The propagation of a relativistic sheet electron beam through a spatially periodic magnetic field (wiggler) has been studied experimentally. The wiggler serves two purposes; it provides beam focusing as well as the magnetostatic pump for the free‐electron laser (FEL) interaction. Experiments conducted to study sheet beam generation and propagation in a short‐period (1 cm) planar wiggler are presented. A 500 keV, 7 A sheet electron beam was propagated through a 3.2 mm waveguide with negligible losses due to intercepted current. In addition, the first observation of wiggler‐induced radiation was obtained from the sheet beam FEL in a short‐period wiggler oscillator configuration.