Gaussian-beam transformation losses in a quasi-optical directional coupler

An analysis is presented of the diffraction of a Gaussian beam incident at an angle of 45 deg on a directional coupler in the form of a planar wire array. It is found that the diffraction produces changes in the beam parameters (dimensions and the phase-front curvature radius) and leads to a displacement of the symmetry axes and change in the propagation direction of a beam that has passed through the array relative to the incident-beam direction and of the reflected beam relative to the specular-reflection direction. Analytical expressions are obtained for calculating the parameters of the transformed beam, and transformation losses are determined for various beam and array parameters.