Near-Field Focusing Plates and Their Design

We describe the design of near-field focusing plates, which are grating-like structures that can focus electromagnetic radiation to spots or lines of arbitrarily small subwavelength dimension. A general procedure is outlined for designing a near-field plate to achieve a desired focus, and its implementation at microwave frequencies is discussed in detail. Full-wave (method of moments) simulations clearly demonstrate a passive near-field plate's ability to overcome the diffraction limit. Finally, it is shown that performance of the plates is weakly affected by losses..