This paper shows the design of a dual-band Butler matrix aimed to cover the bands corresponding to the standards IEEE802.11a/b, with particular interest in WLAN systems, at the 2.4 GHz and 5 GHz bands. Measurements of the individual dual-band components which compose the Butler matrix are presented. Those components are: quadrature hybrid and 0 dB coupler. The phase shifter design is also described. A final design of the Butler matrix is proposed and measured. Over the proposed frequency range, the Butler matrix exhibits phase errors and couplings of within 13.5/spl deg/ and - 6.7 /spl plusmn/ 0.8 dB, respectively. A performance prediction of the Butler matrix connected to an array of isotropic and perfectly matched antennas separated half-wavelength in air is also briefly commentedPeer Reviewe

Collado Gómez, Juan Carlos

Flaviis, Franco de

Grau Besolí, Alfred

English

UPCommons. Portal del coneixement obert de la UPC

Dual-Band Butler Matrix for WLAN SystemsCarlos Collado∗, Alfred Grau† and Franco De Flaviis†∗Technical University of Catalonia, Campus Nord D4-009, Barcelona, 08034, Spain (collado@tsc.upc.es)and †University of California at Irvine, Irvine, California 92697, USA (franco@uci.edu)Abstract— This paper shows the design of a dual-band Butlermatrix aimed to cover the bands corresponding to the standardsIEEE802.11a/b, with particular interest in WLAN systems, at the2.4 GHz and 5 GHz bands. Measurements of the individual dual-band components which compose the Butler matrix are presented.Those components are: quadrature hybrid and 0 dB coupler. Thephase shifter design is also described. A final design of the Butlermatrix is proposed and measured. Over the proposed frequencyrange, the Butler matrix exhibits phase errors and couplingsof within 13.5◦ and −6.7± 0.8 dB, respectively. A performanceprediction of the Butler matrix connected to an array of isotropicand perfectly matched antennas separated half-wavelength in air,is also briefly commented.I. INTRODUCTIONButler matrices are used to design multi-port amplifier[1][2], and especially to design smart antennas with switchedradiation beams [3][4] for communications systems. Some ofthem are dual-band systems. Circuits working at both bandsare useful to increase the integration level.At microwave frequencies is difficult to design a circuitwith the same behavior at two uncorrelated frequencies, sothe above commented systems often share only a dual-bandantenna and the frequency bands are separated using diplexer.The elements of a Butler matrix are quadrature hybrids,a 0 dB coupler and phase shifters. There are two possibleapproaches for the design of those circuits for its use in adual-band system: to use broadband elements or dual-bandelements. The dual-band approach has been followed in thiscase.The design of the dual-band Butler matrix is aimed to beuse in WLAN systems and cover the frequencies correspond-ing to the standards IEEE802.11b at f1 = 2.45 GHz, andIEEE802.11a at f2 = 5.25 GHz and f3 = 5.8 GHz.The proposed microstrip Butler matrix provides enhancedbandwidth for the upper frequency band at 5 GHz in orderto cover all its frequency range. Under our knowledge this isthe first dual all planar Butler Matrix (BM) reported in theliterature.II. ELEMENTS OF THE BUTLER MATRIXAn NxN Butler matrix can be used to feed an array ofN antennas [5]. The scheme of a 4x4 BM is shown in Fig.1. From the transmission point of view, the BM distributesthe incoming signal at one TX/RX port to the ports in thearray of antennas. If conveniently designed, the signals at thefour ANT-ports have constant differential phase shift betweenconsecutive radiators. The superposition of all the phasedbeams results in a more directional radiation beam pointingto a certain direction. The shape of the radiation pattern andFig. 