CEPT
ECC
CPG PTC(13) 017
Electronic Communications Committee
2nd Meeting CPG PTC
London, 16-19 April 2013
Date issued:
8 April, 2013
Source:
Germany
Subject:
Sharing analyses between Wireless Avionics Intra-Communications (WAIC) and systems
in other radio services in the band 2 700 – 2 900 MHz
Summary:
The Annex to this document summarizes initial results of sharing analyses considering the effect of WAIC
systems on radars operated in the band 2 700 – 2 900 MHz.
Proposal:
PTC is invited to consider the sharing analyses in the Annex to this document for development of the CEPT
position on WRC-15 agenda item 1.17.
Background:
In order to determine appropriate radio frequency bands for WAIC applications, ITU-R Resolution 423
(WRC-12) invites ITU-R 1 calls “to conduct, in time for WRC-15, the necessary studies to determine the
spectrum requirements needed to support WAIC systems”. In invites ITU-R 3 it is further detailed that
ITU-R should first consider bands within existing worldwide Aeronautical Mobile Service (AMS),
Aeronautical Mobile (Route) Service (AM(R)S) and Aeronautical Radionavigation Service (ARNS)
allocations below 15.7 GHz.
ANNEX
Radiocommunication Study Groups
Subject: Agenda item 1.17 (WRC-15)
Document 5B/XX-E
XX May 2013
English only
Germany
WORKING DOCUMENT TOWARDS A PRELIMINARY DRAFT
NEW REPORT ITU-R M.[WAIC-SHARING_2700-2900MHZ]
Sharing analyses between Wireless Avionics Intra-Communications (WAIC) and
systems in other radio services in the band 2 700 - 2 900 MHz
1
Introduction
Under Agenda Item 1.17, the band 2 700 - 2 900 MHz has been identified as a possible candidate
band for Wireless Avionics Intra-Communications (WAIC). The band is allocated to the
aeronautical radionavigation service on a primary basis and the radiolocation service on a secondary
basis. Ground-based radars used for meteorological purposes are authorized to operate in this band
on a basis of equality with stations in the aeronautical radionavigation service (see RR No. 5.423).
This document provides an analysis of the impact of WAIC systems into air traffic control radars
operating in the radionavigation service, as well as meteorological and other radars operating in the
radio location service.
The impact of radars into WAIC systems will be assessed at a later stage.
2
Radar technical characteristics
Characteristics of radars using the band 2 700 - 2 900 MHz are given in recommendation ITU-R
M.1464. They include civilian ATC, meteorological, and air defense traffic control radars.
The aeronautical radionavigation radars are used for air traffic control (ATC) at airports, and
perform a safety service (see RR No. 4.10). This is the dominant band for terminal approach/airport
surveillance radars for civil air traffic worldwide. The meteorological radars are used for detection
of severe weather elements such as tornadoes, hurricanes and violent thunderstorms. They also
provide quantitative area precipitation measurements which are important in hydrologic forecasting
of potential flooding. This information is used to provide warnings to the public and is therefore
considered a safety-of-life service.
The radar characteristics used for this study are given in Table 1.
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TABLE 1
Characteristics of aeronautical radionavigation radars
in the band 2 700-2 900 MHz
Characteristics
Radar A
Radar B
Radar C
Radar D
Platform type (airborne, shipborne,
ground)
Ground, ATC
Tuning range (MHz)
2 700-2 900(1)
Modulation
Transmitter power into antenna(2)
Pulse width (s)
Pulse rise/fall time (s)
P0N
P0N, Q3N
P0N
25 kW
450 kW
22 kW
70 kW
1.03
1.0, 89
1.0
1.0, 55.0
0.4, 20
0.5, 27(3)
0.15-0.2
0.5/0.32
(short pulse)
0.7/1
(long pulse)
0.1 (typical)
722-935
(short impulse)
788-1 050
(long impulse)
1 050
Duty cycle (%)
0.07
maximum
0.14
maximum
9.34
maximum
0.1
maximum
2
Not
applicable
Not applicable
Phase-coded sub-pulse width
Antenna pattern type (pencil, fan,
cosecant-squared, etc.) (degrees)
Not applicable
6 MHz
5 MHz
600 kHz
Klystron
Cosecant-squared 30
Antenna type (reflector, phased
array, slotted array, etc.)
