This paper presents a measurement set up developed for millimeter wave characterization of passive or active quasi optical components such as filters, polarizers, amplifiers or multipliers. The main quasi optical elements of this bench are the focusing horns which allow guided wave coupling to the quasi optical components. These horns are designed using the Gaussian beam theory and FDTD software on a personal computer. The quasi optical measurements are performed according to a TRL calibration method in the Ka band for passive circuit characterization such as a dielectric slab. These measurements give the scattering matrix of quasi optical components which can be used for simulation in classical CAD software.