Text preview for : 5991-3470EN Simplifying Complex Benchtop Measurements with USB Switches - Application Note c20140917 part of Agilent 5991-3470EN Simplifying Complex Benchtop Measurements with USB Switches - Application Note c20140917 Agilent 5991-3470EN Simplifying Complex Benchtop Measurements with USB Switches - Application Note c20140917 [7].pdf
Back to : 5991-3470EN Simplifying C | Home
Keysight Technologies
Simplifying Complex Benchtop
Measurements with USB Switches
Application Note
Introduction
Switches and switch matrices are widely used for the routing of RF and microwave signals in high-speed ATE systems.
As today's devices and products become more complex, there is an increasing need for the speed and flexibility of
switching systems capable of connecting multiple signals or instruments to multiple devices under test (DUTs).
On a smaller scale, the same is true in R&D and design validation when developing such products or when creating
test routines that will be used later in manufacturing. Even on the bench or in a small system, dependable switching
can improve efficiency and save time.
For day-to-day testing, the Keysight Technologies, Inc. U1810B USB coaxial switch combines excellent RF perfor-
mance with the convenience of USB connectivity. Operating from DC to 18 GHz, this single-pole/double-throw
(SPDT) unit connects directly to the inputs of instruments such as network analyzers and spectrum analyzers using
a rugged Type-N connector. The plug-and-play USB connection provides power and the control interface. A simple
push button provides manual control, a soft front panel enables more advanced control from the screen of a PC, and
programmatic control is supported using C++, LabVIEW, Keysight VEE, and more.
This application note provides a brief overview of switching topologies before outlining three measurement scenarios
that include the U1810B USB switch. The end of the note provides pointers to related information about the U1810B
and the instruments used in the scenarios.
2
Comparing Switch Topologies Utilizing a Convenient Alternative
Several factors are important in the selection of an appropriate switch The Keysight U1810B USB coaxial switch provides a unique combina-
for a specific application: frequency range, switching speed, settling tion of excellent RF performance and the convenience of USB con-
time, power handling and operating life are near the top of the list. nectivity in a small package. Operating from DC to 18 GHz, this SPDT
Additional considerations include electrical characteristics such as device is configured to route signals between one common port and a
insertion loss, return loss, repeatability, isolation, voltage standing- pair of switched ports. The unit connects directly to instruments such
wave ratio (VSWR) and termination. as network analyzers and spectrum analyzers using a rugged Type-N
connector; the switched ports use female SMA connectors (Figure 2).
Less obvious is the effect of switch topology. In the simplest terms,
two types may be used: the switch ports are either on the same Because the U1810B contains unique electro-mechanical switch tech-
electrical plane or on different electrical planes. Each has plusses nology, it offers exceptionally long operating life. With a specified life
and minuses. of five million cycles (10 million cycles typical), the U1810B reduces
the cost of test and enhances system reliability. Its insertion-loss
In conventional switch designs, all connector ports are on the same repeatability is guaranteed to be 0.03 dB, ensuring measurement accu-
plane. This type of topology is commonly found in the large, front- racy and extending calibration intervals. Isolation of greater than 70 dB
mounted switch matrices used in complex ATE systems. Placing all enhances signal integrity by minimizing crosstalk between channels.
the ports on the same plane saves space and thereby reduces the
size of the resulting switch matrices. The plug-and-play USB connection is used to provide power and the
control interface. This eliminates the need for external power supplies
Figure 1 shows two typical connections between a conventional or switch drivers and simplifies measurement setups, especially when
switch and an instrument: both methods require the use of one or using current-generation Keysight network and spectrum analyzers
more RF cables between the switch, the instrument and the DUT. If that have at least one USB port.
a rigid cable is used, its length and bend angle must be taken into
consideration. If a semi-rigid or flexible cable is used, it has to remain Under manual control, the U1810B provides push-button switching
stationary during the measurement because even the slightest move- between ports 1 and 2. A soft front panel enables more advanced
ment will change the mismatch and affect the measurement accuracy. control from the screen of a PC, and in fully automated testing it can
If cable pairs are used, as shown on the right in Figure 1, they must be be controlled programmatically using C++, LabVIEW, Keysight VEE,
equal in length to ensure phase accuracy. and more.