Antenna polarization
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8 sets,
1 031 to
1 080
1 100
840(3)
2
(typical)
1.3 nonlinear FM
2
55
40:1
55:1
Not applicable
3 dB
Output device
P0N, Q3N
1.32 MW
1 059-1 172
RF emission bandwidth:
–20 dB
P0N,
Q3N
0.6
973-1 040
(selectable
Compression ratio
Radar F
1.4 MW
Pulse repetition rate (pps)
Chirp bandwidth (MHz)
Radar E
89
Not
applicable
2.6 MHz
(short impulse)
5.6 MHz
(long impulse)
1.9 MHz
Solid state
transistors,
Class C
3 MHz
(valeur type)
2 MHz
Magnetron
Solid state
transistors,
Class C
Cosecant-squared 6 to 30
TWT
Cosecantsquared
Enhanced to
+40
Parabolic reflector
Vertical or
left hand
circular
polarization
Vertical or
right hand
circular
polarization
Circular or
linear
31.07.17
Vertical or
left hand
circular
polarization
Vertical or
right hand
circular
polarization
Left hand
circular
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TABLE 1 (END)
Characteristics
Radar A
Antenna main beam gain (dBi)
Radar B
Radar D
Radar E
Radar F
34
32.8
34.3 low
beam
33 high
beam
33.5
4
4.8
5.0
1.6
1.4
1.5
90
75
90
60(3)
Not
applicable
Not
applicable
Not
applicable
33.5
Antenna elevation beamwidth
(degrees)
Antenna azimuthal beamwidth
(degrees)
Radar C
4.8
1.35
1.3
Antenna horizontal scan rate
(degrees/s)
1.45
75
Antenna horizontal scan type
(continuous, random, 360,
sector, etc.)
360
Antenna vertical scan rate
(degrees/s)
Antenna vertical scan type
(continuous, random, 360,
sector, etc.) (degrees)
Not applicable
2.5 to –2.5
Not applicable
Antenna side lobe (SL) levels
(1st SLs and remote SLs)
7.3 dBi
9.5 dBi
3.5
653 kHz
15 MHz
Antenna height (m)
+7.5 dBi
0 to 3 dBi
8
Receiver IF 3 dB bandwidth
Receiver noise figure (dB)
Minimum discernible signal
(dBm)
5 MHz
4.0 maximum
–110
–108
Receiver front-end 1 dB gain
compression point (dBm)
–20
Receiver on-tune saturation level
(dBm)
–45
Receiver RF 3 dB bandwidth
(MHz)
2-2.3
10
8-24
3.3
2.7
110
112
1.2 MHz
4 MHz
2.1
2.0
110 typical
10
400(1)
280.6
Receiver RF and IF saturation
levels and recovery times
Doppler filtering bandwidth (Hz)
Interference-rejection
features(4)
95 per bin
Feedback
enhancer
(5)
Geographical distribution
Worldwide
Fraction of time in use (%)
100
(1)
2.7 to 3.1 GHz.
(2)
Fixed systems operate up to 750 kW or 1 MW.
(3)
Depends on range.
(4)
The following represent features that are present in most radar systems as part of their normal function: sensitivity time
control (STC), constant false alarm rate (CFAR), asynchronous pulse rejection, saturating pulse removal.
(5)
The following represent features that are available in some radar systems: selectable pulse repetition frequencies (PRFs),
Doppler filtering.
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Those radars use a cosecant squared antenna pattern which was modelled using the equations of
recommendation ITU-R M.1851. Radars A and B have similar characteristics in terms of reception,
and give the same results in terms of interference from WAIC system into the radar.
