Wavenumber-bandwidth-limited near fields

Antenna near fields can be accurately computed by the plane wave spectrum (PWS) method. The PWS is directly related to the far field at infinity. That is, at infinity, only a single plane wave contributes to the field. At the close-in distance of just a few wavelengths away from the antenna, integration is performed over all visible wavenumbers and some evanescent wavenumbers. Close (less than a wavelength) to the antenna, integration is performed over all wavenumber space. In between these two extreme distances from the antenna, there is shown to be a finite-sized subregion of all wavenumber space that contains all significant contributions to the field. That is, near fields are shown to be wavenumber-bandwidth-limited. Exploiting this fact, a technique of computing near fields could be created which is faster than both the aperture method and the original PWS method, once a suitable method is developed for determining the wavenumber bandwidth of near fields.