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4.2.3.2 LOW GAIN ANTENNA
SUB-SYSTEMS
4.2.3.2.1 Gain-to-noise temperature ratio. Receiving subsystems
employing low gain antennas shall achieve a gain-tonoise
temperature ratio (G/T) of not less than -26 dB/K over
not less than 85 per cent of the reference coverage volume
defined in 4.2.3.1.1; and not less than -31 dB/K over the
remaining 15 per cent of the reference coverage volume. The
only exception to this is the region greater than 70 degrees in
elevation from the horizontal plane where the GTT shall be not
lcss than -28 dB/K.
4.2.3.2.2 Axial ratio. The axial ratio shall be less than
6 dl3 for elevation angles of 45 to 90 degrees and less than
20 dB for elevation angles of 5 to 45 degrees or the AES
antenna shall have sufficient gain to compensate for additional
polarization loss in excess of that caused by the axial ratios.
The condition for including the compensation shall assume the
satellite axial ratio to be 2.5 dB, with major axes of the
polarization ellipses orthogonal.
4.2.3.2.3 Recommendation.- To the maximum extent
possible, the Gh" should be not less than -26 dBK and the
axial ratio should be less than 6 dB over 100 per cent of the
reference coverage volume.
4.2.3.2 bis INTERMEDIATE GAIN ANTENNA
SUB-SYSTEMS
See paragraph 4.2.3.6.
4.2.3.3 HIGH GAIN ANTENNA
SUB-SYSTEMS
4.2.3.3.1 Gain-to-noise temperature ratio. Receiving subsystems
employing high gain antennas shall achieve a gain-tonoise
temperature ratio (GIT) of not less than -13 dB/K over
not lcss than 75 per cent of the reference coverage volume and
shall be not less than -25 dB/K over the remaining 25 per cent
of the reference coverage volume defined in 4.2.3.1.1.
4.2.3.3.2 Axial ratio. The axial ratio shall be less than
6 dB over the 75 per cent of the reference coverage volume
referred to in 4.2.3.3.1 where the G/T must exceed -13 dB/K
or the AES antenna shall have sufficient gain to compensate
for additional polarization loss in excess of that caused by this
axial ratio. The condition for including the compensation shall
assume the satellite axial ratio to be 2.5 dB, with the major
axes of the polarization ellipses orthogonal.
4.2.3.3.3 Recommendation.- To the maximum extent
possible, the G/T should be not less than -13 dB/K and the
axial ratio should be less than 6 dB over 100 per cent of the
reference coverage volume.
4.2.3.3.4 Discrimination. The antenna gain pattern for
both transmit and receive functions shall discriminate by not
less than 13 dB between the directions of wanted and
unwanted satellites spaced 45 degrees or greater in longitude
over not less than 75 per cent of the reference coverage volumc
defined in 4.2.3.1.1.
4.2.3.3.4.1 Recommendation.- The antenna gain
pattern for both transmit and receive functions should
discriminate by not less than 13 dB between the directions of
wanted and unwanted satellites spaced 45 degrees or greater
in longitude over 100 per cent of the refercrzce coverage
volume dej7ned in 4.2.3.1.1.
-2/11-/00
No. 75
Annex 10 - Aeronautical Telecorrsmunications Volume IIZ
4.2.3.3.5 Phase discontinuity. Beam steering transitions
between adjacent beam positions of a switched beam antenna
shall not cause RF phase transitions greater than 12 degrees in
the transmitted signal for 99 per cent of all possible adjacent
beam combinations.
4.2.3.3.5.1 Recommendation.- Beam steering tmnsitions
between adjacent beam positions of a switched beam
antenna should not cause RF phase transitions greater than
12 degrees in the transmitted signal for 100 per cent of a21
possible adjacent beam combinations.
Nore.- This requirement only applies to individual array
pelforrnance in the case of multiple array antennas.
4.2.3.4 RECEIVER
REQUIREMENTS
4.2.3.4.1 Receiver spurious and linearity petformonce.
The required performance defined in 4.4.2.3 and 4.4.5.4
shall be achieved when the receiving antenna is illuminated
in the direction of maximum gain by a power flux density of
-100 dI3w/m2 distributed across the 1 525 to 1 559 MHz
band.
4.2.3.4.2 Receiver ou t-of-band perfornwnce. The required
performance defined in 4.4.2.3 and 4.4.5.4 shall be achieved in
the presence of out-of-band interference at levels typical of
normal operating conditions.
4.2.3.4.3 Receivedphase noise, The design of the receiver
and the demodulators shall be such as to ensure full
compliance with the performance requirements whenever the
received signal phase noise characteristic does not exceed the
mask defined in Table 4- l.*
4.2.3.4.4 Capture range. The receiver shall be capable of
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