Aerospace & Defense Technology - December 2023 - 25

RF & Microwave Technology
Cable
Cable
Computer
Computer
Example ME7868A Setup for Cable Testing in Aircraft
Example Cable Testing on Ships with ME7868A
Figure 1: Cable measurement configuration using modular VNA.
Warship and Aircraft System
Challenges
Measuring cable phase and magnitude
performance over frequency becomes
critical as systems become more sophisticated
and complex. This is especially
true in larger vehicles, such as aircraft
and warships, where connections can be
tens of meters in length.
In airborne applications, components
of these critical systems are dispersed all
over the aircraft for tactical or practical
reasons. Many microwave/RF assemblies,
power wires, and high-speed data
cables are routed throughout the airframe
to connect these components.
Cables used in typical aircraft are
exposed to environmental and other
hazardous contaminants. Once airborne,
RF cables also experience repeated
shock and vibration, extreme pressure,
and temperature changes. Despite
these conditions, cables must perform
every time or aircrew and the entire mission
are compromised.
Warships out at sea have their own
set of challenges that affect cable
performance. Shipboard systems are
exposed to extreme and highly variable
conditions, including heat or cold and
corrosive salt spray. RF signals must
travel through the cables at consistent
speeds regardless of these environmental
factors.
Repeated stress to cables during missions
over time can lead to compromised
signal integrity. The result is unreliable
communications, degraded self-protection
systems, lower mission completion
rates, and increased lifecycle costs. Signal-to-noise
ratio, low loss, and shieldFigure
2: Modular, chassis-less 2-port VNA provides advantages for measuring cables on aircraft and
warships.
ing are necessary so outside signals cannot
interfere. All of this creates further
challenges in determining the optimal
coaxial cables and connectors for shipboard
communications.
Testing Cabling on Large Vehicles
To maintain performance of these
systems on large military vehicles, interference
mitigation must be a priority.
Often, vector network analyzers (VNAs)
are used to ensure signal transmission.
Phase is a key parameter for detection
and measurement in many shipboard
RF systems to ensure continuous
transmission and reception of RF
signals with high accuracy and consistent
speeds. There are two primary
elements that can affect a coaxial cable
assembly's phase tracking characteristics
- electrical length and temperature.
As temperatures change, cables do
not precisely track together. The result
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is degradation of phase match. Even a
slight change can adversely affect system
performance.
Fully characterizing long RF/µW
cables once they are installed using vector
S-parameter measurements creates a
connection challenge between the VNA
and the widely spaced cable ends. The
interconnect cables required to connect
the VNA ports to the cable under test
add significant insertion loss and phase
instability to the measurements over the
distances involved. Cable replacement
due to wear-and-tear adds considerable
expense to the test setup, as well.
VNA architecture has evolved and can
effectively address the challenges associated
with large military vehicles. Some
current VNAs have portable port modules
that can connect directly to the cable
under test. Figure 1 shows how cable
measurements on ships and aircraft are
made using this type of VNA. It is consid25

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Aerospace & Defense Technology - December 2023

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