6
Attenuators
39
Attenuators
Applications
Agilent fixed and step attenuators1find use in a wide variety of
applications for signal conditioning and level control.
• Reducing signal levels
• Matching impedances of sources and loads
• Measuring gain or loss of a two-port device
Key specifications
• SWR
• Accuracy
• Repeatability
• Life
SWR
Most attenuators use some form of distributed thin-film
attenuating element, designed to operate over multi-octave
ranges and for low SWR match at input and output. The SWR
characteristic is controlled with careful design of the element as
well as the transition from RF connector to the element’s
planar geometry.
When an attenuator is inserted into a test network, the
interaction of its SWR and the network SWR results in
frequency-varying mismatch, which degrades the accuracy of
the measurement. The amount of variation often exceeds the
flatness specification of the attenuator. As an example, if at a
given frequency, a 3 dB attenuator with SWR of 1.22 at each
port is inserted into a microwave network that has a source and
load SWR of 1.35, the variation from the expected 3 dB change
could be as great as ±0.5 dB. This change is due to SWR alone
and points out the importance of the SWR specification in a
precision attenuator.
Accuracy
The accuracy of an attenuator directly affects the uncertainty
of the measurement where the attenuator is used. In many
measurement and metrology applications, attenuators are the
basic standard against which other components and instruments
are calibrated.
Agilent attenuator accuracy specifications always include the
effect of frequency response. And, Agilent attenuators use
“edgeline” coaxial structure technology to achieve low-insertion
loss and SWR resulting in better accuracy.
Agilent attenuators achieve flat-frequency response and
high accuracy through the use of thin-film attenuator cards.
These cards are composed of high-stability tantalum nitride
resistive film, deposited on sapphire or alumina substrates.
Advanced design and state-of-the-art processes in the
deposition stages allow precise control of the geometry and
thus the attenuation value. The result is very flat frequency
response and greater accuracy.
Ultimate specified accuracy of RF/microwave attenuators is
limited by the accuracy to which National Institute of Standards
and Technology (NIST) can measure, plus the uncertainty of the
measurement transfer process which calibrates the production
test equipment. See Figure 1, on the next page, for an accuracy
traceability example. At Agilent, performance to specifications
is verified by fully testing each attenuator with an ATE system
including an automatic network analyzer (ANA). In turn, the ANA
is periodically calibrated using standards traceable to NIST.
Each published specification has been established using a
“specification budget” process. This process provides for
“guardbands” to account for transfer uncertainties between
NIST, Agilent Metrology Labs, and the Agilent production test
systems. Figure 2, on the next page, shows how the specification
budget is allocated.
1
See Waveguide chapter for additional products.
www.agilent.com/find/accessories
Attenuators
40
Attenuators
Repeatability
Fixed attenuators are often used as standards of reference
in microwave measurements. Therefore, the accuracy of the
measurement depends not only on the reference accuracy but
on the repeatability of the insertion processes. Typical production
test situations might require hundreds of connects/disconnects
per day. So, measurement repeatability depends strongly on
the connectors used. Agilent attenuators use precision type-N
and APC-7 connectors, with repeatability that exceeds the
International Electrotechnical Commission (IEC) standard for
7-mm connectors. For higher frequencies, Agilent uses 3.5-mm
connectors that are fully SMA compatible, but are more rugged
and repeatable than SMA. For applications to 50 GHz, Agilent
uses 2.4-mm connectors that also have larger mating surfaces
for rugged and repeatable connections. Design verification testing
of 3.5-mm connectors showed virtually no test deterioration even
after 1000 connections. For step attenuators, the repeatability
of the internal RF connections is also of concern. Agilent uses
an “edgeline” transmission line structure in which the outer
conductor is a continuous ground plane and only the center
conductor is switched to insert or remove an attenuation step.
Keys to achieving long-term repeatability include precision control
of all dimensions that affect contact pressure, careful selection
and control of plating processes, and careful monitoring and
control of the assembly process. The result is a step attenuator
with repeatability specified at 0.03 dB maximum over 5 million
cycles per section.
Life
The life of step attenuators is usually specified in cycles; i.e.,
the number of times a given attenuator section switches from
one position to another and back. Agilent determines life by
cycling attenuators to the point of degradation. Typically, Agilent
attenuators in life cycle tests perform to specification for at least
twice as many cycles as warranted. Agilent step attenuator
families have a specified life of 5 million cycles per section
(except the Agilent 355E,F). This long life results in lower cost
of ownership by reducing periodic maintenance, downtime,
and repairs.
