Attenuators, Couplers and Filters

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1 Objectives: Attenuators, Couplers and Filters To become familiar with the functionality of common RF devices. To characterize both the reflection and transmission responses of these devices. NOTE: IN CONTRAST TO PREVIOUS LABS, EACH PERSON WILL NEED TO TURN IN THEIR OWN PRELAB, THEIR OWN SET OF LAB NOTES AND WILL NEED TO WORK ON THEIR OWN TO ANSWER THE LAB SUMMARY QUESTIONS. STUDENTS MAY WORK TOGETHER IN PERFORMING THE ACTUAL LAB (THIS IS ENCOURAGED IN FACT). A FORMAL LAB REPORT WILL NO LONGER BE REQUIRED. STUDENTS ARE TO USE THEIR RESULTS TO ANSWER THE LAB SUMMARY QUESTIONS THAT WILL BE TURNED IN LEAU OF A REPORT. LAB NOTES ARE TO BE TURNED IN BY FRIDAY, SEPTEMBER 24 TH. RESPONSES TO LAB SUMMARY QUESTIONS ARE DUE BY THURSDAY, SEPTEMBER 30 TH. Equipment: Network/Impedance/Spectrum Analyzer (Agilent 4396B) and User s Guides Transmission/Reflection Test Jig (Agilent 87512A) Waveform Generator (Agilent 33220A) Oscilloscope (Agilent Infinium) Switchable attenuator (HP 8494A / Agilent 8496A) Coupler (MiniCircuits ZX ) Splitter (MiniCircuits ZMSCQ-2-90) Filter (MiniCircuits SBP-70) Low pass filter (black box E ) Several SMA to BNC adapters and cables (no. 1 and no. 2) Prelab: 1. You insert a signal of 20 mw into a 23 db attenuator. What is the received output power in mw and in dbm. 2. You insert a signal of 20 mw into a 10 db coupler. What is the power measured at the through-port in mw and the directivity (ignoring isolation)? 3. You insert a signal of 20 mw into a 10 db coupler. What is the power measured at the coupled-port in mw and in dbm. 4. You insert a signal of 20 mw into a splitter (Port S). What is the power level in mw and dbm that you expect at the outputs (Ports 1 and 2) 5. Bring a disk to class to capture your inband data (images). Setup: Configure the 4396B to Network Analyzer mode. Measure > Analyzer Type > Network > B/R Set the start and stop frequencies to capture the full range of the instrument: 100 khz 1.8 GHz. Configure the scale to 10 db/div [Scale/Ref > Scale/div > 10 > x1]. 1

2 Set the network analyzer output power to 0 dbm (Source > Power > 0 > x1) Connect cable No. 1 to the test jig and cable No. 2 to the B port of the network analyzer. Calibrate the test setup (per Lab 2). PART I: Attenuators Procedure: 1. S 21 characterization of Switchable Attenuator. Set both dials on the switchable attenuator to 0dB. Using the network analyzer setup, determine the minimum and maximum insertion loss across the band. You may need to reduce the Scale/Div to make a clear reading. Record this value in Table 1. Set the dial on the lower attenuator to 10 db and repeat the measurements, recording them in Table 1. Note: for each set up you may need to adjust the scale. Repeat this step for the attenuator settings given in Table 1. Observation: At what point does the measurement become unreliable? What is the cause? At the setting you find an unreliable measurement, increase the source power to 20 dbm. Note this power change point on Table 1. Observation: What do you observe now? Continue the measurements for as long as you deem them to be reliable (note: you won t be able to fill the table). Reset the output power to 0 dbm and scale to 10 db/div upon completing the measurements. Observation: At what frequencies are the settings accurate? Least accurate? 2. Characterization of a splitter. Note that the splitter should have attached to the S-port a blue and black extension cable. This device has SMA connectors on it but we will be using SMA to BNC adapters so as to not need to change our test setup and calibration. Use extreme care in removing and installing the adapters, cables and loads to avoid cross-threading the connections. Connect cable no. 1 to the S-port and cable no. 2 to Port-1. Place the SMA 50 load on Port-2. Capture this S 1S measurement. Observation: Does this response correspond to what you would have predicted? 2

