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Agilent PN 89400-13
Extending Vector Signal Analysis to 26.5 GHz
with 20 MHz Information Bandwidth
Product Note
The Agilent Technologies 89400 Figure 1. The Agilent 89410A
series vector signal analyzers provide vector signal analyzer and
unmatched signal analysis capabilities 71910A wideband surveil-
from traditional spectrum analysis to lance receiver together form
transient analysis, analog and digital a wideband vector signal
demodulation, high-speed spectrum analyzer system.
monitoring, phase noise analysis, and
more. They are used in applications
as wide ranging as surveillance, signal
monitoring, digital communications,
radar signal analysis, and underwater
acoustics.
For some applications, the vector
System Description The vector signal analyzer has two
signal analyzer's information band-
The wideband vector signal analyzer input channels, each with a band-
width and frequency coverage has
system consists of two major compo- width of 10 MHz. Normally, this
been a limitation. Instruments such
nents: an 89410A two-channel vector would represent the maximum band-
as the Agilent 89441A are limited
signal analyzer and a 71910A wide- width of the signal to be analyzed.
to frequencies below 2.65 GHz and
band surveillance receiver with a However, the 89410A is capable of
information bandwidths of 7 MHz.
wideband IF and quadrature outputs. treating the signals on each channel
This precludes the analysis of many
The vector signal analyzer provides as two parts of the same signal. That
spread spectrum, radar, and satellite
the user interface and display, and is, the signal going into channel one
signals which typically occupy more
performs all of the signal processing. represents the real part of a complex
than 7 MHz bandwidth and may exist
The 71910A is basically a microwave signal, and the signal going into chan-
only at microwave frequencies.
spectrum analyzer with additional nel two represents the imaginary part.
features to optimize it for surveillance These two signals are usually referred
By combining two Agilent products--
and signal monitoring applications. to as the in-phase and quadrature-
the 89410A vector signal analyzer
In this application, it converts the RF phase components, or simply I and Q.
and the 71910A wideband surveillance
or microwave signal into a baseband The vector signal analyzer digitizes
receiver--into a single measurement
signal which can be further processed the I and Q signals which are, by them-
system, the unique capabilities of the
by the vector signal analyzer. As the selves, real signals and then combines
vector signal analyzer can be used
front end of the measurement system, them internally into a single complex
on signals with 20 MHz bandwidth at
it also provides the necessary gain signal of the form I+jQ or CH1+jCH2,
frequencies up to 26.5 GHz.
or attenuation. where j represents the square root of
negative one. This new complex signal,
This product note describes how to
which exists only in digital form, has
configure, calibrate, and operate a
a maximum bandwidth of 20 MHz,
measurement system capable of wide
or twice the input bandwidth of the
bandwidth vector signal analysis.
vector signal analyzer.
In the wideband vector signal analyzer to provide access to all the measure- does not. If you intend to make tradi-
system, the analog I and Q signals are ment and analysis features of the tional scalar spectrum measurements
generated in the wideband IF module vector signal analyzer. The example with the system, the display section
of the microwave receiver as shown program is written in Instrument should be included. System configura-
in Figure 2. The IF has a bandwidth BASIC. It can be run on the 89410A, tion is also simplified when the MMS
of 100 MHz which ensures a relatively or on an external controller. Contact display section is available. If the sys-
flat frequency response over the cen- your local Agilent sales representa- tem will be used primarily for vector
ter 20 MHz used in this system. A flat tive for information on how to obtain signal analysis, the MMS display is
IF is important in vector signal analy- the example program. redundant since all analysis and dis-
sis. An IF with a significant amount play can be done by the 89410A.
of amplitude unflatness or group delay System Configuration
distortion would produce significant This section describes the necessary To support measurements of the
errors. This is especially true for mod- components, the physical connections complex (I+jQ) output signal of the
ulation analysis where the IF charac- between components, and the soft- 71910A, the 89410A vector signal
teristics would introduce distortion ware required to create a wideband analyzer must have Option AY7
in the time domain characteristics of vector signal analysis system. Two (Second 10 MHz Channel) and Option
the signal. For example, group delay system configurations are described: AYA (Vector Modulation Analysis)
distortion in the IF would result in one includes the Modular Measure- installed. To control the system or
increased inter-symbol interference ment System (MMS) display and one perform the system calibrations via
in a digitally modulated signal. In this Instrument BASIC as described
system, the microwave receiver is
always used at its widest bandwidth
to obtain the best accuracy. The vec-
tor signal analyzer is responsible for
reducing the measurement bandwidth
to 20 MHz and below.
When the microwave receiver is used
at frequencies below 12.8 GHz, the
spectrum obtained using I+jQ is mir-
rored about the center frequency.
There are two ways to compensate for
this mirroring. The first is to simply
swap the I and Q outputs. While this
works, it's inconvenient and makes
calibration more difficult. A simpler
way to compensate for the mirroring
Figure 2. The IF module generates I and Q signals using quadrature mixer. Calibrations
is to conjugate the complex signal.
compensate for imperfections such as DC offset, gain errors, and delay mismatch. The
In other words, I