USB Coaxial Switches for RF & Microwave Test and Measurement Applications - Application Note 5991-15 part of , text manual preview

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Keysight Technologies
USB Coaxial Switches for RF & Microwave
Test and Measurement Applications

Application Note
Abstract
Coaxial switches are commonly used in applications where RF signal routing
is required between one or more locations, via some form of switch driving
hardware (to power the switch) and software/firmware (to navigate the
various switch paths). Depending on the complexity of the switching matrix,
a considerable amount of setup and configuration will be required. With the
advent of USB, widely recognized for its capability to power up and having a
standard set of embedded drivers in most operating systems (OS), creating a
fully standalone USB switch provides an economically viable alternative for
everyday switching needs. This solution which is literally a pure plug-and-
play device, will save precious development time and hardware setup costs
especially for R&D and design validation groups.

This application note describes features and application examples of a USB
coaxial switch, and various options for measuring multiple devices under test
(DUT) or performing multiple tasks with a single connection.

Introduction
In RF and microwave test systems, coaxial switches are used extensively for sig-
nal routing between instruments and DUTS. Switching matrices allows multiple
tests to be performed with the same setup, eliminating the need for frequent
connects and disconnects. Naturally, this configuration can also be easily auto-
mated and thus increases throughput and efficiency.

Conventional coaxial switches consist of solenoid coils where DC voltages are
needed to bias the coils to latch the RF contact blades to required positions,
typically via an external hardware driver. In the ATE environment, most switch
system integrators will provide a complete driving solution for ease of control
and convenience. A switch driver typically consists of an integrated power
supply with a set of driving interface to support a variety of switching options,
as well as software programmability to facilitate quick design validation and
automated testing.

The U1810B USB SPDT DC to 18 GHz coaxial switch, presents a novel approach
for general switching needs with its standard USB plug-and-play functions that
provide fast and easy setup. Users can conveniently power up the switch via
one of the multiple USB ports on the instrument or PC, without the need for an
external power supply. Precious time can be saved in integrating complex switch
setups (the driving method and pin configuration) as compared to a conventional
coaxial switch.

Inheriting Keysight Technologies, Inc. unique switch technology, the U1810B is
designed to operate for more than 10 million cycles. The exceptional 0.03 dB
insertion loss repeatability is warranted for 5 million cycles. This excellent RF
characteristic significantly reduces downtime for recalibration, improves testing
efficiency, and ultimately maximizes test throughput.

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Applications Examples
Most of the instruments offered by Keysight have built-in USB ports, such as
network analyzers, spectrum analyzers, and oscilloscopes. The U1810B USB
switch can be used easily with any of these instruments, and it's USB 2.0 com-
pliant. Below are some application examples of the USB switch with Keysight's
test instruments.

Using with a network analyzer
Below is an application example where the U1810B is used with a network
analyzer to measure two DUTs with one connection either in frequency or time
domain. Similarly, the U1810B can be used to switch between the DUT and the
reference unit for calibration or compensation. In a traditional test calibration
process, the user needs to remove the reference unit from the network analyzer
after the calibration and connect the DUT to the network analyzer to complete a
measurement. The U1810B helps to eliminate the time and resource to change
the connection between the DUT and the reference unit.

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Using with Keysight's FieldFox Handheld RF
Analyzer
At a cell site, Keysight's FieldFox handheld RF analyzer is used to perform cable
and antenna analysis. With the USB switch, users can extend the capability of
the handheld analyzer to perform return loss, cable loss, and distance-to-fault
(DTF) measurements on two cables. The USB switch can be powered up by
the USB port of the handheld RF analyzer, and hence represents the ultimate
mobility at installation and maintenance sites.

Using with a spectrum analyzer
Spectrum analyzers are commonly used in antenna measurements to measure
the strength of the received signal. With two antennas connected to the USB
switch, the U1810B can be easily toggled to switch between them to perform
the relevant measurements. Once again, this USB switch increases test
efficiency by eliminating the need to disconnect and reconnect the antenna.

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U1810B features
Switch topology
Compared to conventional switch designs where all the connector ports are
on the same plane, Keysight's U1810B helps users to simplify the test setup
without using additional RF cables. Figure 1 below shows a conventional switch
connected to an instrument. Both methods require extra RF cable(s) to be
connected between the switch and the instrument. If a rigid cable is used, the
length and bend angle of the cable has to be taken into consideration. If a semi-
rigid or flexible cable is used, the cable has to be fixed during measurement,
any slight movement of the cable will change the mismatch and affect the
measurement accuracy. Inconsistent cable length pairs may also compromise
the system phase accuracy.

Figure 1. How a conventional switch
is connected to an instrument.

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With Keysight's U1810B, the user can perform the same measurement without
any additional RF cables (Figure 2), thus, avoiding the various test setup and
maintenance issues as highlighted earlier.

Figure 2. How the Keysight U1810B USB switch is connected
to a network analyzer.

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Soft front panel (SFP)

To facilitate ease-of-control of the switches, a fully functional soft front panel
(SFP) provides an alternative virtual interface. With the SFP, users can verify
the device installation and monitor the switch trigger sequence in real time.
This provides a very intuitive way for users to debug and setup their systems,
especially during the initial install. One important additional feature incorporated
is the User Defined Sequence program. It provides an extended user interface to
key in specific switching sequences and delays, especially when more than one
U1810B is connected to the same host. In the User Defined Sequence window
(shown in Figure 3), users can set the individual switch to Port 1 or 2 and the
delay before the second sequence. The generated programmed sequence can
then be either saved for re-access later, or duplicated onto another system.
Another built-in feature is the ability to access the log commands of the switch
executions