Download ILS

Machine Translated by Google
Placement of radio navigation aids at the Minsk-2 airfield
Machine Translated by Google
1. General principles of construction and operation of ILS
The ILS is based on ground-based radio beacons: localizer
(Localizer) (frequency range 108...112 MHz); glide path beacon (Glide Sloop)
(frequency range 329…335 MHz) marker radio beacons (Marker) (emission frequency
75 MHz).
Localizer and glide slope radio beacons create 40 frequency channels each. The KRM
and timing channels are in accordance with each other (“paired”).
To identify radio beacons of a specific ILS, the KRM transmits an
identification signal in parcels of 2 or 3 Morse code letters, the first of which is I.
The identification signal is transmitted at a frequency of 7 messages per minute
Machine Translated by Google
The KRM and timing antennas form radiation fields in space,
asking:
heading plane (vertical plane passing through the runway axis); planning plane
(a
plane inclined to the runway at an angle of about 3 0 and passing through the
optimal landing point on the runway).
The intersection of these planes determines the planning line (glide path).
To set the direction using KRM and timing gear, use:
equisignal method ; method - with
“reference zero” (CSB/ SBO).
CSB/ SBO – Carrier and Side Band/ Side Band Only
Machine Translated by Google
Ext. MRM – internal MRM
(IM – Inner Marker)
BRMP - close (middle) radio marker point
(LMM – Locator Middle Marker)
DRMP – long-range (external) radio marker point
(LOM – Locator Outer Marker)
Machine Translated by Google
Equal-signal
directions of
intersecting lobes formed by the LMC or timing
are being created
two
directional patterns,
antennas.
The KRM antenna creates an RSN in the horizontal plane that coincides
with the heading plane.
The timing antenna creates an RSN in the vertical plane that coincides with
planning plane.
To determine on the aircraft the side of deviation from the RCH, it is used
amplitude modulation of radiation along the diagram lobes
directivity with frequencies of 90 Hz and 150 Hz.
To determine the side and magnitude of deviation of the aircraft from the RSN
signal modulation depth coefficients are compared ,
received from the lobes of the radiation pattern (RGM - difference
modulation depths).
Machine Translated by Google
HSI (CDI)
ND
Indication of deviations from course and planning planes
Machine Translated by Google
2. ILS token channel
Antennas of marker radio beacons have quite narrow
vertically oriented radiation patterns.
When the aircraft is within the radiation pattern, the marker radio beacon signal is received and
color (light) and sound alarms are activated in the aircraft cockpit.
This allows you to determine the type of marker beacon, and
therefore, the distance to the end of the runway at a given time.
Machine Translated by Google
Marker beacon signals are amplitude modulated by code
Morse (dots and/or dashes) and differ in modulation frequencies
(OM - 400 Hz, MM - 1300 Hz and IM - 3000
Hz). To identify OM, a sequence of 2 dashes/s is used,
MM – alternation of dots and dashes 2/s, IM – 6 dots/s.
The range to the landing point in the ILS can also be determined using a groundbased radio beacon of the DME system, installed next to the timing belt. The DME
transponder antenna can be mounted on the same mast as the timing antennas.
Machine Translated by Google
Simplified block diagram of a marker receiver
Machine Translated by Google
Distant (OM - Outer Marker) - blue color
Middle (MM - Middle Marker) - amber color
Internal (IM - Inner Marker) - white color
Machine Translated by Google
3. Radio beacons of equal-signal type
The block diagram of an equal-signal type PM has the form
LFO1 generates frequency oscillations ÿ1=150 Hz
LFO2 generates frequency oscillations ÿ2=90 Hz.
The line of intersection of the F1 (ÿ) and F2 (ÿ) patterns forms an equalsignal direction (RSD), with the help of which the glide path (course) line is set.
Machine Translated by Google
Antennas A1 and A2 form two radiation fields with frequencies
modulation 90 and 150 Hz.
