Near field focusing of apertures and reflector antennas

Large aperture antennas such as reflectors are commonly used for far-field communications. In these applications the aperture field is uniformly illuminated in phase by a feed antenna, and the radiated beam focuses at infinity. In this study we consider focusing the antenna to a point on its axis near the aperture. Interesting results are obtained for the focused location and its spot size, which may be used in near-field focusing of microwave power, or, near field probing by a radiometer.