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Keysight Technologies
Techniques for Precise Measurement
Calibrations in the Field
Using FieldFox Handheld Analyzers
Application Note
Abstract
This application note, which applies to cable and antenna and vector network analysis,
discusses recent advances in vector network analyzer calibration and compares
measurements using different calibration types for a variety of RF and microwave devices
including cables, filters and amplifiers. A FieldFox handheld analyzer is used to make the
various measurements, as it can perform precise measurements and analysis in the field.
Introduction
Installation, troubleshooting and maintenance of RF and microwave systems and components require measurements
of their reflection and transmission characteristics within a variety of indoor and outdoor environments and conditions.
These measurements are typically made using a handheld vector network analyzer (VNA) having a user calibration
that is preformed in the field. Measurement accuracy, calibration convenience, sweep speed and analyzer portability
are extremely important requirements as testing often occurs under extreme conditions ranging from high elevations,
such as outdoor tower and mast installations, to confined spaces, required in shipboard, aircraft and vehicle
applications. The required measurements are easily obtained using a VNA with a simple user calibration and fast
measurement sweep, which are available on FieldFox handheld analyzers.
Measurement accuracy when using a VNA is directly related to the type of user calibration selected and the associated
test configuration. The test configuration includes test cables and adapters required to interface the Device Under
Test (DUT) to the VNA. The types of calibrations available on FieldFox range from the built-in calibration (CalReady),
which is available immediately at instrument turn-on, to more complex user calibrations requiring measurements from
a set of high-quality calibration standards.
Selection of the calibration type (cal type) is often a trade-off between measurement accuracy, speed and the
complexity of the calibration process. For example, Figure 1 shows a comparison of the measured insertion loss (S21)
of a short coaxial cable using two different cal types available on FieldFox. The yellow trace is the cable measurement
using an innovative cal type named QuickCal and the blue trace is the measurement of the same cable using a
traditional Full 2-Port mechanical calibration. The Full 2-Port calibration process requires that the user make seven
connections to various high-quality calibration standards while QuickCal was performed without the need for any
calibration standards. As shown in the figure, there is very little difference between the two measurement results
yet the QuickCal has a fairly simple calibration process that is very convenient in field operations. In general, as each
test configuration may require the use of adapters and test cables between FieldFox and the DUT, it is important to
understand the applications and limitations of each cal type available in FieldFox. This application note will discuss
recent advances in VNA calibration and will compare measurements using different calibration types for a variety of
RF and microwave devices including cables, filters and amplifiers.
Figure 1. Measurement comparison of a coaxial cable using a traditional Full 2-port
calibration (blue) and the rapid QuickCal (yellow) available on a FieldFox vector
network analyzer
Analyzer Hardware Conigurations
This section of the application note will Forward-only Forward Reverse
introduce the various FieldFox hardware
DUT DUT DUT
configurations available for measuring
one-port and two-port devices. FieldFox Port 1 Port 2
handheld analyzers include vector network
analyzers (VNA), cable and antenna test Port 1 Port 2
(CAT) analyzers, spectrum analyzers, and
combination analyzers that include VNA,
CAT and spectrum analyzer capabilities in
one instrument. FieldFox is a field-ready,
precision instrument compliant with
MIL-PRF-28800F Class 2, and MIL-STD-
810G, Method 511.5, Procedure 1, for
operation in explosive environments (type Transmission/reflection Full 2-port
tested). Class 2 equipment is designed (a) (b)
for the most rugged environments which
Figure 2. Network analyzer signal paths when measuring a device under test (DUT) using an analyzer
include unprotected and uncontrolled with (a) Transmission/Reflection (T/R) hardware and (b) Full 2-Port hardware
environmental conditions. Configured
as a VNA, FieldFox measures complex
device parameters, namely the magnitude while additional information regarding the need to physically turn the device around.
and phase of reflection and transmission CAT and spectrum analyzer modes can A switching matrix within the analyzer
characteristics of one-port and two-port be found in Keysight Technologies, Inc. internally routes the incident test signal
DUTs. The measured complex parameters application notes [1] and [2]. between Port 1 and Port 2. In addition to
are also known as scattering parameters the convenience of measuring the DUT
(S-parameters) and will be reviewed later The network analyzer hardware determines in both directions, using a Full 2-Port
in this application note. Configured as a how the DUT is measured, either in configuration can provide the highest level
CAT analyzer, FieldFox also measures the the forward direction only, using a of measurement accuracy by allowing the
reflection and transmission characteristics transmission/reflection (T/R) hardware characterization and removal of most of
of a DUT but only reports the magnitude configuration, or in both the forward and the systematic errors from the test system.
characteristics. Both the VNA and CAT reverse directions using a Full 2-Port
modes include the innovative QuickCal configuration. Figure 2a shows the signal Characterization of systematic errors is
that remove the effects of any test cables paths to and from the FieldFox VNA hav- performed during the user calibration
and adapters attached to the instrument ing a T/R hardware configuration. With a and the Full 2-Port calibration is one of
and also corrects for drift errors in the T/R configuration, the test signal leaves the most accurate methods of VNA cali-
calibration caused by temperature changes. Port 1 of the analyzer and measurements bration. This application note will discuss
Configured as a spectrum analyzer, are made only in the forward direction, and compare several cal types including
FieldFox is a high-performance receiver either as reflection from the input to the Full 2-Port, Enhanced Response and the
capable of measuring the frequency DUT or as transmission through the DUT. less accurate but very simple Response
content of known and unknown signals, With this configuration, the reflected (Normalization) calibrations. A FieldFox
interference and/or noise. FieldFox spec- signals are measured at Port 1 of the VNA with Full 2-Port hardware can per-
trum analyzers not only have capabilities analyzer and forward signal transmission is form all available cal types. FieldFox with
found in benchtop spectrum analyzers, measured at Port 2 of the analyzer. When T/R hardware can only perform Enhanced
but also include a unique feature known using a T/R configuration, measurements Response and Response (Normalization)
as InstAlign that provides improved in the reverse direction would require that calibrations.
amplitude accuracy across the entire RF the DUT be disconnected, turned around,
and microwave frequency range from and re-connected. In contrast, Figure
turn-on and through