TABLE 1 (CON’T)
Characteristics of aeronautical radionavigation radars
in the band 2 700-2 900 MHz
Characteristics
Radar F1
Platform type (airborne, shipborne,
ground)
Ground, ATC, Weather
Ground, ATC, Weather
Tuning range (MHz)
2 700-2 900
2 700-2 900(6)
Modulation
P0N, Q3N
P0N, Q3N
40 kW
160 kW
1.0 (SP)
60.0 (LP)
1.0 (SP)
≤ 250.0 (LP)
Pulse rise/fall time (s)
0.2 (SP), 3 (LP)
0.2 (SP), 3 (LP)
Pulse repetition rate (pps)
320-6 100 (SP)
320-1 300 (LP)
Note 7
320-4 300 (SP)
320-1 500 (LP)
Note 7
Duty cycle (%)
0.1(8) -0.6 (SP)
≤ 8.0(9) (LP)
0.1(8) -0.4 (SP)
≤ 8.0(9) (LP)
3
3
Not applicable
Not applicable
180
≤ 750
10.4 (SP) / 3.8 (LP)
1.1 (SP) / 1.4 (LP)
10.4 (SP) / 3.8 (LP)
1.1 (SP) / 1.4 (LP)
Transmitter power into antenna(2)
Pulse width (s)
Chirp bandwidth (MHz)
Phase-coded sub-pulse width
Compression ratio
RF emission bandwidth:
–40 dB
–6 dB
Output device
Radar F2
Solid state
Solid state
Pencil beam coverage to 70 000 feet
Pencil beam coverage to 100 000 feet
Antenna type (reflector, phased
array, slotted array, etc.)
phased array, 4 faces (4 meter diameter
phased array per face)
phased array, 4 faces (8 meter diameter
phased array per face)
Antenna polarization
Linear horizontal and vertical; circular
Linear horizontal and vertical; circular
Antenna pattern type (pencil, fan,
cosecant-squared, etc.) (degrees)
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TABLE 1 (END)
Characteristics
Radar F1
Radar F2
Antenna main beam gain (dBi)
41
46
Antenna elevation beamwidth
(degrees)
1.6-2.7
0.9-1.5
Antenna azimuthal beamwidth
(degrees)
1.6-2.7
0.9-1.4
Antenna horizontal scan rate
(degrees/s)
Not applicable
Not applicable
Antenna horizontal scan type
(continuous, random, 360,
sector, etc.)
Irregular to cover 360o
Irregular to cover 360o
Antenna vertical scan rate
(degrees/s)
Not applicable
Not applicable
Antenna vertical scan type
(continuous, random, 360,
sector, etc.) (degrees)
Irregular to cover required volume
Irregular to cover required volume
17 dB on transmit, 25 dB on receive
17 dB on transmit, 25 on receive
Antenna side lobe (SL) levels
(1st SLs and remote SLs)
Antenna height (m)
Receiver IF 3 dB bandwidth
Receiver noise figure (dB)
Variable
Variable
1.1 MHz at -6 dB (SP)
1.4 MHz at -6 dB (LP)
1.1 MHz at -6 dB (SP)
1.4 MHz at -6 dB (LP)
< 6 dB
< 6 dB
Minimum discernible signal
(dBm)
-110 dBm/MHz
-110 dBm/MHz
Receiver front-end 1 dB gain
compression point (dBm)
10 dBm
10 dBm
Receiver on-tune saturation level
(dBm)
N/A
N/A
Receiver RF 3 dB bandwidth
(MHz)
1000
1000
Receiver RF and IF saturation
levels and recovery times
13 dBm, < 500 ns
13 dBm, < 500 ns
TBD
TBD
TBD
TBD
Geographical distribution
U.S. and its territories
U.S. and its territories
Fraction of time in use (%)
100
100
Doppler filtering bandwidth (Hz)
Interference-rejection
(6)
(7)
(8)
(9)
features(4)
Tuning range 2.7-3.0 GHz when replacing radar G
Very high PRFs only used at high elevation angles
Duty cycle for short pulse is 0.1% at lowest elevation (horizon) scan
Combination of pulse width and PRF will be matched to keep duty cycle under 8%
For those two radars, the worst case antenna plane in the direction of the aircraft and a random
pointing in azimuth between -45 and +45° relative to the aircraft direction and 1 to 91° in elevation
has been considered.
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TABLE 2
Characteristics of meteorological radars
in the band 2 700-2 900 MHz
Characteristics
Radar G
Radar H
Platform type (airborne, shipborne, ground)
Ground, weather
Ground, weather
Tuning range (MHz)
2 700-3 000
2 700-2 900
Modulation
P0N
Transmitter power into antenna (kW)
500
400 or 556
Pulse width ( s)
1.6 (short pulse)
4.7 (long pulse)
1.0 (short pulse)
4.0 (long pulse)
Pulse rise/fall time ( s)
0.12
Pulse repetition rate (pps)
318-1 304
(short pulse)
318-452
(long pulse)
Duty cycle (%)
0.21 maximum
Chirp bandwidth
Not applicable
Not applicable
Phase-coded sub-pulse width
Not applicable
Not applicable
Compression ratio
Not applicable
Not applicable
RF emission bandwidth:
–20 dB
3 dB
4.6 MHz
600 kHz
Output device
Klystron
Coaxial magnetron
Antenna pattern type (pencil, fan, cosecantsquared, etc.)
