Evaluation Engineering - 18

RF/MICROWAVE SWITCHING

of high-performance switches available
on each," said Campbell. "The benefits of
PXI and LXI for switch applications depend on where you're coming from and
where you're going. If you already have
a PXI test station and you need generalpurpose switching, it makes sense to
add PXI switches to your existing setup.
However, the startup cost of a new PXI
system can be prohibitive if all you need
is switches."
Campbell continued, "The LXI platform
enables simpler integration with your existing test setup since LXI instruments
do not require a PXI chassis and controller. Also, if you have specific, advanced
switching needs, Keysight offers fully
customizable LXI modules to cater to
your specific application."
According to Semancik at MTS, "PXI
offers a widely accepted and convenient
formfactor for most switching applications." MTS offers both 3U and 6U
switching configurations, allowing users to select a solution that best fits their
specific application requirements. "LXI is
a common choice for RFIU solutions that
require a variety of components, such as
amplifiers, attenuators, delay lines, custom circuitry, etc., to be combined within
the switching subsection," he continued,
adding that other control interfaces are
also available.
Stasonis at Pickering Interfaces also
weighed in on PXI and LXI. "For PXI, the
benefit is modularity," he said. "This is
very important for a switching system
with multiple functions-a simple example would be a switching system incorporating changeovers, matrices, and
multiplexers."
Stasonis said LXI does not impose the
mechanical constraints of PXI, providing
the ability to more easily address high I/O
count applications. "The fact that LXI devices have local intelligence means less
reliance on the host computer, freeing this
CPU to concentrate on other instrumentation. LXI is also superior in remote test
applications because of the ubiquity of
Ethernet in business."
And PXI vs. LXI deployments aren't
mutually exclusive. Continued Stasonis,
"We offer our LXI/USB modular chassis
that can support up to six PXI modules

18

EVALUATION ENGINEERING APRIL 2020

and can be controlled via USB or Ethernet,
bringing together the advantages of both
platforms."
As for its part, Universal Switching has
chosen not to participate in the PXI market. "We prefer the stability and flexibility
of the LXI platform as we can provide better solutions for our client base," Alderson
said, allowing the company to offer highperformance solutions in unique configurations without the packaging and size
constraints that the board-based PXI
platform demands.

Switches
At the heart of switching systems are the
switches and relays themselves, including electromechanical, solid-state, and
MEMS devices. The electromechanical
devices still have a large share of the RF/
microwave market for many applications.
"Since MEMs switches and solid-state
switches are still low-power components,
they have limited applicability in the military/aerospace and telecom infrastructure markets that we serve," said Gibson
at VTI Instruments. Semancik concurred,
saying, "Specific application requirements, as expected, continue to drive RF/
microwave needs. Many intermediate and
depot-level test systems require high-performance switching systems which still
largely rely on mechanical devices." And
Heuer at Rohde & Schwarz expects electromechanical relays to be increasingly
important of from DC to 40, 50, and 67
GHz, and he added that solid-state and
high-end electromechanical relays will
enable faster switching between antennas and/or IC ports.
According to Stasonis at Pickering
Interfaces, "Many of the existing MEMS
devices are unable to switch the signal
and power levels we require for our target markets; at present, the technology is
lagging behind what we require. We don't
have the confidence at this point that it is
delivering to its potential. We have more
confidence in solid-state switches and
offer a large range; our sales continue to
be steady."
Alderson at Universal Switching said,
"We build many solid-state switching
products but, in our experience, most
ATE test engineers prefer a relay-based

product due to the characteristics provided by a relay such as low loss, zero distortion, and high isolation-all of which
affect test measurements of a UUT. In our
opinion, the limited availability of MEMs
components and their associated cost/
performance do not yet make them a viable technology to use in the automatedtest-equipment arena."
And Campbell at Keysight commented,
"As testing moves from connectorized devices to wafers, customers need fast, longlived switches for automatic test systems.
Modern solid-state PIN and FET switches
are becoming popular for low-power measurements of RFIC components, handheld
power amplifiers, and SAW filters."
Campbell added that the company's
electromechanical switches feature a
wiping motion that clears debris from the
conductor every time the switch moves.
"Our electromechanical switches offer the best isolation performance in the
market," Campbell said. "In addition,
Keysight released the first 67-GHz switch
(SPDT) back in 2011, and it is still one of
the highest-performance 67-GHz switches
in the market now."
Xidas has been at work since 2015 developing what Sourabh Dhillon, director
of business development, called "the industry's first miniature electromagnetic
RF/microwave relay." The work is based
on a $20 million investment and 15
years of micro-engineering research at
the University of California, resulting in
several patents and an IP portfolio.
Dhillon said the company has just finished engineering evaluation units and
will phase both SPST and SPDT versions
into production in the third quarter of
this year. Dhillon cited several features of
the devices, including footprint, density,
and weight. "We can 'hot' switch up to
5 W of power at 6 GHz in a 4-mm x 4-mm
x 2-mm footprint," he said. "Hot switching
is a key requirement for automated test,
since it's not practical to switch on/off instrumentation prior to moving to the next
channel in your test." He said solid-state
CMOS or traditional MEMs relays of the
same size cannot hot switch and are primarily intended for integration with digital amplifiers where the amplifier can be
switched on/off to enable cold-switching
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