Miniaturized Hybrid Rat-Race Coupler of a 2.5 GHz Loaded by Resistors

Transcription

1 JOURNAL OF NETWORKS, VOL. 8, NO. 7, JULY Miniaturized Hybrid Rat-Race Coupler of a 2.5 GHz Loaded by Resistors Khalid S. Ahmad Foundation of Technical Education, Technical Institute Mosul /Electronic Department, Mosul, Iraq Jarkovo_1988@yahoo.com A. Z. Yonis University of Mosul, College of Electronic Engineering / Communication Engineering Department, Mosul, Iraq as_zuher@yahoo.com Abstract A rat-race coupler is one of the essential components used in microave circuits. Rat-race coupler has numerous applications in satellite communication, phased array radar antenna systems and radar. Recently, ireless communication systems usually require smaller device size, in order to meet circuit miniaturization. Thus, size reduction becoming major design considerations for practical applications. This paper includes design the proposed microstrip rat-race coupler for frequency 2.5 GHz. The area of the proposed rat-race coupler compared ith the conventional structure, the proposed rat-race coupler in this paper has smaller size than the conventional structure. The main outcome of this ork is reducing the area of the proposed coupler by 10%. Microave Office (MWO-225- SUF) tool is used to execute the design of the coupler in this ork. Recently, ireless communication systems usually require smaller device size in order to meet circuit miniaturization and cost reduction. Thus, size reduction is becoming major design considerations for practical applications. Hoever, in the lo microave frequency range, even the physically small size of a conventional hybrid coupler is still too large for some applications. Therefore, attempts continually are made to reduce its size. Lots of attempts are continually contributed to minimize the occupied area of hybrid coupler [6, 7]. This paper ill focus exclusively on the proposed ratrace coupler design. The proposed coupler is occupied a smaller area by 10% than the conventional microstrip coupler. Index Terms Rat-Race Hybrid Coupler, Microstrip, Transmission Line I. INTRODUCTION Rat-race couplers form an indispensable component group in modern MIC (Microave Integrated Circuits) technology. They are key components in the design of microave devices such as poer divider, mixers, phase shifter, and antenna systems due to their simplicity, and a high isolation beteen the ports [1]. Rat-race couplers are passive microave components used for poer division or poer combining in radio frequency circuits design. The radio frequency (RF) poer applied to any one port split equally beteen to neighboring ports, no output signal appears at the opposite port, hich named as isolation port [2]. Rat-race coupler is composed of three (λ/4) sections and one (3λ/4) section, its total circumference is 1.5 avelengths. For an equal-split ratrace coupler, the impedance of the ring Fig. 1, is fixed at 1.41Z 0, (70.7 ), the ports impedance are all 50Ω [1]. The isolated port lets the circuit become a three-port netork. The port into hich the electrical poer fed called the incident port; the ports through hich the desired amounts of coupled poer extracted called coupled ports. Phase beteen the outputs is dependent on hich port is the input. Coupler can provide 180-degree phase shift beteen to output ports and can be operated output ports are in-phase as shon in Fig. 1. [1, 2, 3, 4, 5]. Figure 1. Conventional rat-race coupler (equal poer split) 00 Poer divider 1800 Poer divider. II. PROPOSED RAT-RACE COUPLER DESIGN Recently, ireless communication systems usually require smaller device size in order to meet circuit doi: /jn

2 1466 JOURNAL OF NETWORKS, VOL. 8, NO. 7, JULY 2013 miniaturization. Thus, size reduction is becoming major design considerations for practical applications. The shape of proposed coupler Fig. 2. has changed to get smaller size, here the (3λ/4) section beteen ports 3 and 4 Fig. 2-a. is composed of three parts (λ/4), the middle part changed from convex shape to bol shape, also is changed the (λ/4) part beteen ports 1 and 2 from convex shape to bol shape. In addition ere adding four resistors 50 ohms, in order to get equally split poer beteen to neighboring ports to get 3 db. idth of port 2, is the idth of the ring, and L, is the length of section (λ/4), Fig. 3.. for, 2 for, 2 εr 1 εr 1 1 εe. (1) d 1 8e A. (2) d e 2A 2 2 r B 1 ln 2B 1 ln B r r. (3) here: Z A r r (4) 60 2 r 1 r 377 B. (5) 2Z r Figure 2. Proposed rat-race coupler (equal poer split) 00 Poer divider 1800 Poer divider The area of the proposed coupler (bol shape) operating at 2.5 GHz is cm 2, hile the area of the conventional ring at the same frequency is cm 2. The proposed ring rat race has smaller size than the conventional coupler, the size of the proposed ring reduced by 10%.These areas measured by AutoCAD. III. CONFIGURATION OF PROPOSED COUPLER Rat-Race Coupler can realized by using virtually all kinds of planar transmission lines, for example, strip line, slot line, finline, image line and microstrip line [1]. Microstrip is one of the most popular types of planar transmission lines, primarily because it can fabricated by photolithographic processes and is easily integrated ith other passive and active microave device [8]. In this paper, the rat-race coupler is designed in microstrip techniques. The parameters d, substrate thickness and ε r, dielectric substrate (relative permittivity) are noticeable in design. They relate to the characteristic impedance Z o, and should calculate carefully [8]. In this paper d, and ε r, are chosen 0.175cm and 2.2 respectively. The folloing microstrip expressions used to calculate the geometry of coupler. Where ε e, is the effective dielectric constant 1, is the L. (6) e k o k 2 f. (7) v Where v, is the speed of light, f, is the frequency [8]. The ring of coupler consists from six sections, the length of each section (arc) equal to L, (here L=λ/4) and by using the folloing expression calculate the radius R, of the arc Fig L R. (8) 2 C Where C, is the angle in degree [9, 10], this mean C, equal 60 for each section. RESISTORS Due to changes in the form of a coupler of convex shape (conventional) to the concave (proposed) and in order to get an equal division of poer 3 db and to minimize the return loss from the sharp corner of the bends, has been added four resistors 50 ohms Fig. 3,. IV. SIMULATION RESULTS The to concave parts (λ/4) are added to the coupler. The shape of the proposed coupler had become a concave shape, comparing ith the conventional shape (convex shape). The addition of the to concave parts ould

