X.-T. Fang, X.-C. Zhang, and C.-M. Tong Missile Institute of Air Force Engineering University Sanyuan, Shanxi , China

Transcription

1 Progress In Electromagnetics Research Letters, Vol. 23, , 211 A NOVEL MINIATURIZED MICRO-STRIP SIX-PORT JUNCTION X.-T. Fang, X.-C. Zhang, and C.-M. Tong Missile Institute of Air Force Engineering University Sanyuan, Shanxi 7138, China Abstract A novel miniaturized micro-strip six-port junction is presented. The ne structure effectively reduces the occupied area to 25% of the conventional six-port junction due to to open loaded stubs. The design is validated both by using momentum of Advanced Design System and by measurement. 1. INTRODUCTION During recent years, there has been great interest in six-port circuits due to their abilities of measuring the phase difference beteen to input signals by means of poer readings at four output ports. Various six-port junctions have been proposed and implemented ith distributed transmission lines and lumped elements according to Engen s design criteria [1 5], and they have been used in application of ireless communication systems and Radar systems, extensively. In [2], a novel six-port circuit based on four 9 hybrid couplers as designed. In [4], a six-port reflectometer consisting of four /18 micro-strip ring couplers as presented. They all have suitable structures but occupy too large area. In [5], one miniature lumped six-port reflectometer as proposed. Hoever, hen the operating frequency goes up, the signal loss due to lumped elements becomes high. In this paper, a miniaturized six-port junction based on microstrip technology is introduced. It adopts the conventional constitution hich is composed of a 3 db Wilkinson poer divider and three 9 Received 23 March 211, Accepted 26 April 211, Scheduled 2 May 211 Corresponding author: Xin-Tian Fang (fangxintian@126.com). X.-C. Zhang is also ith Xidian University, Xi an 7171, China. C.-M. Tong is also ith State Key Laboratory of Millimeter Wave, Nanjing, 2196, China.

2 13 Fang, Zhang, and Tong hybrid couplers [6], but its occupied area is only 25% of that of the conventional case. Simulation and measurement results sho that the proposed six-port junction has good performance. 2. CIRCUIT DESIGN The schematic layout of the proposed six-port junction is shon in Fig. 1. It is composed of one miniaturized Wilkinson poer divider and three miniaturized 9 hybrid couplers. They all have λ/4 transmission lines, hich utilize to high-lo impedance shunt stubs to reduce size. In order to develop a miniaturized six-port junction, the poer divider and 9 hybrid coupler ith an equivalent 9 electrical length should be effectively synthesized. As shon in Fig. 2, e can easily deduce the relation of Z, θ, Z a, θ a, Z b and θ b [7]. When θ is π/4, e get /( ) Z a = Z 2 sin θa (1) /( ) Z b = Z tan θ b 2 cos θa 1 (2) here Z a, Z b and Z are the characteristic impedance of transmission lines, and θ a, θ b, θ are electrical lengths. In order to design the poer divider properly, e choose the circular arc loaded by four open s 1 s2 s 3 r 1 s 1 s 3 s 2 r 1 s 4 resistor s 5 T1 T 2 l3 2 s 4 l 2 l 1 l5 s s 7 6 s 11 l 4 s 3 8 s 1 r 1 s 9 resistor s 5 T 1 T 2 2 l 3 l 2 l 1 l 5 s s 7 6 s 11 l 4 s 8 3 s 1 r 1 s 9 Figure 1. Proposed six-port junction.

3 Progress In Electromagnetics Research Letters, Vol. 23, quarter circles, hich replaces a pair of λ/4 transmission lines ith characteristic impedance of Z T = 2Z to minimize the occupied area and decrease electromagnetic coupling of micro-strip lines. By optimizing the idth ( 1 ) of the arc and the radius (r) of the circle, it is easy to get the size of poer divider. In the process of designing 9 hybrid coupler, e keep the four T joints of conventional 9 hybrid coupler and change to pairs of λ/4 transmission lines ith characteristic impedance of Z P = Z and Z R = Z / 2 into to pairs of shorter λ/4 transmission lines embedded ith four rectangles microstrip lines. In the case, miniaturized 9 hybrid coupler can be determined according to four parameters (the idth ( 2, 3 ) and the length (l 3, l 4 )). The proposed six-port junction is designed based on the miniaturized poer divider and 9 hybrid couplers mentioned above. The dimensions of the designed model are: = 1.57 mm, 1 =.82 mm, 2 = 1.87 mm, 3 =.53 mm, r = 6. mm, r 1 = 3.28 mm, l 1 = 1.17 mm, l 2 = 1.57 mm, l 3 = 13.8 mm, l 4 = 8.6 mm, l 5 = 5.66 mm, T 1 = 1.57 mm, T 2 = 2.56 mm, s i =.2 mm (i = 1, 2,..., 11). All slots, gaps, and the high impedance lines have the same idth of.2 mm and are easy for fabrication. The three 9 hybrid couplers have the same size. In these values, l 3, l 4 and r mainly determine the size of miniaturized six-port junction. Compared ith a usual λ/4 transmission line hich has a length about 23 mm, the miniaturized 9 hybrid coupler and poer divider occupy about 21% and 27% of that of the conventional case. Eventually, the proposed six-port junction is fabricated on an Z Z a 4 2 Z b θ b θ a Z b θb 7 6 open open Figure 2. Micro-strip line loaded by to open stubs. Figure 3. Photo of the six-port junction.

