We thank the Defense Spectrum Office (DSO) for funding this work.

1. VNA set-up
<ol>
	<li>Gather all components of the propagation measurement system, including cables, amplifiers, filters, DUTs (which can be subassemblies) and other components.</li>
	<li>Turn on the VNA (Figure 1), and let it warm for at least 0.5 h to ensure that all internal components of VNA are a stable operating temperature and that phase drift is minimized.</li>
	<li>Press the Preset button.</li>
	<li>Attach high quality, phase-stable cables to ports 1 and 2 of the VNA (Figure 2).</li>
	<li>Tighten the connectors at the VNA ports with an 8 in.lbf. torque wrench. To properly torque a connection, hold the end of the handle and gently push the handle without allowing the handle to break all the way over.</li>
	<li>Visually inspect all cables and connectors for obvious signs of wear such as nicks, dents, and imperfect connector threads.</li>
	<li>Check the manufacturer&#8217;s specifications for valid measurement ranges for all cables, connectors, and DUTs. These specifications can include temperature, humidity, frequency, and power.</li>
	<li>Clean connectors on all devices and cable ends. Use swabs specifically designed for cleaning sensitive electronics and connectors. Using cables with dirty connectors can result in damaging the conducting surfaces of cables and produce inaccurate measurements.
	<ol>
		<li>Dip a cotton swab into isopropyl alcohol.</li>
		<li>Gently clean the center conductor (Figure 3A) using the moistened swab. Do not exert too much force on the center conductor, as it is easily damaged.</li>
		<li>Clean the outer conductor of each connector (Figure 3B). Clean the coupling nut threads.</li>
		<li>Dry all cable and connector ends using clean compressed air (Figure 3C). If the compressed air cools the connector, allow the connector to return to room temperature (RT) before making and tightening all connections.</li>
	</ol>
	</li>
	<li>Align and make connections between VNA cables on ports 1 and 2 and the DUT. Tighten with a 12 in.lb. torque wrench for type N connections (Figure 4). Ensure that the cable ends are properly aligned.
	<ol>
		<li>Begin spinning the connector on the DUT side onto the VNA cable threads. Proper connections allow the nut to spin freely with little resistance. Resistance is a sign of cross-threading. Misalignment can damage the connector or cause signal reflections and signal loss. Do not overtighten connector, as this will damage the connector.</li>
		<li>Arrange the cables of the VNA such that they move minimally during calibration. Calibration cables are phase-stable and ideally not bent or moved during calibration.</li>
	</ol>
	</li>
	<li>Adjust VNA measurement parameters according to the specifications of the DUT. The frequency range can also be selected using the center frequency and frequency range known as the &#8220;span&#8221;.
	<ol>
		<li>Select the frequency range. Choose Stimulus Menu | Freq | Start Frequency: 1700 MHz. Choose Stimulus Menu | Freq | Stop Frequency: 1900 MHz.</li>
		<li>Select the measurement type (e.g., S11, S12, S21, S22). Choose Response Menu | Measure | S21.</li>
		<li>Select and adjust the port power. Choose Stimulus Menu | Power | Adjust Port Power: 0 dBm. Ensure that the output power is equal to (or below) the DUT maximum power specification.</li>
		<li>Select and adjust the sweep settings. Choose Stimulus Menu | Sweep | Sweep Type: Stepped. Choose Stimulus Menu | Sweep | time | Sweep Time: 1 sec. Then, choose Stimulus Menu | Sweep | Sweep Setup | Dwell Time: 0 &#956;sec. 
		NOTE: A stepped sweep is the most accurate sweep type, as it steps to each frequency and dwells at a frequency before making a measurement. If using long cables, the dwell time may need to be increased to ensure that the signal arrives at the receiver after the measurement. A 0 &#956;s dwell time is an optimal default setting.</li>
		<li>Select and adjust averaging mode by choosing Response Menu | Averaging | Averaging: IFBW: 1 kHz. 
		NOTE: Choose the appropriate averaging type: &#8220;point averaging&#8221; averages each frequency point a number of specified times (i.e., 2, 4 16, 32, etc.), which reduces the noise floor and uncertainty but increases the sweep time. IFBW uses a filter to measure the power in a small bandwidth, which also reduces the noise floor but requires less measurement time. IFWB averaging tends to be a more optimal averaging technique.</li>
		<li>Choose the displayed data format (e.g., LogMag [default setting], Smith Chart, SWR, etc.) by selecting Response Menu | Format | LogMag.</li>
		<li>Choose the number of data points in the displayed trace using Stimulus Menu | Sweep | Number of Points: 1601. 
