IEEE Geoscience and Remote Sensing Magazine - December 2022 - 13

This operation mode requires the receive signal vector to
be multiplied by different sets of time-varying weights corresponding
to different output beams. The received signal
of feed element n is denoted as a column vector sn
kth output is kk kN k
w tw (),( ), ,().
() = 6 12 el
,, ,
f
()
bS tw ().twc s,,
N
kk nk== =// nn k
Nackk
tact
act,, ,,kk kk00tn tn tn t=+ f
1
1
,,
Here, N () {( ), () ,, ()} defines the
active elements of beam k and c ,nk
and collected
in the matrix S . The weight vector that generates the
T
tw tw t @ With
this, the equations from tutorial part 1 are rewritten for
multibeam SCORE:
(2)
is the weighted output
signal of element n contributing to beam k.
The beam-to-swath mapping is not included explicitly
in the preceding equation; i.e., the kth beam is not related
to any specific subswath. Instead, the mapping is determined
by the digital hardware topology. In the following,
two implementations of multibeam SCORE are discussed:
partitioned swath SCORE and concatenated swath SCORE.
PARTITIONED SWATH SCAN-ON-RECEIVE SYSTEM
A functional realization for the case that the sets of elements
of the different beams do not overlap is illustrated
schematically in Figure 5(a). Here, different beams do not
share the same feed elements; thus, the sets of active feed
elements are disjunctive such that
NN .ij
ac ij= 46 !
tact
,,
+
The configuration in the figure generates Nbeam 3= output
beams corresponding to three subswaths.
The region (subswath) on the ground traversed by
each beam is determined by the angular segment covered
by the set of feed elements constituting that beam.
Flight
Direction
This is because the hardware is implemented such that
the output data stream of each functional subswath DBF
unit (ssw-DBFU) covers only part of the complete swath.
The term functional is used because the actual hardware
realization may still include several ssw-DBFUs in a single
field-programmable gate array (FPGA).
The association between the echo signals and the beamforming
is best understood by relating the range-time
diagram in Figure 4(a) to the beamforming schematic in Figure
4(b): A single echo traversing the swath from near to far
range would first be handled by ssw-DBFU 1, then later successively
switched over to units 2 and 3. In general, the echo
of transmit pulse
i ,,=12 f is successively handled by sswDBFUkN
where each ssw-DBFU covers one
subswath and bk
= f beam
12
,, ,,
is the kth subswath output vector. The dimension
(number of elements) of the weight vector of each
DBF unit is less than the total number of antenna elements
Nel. In the case of the three subswaths shown in Figure 5(a),
the weights are
w
w
w
1111
21222
3133
()
() nn
() nNel
tw tw t
tw tw t
tw tw t
=
=
=
6
6
6
nn .N12 el
,,
,,
,,
f
n1
1
2
+
+
f
f
(),, ()@T
(),, ()@T
(),, ()@T
(3)
where 11 Since multiple pulses traverse the
ground simultaneously, all ssw-DBFUs are active at any
time instance, excluding the duration of transmit events.
The range-azimuth diagram in Figure 5(b) shows the
data after beamforming. The data from any single echo,
e.g., green echo 1, are distributed over several columns.
This is because the data stream of each column is generated
Feed Antenna
Elements
Limiter
FIGURE 3. The multibeam SCORE operation mode, where multiple simultaneous beams scan the signal echo traversing the ground. HPA:
high power amplifier; LNA: low-noise amplifier; TRM: transmit/receive module; Tx: transmitter; Rx: receiver.
DECEMBER 2022 IEEE GEOSCIENCE AND REMOTE SENSING MAGAZINE
13
Phase Shift
Tx In
LNA
Rx Out
Front End
TRM
HPA
Beam 1
Reflector
Slant
Range
Beam 2
Beam 3
IEEE Geoscience and Remote Sensing Magazine - December 2022

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