A simple and analytical design methodology for a novel planar four-port structure to implement power divider (PD) or balun with variable power division is proposed in this paper. It consists of two different 3 dB branch-line couplers and one coupled-line phase shifter whose length can be changed to implement variable power division. Different from the previous designs, the power divider and balun with variable power division can be realized in only one circuit by changing the electrical length θ0 of the coupled line when the impedance ratio g is selected. According to the ABCD parameters and linear algebra calculation, closed-form mathematical equations for the circuit electrical values and scattering parameters can be obtained. A prototype with this proposed circuit, operating at 2 GHz, has been designed and fabricated using microstrip technology. Good agreements between the calculated and measured results verify our design.
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