This paper demonstrates a single topology to implement ultra-wideband in-phase and 180° out-of-phase power dividers which will be dedicated for ultra-wideband frontends and balanced antenna systems that require a decent amount of isolation between ports. Both power dividers are formed of two couples of microstrip-to-slotline transitions terminated with radial stubs and then cascaded with a multisection Wilkinson power divider. A parametric study of the microstrip-to-slotline transition is performed to identify the main parameters' influence on its frequency response, followed by a full-wave optimization. Both power dividers are designed on RO4003C substrates and both have the same size of × mm 2. Simulation results show that the power dividers can operate between 4 and 40 GHz with less than 6 dB insertion loss and with small amplitude and phase imbalances between output ports. And most importantly, both devices have at least 20 dB of isolation between output ports over the entire bandwidth. Keywords-in-phase power divider, out-of-phase power divider, balun, multisection Wilkinson power divider, microstrip-to-slotline transition, ultra-wideband.