Modified Asymmetric Impedance Transformers (MCCTs and MCVTs) and Their Application to Impedance-Transforming Three-Port 3-dB Power Dividers

For size reduction and design flexibility of impedance transformers, two modified asymmetric impedance transformers are suggested. They each consist of one open stub and two different transmission-line sections and are named a modified constant conductance-type transmission-line impedance transformer (MCCT) and a modified constant voltage-standing-wave-ratio (VSWR)-type transmission-line impedance transformer (MCVT), depending on where the open stub is located. As their applications, impedance-transforming MCCT- and MCVT-three-port 3-dB power dividers (MCCT- and MCVT-PDs) are presented, and it is found that the isolation circuits should be composed of not only resistance but also capacitance. For high-power applications, MCCT and MCVT Gysel-type PDs are also suggested, and four isolation circuits are developed systematically based on the isolation impedances of the MCCT- and MCVT-PDs. The isolation circuits of the Gysel-type PDs are comprised of three transmission-line sections, shunt resistances connected to ground, and series capacitances/shunt inductances. One MCCT-PD and one MCVT Gysel-type PD are verified by measurements. The measured results show good agreement with the prediction, giving power divisions of -3.08 dB, return losses better than 23.8 dB, and isolation of 24.07 dB at 1 GHz for the MCCT-PD and power divisions of about -3.42 and -3.5 dB, return losses better than 21 dB, and isolation of 28 dB at 2 GHz for the MCVT Gysel-type PD.