Three classes of active probes all with coaxial inputs and coplanar waveguide probe tips are described. A millimeter-wave active probe for generating signals with frequencies above 50 gHz and supplying same to millimeter-wave and ultrafast devices and integrated circuits on-wafer including a substrate upon which a frequency multiplier consisting of filter sections and impedance matching sections and nonlinear elements are integrated in uniplanar transmission line medium. Also disclosed is a harmonic mixer probe to step down RF received from an integrated circuit to a lower frequency by mixing it with the harmonics of a local oscillator signal. Also disclosed is an S-parameter active probe for on-wafer measurement of the S-parameters of a two port millimeter-wave device or integrated circuit by injecting millimeter-wave frequencies and simultaneously tapping off a portion of the injected signal, the transmitted signal and the reflected signal and stepping all signals down in frequency to a frequency compatible with currently available test equipment such as the HP8510 automatic network analyzer. This is the first and only all-electronic millimeter-wave on-wafer S-parameter measurement device available at present.