Pencil
Pencil
Antenna type (reflector, phased array,
slotted array, etc.)
Parabolic reflector
Parabolic reflector
Antenna polarization
Linear: vertical and horizontal
Linear: horizontal
Antenna main beam gain (dBi)
45.7
38.0
Antenna elevation beamwidth (degrees)
0.92
2.0
Antenna azimuthal beamwidth (degrees)
0.92
2.0
Antenna horizontal scan rate (degrees/s)
18
18 and full manual slewing
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539 (short pulse)
162 (long pulse)
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TABLE 2 (END)
Characteristics
Radar G
Radar H
Antenna horizontal scan type (continuous,
random, 360 , sector, etc.)
360
360° and sector
Antenna vertical scan rate (degrees/s)
14 steps in 5 min
Antenna vertical scan type (continuous,
random, 360 , sector, etc.) (degrees)
Fixed steps:
0.5-20
Antenna side lobe (SL) levels (1st SLs and
remote SLs) (dBi)
and sector
2.0 to +60
20
+15 (estimated)
Antenna height (m)
30
30
Receiver IF 3 dB bandwidth
630 kHz
0.25 MHz
(long pulse)
0.5 MHz
(short pulse)
Receiver noise figure (dB)
2.1
9.0
Minimum discernible signal (dBm)
–115
110
Receiver front-end 1 dB gain compression
point (dBm)
–17
32
Receiver on-tune saturation level (dBm)
–10
Receiver RF 3 dB bandwidth (MHz)
1.6
Receiver RF and IF saturation levels and
recovery times
–10 dBm,
1 s
Doppler filtering bandwidth (Hz)
Estimate 95(1)
0.5
(long pulse)
1.5
(short pulse)
Interference-rejection features
Geographical distribution
Worldwide
Fraction of time in use (%)
100
(1)
Doppler filtering and saturating pulse removal.
Weather radars perform volume scanning based on rotation / elevation variations. Figure 1
describes a typical sweeping pattern in elevation, used for the studies.
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FIGURE 1
Typical elevation variation over time of meteorological radar
The antenna pattern retained for meteorological radars is based on recommendation ITU-R F.1245
which is a pencil beam pattern with average sidelobes.
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TABLE 3
Characteristics of generic military radiolocation radars
in the band 2 700-3 400 MHz
Characteristics
Radar I
Radar J
Radar K
Radar L
Ground, ATC
gap-filler
coastal
2D/3D naval
surveillance
ground air defence
Ground air
defence
Multifunction
various types
2 700-3 100
2 700-3 100
2 700 to 3 100
2 900 to 3 400
Whole band up to
25% BW
Minimum: 2 spaced
at  10 MHz
Maximum:
fully agile
Minimum: 2 spaced
at  10 MHz
Maximum:
fully agile
Minimum: fixed
Maximum:
fully agile
Minimum: 2 spaced at
 10 MHz
Maximum:
fully agile
Modulation
Non-linear FM
P0N, Q3N
Non-linear FM
P0N, Q3N
Non-linear FM Q3N
Mixed
Transmitter power into
antenna
60 kW typical
60 to 200 kW
1 MW typical
30 to 100 kW
0.4(1) to 40
0.1(1) to 200
 100
Up to 2
Pulse rise/fall time (s)
10 to 30 typical
10 to 30 typical
Not given
Not given
Pulse repetition rate (pps)
550 to 1 100 Hz
300 Hz to
10 kHz
 300 Hz
Up to 20 kHz
2.5 maximum
10 maximum
Up to 3
30 maximum
2.5
Up to 10
 100
Depends on
modulation
Not applicable
Not applicable
Not applicable
Not given
Up to 100
Up to 300
Not applicable
Not given
3.5
2.5
15
10
 100
Not given
TWT
TWT
or solid state
Klystron
CFA
Active elements
Antenna pattern type (pencil,
fan, cosecant-squared, etc.)
Cosecant-squared
Pencil beam 3D
or cosecant-squared
2D
Swept pencil beam
Pencil beam
Antenna type (reflector,
phased array, slotted array,
etc.)
