5
TECHNICAL CHARACTERISTICS OF RADARS
Three different types of radars are using this frequency band: Defence, Air traffic control and Meteorology. The
characteristics of representative radars operating in the frequency band 2 700-2 900 MHz are summarized in Table 3. The
spurious level indicated in the Table 3 is the limit from Recommendation 74-01 for the appropriate category of radar.
Parameter
Unit
Frequency Type
Maximum antenna gain
Antenna pattern
Antenna height
Polarization
Feeder loss
Minimum elevation angle
Protection level
1 dB compression point
Blocking level
Transmission power
reference bandwidth
20 dB bandwidth
40 dB bandwidth
Out of band roll off
Spurious level
dBi
Type 1
Frequency
hopping
>40
Not given
Pulse duration
Rise and fall time
Antenna rotation
Scan in elevation
Type 3
dB
°
dBm/MHz
dBm
33
34
kW
kHz
MHz
MHz
dB/decade
<1
Not given
Not given
1000
2500
9.5
dBc
Type 6
Type 7
2 frequencies (Multi frequencies)
m
See figure 4
400
22
1000
1000
Not given
20
24
20
-60
Unwanted emission
mask
Pulse repetition rate
Type 2
ATC and defence
Type 4
Type 5
Single frequency
34
33.5
35
Vertical pattern cosecant-squared (see figure 5)
5-40 (normal 12)
Circular
Not given
Not given
Not given
2 (see ITU-R M.1851)
-122
-20 (see ITU-R M.1464)
Not given
750
60
30
1200
2500
Not given
800
800
5.2
16.8
Not given
2
1.4
22
55
Not given
4
2
Not given
20
Not given
-60 (See Annex 2)
1100
34
35
3
2.8
Not given
Not given
Not given
Not given
Not given
Not given
Not given
To be calculated using elements above + Annex 2 for actual examples
Not given
Hz
<300
~1000
~1000
1000
µs
% of pulse
length
RPM
20 and 100
1
1
0.085
0.4
40
1
1%
10%
10%
0.015μs
0.015μs
Not given
0.169μs
6 - 12
Not given
12 - 15
Fixed
12 - 15
Fixed
15
Fixed
15
Fixed
Meteorology
Type 8
825
15
Fixed
10
See Figure 2
794
1000
Not given
See Annex 1
40
-60 for old radars
and -75 to -90 for
new radars
See Annex 1
Not given
250 - 1200
(See ITU-R M.1849)
0.8 - 2
Not given
10%
Not given
Fixed
See ITU-R M.1849
See ITU-R M.1849
Not given
100
Not
given
43
ITU-R F.1245
7-21 (average 13)
H/V
2
0.5
Table 1 : radar characteristics
spurious emissions (from SE21(11)051) – it is not agreed
There are very large differences in the radar sensitivity to spurious emissions depending on the source of information:
In the draft report of SE21 the protection level is -122dBm/MHz. It is based on the protection level of the radar and a C/N=10dB criteria. In this case, the sensitivity of the
radar is 2dB above the thermal noise (Thermal noise => -114dBm/MHz),
In the Belgian report (Study of the Performance Degradation of the Belgian S-band Air Surveillance Radars due to the Interference of Upcoming 4G Technologies – Test
report) from Intersoft Electronics, the protection levels are:
-115dBm/MHz for the TA-10 radar,
-106dBm/MHz for the ASR-9 radar,
-108dBm for the STAR-2000 radar.
Figure 4 gives the maximum level of interference at the radar antenna port that an ATC radar can withstand from a
LTE signal of 9 MHz operating at a given frequency offset. This is based on measurements carried out on two radars
(Type 2 and 3) in Table 1.
