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Simulation is a vital part of military electronics systems, especially with the growing complexity of these systems. It has long been used to investigate the possible behavior of different systems and their components under different conditions, such as changes in temperature, humidity, shock, and vibration. Out of necessity, simulation methods work hand-in-hand with test equipment and measurement techniques—typically with measurements providing feedback to a simulator on how well an actual electronic system performs under different conditions compared to the virtual or modeled version of that system in software.

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Combining test and simulation functions can help drive the design and development of different military systems, including electronic-warfare (EW), electronic-countermeasures (ECM), and radar systems. For that reason, it is not surprising to find that many companies that are developers of simulation software are also suppliers of test and measurement gear or designers of custom test solutions.

The Visual System Simulator for RADAR from AWR Corp. can provide full behavioral modeling of different types of radar systems, as well as three-dimensional modeling of the antennas that are part of those systems. It can create models by means of manipulating software code or by working with data from actual measurements on those systems.

The simulator models continuous wave (CW) radars, pulsed radars, and pulsed frequency-modulated (FM) chirp radars. It can show the many effects of changes in a radar system because of the environment and how it affects system performance, such as how the height of a radar system above the ground impacts the line of sight for that system, how noise levels change performance, how receiver noise figure and sensitivity modify the system’s range, and how jammers can hinder performance.

The VSS simulation software leverages a large library of system and antenna simulation models, including clutter and phased-array antenna models. The simulator provides quick links to other useful software programs, such as LabVIEW from National Instruments, the parent company of AWR Corp. In working with such measurement programs, the VSS simulation software provides the synergism needed to integrate measurements into the simulations, creating a two-way arrangement that allows measurements to improve simulation models and simulations to enhance hardware designs and prototypes. Using LabVIEW as an example, the VSS simulation software is compatible with any and all measurement instruments it supports.  

Another major test equipment supplier with strong support for signal simulation is Keysight Technologies and its Signal Studio software. The software can model and modify a wide range of different EW and radar signals and work with rack-mount and modular test instruments, such as the firm’s new lines of arbitrary waveform generators (AWGs), to generate CW and pulsed signals as needed for testing. The company offers free-of-charge 30-day trial use of the software for interested parties to explore its many capabilities.

The Signal Studio software allows users to call waveforms from a stored collection or, alternately, to define a waveform by tuning the different parameters to create a specific CW or pulsed signal with precise characteristics. The software employs a familiar Windows-based GUI to speed an operator through waveform creation, also providing pop-up screens to show the waveform as it is being created and modified.

Once a signal is defined, it can be used in a higher-level simulation—such as within the company’s SystemVue system-level simulation—to predict the effects of the simulation waveform on different systems and their components. The waveform file can also be sent to a variety of hardware test instruments offered by Keysight, among them lines of vector signal generators (VSGs) both in traditional rack-mount and emerging modular instrument card formats. The PSG line of VSGs, for example, can produce output waveforms to 44 GHz for defense and aerospace testing.

This signal simulation software provides a great deal of flexibility by offering different operating modes: specifically, the waveform playback and real-time modes. The former permits a user to select from two levels of functionality to control their operating functionality. The latter includes closed-loop control of modifications to signals during signal generation, so that users can instantly see the effects of changes to a waveform’s programming. These different program choices within the software are designed to allow a user to select the level of control needed for an application so that the software can be used cost-effectively and time-effectively.

The Signal Studio software provides extensive pulse creation functions, allowing an operator to quickly build a library of pulses from measured data or defined characteristics. Custom pulse patterns can be created with 80-dB on/off ratios and advanced modulation formats, with such things as frequency, phase, and power offsets defined on a pulse-by-pulse basis. In addition to extensive signal library models for commercial cellular and wireless signals, Signal Studio features library models of different radar signals, multiple-satellite signals for the Global Positioning System (GPS), and a wide range of signals for Global Navigation Satellite System (GNSS) applications.

The Simulink simulator from MathWorks, although technically a “block-diagram” system-level simulation, is often used to generate and model different waveforms and video signals for commercial and military systems. Using mathematical modeling methods, including the firm’s respected MATLAB mathematical software, the simulator has been used to evaluate the impact of modeled waveforms on system performance.

The waveforms created by these software tools will be limited in the real world to the hardware test instruments used to generate those waveforms. As the signal sources story explains, high-frequency signals can be generated by a number of different technologies, from analog circuits to arbitrary waveform generators (AWGs) and direct-digital synthesizer (DDS) signal generators. The performance parameters, such as frequency range, bandwidth, and frequency switching speed, vary widely among the difference signal sources.

Typically, simulation software compatible with a certain type of hardware signal source will include programmability limits for the performance levels of the hardware—not permitting the creation of waveform files with parameters, such as frequency switching speed, that exceed the limits of the hardware. Still with the high-speed signal sources currently available from Keysight, National Instruments, and other test-and-measurement equipment suppliers, simulation software can be readily teamed with available hardware signal sources to create most waveforms needed for simulating and testing military and aerospace systems.

The R&S SMW200A series of vector signal generators (VSGs) from Rohde & Schwarz, for example, includes models covering a total frequency range of 100 kHz to 20 GHz with typical frequency switching speed of 0.6 ms. It offers the performance levels needed to match to any signal simulator on the market for EW and radar testing. These VSGs can be supplied with an optional second signal path, and standard models include an in-phase/quadrature (I/Q) modulator with a modulation bandwidth as wide as 2 GHz for generation of complex modulated waveforms.

Each R&S SMW200A VSG supports pulse modulation with on/off ratios of better than 80 dB and rise/fall times of less than 10 ns. The phase noise is typically -139 dBc/Hz offset 20 kHz from a 1-GHz carrier. The generator includes a large graphical display screen (see figure) to simplify operation and is housed in a traditional 19-in. rack-mount enclosure. This is a test signal source that can generally meet the requirements of the most creative signal simulation software. 

Similarly, the fast-switching model MG37020A signal generator from Anritsu Co. is contained within a 19-in. rack-mount enclosure and includes a large display screen, and also offers the performance needed for creating most EW and radar signals. It covers 10 MHz to 20 GHz with 100-μs typical frequency switching speed, and is characterized by high signal amplitude and low phase noise.

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