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digitisation capability. Furthermore,
these specialised target generators
come at a high cost. According
to the US Department of Defense
(DoD), the price of a single DRFM
module ranges from USD 150,000 to
USD 700,000 [1].
The minimum delay introduced by a
DRFM is mainly limited by its ADC and
DAC. In addition, signal processing
adds a number of processing cycles
to the radar echo signal. Typical
minimum range delays range from
below 100 ns to below 1 µs. A further
consideration is how the analogue
RF signal is represented in the digital
domain (amplitude, phase, I/Q) and
the number of bits, because this is
what mainly determines the DRFM’s
signal fidelity. In addition, spurious-
free dynamic range (SFDR) may
limit the radar’s ability to distinguish
real targets from electronic
countermeasure signals.
With high signal fidelity, DRFMs
having coherent target echo returns
are well suited to specific radar tests,
but are unsuited to handling a broad
variety of signal conditions and
scene effects. Cost as well as limited
flexibility means they are ill-suited to
test the functional parameters of the
radar.
Commercial off-the-shelf
test and measurement
equipment
Today, COTS test and measurement
Fig. 3: Representation of a COTS real-time radar target generator
(R&S®SMW200A vector signal generator and R&S®FSW signal
and spectrum analyser)
equipment can generate radar
targets using similar methods
to those of DRFMs: RF down-
conversion, digital manipulation in
baseband and RF up-conversion. It
does so by combining an RF signal
analyser as the receiver with a signal
generator for the transmitter. Typical
systems operate from 100 kHz to 40
GHz and receive any kind of RF radar
signal in the specified frequency
band with up to 160 MHz bandwidth,
then converting the signal to in-
phase and quadrature-phase data
(I/Q data). I/Q data are applied to
the baseband input of the signal
generator where time delay, Doppler
frequency shift and attenuation
are applied to the specified user
values. The radar echo signal is then
retransmitted to the radar by the
signal generator.
One advantage of this measuring
equipment is its exceptional RF
performance, which is suitable for
additional parametric radar tests
during research and development
or production. The flexible and
modular approach allows the vector
signal generator or the signal and
spectrum analyser to be used in
other setups as well – and in their
dedicated field installation.
The Fig. 4 above shows the Fast
Fourier Transform (FFT) spectrum,
range-Doppler plot and target list
of a radar under test (RUT). The
COTS target generator was setup to
generate a single target with a range
of 2000 m and radial velocity of -25
m/s. As depicted in the figure above,
the radar, which operates with a
signal bandwidth (fsw) of 20 MHz
and a coherent processing interval
(Tcpi) of 500 µs measures the range
and radial velocity accordingly.
The COTS radar target generator is
able to generate up to 20 different
18 l New-Tech Magazine Europe