Aerospace & Defense Technology - May 2021 - 22

Anti-Drone Countermeasures
System overview showing the
dual radar setup

The result is a very robust drone discrimination which cannot be easily
counter-measured.
However, detecting drones is one
thing; acting on the threat they pose is
another. Years of experience have
taught that radar is only part of the solution; other sensors such as cameras
and RF detection provide additional target classification data. Then there's jamming, spoofing, or EMP that can be
used to accurately divert or eliminate a
threat.
For many of these sensors and actors,
a full 3D position is highly desirable.
ELVIRA isn't capable of that; it only provides latitude and longitude of the target. IRIS, on the other hand, is.
The receive antenna of IRIS consists
of eight channels, each receiving the
target return. The direction-of-arrival of
the return signal, with respect to the antenna plane, causes small time differences between the signals of each channel. This becomes our well-known
phased array technology, used to determine the elevation of each detected target. This technology was already developed for the MAX bird detection radar,
so it could be transitioned to IRIS without too much trouble.

Stumbling Blocks
In order to measure micro Doppler
profiles, a radar needs to spend quite
some time on a target, in the order of
several tens of milliseconds. Either the
radar has to rotate slowly, or the beam
must be wide in order to illuminate the
target for long enough. The first leads to
a slow update rate; the latter to loss of
resolution, accuracy and antenna gain.
Dealing with compromises is something engineers are used to, but the sacrifice between antenna gain or update
rate was just plain painful. Therefore, it
was decided to use two back-to-back antenna arrays, both performing as a full
radar system. This obtained a 1 Hz update rate while still rotating at 30 RPM,
with a reasonable beam width and a high
gain antenna. Packing two transmitters,
each transmitting 10 dBW, and two receivers into one stationary radome did
prove to be a challenge, though. Not so
much because of the physical size, but
the required RF isolation between the

transmitters and receivers is very demanding. Hours of brainstorming,
simulation, and experimenting led
to a patented antenna design
which hit these set requirements.

Eye on the Prize
After building and severely testing demonstrators, we became convinced that the concept was feasible.
From that moment onwards, it became extremely important not to
get distracted by new insights
and abilities, but focus 100% on
the project's predefined goals.
So we asked the question, what
do we want? The answer was: We
wanted IRIS to be the successor of
ELVIRA, providing 3D, mobility and a
strongly reduced cone-of-silence. We explicitly kept requirements regarding detection and classification range equal. No
compromise.
Even with reuse of antenna technology and having overcome the hurdle of
packing the tech into a small radome,
many challenges still remained. One of
these challenges was the vast amount of
data produced by, in total, 16 receive
channels. These signals contain the return signal of, for example, a car driving
100 meters in front of the radar as well
as the turning of a 12-inch propeller at
more than a 1-kilometer distance.
That's an enormous requirement of
the dynamic range-to process implied

floatingpoint processing. Only FPGA technology is capable of performing this task in
real-time. In IRIS, an Intel FPGA with
hard floating-point DSP blocks capable
of executing 1.5 TFLOPS is deployed, on
which the majority of the signal processing occurs. The hard work of the embedded FPGA leads to a manageable data
stream of only several gigabits, which
hosts computer executing plot extraction, analysis and tracking.
Two full radar systems, a high-performance FPGA and mechanical direct
drive, and all packed into a 60-centimeter IP66 enclosure, generates a lot of
heat, so thermal design became the
next challenge. For ease of deployment

Close-up of the separation plates realizing the TX/RX RF separation

22

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Aerospace & Defense Technology - May 2021

Table of Contents for the Digital Edition of Aerospace & Defense Technology - May 2021

Aerospace & Defense Technology - May 2021 - Intro
Aerospace & Defense Technology - May 2021 - Sponsor
Aerospace & Defense Technology - May 2021 - Cov1
Aerospace & Defense Technology - May 2021 - Cov2
Aerospace & Defense Technology - May 2021 - 1
Aerospace & Defense Technology - May 2021 - 2
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Aerospace & Defense Technology - May 2021 - 44
Aerospace & Defense Technology - May 2021 - Cov3
Aerospace & Defense Technology - May 2021 - Cov4
https://www.nxtbook.com/smg/techbriefs/22ADT09
https://www.nxtbook.com/smg/techbriefs/22ADT08
https://www.nxtbook.com/smg/techbriefs/22ADT06
https://www.nxtbook.com/smg/techbriefs/22ADT05
https://www.nxtbook.com/smg/techbriefs/22ADT04
https://www.nxtbook.com/smg/techbriefs/22ADT02
https://www.nxtbook.com/smg/techbriefs/21ADT12
https://www.nxtbook.com/smg/techbriefs/21ADT10
https://www.nxtbook.com/smg/techbriefs/21ADT09
https://www.nxtbook.com/smg/techbriefs/21ADT08
https://www.nxtbook.com/smg/techbriefs/21ADT06
https://www.nxtbook.com/smg/techbriefs/21ADT05
https://www.nxtbook.com/smg/techbriefs/21ADT04
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