Atec Agilent-8490 User Manual

• High accuracy

• Low SWR

• Broadband frequency

coverage

• Small size

Agilent 8491A/B, 8493A/B/C,
11581A, 11582A and 11583C

Coaxial Attenuators

Technical Overview

Description

Agilent’s coaxial fixed attenuators
provide precision attenuation, flat
frequency response, and low SWR
over broad frequency ranges (dc to

26.5 GHz) at low prices. Attenuators
are available in eight attenuation

values: 3, 6, 10, 20, 30, 40, 50, and

60 dB; with performances specified
from dc to 26.5 GHz; and with choice
of four connector types: Type-N, SMA1,

and APC 3.52.

These attenuators are all tested

on a state-of-the-art precision analyz­erto assure specifications over
the full frequency ranges. Although
the 8493C is not specified above

26.5 GHz, it performs resonance
free to 34 GHz with only a small
loss in performance.

Precision construction

The attenuators employ a film on

an attenuator card as the resistive

element. The uniformity and repeat­ability of the film deposition process
result in high accuracy and low SWR
over very wide frequency ranges.

The 8493C features thin-film­tantalumnitride on a sapphire
substrate for exceptional precision
performance to 26.5 GHz. In fact, it
performs resonance-free to 34 GHz,
the top frequency limit of the APC-3.5

connector.

The choice of connector type and­material also ensure accurate and
repeatable attenuation. The 8491A/B
attenuators are furnished with Type-N
connectors whose dimensions are
compatible with either MIL-C-71 or
MIL-C-39012 connector specifica-

tions.

These connectors are stainless

steel for long wear and high repeat­ability. The 8493A/B attenuators are
furnished withSMA type connectors.

The connectors are heat treated

beryllium copperfor greater strength

and wear.

Quality assurance in testing

The flat frequency response and low
SWR of the attenuators areassured
over the entire frequency range by
full frequency band testing on a state­of-the-art precision analyzer. Full
frequency band testing ensures that
narrow resonances in the frequency
band are not over-looked. Actual
attenuation values taken at dc, 4, 8,
12, 18, and 26.5GHz are stamped on
the attenuator body for permanent
and easy reference.

Testing each attenuator with a state­of-the-art precision analyzer brings
standards lab accuracy to production
testing because the system can
determine its own measurement
uncertainties and compensate for
them in the testing process. System
calibration is derived from precise
physical standards which are directly
traceable to the National Bureau of
Standards. In addition, automatic
testing eliminates the possibility of
human error in setting instrument
controls, taking data, or making

calculations.

The 8493C is furnished with theAPC

3.5 connector which is compatible
with standard SMA connectors but
is more rugged and offers improved
repeatability over hundreds of con-

nections.

1. As per USASI Committee C83.2 compatible with OSM, ARM, WPM, BRM, NPM, etc.

2. Mate with MIL-C-71 or MIL-C-39012 connectors.

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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 mea­surements 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 appropri­ate uses for these attenuators.

Accuracy

The accuracy of an attenuator directly
affects the accuracy of the measure­ment 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 stabil­ity tantalum nitride resistive film
deposited on a sapphire or alumina
substrate.

Quality assurance in
specifications

The following examples demonstrate
the reliability and comprehensiveness
of specifications. Although the
absolute accuracy for a 3 dB attenu­ator 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 speci­fied 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 attenu­ators 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 applica­tions where pulse distortion must
be kept to a minimum. The excellent
linearity of the Aglilent attenuators is
typified in the accompanying illustra­tion of an actual network analyzer
measurement.

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 < ±° 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 high­volume manufacture with excellent
yield. Furthermore, characteristics are
consistently uniform; hand “touch­up” is not required to meet specifica­tions. 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 attenu­ators 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). Measure­ments 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 purchas­ed and recalibrations are available
through Agilent Customer Service

Centers around the world.

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