882 PIERS Proceedings, Moscow, Russia, August 19–23, 2012

UWB Wilkinson Power Divider Using Tapered Transmission Lines

Faroq Razzaz, Majeed A. S. Alkanhal, and Abdel-Fattah ShetaDepartment of Electrical Engineering, King Saud University

P. O. Box 800, Riyadh 11421, Kingdom of Saudi Arabia

Abstract— In this paper, an UWB Wilkinson power divider using tapered transmission lines isproposed. Using tapered transmission lines in microwave components results in reduction of theelement length and therefore the overall component size while providing wider operational band-widths. This power divider has superior performance in the UWB band (3.1 GHz–10.6 GHz) andis smaller in size as compared to traditional power dividers. The simulation and experimentalresults show good insertion loss which is approximately −3 dB, good return loss that is less than11 dB for the input port over the entire UWB band and less than 16 dB for the other two ports.The power is divided equally between the output two ports and the isolation between the outputports is better than 11 dB.

1. INTRODUCTION

Power dividers are commonly used in microwave circuits such as in balanced mixers, phase shifters,amplifiers and antenna array feed networks. The Wilkinson power divider (WPD) is one of themost common components in microwave systems. The WPDcan be matched at all three ports. It islossless if the output ports are matched, reciprocal, and the output ports are largely isolated. Manydesigns and modifications were proposed to increase the bandwidth of the conventional Wilkinsonpower divider. The bandwidth of Wilkinson power divider can be increased using multisections [1],using open circuited stubs [2] or using tapered transmission lines [3]. Recently, ultra-wideband(UWB) communication systems have been introduced, and they require their own componentsthat can operates over the UWB range (3.1–10.6 GHz). Many works had proposed to design UWBpower dividers. A modified two-section UWB WPD with open circuited stub on each branch wasproposed in [4]. Other UWB WPD was proposed in [5, 6] using open circuited radial stub on eachbranch. Also, an open circuited delta stub was proposed in [7]. In [8] a two section UWB WPD wasdesigned using without stubs. UWB power dividers using tapered transmission lines were proposedin [9–11].

In this paper, an UWB Wilkinson power divider based on tapered transmission lines is proposed.The tapered transmission line is used to decrease the overall size and enhance the bandwidth ofthe power divider. This power divider is designed with only one isolation resistor for output ports.The simulation and measured results show good performance over the UWB range. Roger RT5880substrate with relative permittivity of 2.2 and thickness of 0.508mm has been used in the simulationand fabrication of this power divider.

2. DESIGN

Figure 1 shows the structure of the proposed UWB Wilkinson power divider. This power divider isbased on the tapered transmission lines. To increase the bandwidth of the Wilkinson power dividera tapered transmission line has been integrated with another uniform transmission line section asshown in Figure 1.

The impedance of the tapered transmission line Z(x) varies linearly from Z(0) = Z01 = 2Z0 toZ(L) = Z02, where L is the length of the tapered transmission line section as shown in Figure 2. Thelength of the tapered transmission line is less than quarter wavelength of the center frequency of theUWB spectrum which is 6.85 GHz. The second section is uniform transmission with characteristicimpedance Z greater than Z02. The even-odd mode analysis can be used to analyze the proposedpower divider because it is symmetric in structure. The output ports are isolated and the isolationresistor is equal to 2Z0.

The characteristic impedance Z0 is chosen to be 50Ω, the all other parameters can be determinedand optimized with corresponding to this value and to the center frequency which is equal to6.85GHz. The line impedances Z01 = 100 Ω, Z02 = 65 Ω and Z = 75Ω. The length of the taperedtransmission line L = λ/8 and the electrical length of the uniform section is equal to 33. Theisolation resistor R is 100Ω.

Progress In Electromagnetics Research Symposium Proceedings, Moscow, Russia, August 19–23, 2012 883

l1 l2 l3

W4

W3W2W1 R

Figure 1: The structure of the proposed UWP power divider.

L

Z 02Z 01

Z (x)

Figure 2: Linearly tapered transmission line section.

Figure 3: Simulated S-parametersof the proposed UWB power di-vider.

Figure 4: Measured S-parametersof the proposed UWB power di-vider.

Figure 5: Group delay of the pro-posed UWB power divider.

3. SIMULATION AND MEASUREMENT RESULTS

The designed power divider has been simulated using full-wave electromagnetic simulator software.Rogers RT5880 with a thickness of 0.508mm, and a relative permittivity of 2.2 is used in this design.Table 1 contains the values of all optimized parameters of the designed UWB power divider. Theoverall size of the proposed UWB power divider is 15.51× 15.47 mm2.

The performance of the designed circuit is shown in Figure 3. The simulation results show goodinsertion loss which is approximately −3 dB, good return loss that is less than 11 dB for the inputport over the entire UWB band and less than 16 dB for the other two ports. The power is dividedequally between the output two ports and the isolation between the output ports is better than11 dB.

The measured results are shown in Figure 4. A good agreement with the simulated results isassumed. The measured results show good insertion loss which is approximately −3.6 dB, goodreturn loss that is less than 11 dB for the input port over the entire UWB band and less than15 dB for the other two ports. The power is divided equally between the output two ports and the

884 PIERS Proceedings, Moscow, Russia, August 19–23, 2012

Table 1: Optimized parameters of the proposed UWB power divider.

Parameter W1 l1 W2 W3 l2 W4 l3

Value 1.54 6 0.43 1 4 0.78 3

isolation between the output ports is better than 15 dB. The group delay of the proposed UWBpower divider is approximately flat and is less than 100 ps as shown in Figure 5.

4. CONCLUSIONS

A modified Wilkinson power divider using tapered transmission lines has been proposed for UWBapplications. The designed power divider is compact and easy to fabricate. Quality better perfor-mance is obtained without using stubs and with only one isolation resistor. Good power dividing,matching, and isolations over the entire UWB spectrum range are obtained as demonstrated bysimulation and experimental results.

ACKNOWLEDGMENT

This research is funded by The National Plan for Science & Technology, Kingdom of Saudi Arabia,under project No. 08-ADV210-2.

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