We describe the analysis, design, and construction of a large aperture, wide‐field‐of‐view modulator at 10.8 &mgr;m using the Stark effect in ammonia (NH3). The modulator configuration incorporates a longitudinal electric field produced between closely spaced, large‐diameter germanium windows. The windows are antireflection coated for high transmission, and their relatively low resistivity allows their direct use as (transparent) Stark electrodes. Enhanced modulation depth and improved electrical breakdown performance are obtained by using multiple interaction regions. The modulator is mounted at the entrance aperture of a corner cube reflector, thus allowing two passes of the signal beam in a configuration which is retroreflecting and polarization insensitive. This completed device has an aperture of 5.5 cm, a field of view of 38°, and a measured modulation depth of 25% at 1.4 MHz.