Shaped reflector
Planar array
or
shaped reflector
Frequency scanned
planar array or
reflector
Active array
1.5
1.1 to 2
Typically 1.2
Depends on number
of elements
Linear or circular
or switched
Linear or circular
or switched
Fixed linear or
circular
Fixed linear
33.5 typical
Up to 40
> 40
Up to 43
4.8
1.5 to 30
Typical 1
Depends on number
of elements
Platform type (airborne,
shipborne, ground)
Tuning range (MHz)
Operational frequencies
minimum/maximum
Pulse width (s)
Duty cycle (%)
Chirp bandwidth (MHz)
Phase-coded sub-pulse width
Compression ratio
RF emission bandwidth
(MHz):
–20 dB
–3 dB
Output device
Antenna azimuth beamwidth
(degrees)
Antenna polarization
Antenna main beam gain
(dBi)
Antenna elevation beamwidth
(degrees)
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TABLE 3 (END)
Characteristics
Radar I
Radar J
Radar K
Radar L
Antenna horizontal scan rate
(degrees/s)
45 to 90
30 to 180
Typical 36
Sector scan
instantaneous rotation
scan up to 360
Antenna horizontal scan type
(continuous, random, 360°,
sector, etc.) (degrees)
Continuous 360
Continuous 360 
sector scan
Continuous 360 
sector scan on
Random sector scan
sector scan  rotation
Antenna vertical scan rate
(degrees/s)
Not applicable
Instantaneous
Instantaneous
Instantaneous
Antenna vertical scan type
(continuous, random, 360°,
sector, etc.) (degrees)
Not applicable
0 to 45
0 to 30
0 to 90
Antenna side lobe (SL) levels
(1st SLs and remote SLs)
26 dB
35 dB
 32 dB
typical
 –10 dBi
 26 dB
typical
 0 dBi
Not given
Antenna height above ground
(m)
4 to 30
4 to 20
5
4 to 20
Receiver IF 3 dB bandwidth
(MHz)
1.5 long
3.5 short
10
Not given
Not given
Receiver noise figure(2) (dB)
2.0 maximum
1.5 maximum
Not given
Not given
Minimum discernible signal
(dBm)
–123 long pulse
–104 short pulse
Not given
Not given
Not given
Receiver front-end 1 dB gain
compression point.
Power density at antenna
(W/m2)
1.5  105
5  105
1  106
1  103
Receiver on-tune saturation
level power density at
antenna (W/m2)
4.0  1010
1  1010
Not given
Not given
RF receiver 3 dB bandwidth
(MHz)
400
400
150 to 500
Up to whole band
Receiver RF and IF saturation
levels and recovery times
Not given
Not given
Not given
Not given
Doppler filtering bandwidth
Not given
Not given
Not given
Not given
Interference-rejection
features(3)
(4)
(4)
and
(5)
(4)
and
(5)
Adaptive
beamforming (4)
and (5)
Geographical distribution
Worldwide fixed site
transportable
Worldwide fixed site
naval transportable
Worldwide fixed site
transportable
Worldwide fixed site
naval transportable
Fraction of time in use (%)
100
Depends on mission
Depends on mission
Depends on mission
(1)
(2)
(3)
(4)
(5)
Uncompressed pulse.
Includes feeder losses.
The following represent features that are present in most radar systems as part of their normal function: STC, CFAR,
asynchronous pulse rejection, saturating pulse removal.
The following represent features that are available in some radar systems: selectable PRFs, moving target filtering, frequency
agility.
Side lobe cancellation, side lobe blanking.
Some of these radars perform a mechanical scan in azimuth and in addition an electronically scan in
one azimuth sector and in elevation. The sector taken in azimuth is 120°. The antenna panel has
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been assumed to rotate at the maximum possible speed and in addition a random positioning of the
beam was considered within the azimuth and elevation sectors.
