AFRL's Radiation and Scattering Compact Antenna Laboratory (RASCAL) enables researchers to develop and evaluate advanced aperture technologies that support electronic warfare, radar, communication, and navigation— technologies supplementing a variety of applications as the "eyes and ears" of the warfighter. Current research efforts are concentrated on developing relatively small and inexpensive broadband, multifunctional antennas, as well as conformal and structurally integrated antennas for manned and unmanned air vehicles. Using the RASCAL facility, researchers can perform the necessary fabrication, simulation, testing, and measurement of aperture technologies.

Figure 1. Rolled-edge reflector

RASCAL's fully in-house rapid prototyping capability alleviates the time and costs incurred from outsourcing jobs for breadboard antennas. Researchers create the majority of fabrications using a precision milling machine specifically manufactured for creating circuit board prototypes. This equipment plays an instrumental role in manufacturing many of the nontraditional antenna designs under development. The milling machine accepts a variety of input files, reducing the amount of time spent during the premanufacturing process. Its capabilities include full routing, as well as precision milling and drilling to trace width specifications as small as 0.1 mm on a variety of substrates. Further, researchers can custom-build supplementary hardware, such as mounts or casings, in the on-site prototype lab.

Researchers employ an assortment of computational electromagnetic tools both to simulate the characteristics of antennas under development and to forecast the performance of antennas installed on different platforms. Additionally, they continually develop and expand other tools to bridge the gap between research-grade analysis codes and production-grade code suites available for intuitive, rapid, and effective utilization in practical situations. Examples include rapidly installed antenna geometry tools, tools to migrate designs from prediction to analysis, and rendering tools to aid the antenna platform designer in total system analysis.

The advent of more powerful computer resources and codes that model antennas through numeric simulations have greatly enhanced the designer's ability to forecast device performance. Computer simulation in aperture design provides precise parametric studies (for sensitivity measurement and tolerance definition), as well as a means of concept demonstration for yet undeveloped structures and materials. This capability results in a more cost-effective, convenient engineering process.

The heart of the RASCAL facility is the compact range, which allows researchers to perform timely, low-cost, precision measurements for evaluation and validation, while accommodating complex configurations that cannot otherwise be studied analytically. Antenna aperture measurements typically mandate a large physical distance—the far-field condition. To simulate a uniform plane wave in a limited amount of space, RASCAL is equipped with a precision-manufactured, parabolic rolled-edge reflector (see Figure 1) that collimates the impinging spherical wave from an offset feed, resulting in a uniform plane wave with a 3 × 4 ft quiet zone.

Figure 2. BANTAM range

Researchers lined the enclosure's aluminum walls with a curved pyramid and wedge-shaped absorber to eliminate unwanted reflections from the surrounding structure. The shape and composition of this absorber provide superior performance over larger, conventional absorbers. The absorber acts to reduce measurement noise and provides a 2-18 GHz frequency range. To further reduce the measurement noise floor, a unique trifold entry door not only seals RASCAL during measurements, but can also fold inward to provide access to the tested antenna without disrupting the surrounding area.

In addition to RASCAL's compact range, the facility houses a broadband antenna near-field test and measurement (BANTAM) range, which enables timely, low-cost, near-field test and evaluation of active array technology. Active array evaluation is extremely useful for diagnostic analysis, where far-field data does not reveal the location of a defective element. Simulacrum displays from acquired data allow field distribution imaging of a measured aperture, near-field amplitude distribution data, and mathematically transformed far-field information. Researchers can use the BANTAM range to test large and fragile structures without adding stresses and associated deflections. In addition, BANTAM allows researchers to measure transmit array patterns, which are impossible to measure in a standard compact range.

Researchers built BANTAM inside a rigid aluminum enclosure lined with an 8 in. pyramid and wedge-shaped absorber (see Figure 2) to reduce measurement noise and eliminate unwanted reflections from the array being tested. The absorber also provides a 1-18 GHz frequency range. Currently, BANTAM has planar near-field scan capability, and engineers will add cylindrical near-field scan capability in the near future.

RASCAL provides a unique capability for timely and efficient antenna measurement and evaluation. The compact and near-field ranges feature rapid prototyping capability, modeling and simulation evaluation, and quick setup and teardown of test equipment, all of which results in significantly reduced test and evaluation time and expense.

Mr. Joshua Radcliffe, of the Air Force Research Laboratory's Sensors Directorate, wrote this article. For more information, contact TECH CONNECT at (800) 203-6451 or place a request at http://www.afrl.af.mil/techconn/index.htm. Reference document SN-H-05-01.


Air Force Research Laboratory Technology Horizons Magazine

This article first appeared in the February, 2006 issue of Air Force Research Laboratory Technology Horizons Magazine.

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