target detection (MTD), constant false
alarm rate (CFAR) processor, and signal
detector for simulation purposes.
The chirp signal level is set to 0 dBm,
PRF = 2 kHz and DUTY = 25 percent.
The target model is defined by the
Doppler frequency offset and target
distance, and angles of arrival (THETA/
PHI) are specified in a data file and
vary over time. The Doppler frequency
and channel delay were generated to
describe the target return signal with
different velocities and distance, while
the radar clutter model can be included
and the power spectrum can be shaped.
In this example, the clutter magnitude
distribution was set to Rayleigh and the
clutter power spectrum was formed by a
Weibull probability distribution.
The RF transmitter in Figure 4 includes
oscillators, mixers, amplifiers,
and filters, whereas the gain, bandwidth,
and carrier frequency were specified
based on the requirements of the
system or actual hardware performance
as provided by the RF design team.
Likewise, the RF receiver includes oscillators,
mixers, amplifiers and filters with
gain, bandwidth and carrier frequency
specified according to the system
requirements. Co-simulation with the
circuit simulator Microwave Office is
possible as the transceiver front-end
design details become available. As
will be discussed later, the interaction
between the transceiver electronics and
a beamforming antenna array can be
analyzed via circuit, system, and EM
co-simulation.
To detect the moving object more effectively,
MTD is used. The MTD is based
on a high-performance signal processing
algorithm for PD radar. A bank of Doppler
filters or FFT operators cover all possible
expected target Doppler shifts and the
output of the MTD is used for the CFAR
processing. In this particular example,
measurements for detection rate and
CFAR are provided.
The radar signal waveform must be
measured in the time domain at the
receiver input. Since the target return
signal is often blocked by clutter, jamming,
and noise, detection in the time
domain is not possible and an MTD is
used to perform the Doppler and range
detection in the frequency domain. In
the MTD model, the data is grouped for
corresponding target range and Doppler
frequency. Afterwards, a CFAR processor
is used to set the decision threshold
based on the required probabilities of
detection and false alarm, as shown in
Figure 5.
mmWave Design
Figure 8: Multi-band, multi-range FMCW digital beam-forming ACC radar utilizing
six individual SFPAs.
Figure 9: Example of an edge-coupled single patch antenna optimized in AXIEM
for center return loss and broadside gain to design frequency.
This relatively simple design can be
used as a template for different PD applications.
The radar signal is a function
of pulse repetition frequency (PRF), power,
and pulse width (duty cycle). These
parameters can be modified for different
cases. In the simulation, the radar signal
also can be replaced by any defined
signal through the data file reader in
which the recorded or other custom
data can be easily used. VSS provides
the simulation and model capabilities to
refine the radar architecture, implement
increasingly accurate channel models
(including multi-path fading and ground
clutter), and develop performance specifications
for the transceiver link budget
and detailed antenna radiation pattern
requirements.
The plots in Figure 6 show several
simulation results, including the transmitted
and received chirp waveform, the
antenna radiation pattern, and several
system measurements, including the relative
velocity and distance. In this simulation,
the distance to the target is swept
to reflect a vehicle that approaches and
passes by a stationary radar, resulting
in Doppler frequency that reverses the
sign from negative to positive (red curve)
and produces a null in relative distance
as the target passes by the radar. In an
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