Axially Steered Spots of Near-Field Fresnel Zone Plate Lens With Sweeping Frequency

The frequency performance of near-field fresnel zone plate (NFFZP) is of fundamental interest in electromagnetic field. An NFFZP lens is designed to focus a spherical wave at a spot. The spots of NFFZP lens are electronically steered forward and backward on the axis according to the operating frequency. Several nonlinear formulas are derived to describe the spots movement with sweeping frequency. The focal shifts of the primary and fractional spots are presented and analyzed. Furthermore, the power drift, the depth of focus, the sidelobe level, and the lens resolution are characterized. All the results are verified by performing full-wave simulations in Ku-band.