4 132 Fang, Zhang, and Tong cm 2 (in the conventional case it is about cm 2 ) substrate ith relative permittivity of 2.2 and thickness of.58 mm, as shon in Fig SIMULATION AND MEASUREMENT RESULTS Simulation as accomplished using momentum of Advanced Design System (ADS), hich is an electromagnetic ave simulator based on the method of moment (MoM). Measurement as carried out by an Agilent 37377C netork analyzer. Figures 4 and 5 sho the simulated and measured S-parameters Frequency (db) Figure 4. S-parameters magnitude (S 5i, S 6i, i from 1 to 4) of the proposed six-port junction. The simulated. The measured S 55 S 65 S S 55 S 65 S 66 Figure 5. S-parameters magnitude (S 55, S 65, S 66 ) of the proposed six-port junction. The simulated. The measured.

5 Progress In Electromagnetics Research Letters, Vol. 23, magnitude of the proposed six-port junction. From the simulated and measured results, e can clearly observe that the transmission coefficients of input ports (5 6) to the output ports (1 4) is close to the theoretical predicted value 6 db, and the measured results are less than 6.7 db, hich is a little loer than the simulated result of 6.5 db at the central frequency. At the same time, it can be noted that the return loss and isolation of the to input ports 5 and 6 are loer than 25 db at the center frequency 2.4 GHz and loer than 1 db over the entire operating frequency band of interest ( GHz), hich means that the input ports are ell matched and isolated. The proposed six-port junction has not only good magnitude properties, but also fine phase relationship. Figs. 6 and 7 sho the simulated and measured phases of and of the proposed six-port junction. The phase alteration is linear over the operating frequency band. At the center frequency of 2.4 GHz, the measured phase difference of the adjoining output ports is given by ang( ) = 19.5 ( ) = (3) ang( ) = 2.23 ( ) = (4) ang( ) = ( 1.3 ) = 9.1 (5) ang( ) = ( ) = 27.9 (6) hich indicates that the maximum phase error is less than 1. There are some slight differences of magnitude and phase beteen the simulated and measured results, hich may due to the fabrication tolerances and the infinite dielectric and ground planes assumed in the Figure 6. S-parameters phase (S 5i, i from 1 to 4) of the proposed six-port junction. The simulated. The measured.

6 134 Fang, Zhang, and Tong Figure 7. S-parameters phase (S 6i, i from 1 to 4) of the proposed six-port junction. The simulated. The measured. simulation. Besides this, simulated and measured results are in fairly good agreement. 4. CONCLUSION A novel miniaturized six-port junction based on micro-strip technology is presented. Oing to the open loaded stubs, the ne structure not only has good performance, but also effectively reduces occupied area to 25% of the conventional case. The proposed six-port junction is compact, easy for fabrication and applicable to microave system applications. ACKNOWLEDGMENT The authors ish to thank State Key Lab. of Millimeter Waves for fund support (K297). REFERENCES 1. Engen, G. F., An improved circuit for implementing the six-port technique of microave measurement, IEEE Trans. Microave Theory Tech., Vol. 25, , Li, C., H. Zhang, and P. Wang, A novel six-port circuit based on four quadrature hybrids, International Journal of RF and Microave Computer-Aided Engineering, Vol. 2, , 21.

7 Progress In Electromagnetics Research Letters, Vol. 23, Mohra, A. S., Six-port reflectometer based on four /18 microstrip ring couplers, Microave Opt. Technol. Lett., Vol. 4, , Yao, J. J. and S. P. Yeo, Six-port reflectometer based on modified hybrid coupler, IEEE Trans. Microave Theory Tech., Vol. 56, , Bilik, V., V. Raffai, and J. Bezek, Miniature broadband lumped six-port reflectometers, J. Commun., Vol. 42, 7 14, Yu, J. and Y. Kim, Performance analysis for various structures of six-port phase correlator using hybrid coupler, poer divider and rat-race ring coupler, International Symposium on Computer Science and Its Applications, , Vogel, R. W., Analysis and design of lumped-and lumpeddistributed-element directional couplers for MIC and MMIC applications, IEEE Trans. Microave Theory Tech., Vol. 4, , 1992.