A Balanced-to-Balanced Rat-Race Coupling Network Based on Defected Slots

A new balanced-to-balanced (BTB) rat-race coupling network is presented. The theoretical analysis is performed based on equivalent circuits and design equations are derived to achieve the functions of differential-mode (DM) power division, DM impedance match, common-mode (CM) suppression, and port isolation. The design theories are well vindicated by an exemplary BTB rat-race coupling network centered at 1.8 GHz with a compact size of 0.21λ
_g
²
. The simulated and measured results agree well.