International Civil Aviation Organization
ACP/WGF 27/WP 14
2012-09-10
WORKING PAPER
AERONAUTICAL COMMUNICATIONS PANEL (ACP)
27TH MEETING OF THE WORKING GROUP F
Montreal, Canada, 17 – 26 September 2012
Agenda Item 5 : Interference from non-aeronautical sources
Agenda Item 1.12 (WRC-15) – Characteristics of future wideband EESS SAR systems in 9 GHz
(Presented by Hans Kuhlen, Astrium)
SUMMARY
This working paper provides information on the characteristics of a new
generation of Synthetic Aperture Radar (SAR) instruments for which
compatibility studies are under performance under Agenda Item 1.12 (WRC15). These new SAR instruments are planned for operation in the Earth
exploration-satellite service introducing a new high-resolution spotlight mode
by using up to 1200 MHz in the 9 GHz allocation to EESS (active).
ACTION
This information is provided to the meeting to enable sharing studies with
radars operated in the aeronautical radio navigation bands. The information
has been adopted by CEPT in their recent CPG PTA meeting in London and
will be submitted to the next meeting of ITU-R Working Party 7C in Manta,
Ecuador.
INTRODUCTION
World Radiocommunication Conference 2012 (WRC-12) decided to assign Agenda Item 1.12 (WRC15) to investigate the sharing conditions if the existing allocation to the Earth exploration-satellite
service (EESS active) in the frequency band 9 300-9 900 MHz would be extended by 600 MHz.
An extended allocation would be used by the next generation wideband EESS SAR systems providing
picture resolutions of less than 30cm. Studies on investigations for sharing conditions with incumbent
services in-band and out-of-band have commenced. This paper should enable to commence with
advanced studies on sharing EESS SARs with radar systems.
ACTION BY THE MEETING
The ACP WG-F is invited to take note of the technical characteristics of wideband EESS SARs as
provided in the annex that might in future share frequency spectrum with terrestrial radars in the
aeronautical radionavigation service in the 9 GHz frequency range.
Annex
Characteristics of synthetic aperture radars operating in the
Earth exploration-satellite service (active) around 9.6 GHz
1
PRINCIPLES OF SYNTHETIC APERTURE RADARS (SAR)
A Synthetic Aperture Radar (SAR) is a coherent spaceborne side-looking radar system which utilizes
a satellites flight path to emulate an extremely large antenna or aperture electronically, and that
generates high-resolution remote sensing imagery.
In principle, the SAR is a phased array antenna. But, instead of using a large number of parallel
antenna elements, SAR uses one antenna element in time-multiplex. The different geometric positions
of the antenna elements are result of the moving platform.
The satellite travels forward in the flight direction with the nadir pointing beneath. The microwave
beam is transmitted obliquely at right angles to the direction of flight illuminating a swath. Range
refers to the across-track dimension perpendicular to the flight direction, while azimuth refers to the
along-track dimension parallel to the flight direction. Swath width refers to the strip of the Earth’s
surface from which data are collected by a side-looking radar. It is the width of the imaged scene in
the range dimension. The longitudinal extent of the swath is defined by the motion of the aircraft with
respect to the surface, whereas the swath width is measured perpendicularly to the longitudinal extent
of the swath.
Over time, individual transmit/receive cycles (pulse repetition time, PRT) are completed with the data
from each cycle being stored electronically. The signal processing uses magnitude and phase of the
received signals over successive pulses from elements of a synthetic aperture. After a given number of
cycles, the stored data is recombined to create a high resolution image of the terrain being over flown.
2
MODES OF OPERATION OF SYNTHETIC APERTURE RADARS (SAR)
The SARs operating near 9.6 GHz are controlled via ground command to turn on and off as required
to view only specific areas on the Earth. It is important to note that EESS SAR systems transmit only
for a few seconds (“snapshot”).
The conventional SAR strip map mode assumes a fixed pointing direction of the radar antenna
broadside to the platform track. A strip map is an image formed in width by the swath of the SAR and
follows the length contour of the flight line of the platform itself. In the scanSAR mode, the SAR can
illuminate several subswaths by scanning its antenna into different positions.
FIGURE 1
Modes of operations for SAR system in the 9GHz EESS allocation
Spotlight is a mode of SAR operation for obtaining high resolution by electronically steering the radar
beam to keep the target within the beam and thus form a longer synthetic aperture. The spotlight mode
is capable of extending the high-resolution SAR imaging capability significantly. As more pulses are
used, the azimuth resolution increases.
Spotlight mode of operation is usually at the expense of spatial coverage, as other areas within a given
accessibility swath of the SAR cannot be illuminated while the radar beam is spotlighting over a
particular target area. Details on the imaging geometries of this mode are shown in Figure 3.
Data will typically be collected by taking 49 to 65 sub-swaths of 20 km in range by 0.35 km in
azimuth. This data can then, however, be put into a mosaic of sub-swaths in azimuth to process a 20
km by 20 km image. The larger bandwidths are used with the spotlight mode in order to achieve a
good resolution in range.
All SARs are controlled via ground command to turn on and off as required to view only specific
areas on the Earth. The “on”-command results in a transmission of radio frequency pulses [chirps] for
a short period of around five seconds and duty cycles in the range from 10% to 30%.
