Near-field of a scanning aperture microwave probe: A 3-D finite element analysis

We calculate the field distribution in the near-field zone of a scanning aperture microwave probe using the AN-SOFT/HFSS full three-dimensional (3-D) finite element software. The probe is a narrow resonant slot in the endwall of a rectangular metallic waveguide. We find a sharp collimation of the electric field outside the slot and a strong increase of the electric field magnitude at the aperture plane. We compare numerical results to the two-dimensional-quasistatic model which assumes a narrow and infinitely long slot in a conducting screen. This model satisfactorily describes spatial characteristics of the field distribution only at the distances less than the slot width (proximity zone), while to find the field in the whole near-field zone, full 3-D wave analysis is required.