Research and Development (R&D) Radar Cross Section (RCS) measurement ranges play a pivotal role in understanding the scattering behavior of targets. These ranges, distinct from Quality Control (QC) ranges, provide insights into the far-field RCS, aiding in the interpretation of scattering data across multiple parameters. In this series of articles, we delve into the world of canonical targets, and our journey begins with the PEC Sphere.
The Sphere in RCS Measurement
RCS measurement ranges come in two primary types: R&D and QC. While QC ranges focus on repeatability and specific targets, R&D ranges aim for accuracy across various parameters. The PEC Sphere, a common target, stands out due to its well-behaved scattering profile and versatility in mounting configurations.
Scattering Features of PEC Sphere
The PEC Sphere’s scattering features are fundamental to understanding its role. It exhibits a specular term from its front and a “creeping wave” that circumvents its surface, contributing to the scattering process. These features are delineated across frequency bands, creating distinct regions: Rayleigh, Resonance, and Optical.
Calibration with PEC Sphere
Calibration is crucial for accurate RCS measurements. The PEC Sphere, with its simplistic geometry, becomes a preferred calibration target. The calibration formula involves measured and theoretical scattered fields, ensuring precision. However, the sphere’s simplicity also introduces measurement errors, notably secondary scattering and mutual coupling.
Limitations and Errors
Standard sphere mounting configurations may lead to errors, impacting the quality of RCS measurements. Secondary scattering between the sphere and its support structure and mutual coupling between the Styrofoam and the sphere’s surface can degrade accuracy. Efforts to minimize errors include adjusting the foam column’s height and modifying the absorber cap.
Operators employ various strategies to mitigate errors. Increasing the foam column’s height, shaping the absorber cap to minimize stray signals, and reducing the foam-sphere interface’s footprint help enhance measurement accuracy. An alternative method involves using low reflectivity strings for sphere support.
Utilizing PEC Sphere for Range Health
Beyond calibration, the PEC Sphere serves as a valuable tool for assessing range health. Its constant RCS as a function of angle allows it to act as a two-way field probe. Rotation and traversal techniques reveal the incident field’s magnitude and phase, aiding in range health assessment. Additionally, the sphere helps evaluate the polarization purity of the incident field.
While the PEC Sphere offers a straightforward and versatile solution for RCS measurements and calibration, its simplicity introduces potential errors. In the next article of this series, we will explore the squat cylinder as a mitigating target, addressing some of the limitations associated with the PEC Sphere.
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- Is the PEC Sphere suitable for all RCS measurement ranges?
- The PEC Sphere is versatile but may have limitations; alternatives could be explored based on specific range requirements.
- How does calibration with the PEC Sphere enhance measurement accuracy?
- Calibration with the PEC Sphere compensates for system frequency response, ensuring precise RCS measurements.
- What are the primary sources of measurement errors in sphere mounting configurations?
- Secondary scattering and mutual coupling are common sources of errors in standard sphere mounting configurations.
- Can the PEC Sphere be used for polarization purity assessment?
- Yes, the PEC Sphere, as a body of revolution, has no cross-polarization response, aiding in assessing polarization purity.
- Are there alternative methods for supporting the PEC Sphere during measurements?
- Using low reflectivity strings provides a cleaner configuration and accurate RCS response.