Scalar beam pattern measurements for characterization of sub-millimeter receivers

The scalar beam measurement concept presented in this article is based on scanning the receiver's beam with an isotropic radiating source at three to four parallel cross planes along the presumable optical axis. The receiver is operated in heterodyne mode and the output IF power is recorded for each coordinate point of the radiating source. The collected data provides information for the Gaussian beam profile at the particular distance from the receiver. According to the properties of the fundamental Gaussian beam, the maximum power value is located on the axis of the beam. Therefore, obtaini.ng the coordinates of the beam center (of the maximum intensity) for each measured beam profile allows for the determination of the beam axis orientation. The location of the beam waist and its size can be calculated by solving a system of equations derived from the Gaussian beam theory.