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Performance Variables
A well-designed radome provides environmental protection with minimal
effect on the RF performance of the antenna and system. Electrically,
the main concern for the radome is its contribution of insertion loss.
Insertion loss reduces the available signal, decreasing effective radiated
power and G/T (the ability of the antenna to receive a weak signal).
Radomes can also increase antenna sidelobes, resulting in interference
with other communication systems, and increasing the likelihood of signal
detection and interception from unintended observers. Radomes can also
impact antenna polarization schemes, depolarizing circularly polarized
antennas, for example. Depolarization is generally very small for spherical
radomes, but can be severe for radomes with large incident angles such
as those used on missiles or aircraft. Some other electrical effects
of a radome on antenna performance include change in antenna beam width
and shifting of the antenna boresight.
Figure 10: Hydrophobic surfaces cause water to bead,
minimizing impact to RF performance under wet conditions.
In addition to the effects of the radome material, nothing degrades
radome performance more than a thin sheet of water. Water has a very high
dielectric constant and loss tangent at microwave frequencies.
Non-hydrophobic surfaces cause water to stick to the radome creating
a thin film, which serves as a shield to RF transmission resulting in
significant signal attenuation [5]. Well-designed radomes feature a
hydrophobic surface that causes water to bead up and run off as shown
in Figure 10. Even in high rain conditions, a radome with a hydrophobic
surface has little additional attenuation [6].
In conclusion, a radome is often considered as an "afterthought" to
an RF/microwave system but it is essential to overall system performance
and lifetime cost. A well-designed antenna radome not only provides
environmental protection that extends the operating lifetime of the
antenna and its components, it also contributes to stable electrical
performance over the lifetime of the system with reduced maintenance
efforts and downtime, thus supporting reduced total cost of ownership.
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