		NOTE: The number of points is set so that maximal frequency coverage can be attained between the start and stop frequencies:</li>
	</ol>
	</li>
</ol>
<img alt="Equation 1" src="/files/ftp_upload/60874/60874equ01.jpg" />
In the example above, the step size or frequency spacing is 0.125 MHz, so that frequency(1) = 1700.000 MHz, frequency(2) = 1700.125 MHz, &#8230; frequency(1600) = 1899.875 MHz, frequency(1601) = 1900 MHz.
2. Calibration of the VNA
<ol>
	<li>Choose a manual or electronic calibration, if an electronic calibration module is available and desired (see section 2.11). Either calibration is accurate.</li>
	<li>Choose Manual Calibration by selecting Response | Cal Menu | Start Cal | Calibration Wizard | Unguided.
	<ol>
		<li>Choose the appropriate calibration kit so that an accurate value of the standards in the specific calibration kit are known (Figure 5). Here, choose 85054D, then choose the two-port short-open-load-thru (SOLT) calibration (for a DUT with two ports). Other available calibrations are a one-port for a device with a single port, in addition to a response calibration. The SOLT is the most accurate option11.</li>
		<li>Choose Next to go to the next screen.</li>
	</ol>
	</li>
	<li>Attach an open calibration standard (Figure 6) to the cable attached to port 1. An open calibration standard has an open cavity behind the connector to simulate a free-space impedance of 377 &#937;.</li>
	<li>Attach a short calibration standard to the cable attached to port 2. A short has a metal plate behind the connector so that the incoming voltage is completely reflected.
	<ol>
		<li>Choose Port 1 | OPEN | Type N (50) female open, which performs a measurement of the attached open. A trace will appear on the VNA screen, gently sloping away from a 0 dB reference level on a S11, log-magnitude display format for the open standard. Once the measurement is complete (a check mark will appear above&#160;the standard), press the OK button to continue. This will send the user back to the previous screen.</li>
		<li>Choose a male or female calibration standard with the same sex connector as that of the DUT (i.e., a male calibration standard has the center pin, and a female calibration standard will have an insertable port). Older VNAs require a calibration standard based on the sex of the VNA cable.</li>
		<li>Choose Port 2 | SHORT | Type N (50) female short, which performs a measurement of the attached short. A trace will appear on the VNA screen, gently sloping away from a 0 dB reference level on a S11, log-magnitude display format for the short standard. Once the measurement is complete (a check mark will appear above the standard), press the OK button to continue. This will send the user back to the previous screen.</li>
	</ol>
	</li>
	<li>Swap calibration standards between ports (i.e., attach the open calibration standard to port 2, then attach the short calibration standard to port 1).
	<ol>
		<li>Choose Port 1 | SHORT | Type N (50) female short to measure the short on port 1. A trace will appear on the VNA screen, gently sloping away from a 0 dB reference level on a S11, log-magnitude display format for the short standard. Once the measurement is complete (a check mark will appear above the standard), press the OK button to continue. This will send the user back to the previous screen.</li>
		<li>Choose Port 2 | OPEN | Type N (50) female open to measure the open on port 2. A trace will appear on the VNA screen, gently sloping away from a 0 dB reference level on a S11, log-magnitude display format for the open standard. Once the measurement is complete (a check mark will appear above the standard), press the OK button to continue. This will send the user back to the previous screen.</li>
	</ol>
	</li>
	<li>Remove the short from port 1 and place a broadband load on port 1. A load absorbs the incoming energy, which results in a small reflection over a large range of frequencies.
	<ol>
		<li>Choose Port 1 | LOADS | Type N (50) broadband load to measure the load on port 1. Once the measurement is complete (a check mark will appear above the standard), press the OK button to continue. This will send the user back to the previous screen.</li>
		<li>Keep the current calibration standard on port 2. Do not leave the port open, as it may provide a path for leakage signals. A trace will appear on the VNA screen and vary across the screen. All measured values on a S11, log-magnitude display format will be less than -20 dB for a good load.</li>
	</ol>
	</li>
	<li>Remove the open from port 2, take the broadband load from port 1, and place the broadband load on port 2. Place the open from port 2 on port 1 to prevent leakage signals.
	<ol>
		<li>Choose Port 2 | LOADS | Type N (50) broadband load to measure the load on port 2. A trace will appear on the VNA screen and vary across the screen. All measured values on a S11, log-magnitude display format will be less than -20 dB for a good load. Once the measurement is complete (a check mark will appear above the standard), press the OK button to continue. This will send the user back to the previous screen.</li>
	</ol>
	</li>
	<li>Insert a thru calibration standard between the cables attached to ports 1 and 2. This is typically an adapter with the same sex connectors on both ends.
	<ol>
		<li>Choose THRU to measure the thru calibration standard. Once the measurement is complete, a check mark will appear above the THRU standard on this screen. 