0.15
0.12
0.09
0.06
0.03
0
–0.03
–0.06
–0.09
–0.12
–0.15
Actual value (dB)
Uncertainty in
transfer accuracy
±0.03 dB
±0.10 dB
±0.15 dB
Agilent
reference
standard
calibrated
by NIST
Agilent
calibration
laboratory
standard
Agilent
production
test standard
Figure 1. Accuracy traceability example.
Figure 2. Guardband example.
6
21.0
20.8
20.6
20.4
20.2
20.0
19.8
Attenuation (dB)
19.6
19.4
19.2
19.0
Published
specification
±
1 dB
Agilent production
specification
±
0.8 dB
Guardband
Typical
performance
±0.5 dB
6
Attenuators
41
Fixed
Agilent 8491A/B/C, 8492A, 8493A/B/C
Agilent Technologies coaxial fixed attenuators provide precise
attenuation, flat frequency response, and low SWR over
broad frequency ranges. Attenuators are available in nominal
attenuations of 3 dB and 6 dB, as well as 10 dB increments
from 10 dB to 60 dB. These attenuators are swept-frequency
tested to ensure specification compliance at all frequencies.
Calibration points are provided on a nameplate chart attached
to each unit (except for the Agilent 8491C).
Agilent 8498A high-power attenuator
The Agilent 8498A Option 030 is designed to meet the needs of
high-power attenuation applications in the RF and microwave
frequency range. It is a 25 watt average, 30 dB fixed attenuator
with a frequency range of dc to 18 GHz. The maximum peak
power specification is 500 watts (dc to 5.8 GHz) and 125 watts
(5.8 to 18 GHz). Available only in a 30 dB version, the unit
offers a 1.3 SWR and ±1 dB accuracy at 18 GHz. Large
heat-dissipating fins keep the unit cool even under continuous
maximum input power conditions.
Agilent 8490D 50 GHz fixed attenuator
Agilent Technologies coaxial fixed attenuators have been the
standard for accurate flat response and low SWR. The Agilent
8490D offers exceptional performance to 50 GHz using the 2.4-mm
connector. Attenuation values available are 3, 6, 10, 20, 30, and
40 dB. Ideally suited for extending the range of sensitive power
meters or for use as calibration standards, these broadband
attenuators are manufactured with the same meticulous care
as their lower frequency counterparts.
Agilent 11581A, 11582A, 11583C
attenuator sets
A set of four attenuators (3, 6, 10, and 20 dB) is furnished
in a walnut accessory case. The Agilent 11581A set consists of
Agilent 8491A attenuators; the Agilent 11582A set, Agilent
8491B attenuators; the Agilent 11583A set, Agilent 8492A
attenuators; and the Agilent 11583C set, Agilent 8493C
attenuators. These sets are ideal for calibration labs or where
precise knowledge of attenuation and SWR is desired.
