Antenna-reflector combination operating in the Fresnel region at microwave and millimeter-wave bands

While most passive repeaters are designed and installed so that they operate in the far-zone or Fraunhofer region, geographical conditions sometimes make it necessary to install reflectors closer to an antenna, or reflectors operating in the Fresnel region. In such close arrangements of two apertures, one could regard the antenna-reflector combination as an antenna system. Although the propagation loss on a reflector-equipped hop is usually greater than that on a line-of-sight hop of the same length, it is possible to receive more power from the antenna-reflector combination for certain wavelengths, antenna and reflector sizes and spacing than from the same antenna located at the reflector position. To calculate the antenna-reflector combination gain, methods for circular reflectors have previously been proposed, and examined by experiment. While microwave reflectors employed as passive repeaters are usually rectangular for ease of manufacture and installation, approximations by replacing rectangular reflectors with circular reflectors of the same area, or equi-area circular reflectors, have long been used to calculate the gain of the rectangular reflectors. The authors derive the calculation method for antenna-rectangular reflector combination gain and examine existing reflector-equipped microwave links and experimental millimeter-wave ones with four types of plane reflectors using the method.<>