Coax to microstrip transition
Typical S-parameter response versus frequency

The transition between a coaxial transmission line and a microstrip line is a vital part in the interconnection of microwave circuits. It is one of the simplest microstrip transitions and because both media supports TEM mode it is generally broadband. Two configurations are widely used. The first is the end-launch or edge-mounted configuration where the axis of the coaxial line is aligned with the end of the microstrip line. The second is the vertical-mounted configuration where the coaxial line is perpendicular to the substrate of the microstrip line. The latter is the one implemented in Antenna Magus

The coaxial-to-microstrip line has an ultra-wideband performance (where S11 < -10 dB and S21 > -1 dB) with the upper limit dependent on the exact physical parameters and geometry of the coaxial connector used. Magus, however, does not model a specific coaxial connector.

Typical reflection and transmission coefficient behaviour versus frequency for a 50 Ohm port impedance and epsr = 2 and 2.2 for the coaxial cable and substrate respectively.