Model 8754A
INSTRUMENT DESCRIPTION
Introduction
The 8754A Network Analyzer consists
of
an internally leveled 4to 1300 MHz swept source with crystal
markers, athree input tuned receiver with two independent measurement channels,
and
a
CRT
display with
rectangular
and
polar graticules. Together with appropriate signal separation accessories,the 8754Aisa
complete stimulus/response test system
that
measures magnitude
and
phase characteristics
of
linear net-
works by comparing the incident signal with the signal transmitted by the device
or
reflected from its input.
The basic transmission measurements described here are: insertion loss
or
gain, insertion phase, and trans-
mission coefficient,
S21
or
S12.
Basic reflection measurements are: return loss, from which SWR can be
calculated, and reflection coefficient, SII
or
S22'
from which impedance can be calculated
or
read from a
Smith
Chart
overlay.
Block Diagram Description
The source provides RF to the test device. It uses two varactor tuned microwave oscillators, one swept up
in frequency from 3.6
to
4.3
GHz
and
one swept down in frequency from 3.6 to 3.0 GHz, in a
"see-saw"
configuration. The oscillator outputs are mixed and the difference frequency
is
amplified to provide the 4
to
1300
MHz
RF output.
An
internal leveling loop maintains constant RF
output
powerlevel over the sweep.
The receiver provides signal processing
to
convert incident (R)
and
test (A
and
B)
inputs
to
dc levels for
display. Signal separation accessories route the signal incident
at
the test device
to
the Rinput
and
the
reflected and transmitted signals
to
the A
or
Binputs. The receiver uses the sampling technique to convert
the three input signals
to
1
MHz
IF
for detection while maintaining theirmagnitude andphase relationships.
An
automatic phase lock loop tunes the receiver
to
the frequency
of
the Rinput signal; the A
and
Binputs
are used as full range test inputs. Two measurement channels allow measurement
of
any two parameters
using asingle test setup.
For
simultaneous transmission and reflection measurements
the
A
or
B
IF
is switched
to
the detectors on alternate sweeps. Absolute magnitude
of
the three inputs as well as the magnitude
ratio
and
phase angle difference between the Rinput
and
either
of
the test inputs are processed for display
on
the built-in CRT.
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