Amplitude control of transmitted millimeter-wave beams by monolithic Schottky diode arrays is demonstrated. An array containing 4800 diodes has demonstrated control over the range of 20-50% beam transmittance at 99 GHz and 20-70% beam transmittance at 165 GHz. Modulation testing on a second array (8640 diodes) with similar transmission characteristics has shown array control to 50 MHz with negligible loss of output response. An extensive evaluation performed for the 8640-diode array shows good agreement between array impedance parameters determined from quasi-optical measurements, theoretical calculations, and low-frequency C-V measurements. The results have extended the range of quasi-optical functions demonstrated by solid-state power-combining arrays for application to millimeter-wave systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>