Productive and efficient 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 is vital to ensure realistic testing.
Simulation for these multi-emitter environments traditionally encompasses large, complex, custom systems during the system qualification and verification stage. These systems are usually not widely available to EW design engineers as R&D test equipment. EW designers working on optimization and pre-qualification are at a disadvantage in comparison to wireless engineers performing similar tasks. EW engineers often discover the nature and magnitude of performance problems later in the design phase — leading to delays, design rework, and solutions that are not optimal.
This application note summarizes the technological approaches for EW signal and environment simulation and the latest progress in flexible, high-fidelity solutions. For example, recent innovations in digital-to-analog converters (DACs) have brought direct digital synthesis (DDS) signal generation into EW applications through advances in both bandwidths and signal quality. This paper also covers DDS solutions and other innovations in agile frequency and power control so you can improve your design phase EW engineering accuracy and productivity.
Table of content
Realism and Fidelity in Multi-Emitter Environments
Validation and verification of EW systems are heavily dependent on testing with realistic signal environments. Adding high-fidelity emitters for greater signal density creates a realistic EW test environment. In addition, emitter fidelity and density, platform motion, emitter scan patterns, receiver antenna models, the direction of arrival, and multipath and atmospheric models enhance the ability to test EW systems under realistic conditions. The designs for modern EW systems can identify emitters using precise direction finding and pulse parameterization 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 fidelity 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 flight. Even though flight testing can add test capability, it does so at a high cost. It is typically done later in the program lifecycle, adding risk and further expense 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 are easily repeated to identify iteratively and resolve issues.
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. Figure 1 shows a general overview of the threat frequency spectrum.
Simulating this environment is a significant challenge — especially in the design phase when design flexibility and productivity are at their greatest. The situation is quite different from the typical wireless design task, where a single signal generator can produce the required signal, 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 specific phenomena such as angle-of-arrival (AoA).
The ability to simulate multiple emitters at multiple frequencies depends on the following: pulse repetition frequency; duty cycle; the number of emitters; and the capability 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.
A source’s agility is a factor in its ability to simulate multiple emitters. Source frequency, phase, and amplitude settling time (whichever is greater) is the transition time between playing one pulse descriptor word (PDW) and the next.
Improvements Simplify Integration and Reduce Cost
Simulating more threats to create higher pulse density requires more parallel simulation channels — even if the simulation channel can switch frequency, phase, 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. 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.
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