When Can a Protective Layer of Paint Degrade Performance?
As demand for performance and profit drives satellite operating frequencies beyond 30 GHz, larger earth terminal antennas are required. Earth terminal performance becomes increasingly impacted by any degradation to surface accuracy or structural integrity leading to beam defocusing or pointing error.
Raul Stavoli, Director, Systems Engineering, at SATCOM Technologies' San Jose facility and three co-authors, recently presented at MILCOM 2014 a paper that sets out engineering processes and procedures for determining potential degradation of performance of large antennas due to painted surfaces. The authors describe the technical approach used to assess the effects of paint on an 18-Meter parabolic antenna.
"The standard surface paint color for parabolic antennas is white and very specific formulations of white paint are used throughout the industry," Stavoli said. "Non-standard paint color such as olive drab and desert tan are used for military camouflage applications. However, the work described in this paper is motivated by aesthetic reasons: end-user requirements for non-standard paint colors to blend in with the surrounding environment.
"Non-uniform solar loading due to the use of non-standard paint can cause a loss in earth terminal antenna gain and pointing inaccuracies due to dish defocusing, surface distortion and other changes in the structural geometry.
"The result of our analysis is a paint selection which poses minimal risk to system performance while still meeting the original intended purpose," Stavoli said.
The paper, titled "Paint vs. Performance - The Effects of Paint On Large Aperture Ka-Band Antennas," is co-authored by Stavoli and Tom Hagstrom, General Dynamics C4 Systems; Roy Axford, SPAWAR Systems Center; San Diego and Angela Wang, Lockheed Martin Sunnyvale, California.
The paper and a companion PowerPoint presentation was delivered at MILCOM 2014 earlier this month in Baltimore, Maryland.
"Due to the increasingly large dish diameters and increasingly small signal wavelengths, the effect of surface paints on the antenna assembly are becoming significant, "Stavoli said.
"This paper provides a technical approach to quantitatively characterize these errors as a function of surface paint non-uniform solar absorption. Methods to assess system link availability performance using three-sigma beam spreading losses and one- sigma beam pointing losses due to paint effects are also described. In addition, assessment of service availability using the three-sigma outage duration and expected number of occurrences is provided."
"The analysis methodology presented in this paper that comprises antenna finite element analysis for thermal, structural and radiation models, can be readily applied to the next generation V and Q bands antenna design, in order to determine not only paint effect, but in general the best criteria design to optimize performance on antenna pointing, tracking and gain. As the frequency gets higher, structural and thermal effects become more dominant."
The paper concludes with a description of a structured process to assign risk and opportunity likelihood and consequence to each candidate paint selection.
Click here to download the paper.
Click here to download the PowerPoint presentation.