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Mobile wireless networks of the future will be expected to function in highly diverse environments from densefoliage to dense urban settings. Under these conditions, the phenomenon of multipath fading will be a problem. Here wedescribe a new technique to eliminate multipath fading in such wireless networks. Our technique is based on a freeparameter in the design of Fresnel zone plate antennas, a type of reference phase. The technique exploits our ability tocontrol relative phase between desired signals arriving in the antenna beam and of undesired multipath signals comingfrom outside of the beam direction. By control over relative phase, we can reduce the degree of fading to arbitrarilysmall values.Keywords: antennas, multipath, fading, phase, interference 1. INTRODUCTION There are many instances when it is desired to reduce the phenomenon of destructive interference or "fading"of a microwave or millimeter wave signaL In particular, the mobile wireless networks of the future will be expected tocarry highrate digital video, voice and data in environments of "impressive diversity" from dense foliage to denseurban obstacles. Under these conditions, the phenomenon of multipath fading will be a serious problem.In multipath fading, a microwave antenna receives a signal from a transmitter that is a sum of the desired line-of-sight (LOS) signal and at least partially coherent non-line-of-sight (NLOS) signals. The NLOS signals arise fromreflections off structures, terrain, etc. and from diffraction off obstacles. A schematic of these signal paths is shown inFigure 1 . |
