RF Engineering I
Laboratory #1
1
Using the Network Analyzer
OBJECTIVES
The purpose of this experiment is to get familiarized with the operation and use of
the Network analyzer and learn to make reflection and transmission measurements to nport devices.
EQUIPMENT LIST
1.
2.
3.
4.
5.
6.
7.
(1) HP-8712C, RF Network Analyzer
(1) RF Amplifier (Mini Circuits ZJL-3G)
(1) N-Type Calibration kit (HP-85032E)
(1) Type-N Accessory kit
(1) Power Supply with cables
(2) Network analyzer cables
(2) N(f) to SMA(f) adapters (HP-1250-1636)
DISCUSSION
The Network Analyzer is used to measure S parameters (scattering parameters) of
one or more port devices. The S parameters are very useful to characterize devices at
high frequencies where the traditional measurements are very difficult to measure. These
parameters are defined in terms of traveling waves moving along transmission lines and
they completely characterize the behavior of one of more port devices. The S parameters
are simple to use because
 Matched loads are used in their determination. At high frequencies matched
loads are relatively easy to realize, while the short and open circuits required
for the traditional low frequency parameters are much more difficult to
achieve and furthermore, are more likely to make an active device unstable.
 When only the magnitudes of the S parameters are required, it is not necessary
to be concern with the position of the reference plane, planes at which the
DUT (device under test) begins and the connecting test network ends. The
reference planes only affects the phase of the S parameters.
Consider the two-port device in the figure. The S parameters are define as
Input
a1
b1
Port 1
Two-Port
DUT
Network
Figure 1: S parameters of a 2 port device.
By: Prof. Rubén Flores Flores
Output
a2
b2
Port 2
RF Engineering I
Laboratory #1
2
b1  S11a1  S12a2
b2  S 21a1  S 22a2
 b1   S11 S12   a1 
b    S
 
 2   21 S 22  a2 
where
S11 
S 21 
S 22 
S12 
b1
a1 a
b2
a1
b2
a2
b1
a2
input reflection coefficien t with output properly matched.
2 0
foward transmiss ion coefficien t with output properly matched.
a2 0
ouput reflection coefficien t with input properly matched.
a1  0
reverse transmiss ion coefficien t with input properly matched.
a1  0
The analyzer has an RF signal source that produces an incident signal that is used
as a stimulus to the device under test. Your device responds by reflecting a portion of the
incident signal and transmitting the remaining signal. Figure 2 shows how a DUT
responds to an RF source stimulus.
Figure 2: DUT Response to an RF Signal
The network analyzers require to be calibrated with a set of standards (OPEN,
SHORT and LOAD) terminations. This calibration will enhance the precision of the
measurements discarding any losses due to cables and adapters to the DUT.
Measurement calibration is a process that improves measurement accuracy by
using error correction arrays to compensate for systematic measurement errors.
Measurement errors are classified as random, drift and systematic errors. Random errors,
such noise and connector repeatability is not correctable by measurement calibration.
Also, drift errors, such as frequency and temperature drift are not correctable by
calibration.
Systematic errors, such as tracking and crosstalk, are the most significant errors in
most RF measurements, which can be corrected by calibration.
Repeatable systematic errors are due to system frequency response, isolation
between the signal paths and mismatch and leakage in the test setup. Mismatch error
By: Prof. Rubén Flores Flores
RF Engineering I
Laboratory #1
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result from differences between the DUT's port impedance and the analyzer's port
impedance. If the DUT is not connected directly to the port, the mismatch errors due to
cables, adapters, etc. are considered part of the DUT mismatch errors. If the analyzer is
calibrated all these mismatches are canceled. See figure 3
Figure 3: Mismatch Errors
There are few types of calibration. Each calibration method is suited to the type
of measurement you will be performing. There are:
 Normalization Calibration - Analyzer stores data into memory and
divides subsequent measurements by the stored data to remove
frequency response errors.
 Transmission Calibration - Removes systematic errors caused by
frequency response, isolation and source match. For narrowband
measurements only.
 Reflection Calibration - Removes systematic directivity, source math
and frequency response errors. For narrowband measurements only.
 Conversion Loss Calibration - Use normalization calibration but also
zeroed the internal detectors to help compensate for drift due to
temperature changes.
PROCEDURE
Calibration Steps for the RF Amplifier
1. Enter Measurements Parameters
a. Set input power level to avoid amplifier saturation.
