US aircraft landing systems-VHF-UHF and microwave

The aircraft instrument landing system (ILS), operating in the VHF/UHF frequency bands has been in operation for over 50 years. With the various glide slope systems and the highly directional localizer antenna arrays successful ILS performance can now be achieved under the most adverse electromagnetic conditions. Several disadvantages prevent ILS from meeting the needs of aviation indefinitely. These disadvantages are discussed, and a microwave landing system is described.<
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