Figure 1 : Maximum LTE signal level at the radar antenna port
Table 4: Comparison of the radar receiver selectivity
Frequency offset
10 MHz
20 MHz
30 MHz
50 MHz
France Radar 2
-75 dBm/9 MHz
France Radar 1
-72 dBm/9 MHz
Belgium TA-10
Belgium ASR-9
-56 dBm (CW)
Belgium STAR2000
-19 dBm (CW signal for frequency offset from 20 MHz to 160 MHz)
UK OFCOM Blocking Protection level*
-42 dBm
*Note: UK OFCOM Blocking protection ratio is proposed for all mobile base station operating below 2690 MHz before LNA
80 MHz
95 MHz
-60 dBm/9MHz
-60 dBm/9MHz
-55 dBm/9MHz
-50 dBm/5MHz
-24 dBm/5 MHz
The radar receiver selectivity results given in the table 1 shows that for different radar, the receiver selectivity can be
very different.
The radar receiver selectivity curves presented in figure 4 were measured for two specific radars in France. Some
other radar receiver selectivity measurement results are summarised in table x, which shows for different radars, the
receiver selectivity can be very different.
Figure 2 and Figure 3 give the typical antenna pattern of an ATC radar in elevation and azimuth.
Gain Relative to Maximum
40
Vertical Angle (Degrees)
30
20
10
0
-35
-30
-25
-20
-15
-10
-5
0
-10
-20
Gain (dB)
Figure 2 : ATC radar antenna pattern in elevation
0
-10
Gain Relative to Peak (dB)
-20
-30
-40
-50
-60
-70
-150
-100
-50
0
50
100
Horizontal Angle
Figure 3 : ATC radar antenna pattern in azimuth
Weather radars perform volume scanning based on rotation / elevation variations. Figure 4 describes a typical
sweeping pattern in elevation, based on the elements from Recommendation ITU-R M.1849 [21].
150
Figure 4 : Meteorological radars, typical elevation variation over time
The only difference from Recommendation ITU-R M.1849 [21] where this pattern was provided is that the rotation
speed of the antenna has been chosen constant at 3 rpm instead of variable between 2 and 3 rpm. This is for
simulation simplification purpose.
With this sweeping pattern and an antenna pattern based on Recommendation ITU-R F.1245, the radar antenna gain
towards the horizon (hence in the direction of potential MS stations) varies with time as shown in Figure 5 .
Figure 5 : Meteo radars, typical variation over time of antenna gain towards horizon
(radar antenna gain = 45 dBi)
The cumulative distribution of the antenna gain towards the horizon (elevation 0°) is shown in Figure 6.
Figure 6 : Meteorological radars, probability distribution of antenna gain towards horizon
(radar antenna gain = 45 dBi)
The result is the same when considering a victim receiver seen at a higher elevation angle (5°) from the radar. The
average antenna gain towards the FS station is 7 dBi.
ANNEX 1
Emission masks for S-Band meteorological radars
The two Figures below are indicating the spurious emissions level which are consider to be feasible across a whole
frequency range up to around 15 GHz (5th harmonics). Actual spurious emission levels are expected to be much better in
the band 2500 – 2690 MHz.
Assumptions:
-
0.8 µs pulse width
10% rise time
OOB roll-off of 40 dB/decade
Resulting in:
25 MHz “40 dB bandwidth”
Spurious domain starting at 94 MHz from the radar centre frequency
-
Emission mask for radar at minimum frequency (2712.5 MHz)
0
-10
-20
Frequency (MHz)
-30
-40
-50
-60
-70
-80
-90
-100
2450
2550
2650
2750
2850
Unwanted emisison level (dBc)
Meteo Radar emission Mask
LTE BAND
2950
Emission mask for radar at frequency (2784 MHz) to ensure spurious only
in the LTE band
0
-10
-20
Frequency (MHz)
-30
-40
-50
-60
-70
-80
-90
-100
2466
2566
2666
2766
2866
Unwanted emisison level (dBc)
Meteo Radar emission Mask
LTE BAND
2966
Annex 2
Information on
Out of Band Emissions and generic antenna pattern of Civil ATC radars (UK)
Out of Band Emissions
1. Radar (Type 6)
The centre frequencies of the 2 signals are 2784.5 & 2809.5 MHz and hence an offset will need to be applied to take
account of the fact that the lowest assignable frequency is 2720 MHz.
2
Radar (Type 5)
The centre frequencies of the 2 signals are 2765 & 2885 MHz and hence an offset will need to be applied to take account of
the fact that the lowest assignable frequency is 2750 MHz.