3 Set the start frequency to 20 MHz and the stop frequency to 200 MHz. Using the marker, ascertain the region of operation of this device; that is, over what frequencies does the device work as predicted. Record your data in Table 2. Return the settings to full span (100 khz 1.8 GHz). Remove the cable from the adaptor. Switch the load to Port-1 and the adapter to Port-2. Reconnect the cable and capture the S 2S response. Observation: How does the S 2S out of band response compare to that for the S 1S measurement? Zoom in on the expected response region and determine over what range the device performs as a S 2S splitter. Record this data in Table 2. Return the span to full range (100 khz 1.8 GHz). Remove the cable from the adapter, remove the adapter and the load. Place the load on the S-Port. Connect cable no. 1 to Port-1 and cable no. 2 to Port-2. Capture the S 21 response. Zoom in on the region of operation and measure the isolation between the ports. Remove the splitter from the test set up. Return the load to Port-S and the SMA/BNC adapter to the S- Port cable. 3. Characterization of a coupler. The 20 db coupler should have an SMA/BNC adapter on both its IN and OUT ports. A load should be placed on the coupled port (CPL). Configure the setup for a range of 100 khz-1.8 GHz and a scale of 1 db. Recalibrate the setup. Connect cable no. 1 to the IN port and cable no. 2 to the OUT port and capture this S21 measurement. Record the minimum and maximum insertion loss values in Table 3 along with their frequencies. Remove cable no. 2. Switch the adapter to the CPL port (leaving the load off for now). Connect cable no. 2 to the CPL Port. Change the scale to 10 db/div. Watch the response as you now place the load on the OUT port. Capture this S 31 or coupled response and record the minimum and maximum coupled values (and frequencies) in Table 3. Observation: What do you observe in the response with and without the load? Remove cables no. 1 and 2. Switch the load to the IN port and the adapters to the OUT and CPL ports. Connect cable no. 1 to the CPL port and cable no. 2 to the OUT port. Change the scale to 10 db/div. Capture this S23 response without the load in place. Place the load on the IN port and capture the response. Record the minimum and maximum losses (and frequencies) in Table 3. Remove the coupler ensuring that each port has either an adapter or load on it (these parts are small and expensive, we don t want them lost). 4. Characterization of a filter. The band pass filter should have a SMA/BNC adapter on one end and a black SMA to BNC cable on the other. 3

4 Observe the S 21 magnitude response of this filter. Ascertain the frequency of operation and roughly zoom in on this region. Observation: What are your start and stop frequency settings? Recalibrate the setup for your zoomed in range of operation. Capture the S21 response. Determine the minimum insertion loss and the filter s 3 db bandwidth recording your measurements in Table 4. We now want to capture the phase response of the filter (Format > Phase). In addition, capture the continued phase response (Format > More > Expanded Phase). Observation: How would you characterize phase response inside the 3 db bandwidth as oppose to outside? Finally, we want to consider the delay response of the filter (Format > Delay). Change the scale to 20 nsec/div and use the Reference value and up/down arrows to center the measurement in the screen. Capture this response. What is the minimum and maximum delay within the 3 db bandwidth. Record this in Table 4. Observation: How would you characterize delay response inside the 3 db bandwidth as oppose to outside? 5. Characterization of a low frequency device. Remove the 70 MHz BPF. Set the network analyzer to measure magnitude response (Format > Log Magnitude). Recalibrate the setup from 100 khz to 10 MHz. Connect black box E to the set up. Can you observe the 3 db cutoff frequency? Connect device E between the waveform generator and the oscilloscope. Configure the waveform generator to produce a 1 khz sine wave with a 1 V pp. Measure the output voltage (V out ) on the oscilloscope and record in Table 5. Repeat the above measurement for all frequencies found in Table 5. Laboratory Summary Questions: 1. Based on your Part 1 measurements, what would you say is the minimum power level (dbm) at which the network analyzer provides reliable measurements? 2. Why is important to have good isolation between Ports 1 and 2 on the splitter? 3. What would happen if you used the splitter measured at ~ 1 GHz? Use your captured plots to buttress your response. 4

5 4. Why is it important to have loads on all unused ports? Use captured plots to illustrate your point. 5. What caused the S 32 coupler isolation to be so poor when the load was not place on the IN port? 6. Based on your filter data, what are the desirable inband attributes to have in terms of loss, phase response and delay. Use your captured images to support your response. 7. At the edge of a filters usable range (near +/- 3 db); what do you observe happening to the three responses measured. 8. Use your data from Table 5 to plot the response of black box E. Be sure to covert your voltage measurements to db using the 1 khz measurement as a reference (0 db). What is the 3 db cutoff for this device? What kind of device is this? Why could you not use the network analyzer in this step? Please note any corrections to the procedure and give them to the instructor or TA. Thanks. Table 1. Switchable Attenuator Insertion Loss Attenuator Setting Min loss Max loss Attenuator Setting 0 db 60 db 10 db 70 db 20 db 80 db 30 db 90 db 40 db 100 db 50 db 110 db Min loss Max loss Table 2. Splitter characterization data Measurement Lower cutoff Upper cutoff Frequency Loss Frequency Loss S 1S S 2S S 12 5

6 Table 3. Coupler characterization data Measurement Minimum Insertion Maximum Insertion Frequency Loss Frequency Loss S 21 S 31 S 32 Table 4. Filter characterization data Measurement Frequency Loss (Delay) Minimum insertion Lower 3 db cut off Upper 3 db cut off Minimum delay Maximum delay Table 5. Low frequency device characterization data Frequency V out Frequency V out Frequency V out 1 khz 50 khz 1 MHz 2 khz 80 khz 2 MHz 5 khz 100 khz 5 MHz 8 khz 200 khz 8 MHz 10 khz 500 khz 10 MHz 20 khz 800 khz 15 MHz 6

ECE 4670 Spring 2014 Lab 1 Linear System Characteristics

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