Abstract: A radar apparatus (5) for detecting multipath signal propagation when determining an elevation angle of an object, comprising an antenna array with which the radar apparatus is arranged to form at least three separate antenna beams (11, 12, 13) comprising a first antenna beam (11) having an angle of elevation above horizontal, and a separate second antenna beam (12) having an angle of elevation at or above horizontal which is less than that of the first antenna beam, and a separate third antenna beam (13) having an angle of elevation below horizontal. The apparatus is arranged to transmit radio pulses from the antenna array; to receive return radio signals within the first, second and third antenna beams; to calculate a measure of the magnitude of a return radio signal received within the third antenna beam using all of said received radio signals collectively; and, to detect multipath signal propagation using said measure.

Abstract: Disclosed is a method of detecting an anomalous propagation condition in a Radar system, comprising the steps of: subtracting returns received in a first receive period from returns received in a succeeding second receive period, and repeating this step for a plurality of receive periods; and if the step of subtracting gives a result in excess of a predetermined threshold in one of the plurality of receive periods, then registering this as a possible anomalous propagation condition.

Abstract: An antenna system (1) comprises a directional antenna (2) adapted to rotate through a range of directions in azimuth. It is responsive to radio-frequency (RF) signals received from directions within the range of directions in azimuth. A receiver (7) is arranged to receive the RF signals from the antenna within a signal frequency response band of the receiver and to provide a corresponding output for signal processing. A signal filter (11) is operable to block the output from the receiver when the frequency of the RF signal lies at a frequency within the signal frequency response band of the receiver and a detector unit (8) is arranged to apply the signal filter when the directional antenna is directed to a predetermined azimuth at which an interference source is located and to not apply the signal filter otherwise.

Abstract: A method for calibrating an antenna system (1) including a antenna elements (3) connected to signal receiver units (4) at an RF signal input port thereof comprising, generating an RF calibration signal (62), applying the RF calibration signal to the RF signal input port of the signal receiver units without applying the calibration signal via the antenna elements (3). The response of the antenna system to the calibration signal is measured, and a signal correction is calculated according to the measured response. The signal correction is applied to the response of the antenna system to signals subsequently received at the signal receiver units via the antenna elements of the antenna system.

Abstract: Disclosed is a method of detecting an anomalous propagation condition in a Radar system, comprising the steps of: subtracting returns received in a first receive period from returns received in a succeeding second receive period, and repeating this step for a plurality of receive periods; and if the step of subtracting gives a result in excess of a predetermined threshold in one of the plurality of receive periods, then registering this as a possible anomalous propagation condition.

Abstract: A radar apparatus (5) for detecting multipath signal propagation when determining an elevation angle of an object, comprising an antenna array with which the radar apparatus is arranged to form at least three separate antenna beams (11, 12, 13) comprising a first antenna beam (11) having an angle of elevation above horizontal, and a separate second antenna beam (12) having an angle of elevation at or above horizontal which is less than that of the first antenna beam, and a separate third antenna beam (13) having an angle of elevation below horizontal. The apparatus is arranged to transmit radio pulses from the antenna array; to receive return radio signals within the first, second and third antenna beams; to calculate a measure of the magnitude of a return radio signal received within the third antenna beam using all of said received radio signals collectively; and, to detect multipath signal propagation using said measure.

Abstract: An optical signal transmission apparatus (1) for a rotating antenna comprising a plurality of optical modulators (6) arranged for receiving a respective plurality of analogue RF signals (5) and for modulating a respective plurality of optical signals therewith to produce a plurality of modulated analogue optical signals (8). A plurality of opto-electrical converters (14) each converts a respective modulated analogue optical signal (13) into an analogue electrical signal. The plurality of optical modulators (6) are rotationally coupled in optical communication with the plurality of opto-electrical converters (14) via an optical rotary joint (10) including a reversion prism.

Abstract: An antenna system (1) comprises a directional antenna (2) adapted to rotate through a range of directions in azimuth. It is responsive to radio-frequency (RF) signals received from directions within the range of directions in azimuth. A receiver (7) is arranged to receive the RF signals from the antenna within a signal frequency response band of the receiver and to provide a corresponding output for signal processing. A signal filter (11) is operable to block the output from the receiver when the frequency of the RF signal lies at a frequency within the signal frequency response band of the receiver and a detector unit (8) is arranged to apply the signal filter when the directional antenna is directed to a predetermined azimuth at which an interference source is located and to not apply the signal filter otherwise.

Abstract: A method for calibrating an antenna system (1) including a antenna elements (3) connected to signal receiver units (4) at an RF signal input port thereof comprising, generating an RF calibration signal (62), applying the RF calibration signal to the RF signal input port of the signal receiver units without applying the calibration signal via the antenna elements (3). The response of the antenna system to the calibration signal is measured, and a signal correction is calculated according to the measured response. The signal correction is applied to the response of the antenna system to signals subsequently received at the signal receiver units via the antenna elements of the antenna system.