1. Press POWER hardkey
2. Press Level softkey -2, and dBm.
b. Set desired frequency range.
1. Press the FREQ key to access the frequency softkey menu.
2. Change the low end frequency to 10 MHz, press Start 10 MHz
3. Change the high end frequency to 100 MHz, press Stop 100
MHz
4. You can also set the frequency range by using the Center and
Span softkeys. Press the Center and enter 55 MHz and press
Span and enter 90 MHz.
By: Prof. Rubén Flores Flores
RF Engineering I
Laboratory #1
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c. Set desired number of measurement points. This allows selection of
the number of measurement points in a sweep. As the number of
points increases, frequency resolution increases and sweep speed
decreases.
1. Press the MENU hardkey
2. Press the Number of Points softkey and enter 801.
2. Performing Transmission Response Calibration
a. Select calibration method and calibration kit.
1. Press CAL Enhanced Response.
b. Connect the four standards open, short, load and through cable in
each port as shown in figure 4.
1. The instrument will prompts you to connect the four standards
2. Press Measure Standard after connecting each standard.
Figure 4: Calibration Standards
3. The instrument will measure each standard and then calculate
the new calibration coefficients. The message "Calibration
complete" will appear.
4. Save the calibration into memory.
a. Press SAVE RECALL, Select Disk, Non-Vol RAM
Disk.
b. Press Prior Menu, Define Save, Cal ON
c. Press Prior Menu, Save State to save the instrument
state file. The filename appears on the screen as
STATE#.STA (where # is a number the analyzer selects
from 0 to 999).
Performing RF Amplifier Measurements
1. Connect the DUT as illustrated in figure 5 (RF OUT to amplifier’s input
and RF IN to amplifier’s output)
2. Measure the S11, S21 in Log format
a. Transmission (S21) and Reflection (S11)
1. Press MEAS1, Transmissn, FORMAT, Log Mag, SCALE,
Autoscale
By: Prof. Rubén Flores Flores
RF Engineering I
Laboratory #1
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2. Press MEAS2, Reflection, FORMAT, Log Mag, SCALE,
Autoscale
3. Press DISPLAY, More Display, Split Disp FULL split
4. Use markers to interpret the data
5. Print the amplifier’s frequency response.
Figure 5: Equipment Setup for a Transmission Response Measurement
b. Use Smith Chart to measure reflection (S11)
1. Press MEAS1, Reflection, FORMAT, SmithChart, SCALE,
Autoscale
2. Press MEAS1, Reflection, FORMAT, SmithChart, SCALE,
Autoscale
3. Use markers to interpret the data.
4. Print the Smith chart.
3. Connect the DUT as illustrated (RF OUT to amplifier’s output and RF IN
to amplifier’s input)
4. Measure the S22, S12 in Log format
a. Transmission (S12) and Reflection (S22)
1. Press MEAS1, Transmissn, FORMAT, Log Mag, SCALE,
Autoscale
2. Press MEAS2, Reflection, FORMAT, Log Mag, SCALE,
Autoscale
3. Press DISPLAY, More Display, Split Disp FULL split
4. Use markers to interpret the data.
5. Print the amplifier’s frequency response.
b. Use Smith Chart to measure reflection (S22)
1. Press MEAS1, Reflection, FORMAT, SmithChart, SCALE,
Autoscale
2. Press MEAS1, Reflection, FORMAT, SmithChart, SCALE,
Autoscale
3. Use markers to interpret the data.
4. Print the Smith chart.
By: Prof. Rubén Flores Flores
RF Engineering I
Laboratory #1
6
RESULTS
1. Plot the reflection parameters of the RF amplifier in both Logarithmic Magnitude
and Smith Chart format.
2. Plot transmission parameters of the RF amplifier in both Log Mag and Polar chart
format.
3. Plot the input and output impedance of the RF amplifier.
4. Use instrument markers to fill out the following table.
Frequency
Transmission
|S21|
|S12|
Reflection
|S11|
|S22|
Impedance
|Input|
|Output|
QUESTIONS
1. Why is it necessary to calibrate the instrument?
2. What type of parameters the analyzer measure and what is the advantage over
traditional measurements?
3. Mention the different types of calibration methods and their advantages.
4. Which errors the instrument is capable to minimize and which don’t?
5. Is capable the instrument to measure the S parameters of devices of three or more
ports? If possible, how could I measure the transmission and reflection
parameters?
By: Prof. Rubén Flores Flores