Three-port power dividers are useful microwave devices for the applications of RF systems such as phased-array antennas, power amplifiers, mixers, or active circulators.
The three-port Willkinson power divider split input signals into-equiphase-equiamplitude signals and achieves a perfect isolation at one frequency.
However, the sizes of quarter-wavelength couplers are too large for monolithic microwave integrated circuit (MMIC) applications, which results in high chip cost. The lumped-element approach which uses spiral inductors and lumped capacitors, is one of the efficient solutions to overcome this problem. However, the design of lumped-element circuits is somewhat empirical, and it requires accurate inductor and capacitor models based on measurements. Moreover, the extraction of accurate lumped-circuit model reflecting the experiential results becomes very difficult at higher frequencies than 20GHz.
In this thesis, a new method is proposed to miniaturize λ/4 transmission line of power divider is proposed. The method utilizes simple combination of the shorted coupled-line pair instead of the transmission line with very high impedance and shunt lumped capacitors. The length of the transmission line designed by the above method was miniaturized to 16% of conventional λ/4 transmission line.