Experiments are proposed to measure (first longitudinal, then, later, using Stern-Gerlach (SG) deflection, transverse) polarization of an electron beam by measuring the excitation induced in a resonant cavity. With ideal resonator construction and positioning there would be no resonator excitation caused directly by the beam charge. But, because the electron charge is so large relative to its magnetic moment, special beam preparation and polarization modulation are required to suppress this background. Signal levels and foreground to background ratios are calculated.