| 摘要 |
A receiver device 1 detects a beam of electromagnetic signals FI of known geometry arriving at a variable entry angle of incidence * small Greek alpha *, such as an optical signal from a ground station received by a satellite which always points towards the centre of the earth. It comprises a lens 6 having an aspherical surface 6a to correct the geometry of the incident beam FI according to a formula dependent on the entry angle of incidence * small Greek alpha *, to produce an incident beam FO which is applied to a quadratic detector 3. The correction tends to increase the convergence of the beam with angle of incidence. This suppresses the variations in the energy received by the detector 3 which occur particularly at high angles of incidence, and makes it possible to render substantially constant the signal-to-noise ratio of the detected signal irrespective of the entry angle of incidence * small Greek alpha *.
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