Usual vector measurements need to compare the signal detected through the Device Under Test DUT, with the signal coming directly from the source. Thanks to a very simple original method developed since 1989, vector detection can also be done with a purely electronic reference. In transmission experiments, there is no need for any directional coupler, and the frequency coverage extends from 8 to 1000 GHz. Quasi-optical propagation is used in the millimeter-submillimeter frequency range. Transmission through dielectric slabs in free space will give an easy measurement of the permittivity. Its real part will be obtained from the phase rotation, and its imaginary part from the amplitude decay. With dielectric coating deposited onto metal, the reflection method is necessary for the characterization. Low-loss materials are characterized with the open cavity perturbation technique. Extremely low loss materials can constitute “whispering gallery” resonators, very easy to excite and characterize.