Text preview for : 5992-0094EN English _ 2014-09-16 _ PDF 545 KB c20140919 [16].pdf part of Agilent 5992-0094EN English 2014-09-16 PDF 545 KB c20140919 [16] Agilent 5992-0094EN English _ 2014-09-16 _ PDF 545 KB c20140919 [16].pdf
Back to : 5992-0094EN English _ 201 | Home
Keysight Technologies
Electronic Warfare Signal Generation:
Technologies and Methods
Application Note
Introduction
Productive and eficient engineering of electronic warfare (EW) systems requires the generation of
test signals that accurately and repeatably represent the EW environment. Simulation of multi-emitter
environments, in particular, is vital to ensure realistic and representative testing.
Currently, these multi-emitter environments are simulated with large, complex, custom systems that
are employed in the system qualiication and veriication stage, and not widely available to EW design
engineers as R&D test equipment. Designers working on optimization and pre-qualiication are there-
fore at a disadvantage compared to wireless engineers performing similar tasks. Engineers often learn
of the nature and magnitude of performance problems later in the design phase, leading to delays,
design rework, and solutions that are not well-optimized.
This application note will summarize the available technological approaches for EW signal and en-
vironment simulation, and the latest progress in lexible, high-idelity solutions. For example, recent
innovations in digital-to-analog converters (DACs) have brought direct digital synthesis (DDS) signal
generation into the realm of practicality for EW applications through advances in both bandwidth
and signal quality. DDS solutions and other innovations in agile frequency and power control will be
discussed in the context of improving design-phase EW engineering productivity.
03 | Keysight | Electronic Warfare Signal Generation: Technologies and Methods - Application Note
Realism and Fidelity in Multi-Emitter Environments
Validation and veriication of EW systems is heavily dependent on testing with realistic
signal environments. EW test realism increases as high-idelity emitters are added to
create density. In addition to emitter idelity and density, platform motion, emitter scan
patterns, receiver antenna models, direction of arrival, and multipath and atmospheric
models enhance the ability to test EW systems under realistic conditions. EW systems
are now designed to identify emitters using precise direction inding and pulse param-
eterization in dense environments of 8 to 10 million pulses per second.
The cost of test is as important as test realism, as the relationship between cost and
test idelity is exponential. As test equipment becomes more cost effective and capable,
more EW testing can be performed on the ground--in a lab or chamber--rather than in
light. Even though light testing can add test capability, it does so at great cost and is
typically done later in the program lifecycle, adding risk and further cost to the program
through missed deadlines if the system under test (SUT) fails. It is far better to test early
in a lab environment with as much realism as possible where tests can be easily repeated
to iteratively identify and ix problems.
Challenges of Simulating Multi-Emitter Environments
The modern spectral environment contains thousands of emitters--radios, wireless
devices, and tens to hundreds of radar threats--producing millions of radar pulses per
second amidst background signals and noise. A general overview of the threat frequency
spectrum is shown in Figure 1.
Pulse density (log)
Acquisition, GCI
Fire control
Early warning
VHF UHF L S C X Ku
A B C D E F G H I J
Figure 1. A general representation of the threat density vs. frequency band in a typical operational environment.
The full RF/microwave environment would be a combination of the threat and commercial wireless environments.
04 | Keysight | Electronic Warfare Signal Generation: Technologies and Methods - Application Note
Simulating this environment is a major challenge, especially in the design phase, when
design lexibility and productivity are at their greatest. The situation is very different
from the typical wireless design task, where a single signal generator can produce the
required signal, perhaps augmented by a second signal generator to add interference or
noise.
In EW design the multiplicity and density of the environment--and often the bandwidth--
make it impractical to use a single source or a small number of sources to simulate a
single emitter or a small number of emitters. Cost, space, and complexity considerations
rule out these approaches.
The only practical solution is to simulate many emitters with a single source, and to
employ multiple sources--each typically simulating many emitters--when required to
produce the needed signal density or to simulate speciic phenomena such as angle-of-
arrival (AoA).
The ability to simulate multiple emitters at multiple frequencies depends on the pulse
repetition frequency, duty cycle and number of emitters, and ability of the source to
switch between frequency, amplitude, and modulation quickly.
A limiting factor in the use of a single signal generator to simulate multiple emitters is
pulse collisions. Figures 2 and 3 show the number of pulse collisions expected for the
cases of low and high pulse repetition frequency (PRF).
Low PRF emitter density vs. pulse collision percentage
100
3000 emitters
90
Pulse collision perccentage
1000 emitters
80
70
512 emitters
60
50
40 256 emitters
30
20 128 emitters
10
36 emitters
0
0 1 1 2 2 3 3 4
Millions of pulses per second
Figure 2. As the number of emitters grows, the number of pulse collisions grows even when all emitters use low
PRF.
05 | Keysight | Electronic Warfare Signal Generation: Technologies and Methods - Application Note
High PRF emitter density vs. pulse collision percentage
100
4 emitters
90
Pulse collision percentage
80 3 emitters
70
60 2 emitters
50
40
30
20
10
1 emitter
0
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
Millions of pulses per second
Figure 3. The percentage of pulse collisions climbs very quickly as high-PRF emitters are added to a simulation.
