Analytical study of mm-wave and THz beams, application to RF metrology

Using mm-wave and THz radiation as a reliable measurement tool in spectroscopy and remote-sensing requires accurate beam characterization. Gaussian approximation is a practical model to describe the radiated beam of Laser sources and high-directivity THz/mm-wave horn antennas. The radiated beam is analytically studied in this paper and a simple closed-form formula is presented for the wave-front phase distribution. Analytical results are compared with measurements and good agreement is observed for mm-wave horns. The closed-form formula is used for a parametric error-analysis and uncertainty evaluation as needed in RF metrology. Therefore, the contribution of all the source characteristics and its geometrical parameters to the phase deviation can be shown.