Although Fabry–Perot interferometers have found widest application in the visible portion of the spectrum, their properties are conveniently observed in the microwave region, where high‐quality spherical mirrors are easily fabricated on a lathe, and partially transmitting (high reflectance) flat mesh is commercially available at modest cost. The scaling properties of paraxial beams of such interferometers, as the frequency is varied from optical to microwave for a fixed resonator geometry, are well known. This allows studies that are relevant to contemporary optics research to be carried out in an upper division undergraduate laboratory without the need for sophisticated equipment.