When adding the fields created by antennas A1 and A2 in space
the resulting field is formed, amplitude modulation coefficients
whose frequencies of 90 and 150 Hz depend on the position of the aircraft relative to
ÿ
antenna radiation patterns F1 () and F2 (ÿ).
In on-board equipment from the received total signal
frequency oscillations of 90 Hz and 150 Hz are identified and their difference is determined
amplitudes – the difference in modulation depths (DDM), which depends on
ÿ
aircraft position relative to the antenna patterns F1 () and
F2 (ÿ).
Machine Translated by Google
Machine Translated by Google
Spectral components at all side frequencies and carrier
frequencies are in phase.
When the aircraft is located on the RSN, the amplitudes of the spectral components of the
modulation frequencies of 90 and 150 Hz are the same.
When you deviate to the left or right (up or down) from the RCH, the
amplitude of the 90 Hz modulation frequency component increases or
decreases, and the 150 Hz modulation frequency component, on the contrary,
decreases or increases.
Machine Translated by Google
In the equal-signal direction, RGM = 0.
When deviating from the RSN, the RGM increases, and the sign of the difference
depends on the side of the aircraft deviation from the equal-signal direction.
A voltage proportional to the RGM is generated in the receiver. It is connected to an
indicator device, the vertical arrow of which indicates the position of the course line, and the
horizontal arrow indicates the position of the glide path relative to the aircraft.
Simplified block diagram of on-board control unit (GRP)
Machine Translated by Google
Machine Translated by Google
The signals displayed by the indicator are proportional to the RGM, and their
polarity indicates the direction in which the aircraft deviates from the equal-signal
direction.
The output voltages of the rectifiers are supplied to the adder, the output
signal of which controls the blender of the indicator device (signal “Get. K” and
“Get. G”).
The blanker is removed from the field of view if the output of the rectifiers is
affected by both low frequency oscillations of 90 and 150 Hz.
If at least one of these oscillations disappears, the blanker system does not
operate, and the blanker is exposed in the pilot’s field of view, which indicates the
absence of a signal from the localizer (glide slope) radio beacon.
Machine Translated by Google
4. Features of glide path formation
Significant participation in the formation of the radiation field of the timin
receives the earth's surface near its antenna.
In the MB range, the earth's surface is like a conductor and reflects
radiation incident on it in the upper hemisphere.
Therefore, the resulting timing pattern is formed by the interference of
direct and reflected radiation from the ground.
Machine Translated by Google
Due to interference of direct and reflected RP signals
acquires a multi-petal character.
At the anglesÿatmax,
which these signals are in phase (add),
maxima of the resulting pattern are formed, at angles at which ÿ min
the signals are antiphase (subtracted), its dips are formed.
The directions of the maxima and minima of the pattern are determined by
formulas.
(2k1 + ) ÿ
kÿ
=
=
= 0. 1. .2. . .
sinÿ min
sinÿ max
;k
;2h
4h
Machine Translated by Google
The angles of inclination of the maxima and minima of the pattern relative to
the ground are determined by the relationship between the height of the antenna
suspension and the wavelength.
The shape of the radiation patterns F(ÿ) depends on the ratio of the antenna
height and wavelength, as well as the nature of the underlying surface.
As the height of the suspension increases, the first petal is pressed closer to the
earth's surface, the width of the petals decreases, and their number increases.
Machine Translated by Google
To implement the equal-signal method of specifying the glide path, you need
two intersecting patterns.
To form them, two antennas are used, installed at different heights h1 and
h2 and forming two different patterns.
Machine Translated by Google
Glide path nonlinearity
When rotating the directional pattern of the timing belt in the horizontal plane, its RSN will
describe the surface in the form of a cone with the center at the point where the beacon is
located. The RSN
specified by the KRM lies in the vertical plane passing through the axis of the runway.
The intersection of
the surface of a cone with a vertical plane offset relative to the axis of the cone forms a
hyperbola.
In this case, h=L·tg ÿ, where L is the distance of the timing antenna from the
runway axis. For typical values ÿ = 2,040´ and L = 150 m, we obtain that h = 7 m.