Agilent 86213A attenuator set
Provides a set of four, 3, 6, 10, and 20 dB, 75 ohm type-N
attenuators in a walnut accessory case (Agilent 0955-0765,
0955-0766, 0955-0767, and 0955-0768), respectively. Used
for reducing power and improving match. SWR is 1.12 to
1.3 GHz and 1.3 to 3 GHz. Attenuation accuracy is ±0.5 dB.
Agilent 8493A
Agilent 8492A
Agilent 8490D
Agilent 8498A
Agilent 8491A/B/C
www.agilent.com/find/accessories
6
Attenuators
42
Fixed
Frequency Maximum
Agilent range Maximum input
Attenuation accuracy (± dB)
model (GHz) SWR power 3 dB 6 dB 10 dB 20 dB 30 dB 40 dB 50 dB 60 dB Connectors
8491A dc to 12.4 1.2 to 8 GHz 0.3 0.3 0.5 0.5 1.0 1.5 1.5 2 N (m, f)
3 to 30 dB 1.3 to 12.4 GHz
40 to 60 dB
8491B dc to 18 1.2 to 8 GHz 0.3 0.3 to 12.4 GHz 0.6 0.6 to 12.4 GHz 1.0 1.5 1.5 2 N (m, f)
3 to 30 dB 1.3 to 12.4 GHz 0.4 to 18 GHz 1.0 to 18 GHz
40 to 60 dB 1.5 to 18 GHz
8491C dc to 18 1.2 to 8 GHz 0.3 to 12.4 GHz 0.4 to 12.4 GHz 0.6 0.6 to 12.4 GHz 1.0 ———N (m, f)
3 to 30 dB 1.3 to 12.4 GHz 0.4 to 18 GHz 0.5 to 18 GHz 1.0 to 18 GHz
1.5 to 18 GHz
8492A dc to 18 1.15 to 8 GHz 0.3 0.3 to 12.4 GHz 0.6 0.6 to 12.4 GHz 1.0 1.5 1.5 2 APC-7
3 to 30 dB 1.25 to 12.4 GHz 0.4 to 18 GHz 1.0 to 18 GHz
40 to 60 dB 1.35 to 18 GHz
8493A dc to 12.4 1.2 to 8 GHz 0.3 0.3 0.5 0.5 1.0 ———SMA (m, f)
3 to 20 dB 1.3 to 12.4 GHz
30 dB
8493B dc to 18 1.2 to 8 GHz ±0.3 dB 0.3 to 12.4 GHz 0.6 0.6 to 12.4 GHz 1.0 ———SMA (m, f)
3 to 20 dB 1.3 to 12.4 GHz 0.4 to 18 GHz 1.0 to 18 GHz
30 dB 1.5 to 18 GHz
8493C dc to 26.5 1.1 to 8 GHz 0.5 to 18 GHz 0.6 0.3 0.5 0.7 1.0 ——3.5 mm (m, f)
3 to 30 dB 1.15 to 12.4 GHz 1.0 to 26.5 GHz
40 dB 1.25 to 26.5 GHz
1
0.6 0.5 0.6 1.0 1.3
8498A dc to 18 1.15 to 8 GHz 25 W avg. —— —— 1.0 ———N (m, f)
30 dB 1.25 to 12.4 GHz 500 W peak
1.30 to 18 GHz (dc to 5.8 GHz)
125 W peak
500 W/ms
max. per pulse
(5.8 to 18 GHz)
Specifications
Specifications
Frequency
Agilent range Maximum
Option: 003 006 010 020 030 040
model (GHz) input power Atten. 3 dB 6 dB 10 dB 20 dB 30 dB 40 dB
Connectors
8490D dc to 50 1 W avg. Attenuation: M in : 0 to 50 GHz 2.5 5.4 9.4 19.2 29.2 38.2
Max: 0 to 26.5 GHz 3.9 6.9 10.9 21.3 31.3 42.5
Max: 26.5 to 50 GHz 4.8 7.8 11.3 21.7 31.7 42.5
SWR: Max: 0 to 26.5 GHz 1.15 1.15 1.15 1.15 1.15 1.08
Max: 26.5 to 40 GHz 1.25 1.25 1.25 1.25 1.25 1.15
Max: 40 to 50 GHz 1.45 1.45 1.45 1.45 1.45 1.25
2.4 mm (m, f)
1
1.27 for Option 006.
2 W avg.
100 W peak
6
Attenuators
43
Fixed
Fixed attenuator ordering information
A
8
(0.312)
7.6
(0.30)
2 Flats 180
° apart
7 (0.275) across
Dimension A
3, 6, 10, 20 dB: 27 (1.06)
30, 40 dB: 29 (1.14)
Agilent 8490D
13
(0.50)
40
(1.55)
19
(0.75)
A
8
(0.312)
8
(0.312)
2 Flats 180°
apart
6.4 (0.25) across
8
(0.312)
Dimension A
3, 6, 10, 20 dB: 33.8 (1.330)
30, 40 dB: 36.8 (1.450)
Agilent 8493C
Agilent 8493A,B
Dimensions are in mm (inches) nominal, unless otherwise specified.
Agilent 849 Option Option
0D: dc to 50 GHz 003: 3 dB UK6: Commercial calibration
1A: dc to 12.4 GHz 006: 6 dB test data with certificate
1B: dc to 18 GHz 010: 10 dB
1C: dc to 18 GHz 020: 20 dB
UKS: Commercial calibration certificate
2A: dc to 18 GHz 030: 30 dB
3A: dc to 12.4 GHz 040: 40 dB
2
3B: dc to 18 GHz 050: 50 dB
2
3C: dc to 26.5 GHz 060: 60 dB
2
8A: dc to 18 GHz
Agilent 8490/91/92/93/98 series ordering example
1
3C
010
UK6
1
Each order must specify an attenuation option.
2
Not available on all models. See specification table.
Frequency range Attenuation Calibration documentation
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