Lesson 00 ILS Theory v3

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ILS system description

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ILS definitions

• ILS Operational requirements

• ILS facility requirements– CAT I: Coverage down to 60m above threshold– Cat II: Coverage down to 15m above threshold (= thr passing)– Cat III: Coverage all the way down to rwy and along it

Non-Precisionapproch

CAT I CAT II CAT IIIA CAT IIIB CAT IIIC

MDA(min. høyde over terskel)

300m(1000’)

60m(200’)

30m(100’)

0 0 0

RVR(sikt langs rullebane)

5km(16000’)

800m(2600’)

400m(1200’)

200m(700’)

50m(150’)

0

(minimum decision altitude)

(rwy visual range)

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ICAO Annex 10

• Annex 10 to the convention of International Civil Aviation

• The “Bible” for ILS• Defines all the signal• Defines tolerances for all the signals • Defines Cat I, II, III

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ILS definitions - LLZ

• Course Line - CLwhere DDM is zero in the horizontal plane

• Course Sector - CS;the sector in the vertical plane limited of DDM = 0,155

• LLZ Displacement Sensitivity (DS);change in DDM pr. meter at ILS reference datum (thr) should be 0,00145

– hence; CS is 106,9m at threshold

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ILS definitions GP

• Glidepath;where DDM is zero in the vertical plane

• Glidepath angle;angle between where DDM is zero and the horizontal plane

• Glidepath sector; the sector in the horizontal plane limited of DDM = 0,175

• GP Displacement Sensitivity (DS);change in DDM pr. degree shall be 0,0875

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Important parameters

• LLZ– Polarization– Coverage– Course alignment– Course Structure– Displacement

Sensitivity - DS– Clearence

• GP– Coverage– GP angle/alignment– GP Structure– DS

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LLZ main parameters

• Polarization– when an aircraft is on course line and is in roll attitude of 20

degrees, the measured fault should be less than:CAT I: 0.016 DDM, CAT II: 0,008 DDM, CAT III: 0,005 DDM

• Coverage– 46,3 km within 10° from course line– 31,5 km within 10° og 35° from course line– 18,5 km outside 35° if coverage is required

• Course line– mean course line shall be adjusted and maintained within;

CAT I: +/- 10,5mCAT II: +/- 7,5m (recommended +/- 4,5m)CAT III: + 3,0mat ILS reference datum (threshold)

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LLZ main parameters

• Course structure

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LLZ main parameters

• LLZ DS– The DS shall be adjusted and maintained

withinCat I ± 17 percentCat II / III ± 10 percent

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GP main parameters

• Coverage– sector +/-8° on each side of the LLZ course

18,5 km (10nm) from 1.75 * GP angle (0=3°, 5.25°) and down to 0.45 0 (0=3°, 1.35°)

• GP structure– Bends must be less than;

±30 µA for CAT I±20 µA for CAT II/III.

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GP main parameters

• GP DS– DDM of 75 µA at ±0.12 0 from 0 (0=3°; 3.36° - 2.64°)

– The DS shall be adjusted and maintainedwithinCat.I 0.07 0 - 0.14 0 (0=3°; 3.42°/3.21° - 2.79°/2.58°)

Cat. II/III: 0.10 0 - 0.14 0 (0=3°; 3.3°/3.21° - 2.79°/2.7°)

• GP angle– Maintained within

Cat I: 0.075 0 (0=3°; 3.225° - 2.775°)Cat II/III: 0.04 0 (0=3°; 3.12°/2.88°)

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ILS signal formatCh. 2.3

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The ILS signal format

• CSB - Carrier with double Side Band

• SBO - SideBand Only– Double SideBand - Supressed Carrier (DSB-SC)

v t A m t m tc t( ) sin sin sin 1 90 90 150 150

v t A m t m tc t( ) sin sin sin 90 90 150 150

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90 Hz + 150 Hz

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= CSB

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90 Hz + 150 Hz

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= SBO

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DDM / SDM definition

• DDM = m150 – m90 ;modulation level <2m

• DDM = 2m ;modulation level >2m

• SDM = m150 + m90 ;modulation level >2m

• SDM = 2m ;modulation level <2m

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DDM / SDM Definition

DDM

+ =

CSB SBO

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DDM definition with phase fault

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LLZ / GP linearity

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Airborn receiver

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Principle of airbornereceiver

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LLZ / GP definitions

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Principle of NM7000 transmitterCh. 2.4

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Antenna theoryCh. 3

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Antenna arraysCh. 3.2

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Two antenna element

Phase difference: Total received signal:

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Two antenna element

In phase 180° out of phase

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Two antenna element array

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Image theoryCh. 3.4

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Image theory

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ILS antenna theoryCh. 4

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CSB /SBO feed

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90Hz from two antenna feeds

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150Hz from two antenna feeds

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Result of two antenna feeds

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Radiation patterns for CSB and SBO

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LLZ antenna above groundCh. 4.2

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LLZ antenna above ground

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Beam Bend Potential

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Beam Bend Potential

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NM3525 – 24 el. LLZ

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NM3525 signal distribution

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NM3545 – M-array GPCh. 6.3

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M-array distribution

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Antenna element offsetCh. 6.4

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Monitoring

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