RF and Microwave Amplifiers
SELECTION GUIDE
Microwave broadband signal amplification
– Broadband performance up to 50 GHz, replacing several narrow band amplifiers,
simplifies test setup and optimizes the operating range of your test systems
– Excellent noise figure and high gain, significantly reduces overall test system noise
figure
– High output power, boosts available power for measurements
Introduction
The Keysight Technologies, Inc. 83006/017/018/020 /050 /051A and N4985A test
system amplifiers of fer ultra broadband performance up to 50 GHz. With excellent noise
figure relative to their broad bandwidth and high gain, these products can be used to
significantly reduce test system noise figure. By replacing several amplifiers with a single
broadband product, test setups can be greatly simplified. You can place this amplification
power where you need it by using remotely-locatable Keysight power supplies. In addition,
the Keysight 87415A provides octave band performance from 2 to 8 GHz.
The Keysight 87405B/C and N4985A-S30/S50 low noise preamplifiers provide
exceptional gain and flatness. The 87405B/C preamplifiers are very portable and
come with a convenient probe-power bias connection which eliminates the need for an
additional DC power supply, making them an ideal front-end preamplifier for a variety of
Keysight instruments.
The N4985A-S30/50 system amplifiers are a high-performance broadband amplifier
featuring baseband RF (> 100 kHz) through millimeter wave (> 30 GHz) frequency
coverage. These amplifiers are designed to be a multi-use laboratory RF amplifier as a
gain block for frequency domain applications, or as a time domain pulse amplifier. Its
small size and versatile performance make it an excellent choice for general purpose
gain block with moderate power output in a single package, potentially replacing two or
three narrower-band amplifiers.
N4985A system amplifier
87405B/C preamplifier
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System amplifiers
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What Selection Criteria Do I Consider?
Today’s engineers are constantly seeking for amplifiers
of exceptional gain and power performance over a broad
bandwidth.
There exists a very large number of potential electrical
specifications that can be applied to a microwave power
amplifier selection. These elements are defined by the
following characteristics:
Frequency range
RF and microwave applications range in frequency
from 100 MHz for semiconductor to 60 GHz for satellite
communications. Broadband accessories increase test
system flexibility by extending frequency coverage.
However, frequency is always application dependent and
a broad operating frequency may need to be sacrificed to
meet other critical parameters.
Noise figure
Noise figure is the primary specification for a typical
microwave power amplifier selection. The noise figure is
defined as the ratio of the signal-to-noise power ratio at
the input to the signal-to-noise power ratio at the output.
The noise factor is thus the ratio of actual output noise
to that which would remain if the device itself did not
introduce noise, or the ratio of input SNR to output SNR.
Low noise amplifiers are always preferred as the noise
figure of the system is dominated by the noise figure of
the preamplifier. By adding a preamplifier to noise figure
measurement systems, the total system noise figure can
also be reduced.
F
F
= Fpa + ————
new
F
Where F and G are noise figure and preamplifier gain, both
in linear terms.
NF
= 10 log (F
sys
sys
– 1
pa
) in dB
sys
Output power (P
Among the key specifications for microwave amplifiers are
their power output specifications. Output power at P
refers to the saturated output power, or maximum output
power from the amplifier. This is the output power where
the Pin/P
P
1dB
point. Unlike the gain specification, implicitly it is assumed
that the specification is at an operating point where the
amplifier is exhibiting some degree of non-linear behavior.
With an inherently broadband amplifier, power output as
a function of power input does not vary discontinuously as
a function of frequency. Typically, a wideband microwave
power amplifier that could deliver in excess of several
watts required a solution where numerous narrowband
amplifiers were either multiplexed or switched; often
introducing undesired issues, such as power curve
discontinuities, at frequency cross-over points.
curve slope goes to zero. Output power at
out
refers to the output power during 1 dB compression
sat
& P
1dB
)
sat
Gain
Gain usually is specified within the context of power
output. Often, if no context for power output is given,
then this is assumed to be small signal gain. Conditions
for small signals at the input and output are usually easy
to reproduce and verify, whereas gain and gain flatness
can vary significantly when an amplifier approaches
compression. Gain flatness for an amplifier with a
significant
frequency range is often specified over subsets of the
entire frequency range. Gain and gain flatness typically
include an implicit assumption that the reverse gain from
the output to the input is negligible; i.e. the amplifier is
unilateral.
Typically, gain flatness could only be achieved over narrow
bandwidths with classic reactive matching techniques, such
as those used for internally matched devices. Attempts to
broaden the gain bandwidth of a high-power microwave
amplifier requires trade-offs with resistive matching, or
feedback techniques that take power output. The spatially
combined topology overcomes these limitations.
For systems with a single preamplifier, where the gain of
the preamplifier is greater than or equal to the spectrum
analyzer noise figure, the system noise figure is
approximately equal to the noise figure of the
preamplifier.
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Input and output return loss (VSWR)
Frequency range (GHz)
Isolation
The standing wave ratio, often referred to interchangeably
as VSWR, is the result of wave interference. Peaks and
troughs in a given field pattern remain in a static position
as long as the sources of interference do not change
with respect to each other. Return loss, expressed in
dB, is a measure of voltage standing wave ratio (VSWR).
Isolation is the degree of attenuation from an unwanted
signal detected at the port of interest. Isolation becomes
more important at higher frequencies. High isolation
reduces the influence of signals from other channels,
sustains the integrity of the measured signal, and reduces
system measurement uncertainties.
Return loss is caused by impedance mismatch between
circuits. At microwave frequencies, the material properties
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as well as the dimensions of a network element play a
significant role in determining the impedance match
or mismatch caused by the distributed effect. Keysight
amplifiers guarantee excellent return loss performance
by incorporating appropriate matching circuits to ensure
optimum power transfer through the amplifier and the
entire network.
RF & Microwave Amplifiers Selection Guide
Minimum gain (dB)
15 20 25 30
Up to 4
87405BU7227A
Up to 8
Up to 18
Up to 20
Up to 26.5 U7227B83018A83006A
Up to 30
Up to 50
83050A/N4985A-P15/25 N4985A-S50
Preamplifier
System amplifier
87415A
87405C
83018A
N4985A-S30
83020A
8317A 83020A
U7227F83051A
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