This paper describes a new broadband microstrip to coplanar strip (CPS) line transition, where supporting substrates are joined perpendicularly, one containing the CPS line and the other one the microstrip line. The CPS line is coupled to the microstrip line through a symmetric slot radial stub placed in the ground plane of the microstrip line substrate. A measured return loss greater than 10dB is obtained, with a corresponding -3dB back-to-back insertion loss bandwidth from 1.5 to 3.3 GHz. The proposed transition has several advantages compared to other configurations, especially in the context of phased antenna arrays, which require co-integration of planar radiating elements with differential access ports active circuitry. By changing the CPS by a slot line, a wideband microstrip-to-slot line transition has been also obtained, with a [1.5 - 3.7 GHz] bandwidth (@VSWR=2).