Machine Translated by Google
5. Radio beacons with a “reference zero”
The low stability of the glide path formed by the equal-signal method is also due
to the fact that the RSN is formed according to radiation levels with modulation
frequencies of 90 and 150 Hz, which differ significantly from the maximum.
Beacons with a “reference zero” make it possible to obtain a more stable glide
path. This is achieved by creating additional radiation, the maximum of which
corresponds to the RSN.
This technology is called CSB/SBO (Carrier and Side Band/Side Band Only).
The English name comes from the fact that radio beacons emit amplitudemodulated signals (the spectrum contains a carrier and side frequencies), and
oscillations, the spectrum of which contains only side frequencies (balanced
modulated oscillations).
Machine Translated by Google
Simplified block diagram of a radio beacon
BM – balanced
modulator Ant. RU – antenna distribution device
Machine Translated by Google
ÿ m cos
e1 =Em1F1 ()(1+
ÿ
e2 =Em2F2 ()(cos
ÿ 1t + mcos ÿ 2t)cosÿ t
ÿ 1t - cos ÿ 2t)cosÿ t
eÿ = e1 + e2 =Em1F1 ÿÿ
() 1+ M1 (ÿ )cosÿ
- CSB signal (CSB)
- warhead signal (SBO)
1
ÿ 2t]cosÿ t,
ÿ
t + M2 ()cos
Machine Translated by Google
Spatial modulation depth coefficients
RM with “reference zero”
M1 (ÿ )= m + aF2 (ÿ )/ F1 (ÿ
)
ÿ m - aF2 ( ÿ )/ F1 (ÿ )
M2 ()=
a = Em2 /
Em1 m – AM coefficient.
Equal-signal PM
ÿ = mF1 ()/
ÿÿ F1 (ÿ )+F2 ()
ÿÿ
M1 ()
ÿ = mF2 ()/
ÿÿ F1 (ÿ )+F2 ()
ÿÿ
M2 ()
Machine Translated by Google
6. Two-channel radio beacons
The nature of the heading line distortion is significantly influenced by local objects located in the PM
radiation sector. The secondary radiation field they create adds up to the PM field and, as a result, the
course line turns out to be curved.
The nature of the heading line distortion depends on the diagram of the secondary
radiation, its intensity and location of local objects.
The most dangerous is the secondary radiation field of side-frequency oscillations
modulation, since it is this field that sets the heading line.
Machine Translated by Google
Two-channel radio beacons made it possible to eliminate the contradiction
between the requirements for a fairly wide radiation sector and stability
glide paths
A two-channel PFC contains two channels: narrow and wide, in each of
which use their own antenna system.
The narrow channel antenna system forms narrow patterns with a width of 6–12° in
horizontal plane.
The wide channel antenna system creates wide patterns that provide
specified width of the coverage area (± 35°).
Machine Translated by Google
Dependence of the shape of the pattern on the number of vibrators
N=6, d/ ÿ=0.5
N=20, d/ ÿ=0.5
N=6, d/ ÿ=5
Machine Translated by Google
In two-channel radio beacons, the influence of wide channel signals on a narrow one
the channel should be minimal.
To do this, use the following options for constructing two-channel
radio beacons:
dual-frequency radio beacons, which emit narrow and wide
channels are carried out at different carrier frequencies;
radio beacons with quadrature clearance, in which the modulating voltages of the
same frequencies of the narrow and wide channels are shifted in phase by 90° (are in
quadrature);
combined radio beacons, in the construction of which both are used
specified methods.
Machine Translated by Google
The most common are dual-frequency radio beacons.
The carrier frequency spacing in a dual-frequency localizer ranges from 5 to 14 kHz
for the localizer and 4-32 Hz for the timing belt.
With such a frequency spacing, the mutual influence of the channels and both
carrier frequencies fall within the bandwidth of the onboard receiver.
Machine Translated by Google
A narrow channel forms an almost straight course line, because there are no
reflective objects or ground irregularities in its coverage area
surfaces.
