Designs of High Power Ratio Dividers Using Left-Handed Transmission Line Transformers

Abstract

In general, conventional high power ratio unequal Wilkinson power divider needs high and low characteristic impedance quarter-wavelength transformers between isolation resistor and input port. However, high impedance microstrip quarter-wavelength transformer is not easily implemented in microstrip line process because narrow line width is difficult to be realized. Each of the proposed high power ratio unequal power dividers uses left-handed transmission line transformer which has −90° phase delay to avoid the usage of high impedance quarter-wavelength transformer. The first proposed unequal modified Wilkinson power divider has one $\pi$-shaped impedance transformer in top arm path and one 3/4 wavelength impedance transformer in bottom arm path between isolation resistor and input port. The $\pi$-shaped transformer composed of two shunt short stubs and one series capacitor is used to design a −90° impedance transformer. In order to achieve impedance match and isolation design, the 3/4 wavelength impedance transformer is used to be equivalent to a −90° impedance transformer. To meet output matching requirements, two quarter-wavelength transformers are designed between the isolation resistor and output ports. Besides, to reduce the length of 3/4 wavelength impedance transformer in the first proposed divider, the second unequal split modified Wilkinson power divider is presented. The second divider is utilized three T-shaped transmission lines to realize the role of the 3/4 wavelength impedance transformer in the first divider. Each section of the T-shaped transmission lines uses two series lines and one shunt open stubs to design a 90° transformer, i.e., the total electrical length of the three T-shaped transmission lines equals 270° which is equivalent to the transmission property of the 3/4 wavelength impedance transformer in the first proposed divider. The proposed two dividers have been carefully implemented and verified.