A Wideband Power Divider for Microwave Applications

Transcription

1 A Wideb Power Divider for Microwave Applications F. A. Mughal1, M. M. Ahmed1, K. Hayat1, U. Rafique1 Q. D. Memon2 1 Department Of Electronic Engineering, Mohammad Ali Jinnah University, Islamabad, Pakistan s: engineerfaheem@hotmail.com, {umair, mansoor}@jinnah.edu.pk, khizar_hayt@hotmail.com department of Electrical Engineering, NFC, Institute of Engineering, Fertilizer Research, Faisalabad, Pakistan qamaruddin2k2@gmmail.com Abstract A wideb power divider on single layer microstrip technology is proposed, analyzed fabricated. The proposed divider is designed by using two-section impedance transformers with an input two symmetrical output extension lines. The analysis of the power divider is performed by applying transmission line theory. Better return loss isolation factor is demonstrated over 50% impedance bwidth by applying -15 db bwidth criterion. The prototype of the proposed power divider is fabricated tested to verify the design it has been noticed that the simulated results are in agreement with the measured data. Index Terms Wideb; Power divider; Impedance transformer; Transmission line theory; Impedance bwidth; Isolation factor. I. INTRODUCTION structure were developed they exhibited good power splitting performance over the UWB range. In [8], an UWB power divider having good isolation factor using step-impedance stubs coupled lines was presented. Recently, a compact UWB power divider with good parameters using delta stub was introduced in [9]. In [10][19], various versions of modified Wilkinson dividers with the harmonic suppression were designed implemented. Harmonic suppression techniques involved extra lumped components, extended lines, defected ground structure (DGS), electromagnetic bgap (EBG) structures, anti-coupled lines, embedded resonators, single multi-stubs extension lines. Modified Wilkinson power dividers discussed in [10][19] provided the impedance bwidth ranging from 15 to 25%. Power dividers combiners are frequently employed in RF applications, such as feeding networks for an antenna array power splittingcombining networks for amplifier modules. Wilkinson power divider that offers good isolation factor between the output ports was introduced in 1960 [1], However, the major drawback of Wilkinson power divider is its narrow b operation. Its bwidth can be expended up to 20% for a single stage case but on the expense of poor outof-b rejection. On the other h, wideb applications require wideb power dividers too. For this purpose, some topologies of wideb dividers have recently been developed. In this paper, a wideb power divider based on a single layer microstrip line is proposed, analyzed fabricated. The wideb characteristics are achieved by using bi-section impedance transformer along with input output extension lines. A good isolation has been achieved in the desired b using an appropriate isolation resistor between the output ports. The proposed design offers a simple structure having moderate line impedance, i.e., 35Í2-61Í2 exhibits 50% bwidth using -15 db criterion. The use of cascaded multistage matchingisolation networks at outputs of a single Wilkinson divider is the easiest method to design a wideb power divider. However, this technique dems more resistors for better isolation. In [2], a multisection impedance transformer was placed at the input port of a multi-way junction to obtain good wideb return loss, but this divider suffers from poor isolation due to the absence of isolation resistor at output ports. In [3], three stage wideb Wilkinson divider was explored for differential applications. In [4], once again a three stage wideb Wilkinson power divider was developed with an arbitrary power division ratio between two output ports. In [5], a wideb power divider was implemented on a parallel-strip line which outperforms the conventional divider in terms of isolation bwidths; however, its implementation was relatively difficult. In [6] [7], two wideb power dividers; one based on microstrip-toslotline transition other making use of broadside coupling The design implementation of a wideb power divider is based on a single layer microstrip line is presented. It operates at 2.5 GHz center frequency which is obtained by using bi-section impedance transformer along with extended input output lines. Figure 1 shows a schematic diagram of a proposed power divider. The power splitting performance of the proposed design can be realized by assessing return loss with 3 db transmission from the input to the output ports. It consists of two branch transmission lines ZA ZB, input extended line Z, output extended line Z 2 an isolation resistor R, respectively. For analysis, the proposed circuit is replaced with its even odd-mode as shown in Figure 2. II. DESIGN OF WIDEBAND POWER DIVIDER A. Even-Mode Analysis Even-mode analysis is performed assuming that excitation at port-2 3 are in phase. The voltage at port-2 is equal to that $ IEEE