3 JOURNAL OF NETWORKS, VOL. 8, NO. 7, JULY significantly negatively affect the ork of the coupler. The reason is the emergence of sharp corner in the bends regions of the microstrip line as shon in Fig. 3,. Hoever, this is surpassed by the addition of four resistors ith values of 50 ohms to minimize the return loss. The resistors are attached on the sharp corners in the bend regions of the microstrip line here a, b, are horizontal length of the resistor a, is the idth of resistor a=0.391cm hich correspond 50 ohms b, is the length of resistor b=0.65 cm hich correspond (~λ/14). The resistors section advantage is to reduce the return loss of the sharp corners. The proposed coupler ith a x3.8677cm 2 has reduced size by 10%. Coupler is realized at 2.5 GHz on a PTFE Teflon ith 0.127cm thickness and the dielectric constant of 2.2, Fig. 4,.The proposed coupler has the parameters hich are given Table І. Where 1, is the idth of the port hich correspond 50Ω ( 1 =a), 2, is the idth of the arc (ring), hich correspond 70.7Ω, R is the distance from the origin to the start of the arc. R 1 is the distance from the origin to the center of the arc (R 1 =R+ 2 /2), R 2, is the distance from the origin to the end of the arc (R 2 =R+ 2 ). Substrate thickness d=0.127 cm, relative permittivity ε r = 2.2. The rat-race coupler response is measured in the frequency range GHz. The rat-race coupler is simulated using Microave Office (MWO-225-suf) verssion than -10 db over the frequency range from 1.57 to 3.14 GHz of 180 poer divider. From the graphs, the magnitudes of S-parameters at center frequency 2.5 GHz, here for S 11 are db and db for 0 poer divider and 180 poer divider circuit configuration respectively. The magnitudes of S 31 are db and db for 0 poer divider and 180 poer divider circuit configuration respectively. Besides that they have S 21 and S db and db for 0 poer divider and S 21 and S db and db for 180 poer divider. Figure 4. The configuration of the proposed rat-race coupler Figure 5. Simulation response of 00 poer divider circuit configuration Figure 3. The configuration of the proposed rat-race coupler (all values in cm unit) TABLE I. THE PROPOSED COUPLER PARAMETERS (ALL VALUES IN TABLE IN CM UNIT) 1 2 L R R 1 R 2 a b Fig. 5. and Fig. 6. sho the simulated S- parameter's of 0 poer divider and 180 poer divider. The simulated S 11 is better than -10 db from 2.11 to 2.57 GHz of 0 poer divider, hile the simulated S 11 is better than -10 db from 1 to 3.39 GHz of 180 poer divider. The simulated isolation S 31 is larger than -10 db over the frequency range from 1.8 to 3.37 GHz of 0 poer divider, hile the simulated isolation S 31 is larger Figure 6. Simulation response of 1800 poer divider circuit configuration Fig. 7. illustrates the phase shift for 0 poer divider circuit configuration here port 2 and port 4 are shifted around 90 from port 1 (in-phase). Fig. 8. illustrates the phase shift for 180 poer divider circuit configuration (out-of-phase), here port 2 and port 4are shifted around 90 and 270 respectively from port 1. The in-phase and out-of-phase (<S21-<S41) difference are 3.7 and -173 at center frequency 2.5 GHz, respectively, instead of 0 and

