Abstract: A method and apparatus for adjusting the impedance of an electromagnetic energy-actuated device. An auxiliary test flange includes a substantially planar metallic member. An internal aperture matches the dimensions of the waveguide cavity formed at the mating ports of adjacent electromagnetic energy-actuated devices. The member includes an access groove for a metallic stub, permitting the stub to be inserted from an edge of the member into the aperture. Measurements of energy transfer are made as the stub is inserted to thereby adjust either the capacitive or inductive impedance to energy transfer. After a predetermined degree of energy transfer is observed, one or the other of the devices may be modified by the addition of a permanent auxiliary flange or directly modified in accordance with the optimized aperture reduction.