Atec Agilent-8490 Series - Manual (Page 3)

3
Quality assurance in
specifications
The following examples demonstrate
the reliability and comprehensiveness
of specifications. Although the
absolute accuracy for a 3 dB attenu-
ator is specified as ±0.3 dB, test data
statistics indicate an expected value
of 3 dB ±0.20 dB from dc to 18 GHz.
Similarly a 30 dB attenuator is speci-
fied as ±1.0 dB, but typically is no
worse than 30 dB ±0.75 dB from dc to
18 GHz. The other attenuation values
are also specified as conservatively.
In addition, Agilent precision attenu-
ators meet more comprehensive
performance standards. Linear
phase response is an example. Not
only is wide bandwidth significant,
but also linear phase response is
an important parameter for applica-
tions where pulse distortion must
be kept to a minimum. The excellent
linearity of the Aglilent attenuators is
typified in the accompanying illustra-
tion of an actual network analyzer
measurement.
Applications
Ruggedness, reliability and small
size make these attenuators useful
both on the bench and in systems
applications. With their high accuracy
and low SWR they are ideally suited
for extending the range of sensitive
power meters for higher power mea-
surements and for “padding” poorly
matched devices to improve system
SWR.
These same characteristics lend
themselves to applications as
calibration standards in attenuation
and RF substitution measurements.
With their broad dc to 26.5 GHz
frequency range and reasonable cost,
general applications, such as the
reduction of power level to sensitive
components and instrumentation
systems, are attractive and appropri-
ate uses for these attenuators.
Accuracy
The accuracy of an attenuator directly
affects the accuracy of the measure-
ment where the attenuator is used. In
fact, attenuators are used extensively
as the standard against which other
instruments or devices are calibrated.
Aglilent’s fixed attenuators achieve
flat frequency response (typically a
few hundredths of a dB) and overall
accuracy (typically ±2 % of value
in dB at 26.5 GHz) through the use
of thin-film attenuator cards. These
cards are composed of high stabil-
ity tantalum nitride resistive film
deposited on a sapphire or alumina
substrate.
Center trace is phase response of 8491A
–6 dB attenuator from 1.0 to 2.0 GHz taken
with Agilent 8410 network analyzer. Top and
bottom traces are ±1° calibration. Linear
phase component has been compensated
for with a line stretcher. Response,
therefore, shows nonlinear phase deviation
of < ±1/2° over 1 to 2 GHz band.
Economy
Automated procedures have resulted
in economies of scale in production
and testing. The automated resistive
film deposition process permits high-
volume manufacture with excellent
yield. Furthermore, characteristics are
consistently uniform; hand “touch-
up” is not required to meet specifica-
tions. Automatic testing means
exceptionallythorough, high-accuracy
measurements can be performed in
appreciably shorter time than could
be done manually.
The overall result is outstanding
attenuator performance at attractive
prices.
Calibration Data
Optional calibration data
Use of calibration data has always
been an effective means of reducing
measurement uncertainty at RF and
microwave frequencies. This data is
available for Agilent’s fixed attenu-
ators as Option 849xx- UK6. Data
which is generated by an automatic
network analyzer provides a tabulated
list of attenuation and SWR’s at 26 to
67 frequencies (see table 2). Measure-
ments to 60 dB are directly traceable
to NBS standards and feature very
low measurement uncertainties.
Option 849xx-UK6 data is available
when the attenuators are first purchas-
ed and recalibrations are available
through Agilent Customer Service
Centers around the world.