2 ZA, O fo ZB, fo Z 2, fo ZA, 0 Z 2, f 0 Fig. 1. Topology of proposed wideb power divider. at port-3 there is no current flow through R. As shown in Figure 2, the even-mode half circuit consists of four serial branch lines port-1 having impedance 2Z 0. Port-1 is bisected to obtain the half circuit two impedances of 100Í2 each, combined in parallel an equivalent of 5Oil. Same reason applies for the evaluation of Z to analyze the proposed design. If the proposed divider is matched at the input port, then the even-mode reflection Sfj should be zero at the input port is given by: 7 e 1 Sfi = -J? 1 T = 0. Zfnl+2 The impedance from port-1 to port-2 is given by where Ztm = Z R = Z A Zţ x +j2z l tan 0 1Z tan 6 ' Z QI + 3 Z A TAN0A ZA +jz* 1 tan 6 A ' (1) (2) (3) Z in 2 = Z 1 z; 2+jZ 2 tan O2 z 2+J z ; 2 tan 02 ' Z e q2+jzr tan0b Z p2 = Z B ZR +JZ E Q2TW6 R ' Z Q2 = B. Odd-Mode Analysis Z A Z 2+jZ A tan0 A Z A +jzh tan0 A ' 2 + j2zi tan 0i Zr2 = 2-Z'i 2Zi + j2tan0i (7) (8) (9) (10) In odd-mode, the circuit is driven by an anti-symmetric source that means the excitation at output ports is 180 out of phase. There is a voltage null along the axis of symmetry of the circuit. Thus, for this mode of excitation, all the power is delivered to the isolation resistor no power goes to port-1. Therefore, the output matching condition for odd-mode half circuit which is shown in Figure 2 can be expressed as: Z LL - Z B Zfr+jZş tang B ZR+JZ^ tanö B ' (4) where qo _ 22 Y n2 ~ 1 ^2 + 1 = 0 (H) z l = z i 1 + jza tan 62 z i + j tan 02 The input impedance at port-1 2 can be derived on the basis of transmission line theory [20]. The source to load impedance transformation is expressed in Equation (2). For simplicity, all impedances are normalized to the characteristics impedance Z 0. At the output ports, the divider should be matched isolated from each other. This needs the output port to be matched for both even odd-mode equivalent bisected circuits. Thus, output port reflection coefficient is given by (5) Y*! + jy 2 tan g 2 Y in2 = Y 2 y 2 + ilutan62 ' yo _ 2 jy t cot 6 t, (12) (13) Y a + jy B tan 0 R Y t = Y B (14) 'YB+JYA tan0 B ' Y n 2 = Y 0 implies no reflection at port-2. After simplifying Equation (13), we get ce _ Z R = Zi (15) in2 22 = 0 (6) 0.5Z o ^2+2 Equation (15) leads to an easy rule to choose the value of where R.

3 21i, ZA, fo Z B, fo Z 2> fo z A,0A@fo z B,e Z 2, Zout Zo Cb) Fig. 2. Even-mode half circuit odd-mode half circuit. III. RESULTS AND DISCUSSION As a first part of simulation process, Equation (1)-(15) are used to assess the even-odd mode responses of the proposed power divider. For this purpose, a MATLAB program representing input output matching has been developed Figure 3 shows the obtained results. These plots represent good port matching for the b of interest i.e., 1.5 to 4 GHz. In the second phase, the proposed wideb power divider has been simulated by using EM simulation software names Advanced Design System 2008A. The circuit is designed on Rogers TMM6 having dielectric constant E T = 6 copper cladding of 17 im (0.67 mil) having thickness of 50 mil. The characteristic impedance electrical lengths of input output extended lines; first second branch transmission lines of the proposed power divider are Z = 35 Í2, Z 2 = 55Í2, = 61Í2, Z B = 52Í2, 6>i = 72, 0 2 = 69, 0 A = 26 OB = 53 at the center frequency of 2.5 GHz. Figure 4 shows an image of the fabricated wideb power divider. A flangeless resistor of 100Í1 ± 5%, RFP R manufactured by Anaren is used for RF isolation. It can hle 30 W power from DC to 6 GHz with capacitance of 0.75pF operating temperature -55 C to 150 C. S-parameter measurements are performed using Agilent Technologies E8363B network analyzer for frequency range GHz. Figures 5 6 shows simulated measured performance of the proposed wideb power divider. The measured input output return losses the isolation between the outputs are below -10 db. The simulated measured results for insertion loss are better than 0.4 db which indicates that the proposed wideb power divider can successfully split an incoming signal into two ports. The discrepancy between the simulated measured results could be associated with the fabrication technique limitations. A comparative performance of the proposed power divider is given in Table 1. The data given in table shows that the proposed power divider offer comparable characteristics to that of earlier reported data. But, on the other h, it offers significant ease in terms of its fabrication because it involves lesser number of lumped components. Further, owing to its simpler design, as a matter of principle, it will also dissipate relatively less power. The wideb power divider presented in [3] was fabricated using parallel-strip lines coupled with lumped circuit components. On the other h, in [7], 5-layers technology was used to fabricate based wideb power divider which by its nature is a complicated process. Further, this design did not involve resistor at the output ports thus, lacking in port isolation. This difficulty was overcome by a design reported in [9], where a three layered structure with a slotted resistor had been used to acquire wideb performance with relatively good port isolation. Stubs coupled lines are useful in designing a wideb power divider but it is difficult to fabricate stub lines with moderate impedance range, i.e., 30-90Í2. A wideb power

