| 摘要 |
A telecommunications system (104) is shown which uses the same optical components for receiving and emitting and which is an omni-directional receiver but a directional emitter, and which has no moving mechanical parts. An incoming circularly polarised beam (158) hits a conical reflector (125) and is directed down through a quarter wave plate (130) which converts it to a linearly polarised beam. This is then split and a phase delay is added to a part of the beam using a spiral phase plate (143) to introduce a phase delay dependent upon the angular position in the cross-section of the beam. The reference beam (160) and phase-delayed beam (162) are compared using a pair of phase detectors (166 and 172) in quadrature to produce a pair of voltages from which the direction from which the incident beam came can be determined. When used as an emitter a variable phase delay is introduced to the signal from one vertically polarised emitter horn (142) but not to the signal from another horizontally polarised horn (140) and the two waves combined to produce a beam whose polarisation varies angularly around its cross-section. A linear polarisation filter (132) then passes only radiation having a particular polarisation and reflects radiation having a polarisation 90 DEG different. The quarter wave plate (13) converts the beam to circular polarisation and the beam reflects off the conical reflector (125), with a beam pattern that varies with angle, and is substantially less in the opposite direction to the intended beam direction. |