A source's agility is a factor in its ability to simulate multiple emitters. Source frequency
and amplitude settling time (whichever is greater) is the transition time between playing
one pulse descriptor word (PDW) and the next.
Total pulse density for a single source is limited by the sum of the transition time and the
width of the transmitted pulses, a lockout period parameter as shown in Figure 4. It is
obviously desirable that the lockout period be as short as possible, and therefore that the
source settling times be as brief as possible.
Pulse width
Frequency switching time
Amplitude switching time
Transition time
Lockout period
PDW PDW Time
sent playback
Figure 4. The ability to simulate multiple emitters depends not only on emitter parameters like PRF and pulse
width, but also the frequency and amplitude switching speeds and setting times of the signal source used to
synthesize the emitters. If the source is switching, it cannot play a pulse. If it is playing a pulse, it cannot switch.
The source is unavailable to simulate a different threat during the lockout period.
To simulate high pulse density and the possibility of some overlapping pulses, it is often
necessary to combine multiple sources. As more sources are added to the test conigu-
ration, pulse density should scale easily and seamlessly, ultimately reaching the desired
tradeoff of satisfactory simulation realism and cost.
06 | Keysight | Electronic Warfare Signal Generation: Technologies and Methods - Application Note
Technology Improvements Simplify System Integration
and Reduce Cost
Simulating more threats to create more pulse density ultimately requires more parallel
simulation channels, even if the simulation channel can switch frequency and amplitude
quickly. This is because pulses begin to collide in the time domain as the number of
emitters, their PRFs, and their duty cycles grow larger 1. Pulses that overlap in the time
domain must be played out of parallel generators or selectively dropped based on a PDW
priority scheme. Unfortunately, the increased realism of a higher-density environment
comes at a substantially higher system cost, as shown in Figure 5.
Cost
Value
Legacy simulation
technology Modern
simulation technology
Fidelity
Figure 5. Simulation idelity and cost increase exponentially. System integrators and evaluators must decide the
level of cost vs. idelity that ensures system performance. New simulation technologies enable more simulation
realism and idelity at lower cost.
In the past, simulations have generally been created with a separate component for each
emulation function, such as signal generation, modulation/pulsing, attenuation or am-
pliication, and phase shift. The same PDW would be sent to each functional component
to provide output on a pulse-to-pulse basis. For instance, a synthesizer would generate
the output frequency, while a separate modulator would create pulsed modulation and/
or AM/FM/PM modulation. Ampliiers and attenuators would adjust the signal to the
desired output power level. An example of this system topology is shown in Figure 6.
PDWs Control parameters
Pulse RF Amplifier/ EW simulation
generator generator attenuator output
Synchronization
Figure 6. In the traditional approach, PDW control parameters are sent in parallel to multiple functional ele-
ments, on a pulse-to-pulse basis, to generate and modify the desired signal. This approach results in a complex
system, demanding precise synchronization. 1. Philip Kazserman, "Frequency of pulse co-
incidence given n radars of different pulse
widths and PRFs," IEEE Trans. Aerospace
and Electronic Systems, vol. AES-6. p.
657-662, September 1970.
07 | Keysight | Electronic Warfare Signal Generation: Technologies and Methods - Application Note
Since multiple functional components are required to produce each output channel, time
synchronization is a signiicant coniguration and operational challenge. A wide variety
of settling times and latencies must be fully characterized to optimize pulse density by
minimizing lockout periods.
This approach can be scaled directly to create multiple coordinated channels, as shown
in Figure 7. However systems conigured in this way require a large footprint, occupying
more rack space, and cost escalates quickly.
Figure 7. A signal generation approach using separate functional elements can be scaled up in a straightforward
manner to increase pulse density and generate a more realistic environment. Unfortunately cost and space
requirements scale up rapidly as well. 1
The controller shown in Figure 7 would route PDWs to channels based on emitter
parameters such as frequency, amplitude, and pulse repetition frequency and also the
availability of each channel to implement the PDW. Since a channel cannot execute the
parameters of two different PDWs at the same time, one could be shunted to a backup
channel or dropped according to its priority.
Ultimately, EW receivers must be able to handle 8-10 million pulses per second where
most of the pulse density occurs at X-band. EW receivers must be able to handle pulses
arriving at the same time at different frequencies from different angles. Creating pulses
that are coincident with one another in the time domain should be a goal of simulation to
increase simulation realism.
Though Figure 7 describes a very capable system, the level of integration the system
elements is rather low. Recent developments in analog and digital signal generation
technologies are enabling a higher degree of integration, and solutions which are more
cost- and space-eficient, as described in the section, "Increasing Integration in EW
Test Solutions." There are several methods of controlling simulations depending on test
objectives.
1. Reproduced by permission from David Ad-
amy, EW 101: A First Course in Electronic
Warfare, Norwood, MA: Artech House,
Inc., 2001.