JED - June 2016 - 28

these advanced signals, Atanassov says
systems require higher instantaneous
bandwidth as well as high-speed scanning capability. "The combination is the
key factor in increasing the probability
of intercept."
Plath's Schwolen-Backes agrees. "You
have to ensure that the DF system has
both very good time resolution and very
high scanning speed, and sometimes
this means a bit of a tradeoff with frequency resolution. But, you nonetheless
have to ensure both adequate frequency
and time resolution to measure the signal correctly, and you also have to ensure that the bandwidth of the system
is wide enough and the scanning speed
fast enough. You have to match the right
numbers to the different scenarios."

AN EVOLUTION OF TECHNIQUES

The Journal of Electronic Defense | June 2016

28

Assuming the signal-detection challenge has been met, the real job of a
DF or geolocation system begins. And,
this is by no means a simple task, with
a number of established and new techniques being employed. These techniques are largely developed for, and
intimately linked to, the requirements
of specific applications.
In addition to the classical WatsonWatt interferometer AOA approach to
DF which uses Adcock (or crossed loop)
antennas to compare the amplitude of
the signal received at each antenna

and computes its bearing based on the
differences between them, time-difference-of-arrival (TDOA) geolocation techniques are also in increasingly common
use. With conventional TDOA, a signal is
received at three or more networked receivers sited at different locations and,
because the signal paths will be of different length, the differences in their
time of arrival can be used to calculate
the transmitter's location.
TDOA is particularly useful in urban
scenarios where signal reflections from
buildings and other structures can play
havoc with AOA systems. But, as pointed out by Schwolen-Backes, TDOA also
has its shortcomings. "TDOA is not really

widely used in tactical scenarios because
it doesn't work well with narrowband
signals, and with wide bandwidth signals, you have only short bursts in the
time domain and vice versa. Also, for
effective TDOA in tactical missions, you
have to guarantee that you have a network link, which is often difficult in a
very-fast-moving tactical situation."
Another DF or geolocation technique
is a combination, or hybrid, of conventional AOA and TDOA approaches. Says
Rohde & Schwarz's Strobel, "This technique applies to TDOA receivers and direction finders that can be used either
in DF mode or switched over to TDOA
mode. They can deliver both angle-ofarrival and IQ data (modulation scheme
information) snapshots with high-precision time stamps. The combination combines the advantages of both methods
and also compensates for their disadvantages. And, you can get geolocation
with just one TDOA receiver/DF system."
Strobel points to advanced software as
one of the major improvements to DF/
geolocation systems in recent years.
"Most of our customers' missions are
inside urban environments, where there
is almost never a direct line-of-sight to
the transmitter and many multipath
propagations. Today, however, modern
software algorithms and processing
techniques can overcome these problems by overlaying all the DF results to
make transmitter location accuracies
of five meters. This seems remarkable
considering past capabilities, but it is a
reality now."


http://www.arsproducts.com

JED - June 2016

Table of Contents for the Digital Edition of JED - June 2016

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
Washington Report
World Report
Advances in COMINT/ DF Systems
Technology Survey: Communications and IED Jammers
SIGINT History
EW 101
Report from the 45th Annual Collaborative EW Symposium
AOC News
2016 AOC International Election Guide
Index of Advertisers
JED Quick Look
JED - June 2016 - cover1
JED - June 2016 - cover2
JED - June 2016 - 3
JED - June 2016 - 4
JED - June 2016 - 5
JED - June 2016 - The View From Here
JED - June 2016 - 7
JED - June 2016 - Conferences Calendar
JED - June 2016 - 9
JED - June 2016 - Courses Calendar
JED - June 2016 - 11
JED - June 2016 - From the President
JED - June 2016 - 13
JED - June 2016 - 14
JED - June 2016 - The Monitor
JED - June 2016 - 16
JED - June 2016 - 17
JED - June 2016 - 18
JED - June 2016 - 19
JED - June 2016 - 20
JED - June 2016 - 21
JED - June 2016 - Washington Report
JED - June 2016 - 23
JED - June 2016 - World Report
JED - June 2016 - 25
JED - June 2016 - Advances in COMINT/ DF Systems
JED - June 2016 - 27
JED - June 2016 - 28
JED - June 2016 - 29
JED - June 2016 - 30
JED - June 2016 - 31
JED - June 2016 - 32
JED - June 2016 - Technology Survey: Communications and IED Jammers
JED - June 2016 - 34
JED - June 2016 - 35
JED - June 2016 - 36
JED - June 2016 - 37
JED - June 2016 - 38
JED - June 2016 - 39
JED - June 2016 - 40
JED - June 2016 - 41
JED - June 2016 - 42
JED - June 2016 - SIGINT History
JED - June 2016 - 44
JED - June 2016 - 45
JED - June 2016 - EW 101
JED - June 2016 - 47
JED - June 2016 - Report from the 45th Annual Collaborative EW Symposium
JED - June 2016 - 49
JED - June 2016 - AOC News
JED - June 2016 - 2016 AOC International Election Guide
JED - June 2016 - 52
JED - June 2016 - 53
JED - June 2016 - 54
JED - June 2016 - 55
JED - June 2016 - 56
JED - June 2016 - Index of Advertisers
JED - June 2016 - JED Quick Look
JED - June 2016 - cover3
JED - June 2016 - cover4
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