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Computer simulations have enhanced the efforts of RF/microwave circuit designers for many years, providing precise models for many of the active and passive components comprising high-frequency circuits. Simulation software can even account for the effects of dielectric and conductor losses in circuit materials.

System designers have also come to rely on software to predict the performance of a wide range of designs, including communications systems, electronic-warfare (EW) systems, and radars. By using a variety of software simulation tools, they can quickly evaluate changes in a system block diagram, rather than having to go through the time-consuming processing of prototyping and testing each new change.

Fig. 1

System simulators for defense electronic systems have traditionally performed simulations based on a block diagram, such as from an antenna through receiver and transmitter to a baseband processor. Often, separate simulations may be performed on different types of antennas, with modeling then performed on the different function blocks of a system (e.g., receivers, transmitters, or baseband processors).

Some major contractors with extensive experience in radar systems, such as Rockwell Collins, have developed their own software simulation tools for many different forms of radar—such as fire-control, weather, navigation, and search-and-surveillance systems—with customizable capabilities for each system type. These high-level simulation programs can include the effects of weather, the terrain, and electrical variations in providing precise predictions of system performance.

Whether for radar, EW, or communications simulations, most effective system simulators start with a building-block approach based on models of components or function blocks within a system, such as amplifiers, filters, and mixers (Fig. 1). Numerous commercial system simulators are built upon this approach, including the Advanced Design System (ADS) and SystemVue software from Keysight Technologies. Another prominent offering is the Visual System Simulator (VSS) from Applied Wave Research and its parent company, National Instruments.

​SystemVue, for example, which includes radar system examples, is tightly linked to the company’s ADS software. The latter typically works at component levels in the design of RF/microwave circuits and draws upon modeling the interactions of different components at the system level, whether in commercial or military system designs. While the impedance matches into and out of a small-signal transistor may affect the gain and noise figure of a front-end amplifier based on that transistor, ADS can extend impedance-matching effects from the component to the system level to study the effects between the amplifier and other connected components on the sensitivity and selectivity of a communications or radar receiver.

In fact, Keysight Technologies, in its former incarnation as Agilent Technologies, offers an excellent white paper on the application of its ADS software to simulating radar and EW systems. “Advanced Design System Connected Solutions for Radar and EW Systems” is available as a free download from the still-active Agilent website.

The VSS software is seamlessly integrated with AWR’s Microwave Office software, which is typically used at the component and circuit levels, enabling the combination of software tools to perform simulations flowing from the device through system levels. This linking of device/component simulation tools to system-level simulations is a tremendous aid when comparing measurements to simulations in efforts to optimize overall performance.

To meet the needs of radar designers, the VSS for Radar Systems is a specialized version of the software developed for modeling a range of different radar systems, including ground-, air-, space-, and ship-based radars. Radars can be simulated according to different frequencies and waveform types as well as by types of antenna, using algorithms to predict three-dimensional antenna radiation patterns. The VSS software can also effectively model other electronic systems employed by civilian and military users, such as Global Positioning System (GPS) receivers.

VSS software includes links to commercial test equipment like signal generators and vector network analyzers (VNAs), helping to integrate measured data into modeled simulations. In addition, the VSS Radar Library includes models of the various components found in different radar systems, including a collection of antenna patterns that can be plugged into system simulations when searching for optimum coverage and/or detection capabilities.

Due to the widespread use of radar technology in civilian and military applications, the field for radar system simulators has grown at a steady pace. Some of these simulation tools are written for standard Windows-based PCs, such as PCRadar from Buffalo Computer Graphics. The software provides an automatic radar plotting aid (ARPA) display on a PC monitor and serves as an excellent educational tool for shipboard radar systems (Fig. 2).

Fig. 2

It simulates land mass, moving targets, sea clutter, precipitation, and other effects. It provides target acquisition and tracking, leading vectors and history trails, trial maneuvers, and navigation points. The simulation software, which was designed for the U.S. Navy and Coast Guard for training applications, can also model an SPS-73 radar display.

COMSOL’s MultiPhysics is another versatile simulation software that has been used for predicting very specific effects within phase-array and other types of radar systems. The software has been used, for example, to model different frequency-selective surfaces (FSSs) and their radar cross sections (RCSs). By finding an FSS with minimal RCS, a jet aircraft or missile can be designed to make it more difficult to detect by enemy radar.

COMSOL MultiPhysics has also been used to predict system-level effects previously not modeled in defense systems, such as corrosion in metals. The software tool when equipped with its Corrosion Module, has been used by the Naval Research Laboratory (NRL) to predict how pits grow in different metals as a function of corrosion. The Corrosion Module includes specialized equations that analyze electromechanical reactions and reaction rates between different chemicals and metals, so as to better understand the long-term reliability of defense systems exposed to environmental conditions.

System simulators are, after all, collections of equations, typically organized with a graphical user interface (GUI) that simplifies the application of those equations when analyzing system behavior. For those who want a closer hand with the equations, MATLAB from MathWorks has proven to be an effective tool for modeling radar system behavior, taking into account analog, digital, and RF/microwave circuits, components, and integration.

In particular, when used with the company’s Simulink block-diagram-based system simulation software, MATLAB supports modeling and simulation at all stages of a radar system’s development cycle, including the design of exotic waveforms, analysis of beamforming and target-detection effectiveness, modeling of clutter, and estimations of direction of arrival (DoA). The math-based software has been used for both commercial automotive and military radar systems.

Electromagnetic (EM) simulation software such as the various EM-based tools from Remcom have been widely used for modeling antennas and other radar system components in addition to performing full system simulations. The software has helped analyze RCS patterns, antenna radiation, bistatic scattering, and other characteristics of different military and commercial radar systems, including millimeter-wave automotive radar systems.

For those seeking a painless entry to radar simulation, Apponic offers a no-charge simulation (based on its use of MATLAB software) of an early-warning radar system, while Software Informer provides free Windows-based radar simulation software on its website.

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