Specifications

Frequency range
The top frequency limits of
switches are set by the size
of the coaxial structure and
connectors. SMA connectors
operate from DC to 20 GHz.
SMB connectors operate from
DC to 4 GHz. Switch specifica-
tions such as Insertion Loss,
Isolation, and VSWR degrade
with increasing frequency
operation.
Insertion loss
Insertion loss is a measure
of signal loss in the switch or
signal path (in dB). It is a
function of switch construction,
cable types, cable lengths, cable
connectors, dielectric material,
cable-to-connector construction,
and other components used in
the signal path. For a switch, it
is also a measure of how much
power the switch will dissipate
internally. Low insertion loss
is important because power is
expensive, especially at high
frequencies. Insertion loss for
quality switches is very low and
ranges from 0.2 dB or less at
low frequencies (DC to 4 GHz)
to 0.6 dB at higher frequencies
(20 GHz). Typically, flexible
coax cables have 50% higher
insertion loss compared to
hand-conformable or semi-rigid
coax cable. Flexible cables that
exhibit low insertion loss
at frequencies above 4 GHz
can be very expensive.
Isolation (or crosstalk)
Isolation is a measure of signal
attenuation between two signal
paths (in dB). High isolation in
switches is important to almost
every measurement application,
because it prevents unwanted
signals from interfering with
adjacent ports. High isolation
is a key factor in determining
the quality of a switch. High
quality switches attenuate
signals 90 dB to over 120 dB
between ports at frequencies
of DC to 4 GHz.
VSWR (or SWR)
VSWR is a way of measuring
the amount of reflected power
in a signal path. For a switch,
it specifies how well the con-
nectors and switch are matched
to an ideal 50-ohm transmission
line, for example. It is a measure
of the ratio of the standing
wave’s highest voltage ampli-
tude to the lowest voltage
amplitude in the signal. Low
VSWR is crucial in a test
system when signal routing
configurations involve multiple
components in series. VSWRs
of 1.1 to 1.5 are typical of high
quality switches, representing
99.8% to 96% power transmis-
sion, respectively.
Life (reliability)
The life of a switch is usually
specified in cycles, and a cycle
represents switching from one
position to another and back.
Life specifies how many cycles
the switch can be actuated and
still maintain its specifications.
Repeatability is closely tied to
the life of the switch. Quality
switches typically guarantee
their specifications over the
life of the switch, which can
be over 5 million cycles! Some
switch manufacturers specify
life as the point at which
the switch may experience
mechanical failure. Therefore,
signal degradation can actually
occur much earlier.
Repeatability
Repeatability is a measure of
the change of Insertion Loss
from cycle to cycle (in dB) over
the specified lifetime of the
switch. Repeatability plays an
important role in any test sys-
tem. In automated test sys-
tems where switches are used
for signal routing, every switch
will add to the repeatability
error. Such errors cannot be
calibrated out of the system
due to their random nature.
Quality switches exhibit
0.03 dB variation in Insertion
Loss over the specified life
of the switch.
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