Specifications

Use the bandpass-impulse response to show the location of a
discontinuity in time or distance, as indicated by changes in its
magnitude. Unlike the lowpass mode, no information as to the type of
the discontinuity is available. A typical use for this mode is to measure
devices—such as, filters, waveguide, high-pass networks, bandpass
networks—where a low-frequency response is not available.
The bandpass-impulse response for various impedance discontinuities
is shown in Figure 8-5. As we can see, no information about the type of
discontinuity is available.
An example of using the bandpass-impulse response is the pulse
height, ringing, and pulse envelope of a bandpass filter (Figure 8-6).
Use the phasor-impulse response with bandpass response to
determine the type of an isolated impedance discontinuity.
After the bandpass-impulse response has been isolated, the
phasor-impulse response for a resistive-impedance-level change is a
peak that goes positive (R>Z
0
) for the real part of S
11
and negative for
R<Z
0
. The imaginary part remains relatively constant. In each case the
peak is proportional to the reflection coefficient. The phasor-impulse
response for a shunt capacitance is a negative-going peak in the
imaginary part of S
11
. For a series inductance, it is a positive going
peak.
TIME DOMAIN TIME
MEASUREMENTS DOMAIN
8-6 MS462XX OM
BANDPASS IMPULSE RESPONSE
l
Magnitude Measurement Only
l
Location of Discontinuities
l
No Information on Type of Disconti
-
nuities
CIRCUIT ELEMENTS
R>Z
O
SHUNT C
SERIES L
IMPEDANCE
Bandpass Impulse Response
O
R<Z
11
S LOG MAGNITUDE
Figure 8-5. Bandpass Impulse
Response
LOG MAG.
0.5000
GHz
4.0000
REF=20.000 dB 20.000dB/DIV
LOG MAG.
0.5000 GHz
4.0000
10.000dB/DIVREF=30.000 dB
BP w/G
S21 FORWARD TRANSMISSION S21 FORWARD TRANSMISSION
Figure 8-6. Example of Bandpass-Impulse Response
PHASOR IMPULSE BANDPASS RE
-
SPONSE
l
Real and Imaginary Measurement
l
Information On Type of Discontinu
-
ity