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IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, VOL. 19, NO. 11, NOVEMBER 2009 683

A Novel Triple-Band Microstrip Branch-LineCoupler With Arbitrary Operating Frequencies

Chong-Yi Liou, Min-Sou Wu , Student Member, IEEE , Jen-Chun Yeh , Student Member, IEEE ,Yu-Zhi Chueh , Student Member, IEEE , and Shau-Gang Mao , Senior Member, IEEE

Abstract—This letter presents a novel microstrip branch-linecoupler operating in three frequency bands. The design method-ology of the triple-band branch-line coupler is established byusing a compensation technique to improve the matching prop-erty within each passband region. The proposed coupler withcompact size is realized by folded microstrip open-circuited andshort-circuited stubs. The measured, full-wave simulated andequivalent-circuit modeled results illustrate good agreementamong them, which validates the design method and shows theadvantages of deep rejection between each operating frequency,and the dc grounded input and output ports.

Index Terms—Branch-line coupler, folded microstrip stub, mi-crostrip line.

I. INTRODUCTION

BRANCH-LINE couplers are one of the most rapidly de-

veloping passive components in modern microwave com-

munication systems. Compact size and multi-band operation are

crucial in the development of advanced branch-line couplers. In

the past years, many researches have been aimed at the design

of dual-band branch-line couplers [1]–[6]. The transmission

line with one or two shunt stubs [1]–[3] and the cross couplingbranch [4] were presented to realize a dual-band branch-line

coupler. Furthermore, the composite right/left-handed trans-

mission line was adopted to design a dual-band branch-line

coupler by using surface mounted devices (SMDs) [5], [6].

However, the composite right/left-handed coupler operating

in the high frequency range will suffer significant loss caused

by the SMDs. Recently, a multi-band branch-line coupler with

open stubs has been proposed [7], but the passband frequencies

cannot be allocated arbitrarily.

In this letter, a new triple-band branch-line coupler with arbi-

trary operating frequencies is proposed, and its design method is

presented. Based on the compensation technology [8], two addi-tional capacitances are attached into the triple-band resonator to

improve the matching properties of the triple-band branch-line

coupler. The series connection of three shunt LC resonators can

be transferred to the parallel connection of one shunt LC res-

onator and two series LC resonators [9]; the folded microstrip

Manuscript received July 07, 2009; revised August 03, 2009. First publishedOctober 20, 2009; current version published November 06, 2009. This work was supported in part by the National Science Council of Taiwan, R.O.C., underGrant NSC 96-2221-E-027-022, and Grant NSC 96-2628-E-027-001-MY3.

The authors are with the Graduate Institute of Computer and Communica-tion Engineering, National Taipei University of Technology, Taipei 106, Taiwan(e-mail: [email protected]).

Digital Object Identifier 10.1109/LMWC.2009.2031998

Fig. 1. (a) Equivalent-circuit model of the triple-band branch-line coupler.(b) Equivalent single-band resonator and initial triple-band resonator. (c)Impedance inverter with two shunt capacitances for phase and impedancecompensation.

stubs are equivalent to it, which can be treated as a triple-band

resonator for the branch-line coupler design. Finally, the pro-posed coupler is implemented to validate the proposed design

method. Additionally, this coupler has the advantages of com-

pact size and deep rejection between each operating frequency,

and the dc grounded input and output ports.

II. DESIGN METHODOLOGY

The equivalent circuit of the proposed triple-band branch-line

coupler is depicted in Fig. 1(a). First, the single-band resonator

is shown in Fig. 1(b), and and can be determined by

using the 1st-order low-pass filter prototype [10]. Thus the ini-

tial triple-band resonator is obtained by cascading three res-

onators with difference operating bands [Fig. 1(b)]. Second,to simultaneously improve the phase and impedance matching

conditions of the impedance inverter within the operating bands,

two capacitances are shunted at each end of the quarter-

wavelength transmission line as shown in Fig. 1(c) [8]. Thechar-

acteristic impedance and capacitance are determined by

(1)

(2)

1531-1309/$26.00 © 2009 IEEE

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LIOU et al.: NOVEL TRIPLE-BAND MICROSTRIP BRANCH-LINE COUPLER 685

Fig. 3. Geometry of the triple-band branch-line coupler. ( mm, mm, mm, mm, mm,and

mm.)

Fig.4. Equivalent-circuited modeled, full-wave simulated, and measured S-pa-rameters of the triple-band branch-line coupler.

the triple-band branch-line coupler are 170 MHz, 110 MHz, and

270 MHz.

IV. CONCLUSION

A novel triple-band branch-line coupler with arbitrary op-

erating frequencies has been presented and its design method-

ology based on a compensation technique is proposed. This cou-

pler is realized by using folded microstrip open-circuited and

short-circuited s tubs t o obtain a c ompact s ize at

4 GHz. The measured, full-wave simulated and equivalent-cir-

cuit modeled results agree closely with each other. The coupler

provides the advantage of deep rejection between each operating

frequency, and the dc grounded input and output ports. These re-

sults demonstrate the advantages and practical feasibility of the

triple-band coupler. Finally, the proposed design procedure and

resonator construction can be further applied to design various

multi-band microwave passive circuits, such as power dividers,

couplers and baluns.

Fig. 5. Amplitude imbalance and phase difference of the triple-band branch-line coupler. (a) first band, (b) second band, and (c) third band.

REFERENCES

[1] K.-K. M. Cheng and F.-L. Wong, “A novel approach to the design andimplementation of dual-bandcompact planar 90 branch-line coupler,”

IEEE Trans. Microw. Theory Tech., vol. 52, no. 11, pp. 2458–2463,Nov. 2004.

[2] H. Zhang and K. J. Chen, “A stub tapped branch-line coupler for dual-band operations,” IEEE Microw. Wireless Compon. Lett., vol. 17, no.2, pp. 106–108, Feb. 2007.

[3] C.-L. Hsu, J.-T. Kuo, and C.-W. Chang, “Miniaturized dual-band hy-brid couplers with arbitrary power division ratios,” IEEE Trans. Mi-

crow. Theory Tech., vol. 57, no. 1, pp. 149–156, Jan. 2009.[4] M.-J. Park and B. Lee, “Dual-band, cross coupled branch-Line cou-

pler,” IEEE Microw. Wireless Compon. Lett., vol. 15, no. 10, pp.655–657, Oct. 2005.

[5] C. Collado, A. Grau, and F. D. Flaviis, “Dual-band planar quadra-ture hybrid with enhanced bandwidth response,” IEEE Trans. Microw.

Theory Tech., vol. 54, no. 1, pp. 180–188, Jan. 2006.[6] I.-H. Lin, M. DeVincentis, C. Caloz, and T. Itoth, “Arbitrary dual-band

components using composite right/left-handed transmission lines,” IEEE Trans. Microw. Theory Tech., vol. 52, no. 4, pp. 1142–1149,Apr. 2004.

[7] C.-W. Tang and M.-G. Chen, “Design of multipassband microstripbranch-line couplers with open stubs,” IEEE Trans. Microw. Theory

Tech., vol. 57, no. 1, pp. 196–204, Jan. 2009.[8] S.-G. Mao and M.-S. Wu, “Design of artificial lumped-element

coplanar waveguide filters with controllable dual-passband responses,” IEEE Trans. Microw. Theory Tech., vol. 56, no. 7, pp. 1684–1692, Jul.2008.

[9] J. S. Hong and M. J. Lancaster , Microstrip Filters for RF/Microwave

Applications. New York: Wiley, 2001.[10] D. M. Pozar , Microwave Engineering, 3rd ed. New York: Wiley,

2005.

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