This channel is used to control aircraft at low
deviations from the plane of the landing course, usually at the final stage of landing
(Final Approach).
A wide channel is important at the initial stage of the landing approach (Initial
Approach), when large deviations of the aircraft from the heading plane are possible
and glide path instability is acceptable.
To reduce the influence of wide channel signals on the operation of the
narrow channel of the beacon, a dip is formed in the radiation pattern of the wide
channel antenna system in the radiation sector of the narrow antenna system
channel.
The wide channel signal reflected from local objects is much smaller than the
main signal of the narrow channel and during linear detection in the on-board receiver
it is suppressed by the stronger signal of the narrow channel.
Thus, there is no wide channel signal on the course line and in its vicinity, which
predetermines the high stability of the zone parameters
radiation.
Machine Translated by Google
Features of a two-channel timing belt
In the timing belt, to reduce glide slope curvature, radiation at low elevation
angles (up to 1.5 degrees) is compensated, and an additional channel is used to
obtain information about the aircraft’s position in this area.
An additional channel is created using the third antenna A3, height
the suspension of which is three times higher than the height of the suspension of the lower antenna A1.
The main channel uses antennas A1 and A2, and the additional channel uses
antennas A1 and A3.
Machine Translated by Google
Machine Translated by Google
Within the first from the ground, the widest lobe of the bottom antenna A1 , two lobes of the upper and
three lobes of the additional one are formed
antennas
The phases and amplitudes of the antenna supply currents are selected so that, near the ground, the field
of the additional antenna is antiphase to the fields of the lower and upper antennas and compensates for them.
Therefore, the level of
signals reflected by the earth’s surface decreases,
and, consequently, the curvature of the glide path is reduced.
Elimination of the radiation field near the ground forms a narrow channel in which
The influence of relief and local objects on the operation of the timing belt has been significantly reduced.
In the area of the first lobe of the upper antenna, fields are added
all three antennas. As
a result, the slope of the resulting field pattern, and
This means that the accuracy of setting the glide path increases significantly.
Machine Translated by Google
When the fields of all three antennas are added in space, a carrier frequency
field is formed; a modulation depth of 90 Hz prevails above the glide path, and a
modulation depth of 150 Hz prevails below.
In the area of space above the glide path, a wide channel signal
is suppressed by the much stronger narrow channel signal.
Since the heights of the antennas are sufficiently large compared to the
wavelength, in order to ensure the desired nature of the change in the DGM in
the near zone, the antennas must be shifted towards the runway so that the
line of their placement looks like an arc of radius R in a plane perpendicular
to the runway axis.
Machine Translated by Google
ICAO requirements for ILS performance
Parameter
Radiation frequency,
MHz Number of channels
LOC
G/S
108–111.975
328.6–335.4
40
Emission polarization
horizontal
Carrier instability
±0.005% (0.002%)
frequencies
Carrier frequency spacing for dualfrequency beacon, kHz Modulation
5…14
with a frequency of 90 Hz Modulation
to the left of the course plane
with a frequency of 150 Hz Frequency
to the right of the heading plane
instability
modulation
above the glide path
below glide path
CAT I: ±2.5%; CAT II: ±1.5%; CAT III: ±1%
46.3 km in a sector ±10° from the runway axis;
Beacon coverage area
4… 32
18.5 km in a sector ±8° in the
31.5 km in the sector 10–35° from the runway axis;horizontal plane from the runway axis
18.5 km outside the ±35° sector
Radiation sector
vertical plane
horizontal plane
Identification signal
modulation frequency
transmission speed
0…70
±35° - single-channel
±10° - “narrow” channel
±35° - “wide” channel
2-3 letters Morse code
1020 ±50 Hz
7 words/min
0.45ÿ0 …1.75ÿ0
±8°
Machine Translated by Google
Features of the design of the control gear and timing gear
Machine Translated by Google
Machine Translated by Google
Complex-734
LOC-734
G/P-734
Machine Translated by Google
Equipment Kurs MP-70
Machine Translated by Google
Blenders
Got "K"
Goth. "G"