Aerospace & Defense Technology - June 2023 - 33

RF & Microwave Technology
HIGH PERFORMANCE
INTERCONNECT PRODUCTS
Exploring the Silicon Dioxide Dielectric Construction
Semi-rigid cables have previously been the standard cabling
solution for these applications because their solid copper outer
conductor protects the dielectric material inside and provides
superior shielding performance to a comparable flexible construction.
However, RF cables constructed using a silicon dioxide
dielectric are increasingly used throughout the microelectronics
industry for their excellent insulating properties,
low-loss, and high velocity, and to offer semi-rigid cable solutions
that are highly temperature and radiation resistant.
They also provide superior phase and loss versus temperature
performance as the dielectric does not produce a non-linear
change. In addition, silicon dioxide cables provide exceptionally
low hysteresis, with phase and loss values returning to the same
values at a given temperature even after extreme excursions.
The construction of the silicon dioxide coaxial cable begins
with a solid oxygen-free copper center conductor, a silicon
dioxide insulating dielectric, and a stainless-steel jacket with
copper cladding to act as the outer conductor. Connectors in
silicon dioxide cable assemblies should utilize a crack-free, fired
glass seal to provide optimum microwave performance and
hermetic sealing.
Silicon dioxide excels in severe environments and can perform
at temperatures ranging from just above absolute zero to
above 1,000 °C. In addition, the metal and silicon dioxide
dielectric construction naturally makes the cable resist radiation
of more than 100 megarads.
In fact, this cable type has been qualified and is currently
used on numerous high-profile satellite programs, including
technologies created by NASA and the European Space Agency
in applications seeing exposures in the 10s of Gigarads. It has
also been successfully employed in numerous cutting-edge
hypersonic missile designs.
Takeaways
In conclusion, RF cable assemblies are crucial in mission-critical
applications such as hypersonic missiles and satellites.
These systems operate in extreme environments and require
compact, rugged, and reliable RF interconnects to support
communications equipment within a highly confined space.
When selecting an RF cable for these applications, it is
essential to consider critical performance parameters such as
extreme temperatures, attenuation, and phase stability.
Attenuation depends on the cable size selected, the conductivity
of the conductors, and the dielectric constant. Phase
stability is critical and requires compensation for temperature
variations that can degrade the electrical match between
coaxial cable assemblies. Overall, selecting the right RF cable
for applications that must excel in extreme environments
without the ability for routine maintenance requires a balance
between electrical, mechanical, and environmental
requirements and optimal cable design to ensure reliable and
consistent performance over extended periods.
This article was written by Maria Calia, Director, Space and
Missiles, Times Microwave. For more information, visit www.
timesmicrowave.com.
Aerospace & Defense Technology, June 2023
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