett., 2015, 25, (7), pp [11] Zho, P. nd Wu, K.-L.: An itertive nd nlyticl pproch to optiml synthesis of multiplexer with str-junction, IEEE Trns. Microw. Theory Techn., 2014, 62, (12), pp [12] Zhng, Z.-C., Chu, Q.-X., Wong, S.-W., et l.: Triple- Mode Dielectric-Loded Cylindricl Cvity Diplexer Using Novel Pckging Technique for LTE Bse- Sttion Applictions, IEEE Trns. Compon., Pckg. Mnuf. Technol., 2016, 6, (3), pp