Fabry-Perot resonator design for the measurement of surface reflectivity

There is considerable interest in the development of composite materials used for reflectors within radio telescopes. To determine the surface reflectivity of composites at millimetre-wave frequencies, a measurement setup using a Fabry-Perot resonator has been developed at Q-Band (33-50 GHz). Fabry-Perot resonators are well known to give high-Q resonances and are suitable to measure low-loss materials. Open resonators have the inherent advantage that the quality of resonance is not affected by any sidewalls or corner air gaps, as in waveguide resonators, and various samples of mirrors can be easily swapped within the system. We will outline the design guidelines and measurement procedure of the resonator. Measured results of known metals are provided to demonstrate the setup and to provide relative metrics for future composite material testing.