Simulation of the two-frequency aircraft landing system

The strict and approximate relationship that bases on the binomial series expansion are received in the article for calculating the difference of the modulation (DDM) depth of the signals that emitted by the two-frequency instrument landing system (ILS). A comparison is given of the results that are computed by the approximate and the exact formulas for the DDM. It takes into account that the signals “suppressed carrier sideband only” and “Carrier plus sideband” are out of phase. The behavior of the DDM in the localizer area is presented. The article is interesting for the developers of the ILS and for the specialist in start-up of the localizer and the glide-path transmitter and for the professional radioservices specialists of airport and for the related disciplines university teachers and students.