UK Comments on document 8B/129\
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**Working Party 7C,** LIAISON STATEMENT TO working partY 8B: WRC-07
Agenda item 1.3, Resolution 747 (WRC-03): Possible extension of the
existing primary allocations to the earth exploration-satellite service
(active) and the space research service (active) in the band 9 500-9 800
MHz

1\. The marine radionavigation radar chosen for assessment is not too
unreasonable (System S4), however, the antenna gain should be 32dB not
27dB which will presumably increase the I/N by 5dB.

2\. Antenna rotation rates of up to, say, 50rpm should also be
considered.

3\. In their simplest mode of operation, marine radionavigation radar do
not have a large amount of processing gain, certainly not sufficient to
overcome an I/N of 52dB!!

4\. In Section 5 on page 38 it states that \"EESS waveforms are planned
to be tested with several types of radar systems including marine
radionavigation.\" What radionavigation radars are they planning to use
and are they fully representative?

5\. \"Worst case interference \... only happens for less than three
seconds every 48 hours\" - what other interference occurs, for what
period and with what frequency bearing in mind that worst case
interference could be as high as an I/N of 52dB?

6\. If \"worst case interference\" only occurs for 3 seconds this could
still be very serious if track information is lost at a critical time.
Re-establishing full track information could take several scans.

7\. The long pulse widths are of concern, especially the SAR2.

The 400MHz chirp, 100msec pulse, would occupy say a 20MHz 3dB bandwidth
of a receiver for about 5msec. However, roll-off below 3dB is typically
slow, coupled with the very high estimated interference levels on page
37 of 8B/129, would result in much longer periods.

Interference mitigation techniques used by Maritime radars are designed
to protect principally against the much shorter pulse-width radars
currently in the marine environment. The longer received pulse-widths
will result in long radial \'paints\' on the display and these could
cover large areas of the radar picture. This effect will be worst when
the pulse repetition frequency of the transmitter and victim radar are
similar.

In areas of dense traffic, the high duty-cycle of a SAR will enable more
pulses from the many marine radars to be \'gated through\' the victim\'s
processing. This will exacerbate the already confusing information
presented to the mariner in dense traffic conditions.

8\. The transit time calculation on page 4 of 8B/129 presents a
misleading impression. Their conclusion is that the worst-case
interference will occur for only about 0.6sec and the accumulated time
over 48hours is about 3secs. However the sidelobes of the SAR will also
cause interference.

The SAR2 antenna sidelobe levels are very high. The 5 metre aperture and
0.3° beamwidth indicates a uniformly-illuminated rectangular aperture.
This would have a first sidelobe level of -13dB and the subtended angle
between say the -23dB sidelobes would be about 10 times the beamwidth.
Therefore, in this example, there will be peaks of interference of at
least 29dB I/N (52dB worst case -23dB sidelobe) for a period of about
6secs (10 x 0.6sec),

Collision avoidance relies on the accuracy of target tracking. The long
\'paints\' of interference will degrade the accuracy of a marine radar
tracker and could result in the loss of target tracks.

9\. Statistical aspects of band-sharing are irrelevant for EESS and SRS,
because even very short interference events could severely compromise
safety.

The assumption that the antennas are pointed to their maximum elevation,
whilst giving the worst interference levels, is uncommon and may explain
why interference has not often been reported before.

The radars with which existing satellites would have interfered would
have been military radars, which may use coincidence processing to
suppress the interference, although perhaps at the cost of reduced
sensitivity. Military radars tend also to suffer from lots of
interference from other military radars, and this may explain why
interference has not been reported as being attributed to SARs. It would
be interesting to know whether interference from military radars into
SARs has been reported.

10\. The assumptions about \'processing gain\' are almost certainly
over-optimistic, and very dependent on the \'victim\' radar, and on what
it\'s primary purpose is. It is not CFAR which suppresses low-duty-cycle
asynchronous interference - it would detect it! Coincidence detectors
will tend to suppress it, but not without loss and the more noise-like
the interference, the less that can be done about it.

If the \'worst case\' is not main lobe to main lobe, i.e. the main lobes
never see each other, which would normally be the case for something at
such high altitude, then the intereference will last for about as long
as the main lobe of one radar can see the sidelobes of the other. This
may easily be long enough to lose all the track information.

When tests are done it might be safer to calculate the expected
interference level for the radar being tested, and inject signals at
that level, rather than using the values of a \'representative\' radar,
which allows possible arguments about the effects e.g. of different
bandwidths between the actual radar and the \'model\' radar.