Specifications

There are several ways in which all the information
can be displayed on one trace. One method is a polar
display (Figure 3-17). The radial parameter (dis
-
tance from the center) is magnitude. The rotation
around the circle is phase. We sometimes use polar
displays to view transmission measurements, espe
-
cially on cascaded devices (devices in series). The
transmission result is the addition of the phase and
log magnitude (dB) information of each device’s po
-
lar display.
As we have discussed, the signal reflected from a
DUT has both magnitude and phase. This is because
the impedance of the device has both a resistive and
a reactive term of the form r+jx. We refer to the r as
the real or resistive term, while we call x the imagi
-
nary or reactive term. The j, which we sometimes
denote as i, is an imaginary number. It is the square
root of –1. If x is positive, the impedance is induc-
tive, if x is negative the impedance is capacitive.
The size and polarity of the reactive component x is
important in impedance matching. The best match
to a complex impedance is the complex conjugate.
This complex-sounding term simply means an im-
pedance with the same value of r and x, but with x
of opposite polarity. This term is best analyzed using
a Smith Chart (Figure 3-18), which is a plot of r and
x.
To display all the information on a single
S-parameter requires one or two traces, depending
upon the format we want. A very common
requirement is to view forward reflection on a Smith
Chart (one trace) while observing forward transmis
-
sion in Log Magnitude and Phase (two traces). Let
us see how to accomplish this in the MS462XX.
The MS462XX has four channels. Each channel can
display a complete S-parameter in any format on ei
-
ther one or two traces. All four S-parameters can be
seen simultaneously in any desired format. A total
of eight traces can be viewed at the same time.
While this is a lot of information to digest, the
MS462XX’s large LCD color display makes recogniz
-
ing and analyzing the data surprisingly easy.
NETWORK NETWORK ANALYZERS,
ANALYZERS A PRIMER
3-10 MS462XX OM
-90
180
90
0
POLAR DISPLAY
Figure 3-17. Polar Display
50
INDUCTIVE
CAPACITIVE
SMITH CHART
Figure 3-18. Smith Chart