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3
WAIC characteristics
WAIC characteristics are provided in the preliminary draft new report ITU-R
M.[WAIC_CHAR_SPEC]. According to this document and its annex 4, the EIRP density radiated
outside the aircraft depend on the type of WAIC system, as well as the aircraft compartment, and
varies from -44 to 7.7 dBm/MHz. The EIRP density is manly determined by the maximum transmit
power of a WAIC system, the aircraft shielding effective in a certain aircraft compartment or region
and the duty cycle at which WAIC Gateway Node (GN) has to operate to convey the anticipated
amount of data traffic. A coarse characterization of WAIC system emissions can be made using the
WAIC application categories defined in ITU-R M.[WAIC_CHAR_SPEC], i.e. ‘low rate internal’
(LI), ‘low rate outside’ (LO), ‘high rate internal’ (HI) and ‘high rate outside’ (HO). However, even
within these categories, EIRP levels outside the aircraft caused by different GNs can vary
significantly, depending on the effective aircraft shielding applicable for the installation location
and the duty cycle of a particular GN. This fact has to be reflected in any conclusion derived from
the study results presented hereafter.
4
Study scenario
The purpose of the study is to determine for all possible EIRP density values, the separation
distance above which the protection criterion of the radar would be met.
The scenario is based on an aircraft flying at a constant speed above an ATC or meteorological
radar, at a given altitude, with a radial trajectory to and from the radar. The results in terms of
separation distance are valid whatever the speed of the aircraft. This does include an aircraft at
parking at the airport. However, it should be noted that the interference time characteristics (such as
the separation between interference power peaks, as well as the width of interference power peaks),
will vary with the speed of the aircraft, as well as radar parameters (antenna rotation speed, beam
width in azimuth), along with the geometry.
The radar antenna height is 12 m for the ATC radar and 13 m for the meteorological radar. Those
values are typical values given by civil aviation and EUMETNET for radars operated in Europe.
The calculation takes into account the Earth curvature as shown in Figure 2.
FIGURE 2
Constant altitude scenario description
distance
h radar
h aircraft
The slant range between the radar and the aircraft is then given by the following equation:
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D
 distance 




Rt

h
aircraft 

Rt  hradar ²  Rt  haircraft ²  2Rt  hradar Rt  haircraft cos
(1)
where:
Rt:
Earth radius (6 378 000 m)
hradar:
Radar altitude (m).
haircraft:
Aircraft altitude (m).
distance:
Separation distance between radar and aircraft (m).
The propagation loss is based on free space loss, and given by equation (2).
Lbf = 32.4  20 log   20 log D
(2)
where:
f:
frequency (2 800 MHz)
D:
slant range (km).
For each aircraft position, the position of the radar antenna and its gain towards the aircraft location
is computed using the relevant antenna pattern. This gain is used in the link budget calculation
along with the EIRP and the propagation loss to derive the interference level, which is then
compared to the protection criterion.
5
Calculation results for the ATC radars
Figures 3 to 10 provide the distance that would be required between the ATC radar and an aircraft
flying at a given altitude, regardless of the speed of the aircraft, in order to meet an I/N of -10 dB
for all radars given in Table 1.
FIGURE 3
Separation distance between ATC radar A or B and the aircraft vs WAIC EIRP density
For instance, an aircraft flying at 1000 m altitude (yellow curve) with a WAIC system radiating at 20 dBm/MHz outside the aircraft would start to create harmful interference as soon as it gets closer
than 30 km to the radar.
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FIGURE 4
Separation distance between ATC radar C with a tilt angle of -2.5° and the aircraft vs WAIC
EIRP density
FIGURE 5
Separation distance between ATC radar C with a tilt angle of +2.5° and the aircraft vs WAIC
EIRP density
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FIGURE 6
Separation distance between ATC radar D and the aircraft vs WAIC EIRP density
FIGURE 7
Separation distance between ATC radar E and the aircraft vs WAIC EIRP density
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FIGURE 8
Separation distance between ATC radar F and the aircraft vs WAIC EIRP density
FIGURE 9
Separation distance between ATC radar F1 and the aircraft vs WAIC EIRP density
The strong variations in the curves are due to the choice of randomly pointing the radar antenna
beam. The peak envelope of the curves should actually be considered.
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FIGURE 10
Separation distance between ATC radar F2 and the aircraft vs WAIC EIRP density
The strong variations in the curves are due to the choice of randomly pointing the radar antenna
beam. The peak envelope of the curves should actually be considered.
6
Calculation results for MET radars
Figures 11 and 12 give the distance that would be required between the MET radar and an aircraft
flying at a given altitude, regardless of the speed of the aircraft, in order to meet an I/N of -10 dB
for the two radars in Table 2.
