Abstract: A method and means for monitoring a Microwave Landing System (MLS) that provides statistical independence of the monitoring process from the MLS to insure the integrity of the MLS signal format. The r.f. signal transmissions are received by a monitor receiver and down converted to i.f. signals. The i.f. signals are decomposed into in-phase (I) and quadrature (Q) components. The I and Q components are applied to a digital signal processor that derives all synchronizing information from the I and Q components and that effectively reconstructs the complete MLS signal format from the I and Q components. The reconstructed signal format is compared with predetermined standards and an alarm is generated if the reconstructed signal format is out of tolerance. The integrity of the monitoring process is insured by periodically substituting i.f. signals that simulate the MLS signal format but that are out of tolerance.

Abstract: A method for obtaining the far field pattern of a phased array MLS antenna using measurements by a monitor located in the near field of the MLS antenna. The near field pattern differs from the far field pattern because of the presence of phase error terms in the measured near field pattern. The method comprises computing the Fourier transform of the complex conjugates of the phase error term of the near field pattern and convolving that transform with the measured near field pattern to obtain the far field pattern.

Abstract: A system for demodulating and decoding differential phase shift keying (DPSK) transmissions utilizes a bandpass filter, an analog to digital converter and a digital signal processor. Removal of the effects of unknown frequency component is achieved by applying a complex phase correction/rotation factor after DPSK demodulation. The actual phase of the complex signal is never computed directly. All of the processing from Rader decomposition through carrier tracking filter is performed on the complex values and therefore requires only multiplication and addition operations which can be performed at high speed in a microcomputer or in dedicated arithmetic hardware.

Abstract: In a Microwave Landing System (MLS) transmitting landing guidance signals and data signals according to a time division multiplex signal format, a method and means for replacing faulty primary equipment with standby equipment. Redundant electronics units are provided for generating guidance and data signals. Transfer control means connect alternate ones of the electronics units to the appropriate antenna of the system such that no two consecutive transmissions of the same guidance or data signal is made by the same electronics unit. The signals transmitted by the system are monitored for accuracy and conformity to the signal format. If a fault is detected in a monitored signal, the electronics unit responsible for generating the faulty signal is no longer used and system operation continues with non-faulty units, unless the faulty detected indicates antenna misalignment. If antenna misalignment occurs, system operations are halted.

Abstract: Method and means for monitoring the performance of a phase array antenna. The antenna comprises an array of individual radiating element seach of which radiates a prescribed proportion of the energy to be transmitted thereby shaping such energy into a beam. Individual phase shifters are associated with each radiating element, the phases of which control the direction of the beam pointing. The method of the invention involves sampling the beam by means including a single receiver located along a fixed radial from the array. The beam scans at a constant rate. The samples are collected at non-uniform intervals of time during a beam scan. The samples are, however, separated by equal increments of arcsine .theta., where .theta. is the pointing angle of the beam. The samples are analyzed by means including a Fourier transform to provide the value of the amplitude and phase of the signal radiated by each of the radiating elements.

Abstract: In a microwave landing system the individual words of a train of command words generated by the antenna beam steering unit are applied to a polynomial generator where each is, seriatim, summed with a polynomial check word generated in a previous operation. The result is shifted once toward the most significant bit to increase the degree of the resultant polynomial. Division by a predetermined generator polynomial is accomplished and the remainder is stored as the check word to be used in the next to follow operation. The check word polynomials are compared at preset intervals with stored check words to monitor the train of command words.