FIGURE 2
EESS SAR imaging geometry for high-resolution spotlight mode (wideband with 1200MHz chirp
bandwidth)
Satellite track
DAT
vsat = 7630m/s
SAR antenna
Phase centre
Antenna cone 1.13° (or elevation beam width)
Ant cross-cone 0.53° (or azimuth beam width)
DR

Incident Angle
Grazing Angle

Off-Nadir Angle or
Look Angle
(Antenna beam orientation)
Sub-satellite ground track
or along track
or azimuth direction
Rf
NADIR
Φ
Ψ
Rn
h = 510 km
φ
Symmetrical case
for left side of
satellite
20°
190
Sw
ath
km
Acc 550 km
ess
Ran
ge
wid
th
φ
ψ
Pixel
resolution
δR
δAT
Spot area
5x5km²
55°
Cross track
or range
or elevation direction
Simplified flat spot area
3
PARAMETER
Technical characteristics of spaceborne active sensors in the 9 GHz frequency range are given in
Table 1. Corresponding antenna gain patterns of all SAR systems are provided in Tables 2 to 5,
respectively.
TABLE 1
Technical characteristics of EESS SAR systems
Parameter
SAR1
SAR2
SAR3
SAR4
Orbital altitude (km)
400
619
506
510
Orbital inclination (degrees)
57
98
98
98
RF centre frequency (GHz)
9.6
9.6
9.6
[9.6](*)
1 500
5 000
25 000
7 000
Linear FM chirp
Linear FM chirp
Linear FM chirp
Linear FM chirp
10
400
450
1 200
Pulse duration (s)
33.8
10-80
1-10
50
Pulse repetition rate (pps)
1 736
2 000-4 500
410-515
6000
Duty cycle (%)
5.9
2.0-28.0
0.04-0.5
30
Range compression ratio
338
< 12 000
450-4 500
60 000
Slotted
waveguide
Planar array
Planar phased
array
Planar array
Antenna peak gain (dBi)
44.0
44.0-46.0
39.5-42.5
47.0
e.i.r.p. (dBW)
75.8
83.0
83.5-88.5
85.5
Antenna orientation from
Nadir
20˚ to 55˚
34˚
20˚ to 44˚
18.5° to 49.3°
Antenna beamwidth
5.5˚ (El)
0.14˚ (Az)
1.6-2.3˚ (El)
0.3˚ (Az)
1.1-2.3˚ (El)
1.15˚ (Az)
1.13° (El)
0.53° (Az)
Antenna polarization
Linear vertical
Linear HH or
VV
Linear
horizontal/
vertical
Linear
horizontal/
vertical
551
500
600
500
Peak radiated power (W)
Pulse modulation
Chirp bandwidth (MHz)
Antenna type
System noise temperature (K)
(*)
final value depends on the decision eventually taken under Agenda Item 1.12 (WRC-15)
TABLE 2
SAR1 antenna gain pattern near 9.6 GHz
Pattern
Gain G(θ) (dBi) as a function of off-axis angle θ
(degrees)
Vertical
(elevation)
Gv (θ v ) = 44.0 – 0.397(θ v )2
Gv (θ v ) = 24.5
Gv (θ v ) = 9.5
Gv (θ v ) = 22.5
Horizontal
(azimuth)
Gh (θ h ) = 0 – 612.2(θ h )2
Gh (θ h ) = –12
Gh (θ h ) = 0 – 27.0 (θ h )
Gh (θ h ) = –35
Beam pattern
G(θ) = {Gv (θ v )  Gh (θ h ), –3} max
Angular range
(degrees)
θv
7.1 < θ v
30  θ v
θv
0.14
0.44
< 7.1
< 30
< 60
> 60
θ h < 0.14
< θ h < 0.44
< θ h < 1.3
θ h  1.3
TABLE 3
SAR2 antenna gain pattern near 9.6 GHz
Pattern
Gain G(θ) (dBi) as a function of off-axis angle θ
(degrees)
Vertical
(elevation)
Gv (θ v ) = 46.0 – 0.835(θ v )2
Gv (θ v ) = 31.0
Gv (θ v ) = 26.0
Gv (θ v ) = 10.0
Horizontal
(azimuth)
Gh (θ h ) = 0 – 444.5(θ h )2
Gh (θ h ) = – 16
Gh (θ h ) = – 20.0 (θ h )
Beam pattern
Angular range
(degrees)
θv
3.8 < θ v
15  θ v
θv
< 3.8
< 15
< 30
> 30
θ h < 0.3
0.3 < θ h < 0.7
θ h  0.7
G(θ) = {Gv (θ v )  Gh (θ h ), –3} max
TABLE 4
SAR3 antenna gain pattern near 9.6 GHz
Pattern
Gain G(θ) (dBi) as a function of off-axis angle θ
(degrees)
Angle range
(degrees)
Vertical
(elevation)
Gv (θv ) = 42.5 – 9.92(θv )2
Gv (θv ) = 31.4 – 0.83 θv
Gv (θv ) = 10.5 – 0.133 θv
0
< θv
1.1 < θv
θv
< 1.1
< 30
> 30
Horizontal
(azimuth)
Gh (θh ) = 0.0 – 9.07(θh )2
Gh (θh ) = +1.9 – 12.08 θh
Gh (θh ) = – 48
0
< θh
1.15 < θh
θh
< 1.15
< 4.13
> 4.13
Beam pattern
G(θ) = Gv (θv ) + Gh (θh )
TABLE 5
SAR4 antenna gain pattern near 9.6 GHz
Gain G() (dBi) as function of off-axis angle 
(degrees)
Angular range (degrees)
Vertical
(elevation)
Gv(v) = 47.0 – 9.91(v)²
Gv (θv ) = 35.91 – 0.83 θv
Gv(v) = 11.0
v < 1.1
1.1 ≤ v ≤ 30
v > 30
Horizontal
(azimuth)
Gh(h) = 0 – 45.53(h)²
Gh(h) = -10.97-2.00 h
Gh(h) = -35.0
h ≤ 0.5
0.5 < h ≤ 12
h > 12
Beam pattern
G() = Gv(v) + Gh(h)
Pattern
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