1. Schematic of the proposed dual-band Butler matrixTABLE IDIFFERENCES OF PHASES BETWEEN CONSECUTIVE ANTENNASHybrid Shift TX/RX1 TX/RX2 TX/RX3 TX/RX4phase phase(∆ϕh) (∆φ)90◦ −45◦ 45◦ −135◦ 135◦ −45◦90◦ 135◦ −135◦ 45◦ −45◦ 135◦−90◦ 45◦ −45◦ 135◦ −135◦ 45◦−90◦ −135◦ 135◦ −45◦ 45◦ −135◦the direction where it points depends on which TX/RX portis used, so it is possible to switch between 4 beams, whichmoreover are orthogonal and uncorrelated.As shown in Fig. 1 a BM consists of quadrature hybrids,cross-overs and phase shifters which provide adequate phaseshifts to operate appropriately. Following the numeration ofFig. 1, if the differential phase ∆ϕh = ϕh(S31) − ϕh(S41)(where ϕh(S31) and ϕh(S41) are the phases of the S31 andS41 parameters respectively) of each hybrid is ∆ϕh = −90◦,then the phase shifter has to change the phase of the incomingsignal by ∆φ = 45◦. On the other hand, if those differentialphase shifts were to be ∆ϕh = 90◦, the amount to shift inthat case would be ∆φ = −45◦.However these two solutions are not the unique possibilities.Table I shows the differences of phases between consecutiveantennas of all four possible combinations or designs, for eachTX/RX ports of the BM.It is obvious that the performance of the overall system isthe same for each solution, however in order to design a dual-band butler matrix, we can take advantage of this flexibilityby choosing the best suitable solution for each frequency,once one is concerned about the design of each individualcomponent, and in particular during the design of the phaseshifter commented later in section II-C.We have tested individually the components: hybrid, 0 dBcoupler and phase shifter, which were later combined together0-7803-8846-1/05/$20.00 (C) 2005 IEEE 2247Fig. 2. Simulation (solid lines) and measurements (non-solid lines) of theinsertion loss for the H1-H3 path, S31 (circles line), and the H1-H4 path, S41(diamonds line).TABLE IIMEASUREMENT DATA AT THE CORRESPONDING FREQUENCIES FOR THEUS WLAN SERVICESFrequency S31 S41 ∆ϕh (◦) Isolation Return(dB) (dB) (dB) Loss (dB)f1 = 2.45 GHz -3.1 -3.4 -89.7 -30 -28f2 = 5.25 GHz -3.6 -3.2 91.1 -27 -27f3 = 5.8 GHz -3.3 -3.5 91.5 -24 -24to design the butler matrix of Fig. 7. The used dielectric wasRO3006 with relative dielectric constant 6.15, thickness 0.635mm and metallization thickness 0.017 mm.A. Dual-band hybridPlanar dual-band hybrids can be designed using 3 branch-line 3 dB couplers in which the length of the coupling lines inone pair of the parallel arms is twice longer (λ/2) than in theother (λ/4) [6]. These couplers can be designed to operate attwo uncorrelated frequencies and they have large bandwidthsat each frequency band. Fig. 7 shows the prototype that is usedfor the BM design.The hybrid was designed to provide operativity for both theIEEE802.11b and IEEE802.11a standards, in the 2.4 GHz andthe 5 GHz band respectively. This hybrid was optimized toenhance the bandwidth of the upper frequency band in orderto deal with the services allocated between 5.15 GHz and 5.85GHz, in both the US and EU.Figures 2, 3 and 4 shows the good agreement betweensimulation and measurements of the S parameters, and table IIresumes the more relevant data at the corresponding frequen-cies for the US WLAN services.B. Dual-band 0 dB couplerA planar cross-over can be made by cascading two quadra-ture hybrids [3]. The layout of the proposed cross-over canbe seen in Fig. 7. It was designed by cascading two dualhybrids like that described in the previous section and it is theFig. 