We proposed a novel method to design a broadband plasmonic unequal-power splitter with a rectangular ring resonator directly connected to the input and output waveguides. By properly assigning the locations of the input and output waveguides, the splitting ratio is controlled by manipulating the output waveguide widths while the reflectance is eliminated by adjusting the input waveguide width without varying any other design parameters. To obtain the design parameters of the input and output waveguide widths, analytical expressions of the splitting ratio and the reflectance are established by using the equivalent circuit based on the transmission line model. Design examples of unequal-power splitters with splitting ratio of 0.5 are numerically demonstrated. The analysis based on equivalent circuit is well confirmed by the finite difference time domain simulation. The simulated results show that the unequal-power splitters have a flat and wide band over the wavelength range from 1500 nm to 1600 nm by using a compact rectangular ring resonator with the dimensions of 550 nm x 275 nm.