Despite steady improvements in the VHF/UHF Instrument Landing System (ILS)--the international standard for the last three decades--higher-frequency, alternative landing systems have proliferated. For the military, microwave landing systems offer, among other advantages, the ability to provide compact, mobile equipment. ILS employs antennas with apertures as large as 100 feet; at Ku-band (about 15 GHz), the same performance can be obtained with 3-4 foot aperture antennas. For civil aviation, landing systems operating at lower microwave frequencies are contending to replace ILS as the International standard. A key distinction among proposed microwave landing systems and the present standard is how each uses RF and higher-frequency energy to determine aircraft position. ILS employs fixed overlapping beams, whereas most military systems employ a narrow scanning beam that is encoded with angular position. Among the entries contending for international standardization, Doppler MLS determines angular position from the apparent Doppler shift from a reference frequency caused by a signal that is sequentially switched down a linear array of radiators, in contrast with Time-Reference Scanning Beam MLS, which measures the time difference between the to-fro passages of horizontal and vertical scanning beams. /Author/

  • Availability:
  • Corporate Authors:

    Institute of Electrical and Electronics Engineers (IEEE)

    3 Park Avenue, 17th Floor
    New York, NY  United States  10016-5997
  • Authors:
    • Poqust, F
  • Publication Date: 1978-3

Media Info

  • Pagination: p. 30-36
  • Serial:
    • IEEE Spectrum
    • Volume: 15
    • Issue Number: 3
    • Publisher: Institute of Electrical and Electronics Engineers (IEEE)
    • ISSN: 0018-9235

Subject/Index Terms

Filing Info

  • Accession Number: 00176628
  • Record Type: Publication
  • Source Agency: IEEE Spectrum
  • Files: TRIS
  • Created Date: Jul 29 1978 12:00AM