To measure and test basic parameters of RF/wireless function blocks. These blocks include a coupler, a mixer,
an amplifier, a splitter, a voltage controlled oscillator, a couple bandpass filters, and a couple attenuators.
For part 1, we will focus solely on attenuators, filters, splitters, and couplers.
2. Equipment
Mini-Circuits splitter/combiner (ZX10-2-42-S+). Here is the datasheet.
Mini-Circuits 6dB Attenuator.
Mini-Circuits 12dB Attenuator.
Mini-Circuits bandpass filter (VBF-2360+). Here is the datasheet.
Mini-Circuits bi-directional Coupler (ZABDC10-25HP-S). Here is the datasheet.
Mini-Circuits 50 Ohm terminators (Quantity = 2).
Custom Oregon Tech "OIT" bandpass filter. Here is a picture of the filter.
50 Ohm coaxial cable assemblies for testing along with an assortment of adapters/connectors (N-type and SMA type).
Network Analyzer with a max frequency of at least 3 GHz. In this lab we will use
Agilent FieldFox RF Analyzer N9912A.
3. Report guidelines
For the lab report, you will create a PowerPoint presentation (or use a similar presentation program), save it as a PDF, and
submit it on-line according to the instructions given in class. The presentation should be tutorial in nature; your target audiences are
other engineers and scientists who are interested in learning more about circuits and electromagnetism.
Your presentation will have 16 slides. Please include a slide number in the footer of each slide. To earn full credit your presentation must
contain the slides in the order asked for in this lab. If you miss a slide, please leave a blank slide in its place so that you have
still have exactly 20 slides total. Your first two slides should be:
Slide 1: Title slide with our name, student ID number, date, lab name, class number/title.
Slide 2: A team picture or insignia with the names of your teammates.
4. Measuring the performance of RF attenuators
The Mini-Circuits components you are going to measure are shown in Figure 1.
The lab is split into two parts. Here you will work on part 1 of 2.
Figure 1. Mini-Circuits components measured in this lab (for parts 1 and 2).
There are two different attenuators measured in this lab: a 6dB and a 12 dB attenuator.
For the first part of this lab, you are going to use the network analyzer to measure the scattering parameters (
S11 and
S21) and VSWR for these attenuators.
Attenuators are basic RF building blocks, and their function is to reduce signal levels by dissipating
RF power as heat.
When we refer to a "6dB attenuator", we mean a well-matched two-port device that will reduce the signal level
by 6dB over a certain bandwidth. An ideal 6dB attenuator
has insertion loss = 20log10|S21|=-6dB and
return loss = -20log10|S11| = ∞ dB from "DC to daylight". Of course, there is no such
thing as an ideal circuit element. In this section we'll see how well some relatively
inexpensive Mini-Circuits attenuators perform.
Power the network analyzer from a wall outlet and turn the device on. Connect two 50 Ohm cables to the device
like the example shown in Figure 2.
Calibrate the network analyzer to measure |S11| and |S21| over a frequency range
of 1 GHz to 4 GHz. If using the FieldFox Network Analyzer N9912A, please follow this
N9912A QuickCal guide to perform a
QuickCal. This calibration procedure will "calibrate out" the effects of the test cables
themselves in subsequent measurements. Why do we perform a calibration? Because,
when we measure a device under test (DUT), like a Mini-Circuits attenuator,
we want to measure the
characteristics of the DUT itself,
and not the cables and adaptors that are connected to it. This requires calibration.
When measuring low frequency circuits like the output of a 555 timer with an oscilloscope,
you usually don't need
to worry about about calibration, since the oscilloscope probes and cables usually
have only a very small effect on the electrical performance of a circuit. However, in the world
of RF and microwaves, cables and adapters can have a significant effect on system performance.
Figure 2. Network Analyzer with 50 Ohm test cables.
Connect the 6 dB attenuator to the network analyzer. Figure 3 illustrates the connection.
Figure 3. 6 dB attenuator connected to network analyzer via 50 Ohm test cables.
Measure |S21| (dB), |S11| (dB), and VSWR of the Mini-Circuits 6 dB attenuator. Present
screenshots of your measurements in slide 3
and slide 4.
In these slides, please answer the following questions: Is the attenuator well matched (to 50 Ohms)?
How does the performance of the real 6 dB attenuator compare to that of an ideal 6 dB attenuator?
Measure |S21| (dB), |S11| (dB), and VSWR of the Mini-Circuits 12 dB attenuator. Present
screenshots of your measurements in slide 5
and slide 6.
In these slides, please answer the following questions: is the attenuator well matched (to 50 Ohms?
How does the performance of the real 12 dB attenuator compare to that of an ideal 12 dB attenuator?
5. Measuring the Performance of a Mini-Circuits Bandpass Filter
For this part, you are going to use the network analyzer to measure the insertion loss and VSWR of
a VBF-2360+ Mini-Circuits bandpass filter (BPF). Here is the BPF's
datasheet.
Configure the network analyzer with the same frequency range and calibration
settings as the previous section (1 GHz to 4 GHz).
Measure the insertion loss and return loss of the bandpass filter and compare
your measured results to the measurements given in the bandpass filter's data sheet
in slide 7
and slide 8
(For comparison, present your measured results side-by-side with the corresponding measured data from the
spec sheet).
