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Abstract

A dual polarisation waveguide probe system for use with a satellite dish (10) for receiving satellite signals orthogonally polarised in the same frequency band and for providing improved isolation between these polarised satellite signals is disclosed. The probe system has a waveguide (28) incorporated in a low-noise block receiver (12) into which two probes (34, 38) are located for receiving linearly polarised energy of both orthogonal senses. The probes (34, 38) are located in the same longitudinal plane on opposite sides of a single cylindrical bar reflector (36) which reflects one sense of polarisation and passes the orthogonal signal with minimal insertion loss, and then reflects the rotated orthogonal signal. The probes (34, 38) are spaced .lambda./4 from the reflector (36). A reflection rotator (44) is also formed using a thin plate which is orientated at 45.degree. to the incident linear polarisation with a short circuit (46) spaced approximately a quarter wavelength (.lambda./4) behind the leading edge of the plate (43). This structure splits the incident energy into two equal components in orthogonal planes, one component being reflected by the leading edge (43) and the other component being reflected by the waveguide short circuit (46). The resultant 180.degree. phase shift between the reflected components causes a 90.degree. rotation in the plane of linear polarisation upon re-combination so that the waveguide outputs (34a, 38a) are located in the same longitudinal plane. Various embodiments and advantages of the invention are described.

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First Claim