by X. Li, L. Yang, S.X. Gong, Y.J. Yang, T. Hong and X. Chen, Xidian University, Shaanxi, People’s Republic of China
Power dividers are very important components in microwave and millimeter-wave circuits. In recent years, there has been increasing demand for dual-frequency equipment due to the development of multiband technologies.
Various power dividers operating at two or more frequencies based on lumped and distributed elements have been reported,1-5 but they use increased circuit complexity and introduce parasitic effects. In this article, a novel design of a dual-band Wilkinson power divider, without additional lumped and distributed elements other than a single resistor, is presented. Moreover, the designed structure can enhance the bandwidth for small band-ratios. The two frequency bands of operation are selected by varying the electrical lengths and impedance values of three transmission lines. The proposed circuit also features a simple structure with realistic impedance values and a distributed design with reduced parasitic effect. The design parameters of the dual-band power divider are presented in explicit closed form. The validity of this analysis is confirmed through the design, simulation and experimental results for a power divider operating at 1 and 2.5 GHz.
Theory and Design Equations
Figure 1 Schematic of a dual-band Wilkinson power divider.
Figure 2 Proposed dual-band transformer structure.
Figure 1 shows the schematic representation of the proposed Wilkinson power divider for dual-band operation. The proposed impedance transformer, which is composed of two-section transmission lines and a shunt element, is depicted in Figure 2. Mathematically, the Z-parameters of this half-circuit can be derived as:
where M2, M3 and M4 are defined as:
Subsequently, these expressions can be simplified as
Since θ1 and θ2 are both functions of the two operating frequencies ƒ1 and ƒ2 (ƒ2>ƒ1), θ1 and θ2 can be expressed as
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