The earth sensing community is poised to exploit more and more heavily a frequency allocation around 9.6 GHz which they employ for high-power (1-5 kW) space-borne downward-pointing synthetic aperture radars.  These vehicles are noted as the SARn series, of which SAR1 has been operating since 1995 --

http://www.space.gc.ca/asc/eng/satellites/radarsat1/default.asp

and the next launch, of a more powerful vehicle, is currently slated for 2007 February, see http://news.eoportal.org/eomissions/061127_terrax.html

The table shown below gives typical operating parameters for these SARs.  Note that the average power is about an order of magnitude lower than the peak.  More recent and future proposed systems (of which there are several) will have higher bandwidths because the ITU is poised to approve an expansion of the 9.6 GHz allocation by an additional contiguous 200 MHz (its Agenda Item 1.3 of WRC07); future 9.6 GHz SAR will radiate nearer to the radio astronomy protected band at 10.6 GHz.

The possible ill effects of the SARn instruments upon radio astronomy should be readily apparent; in a main-beam encounter, most of the energy incident on an antenna (typically a large fraction of a Watt) also lands on the receiving device.  The situation is in fact probably more complicated than with CloudSat (http://www.iucaf.org/CloudSat/), a similarly powered satellite working at 94.05 GHz, because the 9.6 GHz devices are not purely downward-pointing.  The following table has been taken from an ITU document (actually, 8B/39 of the current cycle, preceding WRC07) used for generic compatibility studies between SARn missions and nearby (in frequency) radiolocation (i.e. radar) services.

 

Parameter

SAR1

SAR2

SAR3

Orbital altitude

400 km

619 km

506 km

Orbital inclination

57˚

98˚

98˚

RF centre frequency

9.6 GHz

9.6 GHz

9.6 GHz

Peak radiated power

1 500 W

5 000 W

5 000 W

Pulse modulation

Linear FM chirp

Linear FM chirp

Linear FM chirp

Pulse bandwidth

10 MHz

400 MHz

450 MHz

Pulse duration

33.8 ms

10-100 ms

1-10 ms

Pulse repetition rate

1 736 pps

2 000-5 000 pps

410-515 pps

Duty cycle

5.9%

2.0-40.0%

0.04-0.5%

Range compression ratio

338

<12 000

450

Antenna type

Slotted waveguide

Planar array

Planar Phased Array

Antenna peak gain

44.0 dBi

~46.0 dBi

54.5-57.5 dBi

Antenna orientation

20˚ to 55˚ from
Nadir

34˚ from
Nadir

20˚ to 44˚ from Nadir

Antenna beamwidth

5.5˚ (El)
0.14˚ (Az)

1.6-2.3˚ (El)
~0.3˚ (Az)

1.1-2.3˚ (El)
0.036˚ (Az)

Antenna polarization

Linear vertical

Linear HH or VV

Linear
horizontal/vertical

System noise temperature

 551 K

~500 K

600 K

 


Afterword: Radio astronomy has been operating for several years in the presence of EESS missions which focus high-power radar beams on the earth for global imaging; not only RadarSat1 noted above, but others like envisat which operates at Ku and C-band (http://envisat.esa.int/instruments/ra2/) and more recently, CloudSat (www.iucaf.org/CloudSat/) at 94 GHz.  As new astronomy systems are rolled out which grant increased access to unprotected portions of the spectrum, new hazards will be encountered.  Allocations for earth-exploration systems like those discussed here can be found in the Radio Regulations in a very large number of bands, namely (in GHz)  0.432-0.438, 1.215-1.240, 1.240-1.300, 3.100-3.300,5.250-5.255, 5.255-5.350, 5.350-5.460, 5.470-5.570, 8.550-8.650, 9.500-9.800, 13.250-13.400, 13.400-13.750, 17.200-17.300, 24.050-24.250, 35.500-3.600, 94.000-94.100 and 130-134 GHz.

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