Maintenance and testing tips to ensure optimum radar performance
By Jon Tripp
It’s patronizing to say that shortcuts and poor maintenance habits in the aviation industry can have deadly consequences. However, all too often, such practices are common in regard to the repair and maintenance of nose radomes. Whether intentionally ignored for expediency or merely misunderstood due to the evolution of radomes, OEM specifications are often not strictly followed. This practice must be stopped or weather radar performance may be significantly impacted
The function of the nose radome has dramatically changed over the past two decades. While once it served primarily as a protective shell and aerodynamic fairing for a radar system, the nose radome has evolved into a protective shell that also serves as a window for electromagnetic radiation generated and received by the weather radar. The advent of predictive wind shear radar systems has upgraded the radome structure to functional electrical component status in addition to its protective properties.
The term "radome," derived from the words radar and dome, was originally interpreted as a dome-shaped, radar-transparent structure installed on an aircraft; but is now a general term for any radar enclosure whether it is airborne or ground-based. The information in this article pertains to aircraft-mounted, dome-shaped radar enclosures of the fluted core and honeycomb core radomes currently used on modern commercial jet transport aircraft. However, the information can also be applied to general aviation private planes and/or ground-based radar enclosures of various configurations.
Maintenance of the radome is required to preserve the electrical transmission properties of the unit to design levels. Diminished wind shear detection capabilities of the weather radar system is certain if poor maintenance or inadequate or inappropriate repairs are performed on the radome structure.
The FAA requires aircraft equipped with predictive wind shear radomes to maintain performance at a class "C" level or better. Boeing (which now includes Douglas Heritage products), Douglas and Airbus qualify commercial aircraft radomes through laboratory testing to a class "C" level. As an extra margin of safety, radar system manufacturers are required to demonstrate radar performance to acceptable standards of wind shear detection and performance using a radome with a classification one level lower than the radar system is certified to.
Radomes are classified according to their respective transmission efficiency for the "window," or the part of the radome that is illuminated by the radar antenna in a continuous azimuth or elevation scan. The average transmission efficiencies are rated as follows, from highest to lowest:
Class "A" radomes have 90% efficiency
Class "B" radomes have 87% efficiency
Class "C" radomes have 84% efficiency
Class "D" radomes have 80% efficiency
Class "E" radomes have 70% efficiency
The core selection of the radome reflects the design philosophies of the respective OEM and each core material affects radar performance differently through the core’s inherent properties. Of course, each OEM or manufacturer believes their products and designs are superior to their competitors’ designs. Each has their advantages as well as drawbacks when used on an aerial platform, and each has varying degrees of radar transmission capability, or transmissivity, which is defined as "the act or process of signal transmission by radio waves." Peak radar efficiency and resolution require a clear, distortion-free antenna view through the radome window for transmissivity and reflection (return energy to the radar), with minimal defraction (bending of the radar energy as it passes through the radome).
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