IEEE Aerospace and Electronic Systems Magazine - June 2020 - 56

Fast Fully Adaptive Signalling for Target Matching
Table 2.

Interference and Target Parameters
Parameter

Value

Interference update interval

1 CPI
2

Number of LFMs in interference - QSTART
Interference start LFM base frequencies - f0

497, 697 MHz

Interference start LFM bandwidths - B

6, 6 MHz

Number of LFMs in interference - QEND

1

Interference end LFM base frequency - f0
Interference end LFM bandwidth - B
Target response update interval

1194 MHz
12 MHz
1 CPI

Number of LFMs in target - PSTART

Frequency character of (a) the original LFM waveform and (b) the
full bandwidth ERA waveform based on the same LFM.

1

Target start LFM base frequency - f0

420 MHz

Target start LFM bandwidth - B

60 MHz

Number of LFMs in target - PEND

1

Target end LFM base frequency - f0
Target end LFM bandwidth - B
Target range
Target range profile duration

1010 MHz
80 MHz
5m
384 nS

SIMULATION-NONADAPTIVE TRANSMISSION
The ERA processed full-band LFM waveform case represents a baseline against which the adaptive waveforms may
be assessed. Simulation results employing this waveform
are shown in Figure 6. It is clear from Figure 6(c) and (d)
that waveforms with flat frequency content are employed
in both the target probe and the TMI phases. The mean
SINR attained, excluding the environment sensing phase
CPIs, is 2.7 dB. It can be seen in Figure 6(h) that the
designed transmit waveform exhibits higher sidelobe levels
than the original LFM waveform. This increase being due
to the nonadaptive waveform being subjected to the same
ERA design process as the notched and TMI versions
resulting in spectral containment and phase modifications.
The sharp spectral cutoff at the required band edges is
clearly illustrated in the frequency domain in Figure 7.

SIMULATION-ADAPTIVE NOTCHED TRANSMISSION
The adaptive notched mode uses the notched waveform,
created for target interrogation, in the exploitation phase.
The target SINR is significantly higher, at a mean of 23
dBs, than the nonadaptive case, see Figure 8(g). The autocorrelation sequence is degraded by the inclusion of the
notches in terms of sidelobe levels, although resolution is
56

Figure 7.

only marginally affected as the waveform continues to
exploit the wide bandwidth. It can be seen in Figure 8(b)
that the notch depth achieved by the ERA is limited to
approximately 25 dB.

SIMULATION-FULLY ADAPTIVE TRANSMISSION
The TMI waveform created by the FFAST algorithm produces an increase in SINR over the probe waveform, a
mean of 40 dBs, as the majority of the energy contained in
the transmitted signal is concentrated within regions of significant target response. The autocorrelation is degraded in
sidelobe terms, but also in resolution as the frequency content of the waveform is significantly reduced, see Figure 9.

HITL-NONADAPTIVE TRANSMISSION
The over-the-air transmissions suffer degradation as seen in
the signal incident at the target, see Figure 10(c). The SINR
is lower, À6.8 dB, than in the equivalent simulation case.
The bandwidth restriction caused by the hardware system
can be easily observed in plot (a), where the low- and highfrequency components of the interference estimate are attenuated by the hardware response.

HITL-FULLY ADAPTIVE TRANSMISSION
Figure 11 shows results for the full FFAST algorithm with
TMI, within the HITL context. The TMI provides an
improved SINR of mean 25.5 dB. The autocorrelation
sequence suffers both higher sidelobes and decreased
resolution.

DISCUSSION
Comparing the three simulation scenarios, the SINR varies
from approximately 3 dB for the LFM case, to 23 dB for the

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