4 Fig. 3. S-parameters of half circuits even-mode odd-mode. Fig. 5. Simulated measured results of the proposed wideb power divider input return loss output return loss. Fig. 4. Prototype of the fabricated wideb power divider. impedance transformer has been employed with extended transmission lines at input output ports. The divider is characterized based on symmetrical 3-port circuit model under even odd-mode excitations. Good return loss, power splitting ratio isolation factor has been achieved over wide range of frequencies. The measured results at the center frequency, i.e., 2.5 GHz are in good agreement with the simulated data. It is demonstrated that the proposed design offers 100% bwidth across the center frequency along with substanial ease in its fabrication. divider with similar issues is reported in [8]. The design proposed in this paper offers a simple design structure with matching wideb performance. There is no involvement of slotted or multilayer microstrip structure. It neither needs extra lumped component nor it require extremely small or large line impedances. IV. CONCLUSION A modified Wilkinson power divider is proposed for wideb applications. In this modification, a two section REFERENCES [1] E. Wilkinson, "An N-way hybrid power divider," IRE Transactions on Microwave Theory Techniques, vol. 8, no. 1, pp , [2] M. Kishihara, K. Yamane T. Kawai, "A design of multi-stage, multi-way microstrip power dividers with broadb properties," IEEE Microwave Wireless Component Letters, vol. 1, pp , [3] L. Chiu Q. Xue, "A wideb compact parallel-strip 180 Wilkinson power divider for push-pull circuitries," IEEE Microwave Wireless Component Letters, vol. 16, pp , [4] H. Oraizi A. R. Sharifi, "Design optimization of broadb asymmetrical multi-section Wilkinson," IEEE Transactions on Microwave Theory Techniques, vol. 54, pp , 2006.

5 TABLE I BRIEF SUMMARY OF REPORTED WIDEBAND POWER DIVIDER DESIGNS. Ref. Approach Freq. Range (GHz) Bwidth [3] Parallel strip lines using 6 resistors [7] Multi-layer microstrip without resistor [8] Stubs + Coupled lines [9] 3-layer slot line structure with a slotted resistor Proposed work Coupled lines with single resistor * -Simulated - - -Measured Simulated - Mëésùied [9] K. Song Q. Xue, "Novel ultra-wideb (UWB) multilayer slotline power divider with b-pass response," IEEE Microwave Wireless Component Letters, vol. 20, no. 1, pp , [10] B. Zhou, H. Wang W. X. Sheng, "A modified UWB Wilkinson power divider using delta stub, Progress In Electromagnetics Research Letters, vol. 19, pp , [11] J. S. Kim, M. J. Park K. B. Kong, "Modified design of Wilkinson power divider for harmonic suppression," Electronics Letters, vol. 45, no. 23, pp , [12] K. Srisathit, P. Jadpum W. Surakampontorn, "Miniature Wilkinson divider hybrid coupler with harmonic suppression using T-shaped transmission line," Asia Pacific Microwave Conference, pp. 1-4, [13] D. J. Woo T. K. Lee, "Suppression of harminics in Wilkinson power divider using dual-b rejection by asymmetric DGS," IEEE Transactions on Microwave Theory Techniques, vol. 53, no. 6, pp , [14] C. M. Lin, H. H. Su, J. C. Chiu Y. H. Wang, "Wilkinson power divider using microstrip EBG cells for the suppression of harmonics," IEEE Microwave Wireless Component Letters, vol. 17, no. 10, pp , [15] J. Zhang, L. Li, J. Gu X. Sun, "Compact harmonic suppression Wilkinson power divider with short circuit anti-coupled line," IEEE Microwave Wireless Component Letters, vol. 17, no. 9, pp , [16] J. Yang, C. Gu W. Wu, "Design of novel compact coupled microstrip power divider with harmonic suppression," IEEE Microwave Wireless Component Letters, vol. 18, no. 9, pp , [17] J. Wang, J. Ni, X. Y. Guo D. Fang, "Miniaturized microstrip Wilkinson power divider with harmonic suppression," IEEE Microwave Wireless Component Letters, vol. 19, no. 7, pp , [18] K.-K. M. Cheng W. C. Ip, "A novel power divider design with enhanced spurious suppression simple structure," IEEE Transactions on Microwave Theory Techniques, vol. 58, no. 12, pp , [19] W. C. Ip K.-K. M. Cheng, "A novel unequal power divider design with dual-harmonic rejection simple structure," IEEE Microwave Wireless Component Letters, vol. 21, no. 4, pp , [20] D. M. Pozar, Microwave Engineering, New York:Wiley, Fig. 6. Simulated measured results of the proposed wideb power divider insertion loss isolation factor. [5] L. Chiu Q. Xue, "A parallel-strip ring power divider with high isolation arbitrary power-dividing ratio," IEEE Transactions on Microwave Theory Techniques, vol. 55, no. 11, pp , [6] M. E. Bialkowski A. M. Abbosh, "Design of a compact UWB out-ofphase power divider," IEEE Microwave Wireless Component Letters, vol. 17, pp , [7] A. M. Abbosh, "A compact UWB three-way power divider," IEEE Microwave Wireless Component Letters, vol. 17, pp , [8] S. W. Wong L. Zhu, "Ultra-wideb power divider with good inb splitting isolation performances," IEEE Microwave Wireless Component Letters, vol. 18, no. 8, pp , 2008.