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Evaluating ILS and MLS Sites without Flight Tests

  • P. R. Mahapatra (a1) and M. M. Poulose (a2)

Instrument landing systems (ILS) and the upcoming microwave landing systems (MLS) are (or are planned to be) very important navigational aids at most major airports of the world. However, their performance is directly affected by the features of the site in which they are located. Currently, validation of the ILS performance is through costly and time-consuming experimental methods. This paper outlines a powerful and versatile analytical approach for performing the site evaluation, as an alternative to the experimental methods. The approach combines a multi-plate model for the terrain with a powerful and exhaustive ray-tracing technique and a versatile and accurate formulation for estimating the electromagnetic fields due to the array antenna in the presence of the terrain. It can model the effects of the undulation, the roughness and the impedance (depending on the soil type) of the terrain at the site. The results computed from the analytical method are compared with the actual measurements and good agreement is shown. Considerations for site effects on MLS are also outlined.

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1 M. M. Poulose , P. R. Mahapatra and N. Balakrishnan (1985). Microwave landing system– a favoured alternative to the current ILS. IETE Tech. Review, 2, 375.

7 S. Ramakrishna and M. Sachidananda (1974). Calculating the effect of uneven terrain on glidepath signals. IEEE. Trans, on Aerospace and Electronic Systems, AES-10, p.380.

8 J. B. Keller (1962). Geometrical theory of diffraction. J. Opt. Soc. America, 52, 116.

9 R. G. Kouyoumjian and P. H. Pathak (1974). A uniform geometrical theory of diffraction for an edge in a perfect conducting surface. Proc. IEEE, 62, 448.

10 D. S. Ahluwalia R. M. Lewis and J. Boersma (1968). Uniform asymptotic theory of diffraction by a plane screen. SIAM J. Appl. Math., 16, 783.

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The Journal of Navigation
  • ISSN: 0373-4633
  • EISSN: 1469-7785
  • URL: /core/journals/journal-of-navigation
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