3. Simulation (solid lines) and measurements (non-solid lines) of thereturn loss, S11 (circles line) and isolation, S21 (diamonds line).Fig. 4. Simulation (solid line) and measurements (doted line) of the phasedifference between port H3 and H4.result of an optimization process using the method of momentssimulator (Momentum) from [7].Figures 5 and 6 shows the simulations and measurementsdata of some of the main S parameters. The measured insertionlosses are smaller than 0.7 dB for the three frequencies (2.45GHz, 5.25 GHz and 5.8 GHz) and the return losses andisolations better than 20 dB.C. Phase shifterThe phase shifter has to delay the signals an amount equal tothe delay of the crossover, φc, plus the needed phase shift ∆φ.That is, φp = φc +∆φ being φp the phase shifter phase delay.That means that the simulated phases φc of the crossover ateach frequency, which are 47◦, 64◦ and −28◦ at 2.45 GHz,5.25 GHz and 5.8 GHz respectively, have to be added to oneof those suggested in the second column of Table I taking intoaccount that the designed hybrid has a 90◦ differential phaseshift between H3 port and H4 port (see Fig. 7) at 2.45 GHz, and2248Fig. 5. Simulation (solid lines) and measurements (non-solid lines) of theinsertion loss for the C1-C3 path, S31 (circles line), and the C1-C4 path, S41(diamonds line).Fig. 6. Simulation (solid lines) and measurements (non-solid lines) of thereturn loss, S11 (circles line) and isolation, S21 (diamonds line).−90◦ from 5.25 GHz to 5.8 GHz. Table III shows a summaryof the suitable phase shifts amounts for each component ofthe BM for two solutions of a total of four, at the three designfrequencies. Those four possible combinations are the onescommented previously in table I.A 50 Ohms transmission line of length 60.2 mm producesimilar phase shifts that those values typed with bold style atTable III, therefore we chosen those as goals for the design of amore accurate phase shifter. The final design is a transmissionline with specifically located and shaped meandered curves andit can be seen at Fig. 7. Such circuit produces the requiredphase shifts within a margin of error smaller than 2◦, hasinsertion losses smaller than 0.6 dB and return losses betterthan 20 dB.III. BUTLER MATRIX LAYOUT AND MEASUREMENTSThe layout of the whole Butler matrix is shown in Fig. 7.The total area is 60x60 mm. In this version, no efforts to reduceTABLE IIIPHASE SHIFTS AT THE THREE DESIGN FREQUENCIESf1 f2 f3Hybrid (∆ϕh) 90◦ −90◦ −90◦Crossover (φc) 47◦ 64◦ −28◦Phase shifter (φp)Solution 1: (∆φ = −45◦at f1 and ∆φ = 45◦ at f2,3) 2◦ 109◦ 17◦Phase shifter (φp)Solution 2: (∆φ = 135◦at f1 and ∆φ = −135◦ at f2,3) 182◦ −71◦ −163◦Fig. 7. Layout of the dual-band Butler matrix.its size have been made and smaller design could be achievedby replacing the straight transmission lines of the hybrids bymeander lines [8] or loading its branches with open stubs [9][10].Figures 8 and 9 shows the insertion losses of the networkwhen it is feed at the port number 1 and 2 respectively. Notethe large bandwidth of the second band around 5.5 GHz, inboth ports. Port 3 and port 4 gives the same results due to thenetwork symmetry.Table IV shows the insertion losses at the 3 frequencies ofinterest when the signal is input in port 1 and 2.And Table V shows the differential phase shift betweenantenna ports, when the BM is feed at port 1 and 2. Similarly,the phases generated when feed from port 3 and port 4 are thesame but with opposite sign, due to the network symmetry.IV. CONCLUSIONA planar microstrip dual-band Butler matrix has been pro-posed. It was designed to be use in multiband (2.45 GHz, 5.25GHz and 5.8 GHz) operation services (WLAN systems). TheTABLE