[en] Calibration measurements were performed on Auburn ECE antenna system to determine the beam waist size and location at several characteristic frequencies typically used in TEXT-U experiments, and compare these with known manufacturer's specifications. A halogen bulb, acting as a microwave source, swept a grid of points in a plane parallel to antenna lens' surface. The intensity of the collected signal was recorded and later fitted to a Gaussian for several values of the radial distance from the lens, thus enabling us to estimate the beam waist size and position. Knowledge of the minimum spot size possible allows us to determine the maximum resolution in measuring the wavelength of the T_e fluctuations in the plasma. Results indicate that the Auburn optical system produces the beam with the waist size bigger than was originally expected