Abstract: An apparatus and method are disclosed for determining an aperture illumination of a phased-array antenna. The apparatus and method evaluate a monitor signal obtained from a first output (A1) of a monitor waveguide (MH). The apparatus and method are also suited for antennas having a very restricted scan angle coverage, such as elevation antennas in MLS systems. To obtain information from a portion of the monitor signal corresponding to at least one cycle of the far-field pattern of the antenna, portions of the monitor signal which are visible at different monitor angles are combined for evaluation. This is accomplished by also evaluating signals obtained from a second output (A2) of the monitor waveguide which is spatially separated from the first output (A1), or from outputs of additional monitor waveguides, at different monitor angles.

Abstract: Landing aids using phased-array antennas must be very carefully calibrated. Conventional methods use probes which are inserted into each individual radiating element of the array antenna. For 6-bit phase shifters, this method is not suficiently accurate. A method and an apparatus are disclosed wherein the aperture illumination of the array antenna is determined from the output of an integral waveguide and compared with a desired aperture illumination. The difference between actual value and desired value is compensated for iteratively with the aid of an adaptive control system.