Abstract: In an apparatus for maintaining the orientation of an antenna system with respect to a beacon, radio signals are received in four quadrants and converted into sum and difference signals, which are transformed in frequency, amplified in an amplifier (6) and detected in a first- and second-phase detector (9, 15) present in a corresponding channel (7, 8) to derive error voltages in first and second time intervals respectively for aligning the antenna system with respect to the beacon. During the tracking mode of the apparatus, the difference and sum signals separately pass in first, second and third, fourth time intervals, respectively. a VCO (21) supplies two orthogonal signals as reference voltages, to the phase detectors. In the tracking mode the VCO driven by a signal derived from the signals obtained in the first channel (7) in the fourth time interval and in the second channel (8) in the third time interval.

Abstract: In a pulse radar apparatus the receiver comprises a main transmission channel connected to a directional antenna and an interference canceller connected to said channel for selecting target returns obtained through the major lobe of the antenna radiation pattern. The canceller contains an auxiliary transmission channel connected to an omnidirectional antenna for the intermediate-frequency detection of target returns and of signals composed of noise and/or continuous-wave interference signals; a subtraction unit; and a phase- and amplitude-compensating network having two circuit arrangements, one for the in-phase output signal and one for the quadrature output signal of the auxiliary transmission channel for generating output signals for the subtraction unit. Each circuit arrangement consists of a first mixer connected to the subtraction unit and the auxiliary transmission channel, a filter connected to the first mixer, and a second mixer connected to the filter and the auxiliary transmission channel.