Advanced RF Simulation Reduces Cost and Schedule Risk

Advanced RF Simulation Reduces Cost and Schedule Risk

Designing the next generation of RF systems, such as high performance active electronically scanned arrays (AESA), requires contributions from a multidisciplinary team of engineers. Customers within the Department of Defense (DoD) require performance beyond the current state of the art in order to stay ahead of adversaries’ capabilities. As engineering teams work to meet these requirements, invariably, limitations in the available design, fabrication, and verification technologies consume the teams’ budget for design flexibility, performance, and novel solutions. Ultimately, this leads to concessions in the design and puts the overall project at risk for cost and schedule overruns.

Figure 1. Numerous sources of error roll up to consume precious design margin (left). Advanced RF simulation software providing high accuracy physics solutions opens up design margin for increased confidence and flexibility in design choices.

Teams must consider the sources of error that drive down design margins and seek newer technologies to ensure projects meet performance and cost objectives on schedule. The process of going from ideation to simulated design to fabricated and measured prototype accrues errors at each step. Identifying technologies that can advance the design process while reducing such errors becomes more critical as the systems become more complex. Leveraging the latest advancements in RF simulation software is one such area that can reduce critical errors while also improving the timeliness of the design process (see Figure 1).

Figure 2. The simulation runtime for large-scale systems such as phased arrays can vary drastically between the current generation of commercial software and newer products. This figure demonstrates a phased array simulation on identical hardware run with a leading commercial EM software and a modern tool - Nullspace EM.

Accuracy at the expense of speed is not always tenable and limits the ability of engineers to perform further analysis such as parametric studies, optimizations, and uncertainty quantification. Fortunately, the latest generation of RF simulation software demonstrates the best of both worlds: accuracy and speed. For example, Figure 2 shows a comparison of a large-scale AESA simulation using legacy and next-generation software and performed on identical computing hardware. In the case of the legacy commercial software, a single beam steering solution required an entire work week to compute, whereas the newer software computed data for all beam steering solutions in just over 16 hours. Using traditional software, a design engineer would be unlikely to perform any analysis beyond the single beam solution, thereby exposing the entire design process to performance risks not identifiable until the fabrication and characterization stage of development. Taking advantage of simulation software providing both accuracy and substantial speed improvements, opens new doors for design exploration or simply faster time to market.

AESA Radome Case Study

Radomes provide environmental protection to antennas and arrays such as AESAs. Since radomes are not completely RF transparent, there is a natural tug-of-war between the performance of the underlying antenna and the protection provided by the radome. The impact of the radome on antenna performance must be considered, but historically design engineers have had limited practical capability to perform detailed analysis before going to fabrication. Further, for AESAs, any calibration effort must be delayed until the antenna is fabricated and ready for testing.

Figure 3. The legacy design workflow for radome-antennas consists of disaggregated and limited design tools. Delays in identifying design flaws results in a higher cost to remediate the flaws and delays the project schedule.

Figure 3 shows the typical design workflow for AESAs with radomes. Designers often begin with an antenna element design, proceeding to an array factor analysis, and possibly a subscale array simulation. For the radome, analytic plane wave analysis to determine the general material stack-up precedes simplified simulations of the element with the stack-up. Depending on computational resources, designers might perform a smaller sub-scale simulation of the array with the radome. Due to limitations of the various simulation tools up to this point, the design team often must proceed to fabrication without full-scale simulation data. As such, identification of any design flaws must be delayed until fabrication. As with other design processes, delays in identifying issues results in higher costs to fix and longer schedule delays. Finally, inability to accurately simulate the full antenna-radome limits the efficacy of calibration in a post-production environment since practical AESAs are often limited to boresight-only calibration due to the time and difficulty of performing more complex calibrations.

Next-generation EM simulation software, such as that referenced in Figures 1 and 2, can dramatically enhance the workflow described above by allowing design teams to perform full antenna-radome simulations, potentially with speed sufficient to enable optimizations and uncertainty quantification (UQ) with project schedules. UQ in particular is practically always ignored, at peril to the project’s long-term success, due to legacy software limitations.

The highlighted modern simulation software provides a rich Python-based application programming interface (API) to control every aspect of the simulation from CAD generation and modification to post-processing. This provides design teams with the ability to parametrically control aspects of the system design to enable optimization and UQ studies.

Figure 4. The (left) E-plane and (right) H-plane beam steering errors show increasing error with increasing steering angle as expected. The different major components of the radome structure each contribute to the overall error observed for the full array. Simulation results obtained with Nullspace EM.

As an example, Figure 4 shows an illuminating result for a 30x15 triangular lattice dipole AESA simulation involving a quartz cyanate ester (QCE) - foam - QCE multilayer radome. The goal here was to obtain rigorous simulation data for all possible beam steering angles and assess the beam steering error in the simulation stage of the design workflow. Further, with the speed and accuracy provided by the modern software, components of the full antenna-radome assembly could be programmatically eliminated to evaluate which were the major contributors to the error (see Figure 4). Based on the data from Figure 2, designers can rely upon at least a 7X speed-up for this type of analysis. With schedule permitting, a team can further reduce design risk by performing more sophisticated analyses. One such is highlighted in Figure 5 in which the radome from Figure 4 is deformed similar to how real world conditions may impact an antenna-radome’s structure. While structural deformations are always a concern, virtually no full-scale analysis is ever done on large AESAs due to the computational complexity.

Figure 5. The AESA was simulated with deformations to the radome typical of environmental distortions. (Left) vertical-only and (right) all-direction deformations demonstrate the impact of effects on beam steering error that can typically only be observed in the field. Simulation results obtained with Nullspace EM.

With the modern software, a variety of UQ can be pursued including this type of analysis that cannot be calibrated out at production time. In this example, two analyses were performed in which vertical-only and all-direction deformations occurred. The H-plane beam steering error is shown for the nominal radome and the radome under deformation. Without the speed and accuracy of such modernized software, these advanced simulations could not be performed in a realistic timeframe.

As RF device needs become more sophisticated and complex, new simulation software technologies must be ready to enable design teams to achieve higher performance, with greater confidence, and in a timelier manner. Modern simulation software can satisfy these needs and usher in a new generation of radar and communication systems.

This article was written by Dr. Daniel Faircloth, Chief Technology Officer of Nullspace, Inc. For more information, visit here .