IVINSERTION LOSSES AT THE THREE FREQUENCIES OF INTERESTPort number f1 f2 f31 6.7± 0.4dB 7.0± 0.3dB 7.0± 0.5dB2 6.4± 0.5dB 6.9± 0.4dB 6.9± 0.4dB2249Fig. 8. Measurements of the insertion loss for the 1-5 (solid line), 1-6 (dashedline), 1-7 (dotted line) and 1-8 (dash-dot line) paths.Fig. 9. Measurements of the insertion loss for the 2-5 (solid line), 2-6 (dashedline), 2-7 (dotted line) and 2-8 (dash-dot line) paths.BM exhibits phase errors and couplings of within 13.5◦ and−6.7± 0.8 dB, respectively.An ideal design of the proposed BM should create fourradiation beams, two of them pointing at ±14.5◦ (boresightangle) for a progressive phase between antenna ports of ±45◦,and the other two pointing at ±48.75◦ for a progressive phasebetween antenna ports of ±135◦. An array of four isotropicantennas separated 0.5λ0, being λ0 the wavelength in the air,and with perfectly matched antenna ports to the BM networkwas considered. A side lobe level (SLL) of 11.3dB should beexpected in that case. Comparing the theoretical case with themeasurements of the fabricated BM, errors in the scanningangles were predict to be approximately 1◦ and 1.25◦ forprogressive phases of ±45◦ and ±135◦ respectively. The SLLwas observed to be within 11.3dB and 9.4dB.TABLE VPROGRESSIVE PHASE BETWEEN ANTENNA PORTSPort f1 f2 f3number1 44.6◦ ± 7.4◦ 135.1◦ ± 8.7◦ 137.5◦ ± 9.9◦2 −132.1◦ ± 7.1◦ −42.7◦ ± 11.2◦ −44.0◦ ± 10.3◦ACKNOWLEDGMENTCarlos Collado wants to thank the Ministry of UniversitiesResearch and Information Society (DURSI) of the Generalitatde Catalunya for hosting him at the Electrical Engineering andComputer Science Department at the University of California,Irvine. The authors also want to thanks the support of theBalsells fellowships and the California-Catalonia EngineeringInnovation Program 2004.REFERENCES[1] M. Lisi, “An introduction to multiport power amplifiers,” MicrowaveEngineering Europe, 1992.[2] L. Accatino, A. Angelucci, and B. Piovani, “Design of butler matricesfor multiport amplifier applications,” Microwave Engineering Europe,pp. 45–50, Apr 1992.[3] T. Denidni and T. Libar, “Wide band four-port butler matrix for switchedmultibeam antenna arrays,” Personal, Indoor and Mobile Radio Commu-nications, vol. 3, Sept 2003.[4] J. Butler and R. Lowe, “Beam forming matrix simplifies design of elec-tronically scanned antennas,” Applied Superconductivity, IEEE Transac-tions on, vol. 9, pp. 170–173, Apr 1961.[5] H. Moody, “The systematic design of the butler matrix,” Antennas andPropagation, IEEE Transactions on, vol. 12, no. 6, pp. 786–788, Nov1964.[6] C. Collado, A. Grau, and F. D. Flaviis, “A dual-band planar quadraturehybrid with enhanced bandwidth,” Microwave Theory and Techniques,IEEE Transactions on, 2004, submitted.[7] “http://www.agilent.com,” Nov 2004.[8] A. Corona and M. J. Lancaster, “A high-temperature superconductingbutler matrix,” Applied Superconductivity, IEEE Transactions on, vol. 13,no. 4, pp. 3867–3872, Dec 2003.[9] K.-K. Cheng and F.-L. Wong, “A novel approach to the design andimplementation of dual-band compact planar 90◦ branch-line coupler,”Microwave Theory and Techniques, IEEE Transactions on, vol. 52,no. 11, pp. 2458–2463, Nov 2004.[10] T. Hirota, A. Minakawa, and M. Muraguchi, “Reduced-size branch-line and rat-race hybrids for uniplanar mmic’s,” Microwave Theory andTechniques, IEEE Transactions on, vol. 38, no. 3, pp. 270–275, Nov1990.2250

Dual-band Butler matrix for WLAN systems

UPCommons

https://upcommons.upc.edu/bitstream/2117/1366/1/colladodigest2005.pdf

Dual-band Butler matrix for WLAN systems

Abstract

Similar works

Full text

Available Versions

UPCommons. Portal del coneixement obert de la UPC

UPCommons