4 1468 JOURNAL OF NETWORKS, VOL. 8, NO. 7, JULY but these results are acceptable and satisfy the requirements of 0 and 180 poer divider. The results are not identical ith the conventional coupler, but they are acceptable. TABLE II. THE COMPARISON SIMULATED S-PARAMETERS WITH THE CONVENTIONAL STRUCTURE FOR 0 POWER DIVIDER S-parameter (db) S 11 S 21 S 31 S 41 Conventional proposed Figure 7. Phase shift for 0 poer divider circuit configuration Fig. 10 and Table III sho the comparison simulated S-parameters ith the conventional structure for 180 poer divider Figure 8. Phase shift for 180 poer divider circuit configuration. Figure 10. Simulated results of S 11 and S 21 and S 31 and S 41 for 180 rat-race coupler here the results are illustrated in Table ІІІ. TABLE III. THE COMPARISON SIMULATED S-PARAMETERS WITH THE CONVENTIONAL STRUCTURE FOR 180 POWER DIVIDER S-parameter (db) S 11 S 21 S 31 S 41 Conventional proposed Figure 9. Simulated results of S 11 and S 21 and S 31 and S 41 for 0 rat-race coupler Fig. 9. and Table ІІ sho the comparison simulated S-parameters ith the conventional structure for 0 poer divider. Where the results are illustrated in Table ІІ. The proposed coupler's magnitudes S 11 =-10.8 db, S 31 =-22.4 db, S 21 = S 41 =-3.47 db, hile the magnitudes of the conventional coupler are S 11 =-40.2 db, S 31 =-68.6 db, S 21 = S 41 =-3 db, at the center frequency 2.5 GHz. The proposed coupler's magnitudes S 11 =-23.5 db, S 31 =-36.1 db, S 21 =-3.09, S 41 =-2.98 db, hile the magnitudes of the conventional coupler are S 11 =-40 db, S 31 =-68.4 db, S21= S 41 =-3 db, at the center frequency 2.5 GHz. The results are good and can be adopted. V. CONCLUSION The comparison shos that the results are acceptable and must be sacrifice a little in the magnitude of S- parameters in order to get a smaller space. A microstrip rat-race coupler is built on the PTFE Teflon Substrate ε- r=2.2. This project is designed for frequency 2.5 GHz. The design steps have presented. The demand for microstrip rat-race coupler ill continue to increase because of their small size and lo mass.

5 JOURNAL OF NETWORKS, VOL. 8, NO. 7, JULY ACKNOWLEDGMENT The Authors are grateful to the electronic department Technical Institute in Mosul, for providing the facilities in carrying out this study. REFERENCES [1] I. Bahl and P. Bhartia, "Microave solid state circuit design,"2nd ed., Wiley, pp. 900, [2] C. M. Chung, "Small Hybrid Rat-race coupler", City University of Hong Kong, Project of Engineering, [3] G. C. Hock and C. K. Chakrabarty, "Design of a 5.8 GHz Rat-Race Coupler on the RO4003C Substrate, "International RF and Microave Conference Proceedings, Putra jaya, Malaysia, September 12-14, [4] S. A. Maas, "The RF and Microave Circuit Design Cookbook", Artech House, pp , [5] Z. Wang, J. S. Jang, and C.W. Park, "Tri-Band Rat-Race Coupler using Resonators," IEEE, 29 August [6] Y. J. Sung and Y. S. Kim, "Size reduction and harmonic suppression of rat-race hybrid coupler using defected ground structure," IEEE Microave and ireless components letters, vol. 14, no. 1, January [7] F. Zhang and C. Li, "Novel Rat-race Hybrid Coupler for RF Front-end Module," Springer Science and Business Media, LLC, September [8] D. M. Pozar, john, "Microave Engineering," 2nd ed., Wiely & sons, pp , [9] T. Johnson and H. Neill, "Complete Mathematics," Hachette UK Company, pp , [10] EL entsd ireless A. D. Polyanin and A. I. Chernoutsan, "A Concise Handbook of Mathematics, Physics, and Engineering Sciences", CRC Press Taylor and Francis Group, pp. 48, Khalid S. Ahmad as born in Baghdad province, Iraq, on June 01, 1964.He received the B.S. degree of electrical engineering from Air Force Technical Academy in Sarajevo city of Bosnia and Herzegovina, M.S. degree in electrical engineering from Belgrade University, Serbia in 1985 and 1987 respectively. No, he is an assistance lecture in the department of Electronic Engineering, Mosul Technical Institute, Iraq. His research interests include spiral antenna, microstrip antenna, phase array antenna and couplers. He is a member of Syndicate of Iraqi Engineering. A. Z. Yonis has strong expertise in ireless access technologies and mobile communications such as LTE, LTE-Advanced, WiMAX and applications to communication systems. His educational attainments are B.Eng. from Technical College of Mosul in Iraq, MSc. and PhD. from Faculty of Electrical and Electronic Engineering at University Tun Hussein Onn Malaysia in Malaysia. He became an engineer at college of electronic engineering at university of Mosul- Iraq since He has many published papers in International journals and conferences. He is a member of IEEE, IAENG, SCIEI, SIE, CBEES, SDIWC, IACSIT, and Syndicate of Iraqi Engineers.