FIGURE 11
Separation distance between the MET radar G and the aircraft vs WAIC EIRP density
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For example, a WAIC system with an EIRP of -20 dBm/MHz outside the aircraft would start to
create harmful interference into the MET radar at a distance below 100 km when flying at an
altitude of 1000 m (yellow curve).
FIGURE 12
Separation distance between the MET radar H and the aircraft vs WAIC EIRP density
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7
Calculation results for RLS radars
Figures 13 to 16 provide the distance that would be required between the ATC radar and an aircraft
flying at a given altitude, regardless of the speed of the aircraft, in order to meet an I/N of -10 dB
for all radars given in Table 3.
FIGURE 13
Separation distance between radar I and the aircraft vs WAIC EIRP density
FIGURE 14
Separation distance between radar J and the aircraft vs WAIC EIRP density
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The strong variations in the curves are due to the choice of randomly pointing the radar antenna
beam. The peak envelope of the curves should actually be considered.
FIGURE 15
Separation distance between radar K and the aircraft vs WAIC EIRP density
The strong variations in the curves are due to the choice of randomly pointing the radar antenna
beam. The peak envelope of the curves should actually be considered.
FIGURE 16
Separation distance between radar L and the aircraft vs WAIC EIRP density
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The strong variations in the curves are due to the choice of randomly pointing the radar antenna
beam. The peak envelope of the curves should actually be considered.
8
Interference Mitigation Techniques
The previous analysis showed that protection criteria for coexistence can be fulfilled at practical
separation distances if the overall EIRP emitted by the aircraft is limited to less than
around -50 dBm/MHz. Such mitigation measures in case of LI and HI WAIC systems could be
additional shielding measures for the windows increasing the attenuation of the aircraft fuselage and
hence directly decreasing the peak transmit power level.
A further strategy could involve frequency separation of WAIC systems and radars. One possibility
could for example be, to operate WAIC systems only in portions of the frequency band not utilized
by the radar, for example at the band edges. This might be acceptable, since it is assumed, that radar
systems can anyhow not be operated all the way towards these edges in order not to interfere with
systems in the adjacent bands.
Furthermore, a reduced duty cycle, frequency hopping (e.g. time frequency coding), transmit power
control, the use of directive antennas on WAIC system side or combinations of these techniques
provide options to reduce the average power radiated outside the aircraft. These techniques will
have no or only limited impact on the peak EIRP density level but rather on probability of
occurrence of interference (i.e. WAIC system instantaneously transmits in the frequency range
instantaneously received by the radar). In order to assess this statistical property it would be
required to use a radar protection criterion, which takes this probability of interference into
consideration.
Another technique to mitigate interference is the detection of incumbent systems which transmit at a
certain frequency channel and avoidance of this frequency channel as soon as a certain threshold
receive power level is exceeded. The channel may be used again when the separation distance
between the incumbent system and the WAIC equipped aircraft becomes large enough again to
ensure protection of the incumbent system from harmful interference. Since this technique avoids
interference through adaptive selection of a certain frequency resource, measures which reduce
EIRP density are not necessarily needed. Combinations of the above methods are however possible.
As an example, Figures 17 and 18 give the results of separation distances for an aircraft at 500 m
under the assumption that a WAIC system would cease emissions as soon as the effective radar
antenna gain increases above a certain level (in this case Gmax-0dB, Gmax-10dB, Gmax-20dB, Gmax30dB and Gmax-40dBi).
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FIGURE 17
Separation distance between ATC radar A and the aircraft vs WAIC EIRP density and radar
antenna gain towards aircraft
FIGURE 18
Separation distance between MET radar G and the aircraft vs WAIC EIRP density and radar
antenna gain towards aircraft
9
Conclusions
This paper analyzes the impact of WAIC systems into ATC, meteorological and radiolocation radar
receivers operating in the band 2 700 – 2 900 MHz. It determines for a given WAIC EIRP density
level what would be the separation distance between the radar and the WAIC system equipped
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aircraft for which interference would start to appear in the radar. The results should be used as a
basis to define relevant sharing conditions (including relevant EIRP limits). It has been discussed
the possibility that interference mitigation techniques can be adopted in WAIC systems. In order to
enable the operation of WAIC in this frequency band, these mitigation techniques can accomplish
both, attenuation of the effective radiated power outside the aircraft and minimizing the probability
of occurrence of interference.
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