IEEE Geoscience and Remote Sensing Magazine - March 2015 - 18

Level (dBnV/m)

60
55
50
45
40
35
30
25
20
15
10
5
0
-5
-10
-15

1.220000000 GHz
6.897 dBnV/m

1215

1.439999500 GHz
4.629 dBnV/m

1240 1260 1280 1300 1320 1340 1360 1380 1400 1420 14401454
Frequency (MHz)

Level (dBnV/m)

(a)
60
55
50
45
40
35
30
25
20
15
1.22000000 GHz
10
0.376 dBnV/m
5
0
-5
-10
-15

1.428821000 GHz
3.243 dBnV/m
1.440000000 GHz
2.623 dBnV/m

applicable state for assessing
instrument compatibility, as
the radiated susceptibility requirements for the radiometer only apply during the quiet (non-transmitting) time
within each PRI. In this case,
the radar's emitted noise
level is demonstratively low
across most of the radiometer protected band, at about
12 dB below the 2.8 dBuV/m
allowed limit shown as the
red bounding line from 1370
to 1450 MHz. (An exception is the 1440-MHz radar
clock harmonic appearing
a few dB above the limit
but deemed acceptable, as it
falls outside the actual radiometer receiver passband.)
Although the transmit operating state is exempt from
radiated emissions requirements, it is informative to
look at this case too as an
upper bound on spillover
into the radiometer band.
Even for the transmit case,
emissions levels are low -
with most of the spectral
energy falling within the
E-field limit.

VII. SUMMARY OF SMAP
RADAR INNOVATION
1215
1240 1260 1280 1300 1320 1340 1360 1380 1400 1420 1440 1454
AND NOVELTY
Frequency (MHz)
This work represents the first
(b)
satellite geoscience radar
system developed with a freFIgURE 7. E-field radiated emissions spectra for the radar electronics operating in: (a) receive-only state;
quency-hopping capability
(b) transmit state. Emitted noise levels are generally very low-around 12 dB below the stringent 2.8 dBuV/m
for mitigating terrestrial RFI.
allowed limit in the 1370-1450 MHz radiometer protected range, except for a spur at 1440-MHz that was
The lookup table approach
deemed acceptable. Even for the transmit case, in which the radar is exempt from radiated emissions limits,
for automatically commandthe measured levels are very low and in fact compliant for much of the spectrum.
ing RF operating frequency
based on orbit latitude-longitude
and
based
on
L-band
RFI
surveys allows the SMAP
error, which is still small compared to the overall 0.1-dB
radar to operate and adapt in a changing global RFI environcalibration stability requirement.
ment. Within the radar electronics payload, the systems-level innovations developed to mitigate terrestrial RFI include:
C. Radiated emissions testing
1) a dynamically tunable operating frequency, to allow the
Radiated emission levels from the radar were measured
instrument to frequency-hop around noisier parts of
during EMC testing to ensure instrument self-compatthe spectrum, and over particular regions of the Earth;
ibility, particular over the protected frequency range of
2) sharp RF/digital receiver filtering with a high degree
the radiometer. Fig. 7 shows the E-field radiated emissions
of selectivity for rejecting out-of-band interference
spectra for the radar subsystem electronics operating in
(80+dB rejection);
"receive-only" and "transmit" states. Receive-only is the
18

ieee Geoscience and remote sensing magazine

march 2015

Table of Contents for the Digital Edition of IEEE Geoscience and Remote Sensing Magazine - March 2015