JED - November 2013 - 31

By Ollie Holt

can use the maximum measured amplitude, and if you
know the signal's Effected Radiated Power (ERP), you
could estimate range using the radar range equation.
Again this is only a rough estimate because of the variability in ERP levels, signal paths losses and amplitude
measurement accuracy.
Another method that can be implemented with a
few receivers is Time Difference of Arrival (TDOA).
This technique measures the difference in arrival time
of the same signal arriving at two or more separated
antennas. If the antennas are close, the receivers need
to be able to measure time with very fine resolution.
This can be a challenging requirement. The alternative is to space the antennas as far apart as possible.
For radar pulses, it is an easier problem because they
are just measuring time with an accurate clock when
the rising edge occurs. For a communication signal,
additional signal processing is required to make sure
the system is measuring time of arrival on the same
artifact of the signal.
Another measurable parameter is signal phase.
Looking at the phase difference between multiple
antenna positions at the same exact time can provide
an estimate for DF. The more antennas you use, the better your accuracy. These antennas all need to have the
same field of view. There are different configurations for
using phase as a DF method. Long baseline configurations, referred to as long baseline interferometry (LBI),
require at least one antenna that is separated from the
others by multiple wavelengths. Another method is
short baseline interferometry (SBI), meaning all the
antennas are very closely spaced. In SBI configurations
the elements are not separated by multiple wavelengths,
so it may provide multiple ambiguous solutions.
Each technique has advantages and disadvantages.
Amplitude is relatively simple and low cost to implement, but with only average performance. TDOA can
provide very good performance, but with either very
complex time measurement hardware or antennas
spaced very far apart and complex signal processing.
Delta phase measurements can be implemented relatively easily in the receivers and, using a combination
of SBI and LBI, this can provide good results.
Our next survey will cover FPGA boards for EW and
SIGINT applications. It will appear in the February
2014 JED. a

The Journal of Electronic Defense | November 2013
The Journal of Electronic Defense | November 2013


n keeping with the theme of EW receivers we
started earlier this year, this month's survey
covers communication intelligence (COMINT) and
direction finding (DF) receivers. These receivers
are designed to perform signal intercept, data
collection, data analysis and emitter location
of communication signals in the HF, VHF, UHF and
SHF bands. Today's COMINT systems support simultaneous detection and processing of multiple wideband
and narrowband signals using frequency-hopping and
direct-sequence spread-spectrum waveforms. Typical
COMINT receiver systems consist of multi-channel
highly scalable receiver architectures.
Advances in analog-to-digital (A/D) converters and
tuner technology have led to improvements in COMINT
receiver systems. These same advances in A/D technology allow creation and transmission of more complex
signal waveforms, which in turn drives challenges to
the detection and processing of communication signals.
With the availability of low cost tuners, A/D converter
chips, and high-speed/high-gate-count field programmable gate array (FPGA) modules that can easily perform
complex signal processing algorithms, COMINT receiver
systems can be configured to perform intercept, data
collection and real time data analysis along with emitter
location. Most of these COMINT receiver systems have
similar block diagrams (tuners, A/D converters and
signal processing) with the ability to scale them into
different sizes (number of receiver channels). With the
addition of software modules, detection and analysis of
different signal types can be easily supported.
Let's discuss a bit about DF. This survey asked what
technique was used for performing DF. There are many
different DF techniques, and each one can provide some
level of performance. Usually better DF performance
comes with increased receiver complexity and cost.
Let's examine what parameters of a signal a receiver
can measure that could provide information on the
angle from which the signal originated? The simplest
parameter to measure is amplitude. If you could place
four antennas in an orthogonal configuration, and
you have a relatively good idea of the antenna patterns, with four receivers measuring the amplitude at
each antenna, the relationship between the different
received amplitudes and known antenna patterns can
provide a rough estimate of angle of arrival. Also you



JED - November 2013

Table of Contents for the Digital Edition of JED - November 2013

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
World Report
What’s New in Naval ESM
Technology Survey: COMINT/DF Receivers
EW 101
AOC News
Index of Advertisers
JED Quick Look
JED - November 2013 - cover1
JED - November 2013 - cover2
JED - November 2013 - 3
JED - November 2013 - 4
JED - November 2013 - 5
JED - November 2013 - The View From Here
JED - November 2013 - 7
JED - November 2013 - Conferences Calendar
JED - November 2013 - 9
JED - November 2013 - Courses Calendar
JED - November 2013 - 11
JED - November 2013 - From the President
JED - November 2013 - 13
JED - November 2013 - 14
JED - November 2013 - The Monitor
JED - November 2013 - 16
JED - November 2013 - 17
JED - November 2013 - 18
JED - November 2013 - 19
JED - November 2013 - 20
JED - November 2013 - 21
JED - November 2013 - World Report
JED - November 2013 - 23
JED - November 2013 - What’s New in Naval ESM
JED - November 2013 - 25
JED - November 2013 - 26
JED - November 2013 - 27
JED - November 2013 - 28
JED - November 2013 - 29
JED - November 2013 - 30
JED - November 2013 - Technology Survey: COMINT/DF Receivers
JED - November 2013 - 32
JED - November 2013 - 33
JED - November 2013 - 34
JED - November 2013 - 35
JED - November 2013 - 36
JED - November 2013 - 37
JED - November 2013 - 38
JED - November 2013 - 39
JED - November 2013 - 40
JED - November 2013 - 41
JED - November 2013 - 42
JED - November 2013 - 43
JED - November 2013 - EW 101
JED - November 2013 - 45
JED - November 2013 - 46
JED - November 2013 - AOC News
JED - November 2013 - 48
JED - November 2013 - Index of Advertisers
JED - November 2013 - JED Quick Look
JED - November 2013 - cover3
JED - November 2013 - cover4