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EKT 441: MICROWAVE ENGINEERING
ME1000 RF Circuit Design Courseware
Power Amplifier Measurement
with Vector Network Analyzer
in collaboration with
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Lab 6 – Power Amplifier Measurement with Vector Network Analyzer
Objectives
1) To characterize power amplifier with reflection and transmission measurement via Vector Network Analyzer.
2) To measure gain compression using power sweep via Vector Network Analyzer
Basic Equipment Setup
Figure 1. General Equipment configuration for PA measurement using VNA.
IMPORTANT INFORMATION:
In measuring a high gain amplifier, it is possible of overloading the amplifier input by causing it to saturate, demonstrate significant non-linearity, and possibly damaging the unit. It can also damage the test equipment due to high power amplification. You should either add more attenuation to the input or output of the amplifier or reduce the RF power of the signal source before repeating the measurement.
For this laboratory, you recall the TRM calibration data from lab 1 by pressing <Save/Recall> and using the knob to select the saved calibration data in the non-volatile memory and finally pressing RECALL STATE
It is best to look at just one channel at a time. That is, when you are looking at transmission measurements, turn Ch 1 off, and when you are doing reflection measurements turn Ch 2 off. When viewing signals, the <Scale>, <Format> and <Marker> menus will be most helpful. Under <Scale>, the AUTO SCALE button can be quite handy at first, but you will likely use it less and less as you get more comfortable with manipulating the display.
Finally, if you hit <Preset> your calibration will need to be recalled. You can verify your calibration at anytime with a TRM short PCB board for reflection and a TRM thru PCB board for transmission. (Preset also sets the “calibration kit” selection to the default kit which generally does not correspond to the TRM PCB boards you will use.)
Transmission Measurements
1. Recall the TRM calibration data (saved in previous lab) from the non-volatile memory.
2. Connect the PA as shown in Figure 1.
3. Do the following setting to reduce the input source power to the PA.
Power : power range manual (PWR RANGE > Man)
: power range –45 to –20 dBm (PWR RANGES 3)
: source power, –40dBm (Enter using keypad follow by <x1>)
4. At the PC/Notebook, open the USB Radio Software. Click Connect to USB Radio button. Under the TX Frontend Control area, click On PA to power up the PA. You shall see the led light blinking in the PA PCB after power on.
5. Choose the following setting to determine the small signal gain of the PA for frequency range of 700 MHz to 1 GHz:
Start : 700 MHz
Stop : 1 GHz
Format : log magnitude
Meas : transmission (or S21)
Scale : autoscale
OBSERVATIONS / DATA RECORDING
a) Find the maximum gain, and the frequency at which it occurs?
Gmax = _____ dB at ______MHz
b) Find the frequency below this at which the gain is reduced by 3dB from the maximum gain.
Gmax – 3dB occurs at _____ MHz.
c) Find the gain at frequency of 868 MHz.
Gain @ 868 MHz = ______dB
6. Change the following setting to determine the isolation of the PA:
Format : log magnitude
Meas : isolation (or S12)
Scale : autoscale
OBSERVATIONS / DATA RECORDING
a) Find the isolation 868 MHz
Isolation @ 868 MHz = ______dB
[Note – Use averaging, smoothing and smoothing aperture if necessary]
b) Elaborate the importance of isolation in amplifier.
Reflection Measurements
- Choose the following setting to determine the input return loss of the PA:
Format : log magnitude
Meas : reflection (or S11)
Scale : autoscale
OBSERVATIONS / DATA RECORDING
a) Find the minimum input return loss, and the frequency at which it occurs?
Min return loss = _____ dB at ______MHz
b) Find the maximum input return loss, and the frequency at which it occurs?
Max return loss = _____ dB at ______MHz
c) Find the input return loss at frequency of 868 MHz.
Return loss @ 868 MHz = ______dB
[Note – Use the marker function to search for maximum and minimum]
- Choose the following setting to determine the output return loss of the PA:
Format : log magnitude
Meas : reflection (or S22)
Scale : autoscale
OBSERVATIONS / DATA RECORDING
a) Find the minimum output return loss, and the frequency at which it occurs?
Min return loss = _____ dB at ______MHz
b) Find the maximum output return loss, and the frequency at which it occurs?
Max return loss = _____ dB at ______MHz
c) Find the output return loss at frequency of 868 MHz.
Return loss @ 868 MHz = ______dB
[Note – Use the marker function to search for maximum and minimum]
Gain compression measurement with power sweep.
- Perform a power sweep at 868 MHz by setting the following:
Sweep Setup : CW Frequency to 868 MHZ
: Sweep Type to Power Sweep
Power : Power Range 1 (–25dBm to 0dBm)
Start : –25 dBm
Stop : –10 dBm
Meas : transmission (or S21)
OBSERVATIONS / DATA RECORDING
a) Define and elaborate the meaning of 1dB compression point.
b) Plot the gain vs power sweep graph. Use marker to locate the P1dB point.
c) What is the VNA setting at 1dB compression point?
P1dB = ______dBm
d) What is the measured gain at 1dB compression?
Gain@P1dB = ______dB
e) Is the above P1dB measure refer to input or output ?
Input P1dB or Output P1dB
References
· Application Note 1287-1, “Understanding the Fundamental Principles of Vector Network Analysis”, Agilent Technologies.
· Application Note 1287-2, “Exploring the Architectures of Network Analyzers”, Agilent Technologies.
· Application Note 1287-3, “Applying Error Correction to Network Analyzer Measurements”, Agilent Technologies.
· Application Note 1287-4, “Network Analyze Measurements: Filter and Amplifier Examples”, Agilent Technologies.
· Product Note 8753-1, “RF Component Measurements: Amplifier Measurements Using the Agilent 8753 Network Analyzer”, Agilent Technologies.
· Thomas H. Lee,“Planar Microwave Engineering”, Cambridge University Press, 2004.
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