ured the same as FMCW; however,
the down-converted IF signals are
processed differently. After calculating range, the angle information of the target is calculated by
evaluating the phase differences
between the four receive channels.
The DBF mode requires a calibration of the radar front-end to eliminate deterministic phase variations
between the receive channels.
24 GHz MULTI-CHANNEL
A 24 GHz radar is widely used in
commercial and industrial applications, offering high accuracy, low
power consumption and small size.
These characteristics also make a
24 GHz radar a good fit for commercial and consumer UAV manufacturers, particularly considering
the desire to reduce payload and
power requirements. One such system developed by Analog Devices
is shown in Figure 2.
camera detection, which only captures a 2D image within the camera’s field of view, FMCW radars
provide a continuous, inherent average of the information from the
target’s reflection. This provides a
wide, 3D field of view by measuring the distance, speed and angle,
from as close as a few centimeters
to several hundred meters between
the sensor and the targets.
Range-Doppler—In range-Doppler mode, the range and speed
of the target are analyzed. Range-Doppler is one of the most powerful modes because it processes
multiple transmit ramps or chirps
simultaneously using a 2D Fourier
transform. The processed range-Doppler data is displayed in a 2D
map that enables targets with different velocities to be separated,
even if they are the same distance
from the sensor. This is important
to distinguish multiple targets moving at high speed in different directions, e.g., resolving complicated
air traffic scenarios with targets
traveling in opposite directions or
during overtaking maneuvers.
DBF—With digital beamforming
(DBF), the distance and the angle
to the target are displayed. The re-
ceive signals from the four receive
channels are used to estimate the
angle of the target, and the data
contains the spatial distribution of
the targets in the xy-plane. In the
DBF mode, the system is config-
and track objects, e.g., blind spot
detection and automotive driver
assistance systems (ADAS). Com-
pared to optical or ultrasonic sen-
sors, radar can accurately detect
and measure objects over a much
longer range and wider field of
view in very difficult environments,
including dust, smoke, snow, fog
and poor lighting. A typical radar
has various modes, each best de-
pending on what needs to be de-
tected and tracked.
FMCW—Operating in the frequency modulated continuous
wave (FMCW) mode, the radar
measures the distance to stationary
targets. By modulating the frequency, also referred to as an FMCW
ramp or chirp, the radar measures
the response of the reflected wave
to derive range, velocity and the
angle of the target. Figure 1 shows
how the target’s range, velocity and
angle are derived in FMCW mode.
The range resolution depends
on the transmitter’s carrier sweep
bandwidth; the higher the bandwidth, the higher the resolution of
the radar sensor. The velocity resolution depends on dwell time and
carrier frequency; the higher the
carrier frequency or dwell time, the
higher the resolution. Angular resolution depends on the carrier frequency; the higher the carrier frequency, the better the resolution.
Compared to laser detection,
which measures a single spot, or
Fig. 2 Multi-channel radar sensor developed by Analog Devices.
Ramp Generator Transmit Channel
A common misconception is the
radar can operate at 77 GHz rather than 24 GHz. Current regulations dedicate the 77 GHz band
to automotive vehicles and do
not allow use with UAVs. While
77 GHz offers higher bandwidth
for improved resolution, today’s
regulations prohibit a 77 GHz radar being used for UAV applications.