Impact of materIals
on mIcrowave cable
performance
Cables are often the last component considered during system designs. In many
situations, cables are the system’s lifeline. For example, if the cable system used
for data transmission in a spacecraft fails, the communication between the craft
and the ground station could be lost. Cable reliability is based on both durability
and signal integrity and the materials used to engineer the assemblies have a
direct impact on their life in any environment.
The environments in which microwave cable assemblies are being used are be- coming more challenging with exposure
to such conditions as extreme temperatures,
chemicals, abrasion and flexing. Additional
challenges include the need for smaller, lighter
packaging for cable systems that last longer and
cost less. To ensure signal integrity and product
reliability, it is essential to identify the electrical, mechanical, environmental and application-specific constraints that can affect the cable’s overall performance. These variables have
a direct impact on the materials used for cable
dielectric and jacketing as well as the construction of the cable. Also, testing and data analysis
are key to ensuring that the cable will, in fact,
perform reliably in a specific environment.
IdentIfyIng ConstraInts
Environmental influences are having more
of an impact on RF/microwave cable assemblies. Electrical performance is probably the
first and foremost consideration and many
factors can potentially compromise signal integrity, such as internal and external electromagnetic interference (EMI), voltage standing
wave ratio (VSWR) and insertion loss. Electrical performance is typically very reliable when
no other environmental factors are involved.
However, when mechanical, environmental,
or application-specific stress is added, maintaining reliable electrical performance can be
more challenging.
Mechanical stress occurs when cables are
exposed to various types of movement. Flexing
creates kinetic energy in the cable, which can
cause severe damage if not properly managed.
One of the biggest causes of mechanical stress
on cables is when the cable is part of equip-
ment handled by a person. An operator can
kink, pinch or crush a cable by stepping on it
or rolling over it. Therefore, crush and tensile
strength is essential in mitigating mechanical
stress. Also, cables used with portable equip-
ment can come into contact with sharp sur-
faces that cut cables or expose them to abra-
sion. When the complexities of compensating
for vibration or gravity are added, mechanical
stress can significantly compromise stability
and cause premature failure of a cable.
PAUL PINO
W. L. Gore & Associates, Inc., Landenberg, PA
