## About CREATE- RF

As integral components of almost all DoD weapon systems, antennas and radars perform critical communication, identification, and navigation functions necessary for warfighter effectiveness and survivability. Computational Electromagnetics (CEM) tools have matured in recent years and are widely used for antenna concept exploration and design by the DoD and its contractors.

COMPUTER REQUIREMENTS

SENTRi runs natively on Linux and Windows operating systems and computers from workstations to high performance parallel computers (only Linux on parallel systems). On the desktop, engineering workstations with single or dual CPUs and 128GB or higher would be optimal. For parallel systems, SENTRi is Linux only, nodes would be best configured as the fore-mentioned workstation, high-speed infiniband is recommended, and a 128 node parallel system is the largest to date run with the production version of SENTRi.

FREQUENCY DOMAIN

SENTRi is a frequency domain code—which means one frequency at a time is solved; frequency sweeps are handled by running a series of solutions as defined by the user. SENTRi was designed as a frequency domain code to provide a higher degree of accuracy. In addition, frequency domain methods provide faster solutions for far field sweeps, calculation of S-parameter matrices for multi-port microwave circuits, and scanning of phased array antennas.

MATERIAL MODELING

SENTRi is designed for the modeling of complex structures—including highly, heterogeneous material structures with multi-scaled features. SENTRi’s material modeling includes dielectric, magnetic, impedance boundary conditions, and complex valued resistive sheets. Volume materials can have combined dielectric and magnetic properties, and can be isotropic or anisotropic. Volume materials can also have continuously varying properties with definitions provided by user-authored Python scripts. Similarly, Python scripts are used for defining the frequency varying properties of dispersive materials and for position varying resistive sheets.

ELEMENTS AND BASIS FUNCTIONS

SENTRi’s use of all volume element shapes – hexahedral, prism, pyramids, and tetrahedral – allows for flexibility, use of automated mesh generation, and faster solutions. Hexahedral and prism shapes, in particular, are much more efficient at modeling thin material layers than tetrahedral shaped elements. Surface meshes use both quadrilateral and triangular shaped elements. In SENTRi v6, first and second order elements are used with second-order allowing the use of curvilinear elements. For SENTRi v7 and above, first to fourth order hierarchical basis functions are available with geometry definition separate from the basis – i.e. a first-order element can have curved geometric definition.

FAST SOLVERS

For large problem sizes, SENTRi uses the Adaptive Cross Approximation (ACA) method as its fast solver. ACA is utilized for compressing dense matrices from the boundary integral method, dense matrices from Schur complements of finite element domains, and block matrices from multiple right-hand side forcing functions of far field calculations. Graph shows SENTRi’s performance on an all boundary integral scattering solution of a C-130 aircraft perfectly electric mold-line, solving 1442 look angles on 36 parallel computer nodes (1152 cores). To further increase performance, SENTRi uses a hybrid shared / distributed memory parallel architecture to minimize inter-node communication.

PORT FEEDS

SENTRi’s has multiple types of port feeds for model construction flexibility. Available feed include: waveguide ports, voltage gap ports, wireport, lumped surface port, and lumped volume port. Ports can be loaded with complex value impedances. For waveguide ports, analytical field models are used when they have standard shapes otherwise ports numerical eigenvector solutions are used. Evanescent modes are represented for proper calculation of propagating S-parameters. A ‘superposition’ capability in SENTRi post-processing allows phasing of the port feeds—used for circular polarization of antennas or scanning phased arrays.

POST-PROCESSING

SENTRi has a number of post-processing features to calculate quantities such as near-fields, far fields, input impedances, and other engineering quantities from the basic solution. Post-processing functions are available as part of SENTRi’s graphical user interface (GUI) and as separate console applications, the latter of which are often used within scripts to automate a series of analysis runs. The post-processing GUI allows for the display of data in a number of formats in addition to export/import capability for user-controlled comparison of data.

DOMAIN DECOMPOSITION

The Domain Decomposition Method (DDM) can provide computational efficiencies an order of magnitude or greater than standard techniques. DDM does this in two main ways: it reduces the amount of message passing between compute nodes on a parallel computer, it takes advantage when solution domains have repeatable geometries. DDM also enables user productivity by providing a ‘divide and conquer’ scheme for geometry modeling.

FlexMPI

Utilization of applications on parallel computers with message passing systems is complicated by the numerous versions of available MPI libraries. Instead of installing a generic MPI library with SENTRi which may cause performance and stability issues, a system called developed by the Stellar Science company called FlexMPI is used. FlexMPI system queries an operating system to determine what MPI libraries are installed and performs a compiler link with SENTRi.

Hybridized with SENTRi version 6 and available from the CREATE™-RF program, Aurora is an asymptotic approximate EM solver employing the physical-optics shooting-and-bouncing-rays (PO-SBR) technique for computing installed antenna patterns and plane wave scattering from electrically large platforms. Helping fulfill CREATE™-RF's antenna-on-platform integration analysis objective, Aurora has modeled antenna patterns from parabolic reflectors up to aircraft carriers, and scattering from full size aircraft. It supports Windows and Linux and executes efficiently on HPC systems.

HYBRID SENTRi/AURORA IN-SITU ANTENNA ANALYSIS

SENTRi accurately predicts antenna patterns, such as the cross-slot shown above. As frequency rises, modeling platform interaction grows to be intractable. The SENTRi/Aurora hybrid accelerates and makes tractable platform integration analysis on otherwise unreachable problems. Reduced solve times also aid engineers in quickly understanding the impact of features such as propellers on the CV-22 Osprey at 2.4 GHz in less than an hour on a laptop.

LARGE SCALE PROBLEM CAPABLE

Using 8,192 cores on the Excalibur DSRC†, Aurora simulated a 2.4 GHz horizontal dipole antenna on a Nimitz class carrier with 13 FA-18 Hornets in 7 minutes.

†https://arl.hpc.mil/hardware/index.html

FLO-K is CREATE™-RF’s rapid design code for periodic structures such as frequency selective surfaces, phased array antennas, band gap structures, etc. FLO-K utilizes a finite element method coupled to a floquet modal expansion. Full three-dimensional structures with dielectric, magnetic, and impedance sheets can be modeled with FLO-K. Both rectangular and triangle lattices can be constructed, Structures can be modeled as screens (transmitted / reflected) or backed by impenetrable surface (reflected only).

CREATE-RF TRAINING

A cost-free, two-day training session for CREATE™-RF tools is provided up to four times a year in Dayton, OH. This is a basic introductory training that covers modeling building, defining run-time parameters, and post-processing. Attendees will come away with a knowledge of how the SENTRi, Aurora, and FLO-K codes for their own applications. Also covered are the CAD generation and meshing capabilities of the CREATE™-MG Capstone and Sandia National Laboratory’s Cubit applications.

No-cost on-site training is also available for government agencies and/or defense industries when a group of fifteen or greater can be assembled. Laptops for attendees are also provided for both the Dayton and on-site training.