Figure 1. The use of extra RF cables adds complexity and may affect the
accuracy or repeatability of measurement results.
Figure 2. The U1810B USB coaxial switch simplifies test setups while adding
For some applications, good measurement results can be obtained versatility.
when the switch ports are on different planes. This topology makes
it possible to add switching to the test instrument or system without
requiring additional RF cables. While this may simplify setups and
eliminate the issues described above, it puts practical limits on the
breadth and complexity of the switching solution. For example, creat-
ing multi-tier switching or a switch matrix would take up considerable
space and require use of long interconnect cables.
3
Illustrating Example Applications
Three simple measurement scenarios demonstrate what can be done
with the U1810B USB switch: network analysis, cable-and-antenna
testing and spectrum analysis.
Simplifying network analysis
Adding a pair of U1810B switches to a two-port network analyzer
can be used to enable comparisons between two devices or simplify
calibration or compensation (Figure 3). In this configuration, one
connection can be used to measure two devices in either the
frequency or time domain.
During calibration or compensation, the process typically requires a
series of connections and disconnections involving the reference unit
and the DUT. With a pair of U1810Bs, the reference can remain con-
nected and be measured as needed while a series of DUTs is
connected and measured.
To increase throughput with a four-port network analyzer, the addition
Figure 3. Switching saves time in network analysis when comparing DUTs
of four USB switches enables connection of up to eight devices--
or when performing calibration or compensation.
DUTs, cal units, references, etc.--to the analyzer (Figure 4).
Figure 4. A quartet of U1810B switches doubles the number of devices that
can be connected to a four-port network analyzer.
4
Enhancing cable-and-antenna testing
Installation and maintenance of specialized systems--radio networks,
satellite ground stations, radars--often requires field verification or
adjustment of cables, antennas, filters, diplexers and duplexers. When
engineers and technicians venture out to remote locations in poten-
tially harsh conditions, they want to carry a minimum of equipment
and complete their measurement tasks as quickly as possible.
With capabilities such as cable-and-antenna testing (CAT) and
network analysis, the Keysight FieldFox handheld analyzers deliver
bench-caliber RF and microwave measurement results in the field.
Adding a U1810B USB switch to FieldFox can reduce the time spent
connecting, disconnecting and reconnecting cables or devices. As
shown in Figure 5, two cables can be connected through the U1810B
to the FieldFox analyzer. This could be used to quickly compare a
known-good cable to one or more potentially damaged cables, and this
scenario can include distance-to-fault measurements with a suitably
configured FieldFox. Measurements such as return loss and cable
loss also can be performed.
Extending spectrum analysis
A variety of systems use multiple transmitters and receivers.
Examples include multi-channel radar systems and wireless LAN or
mobile communications systems that use multiple-input/multiple-
output (MIMO) technology.
Even though the addition of a USB switch to a Keysight X-Series signal Figure 5. A single USB switch unit is a useful and time-saving addition
analyzer won't enable correlated measurements between signals, it to a field measurement kit.
will accelerate back-and-forth comparisons between a pair of con-
nected transmitters, antennas or other DUTs up to 18 GHz (Figure 6).
Figure 6. In spectrum analysis applications, the U1810A coaxial switch
enables quick comparisons between different signals or antennas.
5
Conclusion
Even in small-scale configurations, high-quality switching offers
convenience and efficiency by reducing the number of connects,
disconnects and reconnects needed to accomplish common day-to-
day measurements. Because the U1810B utilizes advanced electro-
mechanical switching technology, it can be expected to provide long
life and excellent electrical performance in a variety of applications.
Related Literature