6. Measuring the Performance of a Mini-Circuits Power Splitter/Combiner
For this part, you are going to use the network analyzer to measure the isolation, insertion loss and return loss
of a ZX10-2-42-S+ Mini-Circuits power splitter/combiner. Here is the splitter/combiners
datasheet. A photo of the power splitter/combiner is shown in Figure 4.
Note from the photo that the ports are labeled "S", "1", and "2". The label "S" stands for sum port.
The device can be used as a power combiner:
if an input signal is applied at port 1 and another input signal is applied at port 2,
the vector sum of the two signals will appear as a single output at port S.
Reciprocally, the device can be used as a power splitter:
if an input signal is applied at port S, equal outputs appear at
ports 1 and 2. A properly designed power splitter should also provide high isolation between
ports 1 and 2 (a signal applied at port 1 should not
appear at port 2 and viceversa) and good return loss for all ports.
Figure 4. Photo of the power splitter/combiner.
Adjust the network analyzers frequency range to be 2 GHz to 4 GHz, and perform a second
calibration with the new frequency range.
Connect discrete 50 Ohm loads to the ports labeled "1" and "2" on the Mini-Circuits splitter/combiner module,
as shown in Figure 5 (a). Connect port 1 of the network analyzer (labeled "RF OUT" on the FieldFox) to port "S"
of the splitter/combiner. Set the network analyzer to measure S11 (dB). This will measure the reflection (i.e.
return loss) at port "S" of the splitter/combiner. Present a screenshot of your measurement in
slide 9 and compare your results with those in the datasheet.
Following a similar procedure as above, make the following measurements:
Reflection at port "1". See Figure 5 (b) for measurement setup. Present screenshot
of your measurement in slide 10.
Reflection at port "2". See Figure 5 (c) for measurement setup. Present screenshot
of your measurement in slide 11.
Insertion loss between ports "S" and "1". Network analyzer for this part should be set to measure S21.
See Figure 5 (d) for measurement setup. Present screenshot
of your measurement in slide 12.
Insertion loss between ports "S" and "2". Network analyzer for this part should be set to measure S21.
See Figure 5 (e) for measurement setup. Present screenshot
of your measurement in slide 13.
Isolation between ports "1" and "2". Network analyzer for this part should be set to measure S21.
See Figure 5 (f) for measurement setup. Present screenshot
of your measurement in slide 14.
Figure 5. Procedure for measuring performance of RF splitter/combiner.
7. Measuring the Performance of a Mini-Circuits Coupler
For this part, you are going to use the network analyzer to measure the coupling, isolation,
insertion loss and return loss
of a ZABDC10-25HP-S Mini-Circuits bi-directional coupler. Here is the directional coupler's
datasheet. Directional couplers find many applications.
One simple application is to couple or "siphon off" a small amount of power from the main signal to
monitor the power and frequency of the main signal. Directional couplers can discriminate between
forward and backward traveling waves, and therefore they can also be used to measure VSWR and return loss
of devices as explained in this
link.
Microwaves101.com offers a good treatment of directional couplers at this
link.
Figure 6 illustrates the procedure for measuring the performance of the directional coupler.
Adjust the network analyzers frequency range to be 1.5 GHz to 2.5 GHz, and perform a second
calibration with the new frequency range.
Measure the return loss at the port labeled "IN". See Figure 6 (a) for measurement setup.
The network analyzer for this part should be set to measure S11 (dB). Present screenshot
of your measurement in slide 15. Compare your results with datasheet.
Measure the insertion loss between ports "IN" and "OUT". See Figure 6 (b) for measurement setup.
The network analyzer for this part should be set to measure S21 (dB). Present screenshot
of your measurement in slide 16. Compare your results with datasheet.
Measure the coupling between ports "IN" and "CPL IN". See Figure 6 (c) for measurement setup.
The network analyzer for this part should be set to measure S21 (dB). Place a measurement marker at 2 GHz
and record the coupling C at this frequency.
Present screenshot
of your measurement in slide 17. Compare your results with datasheet.
Measure the isolation between ports "IN" and port "CPL OUT". See Figure 6 (a) for measurement setup.
The network analyzer for this part should be set to measure S21 (dB). Place a measurement marker at 2 GHz
and record the isolation I at this frequency.
Present screenshot
of your measurement in slide 17. Compare your results with datasheet.
Compute the directivity D of this coupler at 2 GHz? The equation is: D = |C|-|I| where C = coupling in dB
and I = insertion loss in dB. The absolute value signs in this equation make sure that the signs are correct.
Present your calculation and result in slide 18. Compare your results with datasheet.
Figure 6. Procedure for measuring performance of RF coupler.
8. Measuring the Performance of custom "OIT" bandpass filter.
Figure 7 shows the custom designed "OIT" bandpass filter connected to the network analyzer.
This filter was designed using AWR microwave office.
Figure 7. Custom OIT bandpass filter connected to network analyzer.
Adjust the network analyzers frequency range to be 1 GHz to 2 GHz, and perform a second
calibration with the new frequency range.
Measure the return loss and insertion loss of this filter and present screenshots in slide 19
and slide 20. What is the center frequency of this bandpass filter? What is the approximate 3dB bandwidth?