		NOTE: The isolation measurement can typically be omitted during calibration as isolation measures the crosstalk between cables and its value is often very small compared to other standards. The calibration measurements above can be done in any order.</li>
	</ol>
	</li>
	<li>Once all standards have a check mark above them, save the calibration. Choose Next | Save as User Calset. Enter a name for the calibration and press the SAVE button.</li>
	<li>Check the calibration as detailed in section 3.</li>
	<li>If a manual calibration is not chosen, choose the electronic calibration option12. Attach the electronic calibration kit (Figure 7) to the cables between ports 1 and 2. Select Response | Cal Menu | Start Cal | Calibration Wizard | Electronic Calibration with the electronic calibration option.
	<ol>
		<li>Choose 2-port ECal | Next, then select the Measure button. The electronic calibration module will automatically measure a number of different standards and prompt the user to save the calibration at the end.</li>
		<li>Choose Next | Save as User Calset. Enter a name for the calibration and press the SAVE button. 
		NOTE: For an electronic calibration only the cables from ports 1 and 2 are connected to the module. All calibration standards are contained in the module. The electronic calibration will calibrate the internal standards automatically. If the electronic calibration module does not have the same connector types as the cables, then an additional calibration will need to be completed to modify the calibration error corrections contained within the module to account for the adapters. Make sure to check with the manufacturer for guidance.</li>
	</ol>
	</li>
</ol>
3. Checking the calibration
<ol>
	<li>Use a thru to check the calibration.
	<ol>
		<li>Connect a thru adapter (Figure 6) without obvious signs of wear to the cables between ports 1 and 2. Do not measure the thru standard. Choose a different thru.</li>
		<li>Choose Response | Measure | S21, then Response | Scale | Scale. Set the Per Division value to 0.1 by pressing the down arrow button. Choose Stimulus Menu | Trigger | Single to measure the insertion loss of the thru. A single sweep will appear across the frequency range. 
		NOTE: The value of the thru on a log magnitude plot lies within 0.05 dB of the 0 dB reference (Figure 8) for sufficient calibration. This is an empirical value obtained over many years of calibrations. This can be seen by changing the scale to 0.05 dB per division.</li>
		<li>Once the thru has been checked, return the scale back to 10 dB/division by choosing Response | Scale | Scale and set the Per Division value to 10. Choose Response | Measure | S11.</li>
		<li>Choose Stimulus Menu | Trigger | Single to measure S11. The value of a good thru is the following: |S11| = -20 dB (1% reflection in power and 10% reflection in voltage). 
		NOTE: The Smith Chart13 representation displays impedance. Measurements of S11 and S22 appear as a small circle in the center of the chart. The impedance value is within 0.5 &#937; from the 50 &#937; reference for sufficient calibration.</li>
	</ol>
	</li>
	<li>Use a 50 &#937; load to check the calibration.
	<ol>
		<li>Attach a 50 &#937; matched load to the port 1.</li>
		<li>Choose Stimulus Menu | Trigger | Single to measure S11. 
		NOTE: A matched load is less than -20 dB (the reflection coefficient of an ideal load is 0). This will also appear as a small circle at the center of the Smith Chart (Figure 9).</li>
	</ol>
	</li>
	<li>Use an open calibration standard to check the calibration.
	<ol>
		<li>Connect an open calibration standard.</li>
		<li>Choose Stimulus Menu | Trigger | Single to measure S11. An open is 0 dB on a log-magnitude plot (the reflection coefficient of an ideal open is 1). On a Smith Chart, the open appears as a small circle at 0 on the far right (Figure 9) for sufficient calibration.</li>
	</ol>
	</li>
	<li>Use a short calibration standard to check the calibration.
	<ol>
		<li>Connect a short calibration standard.</li>
		<li>Choose Stimulus Menu | Trigger | Single to measure S11. A short is 0 dB (the reflection coefficient of an ideal short is -1) on the log-magnitude plot. On the Smith Chart, the value appears as a circle on the far left (Figure 9) for sufficient calibration. 
		NOTE: If a calibration test fails, check the connections and repeat the calibration. If the calibration is good, continue to section 4.</li>
	</ol>
	</li>
</ol>
4. Measurement of components or system losses
<ol>
	<li>Connect the DUT to the VNA. If the DUT has more than two ports (i.e., switches, power dividers, etc.), attach 50 &#937; matched loads to the ports that are not connected to the VNA, as power will be reflected from these ports and change the measurement.</li>
	<li>Select Response | Measure | S21.</li>
	<li>Select Stimulus Menu | Trigger | Single to measure the DUT.</li>
	<li>Select File | Save Data As&#8230; . Type in a file name in the file name box. Choose a file type of either .CSV or Trace (*.s2p). Choose the Scope (the default value of Displayed Traces is appropriate here). Choose a Format (e.g., log magnitude and angle, linear magnitude and phase, real and imaginary, and displayed format [such as a Smith Chart]). Press SAVE to save the data.</li>
	<li>Check and analyze the test results of a bandpass filter. An example is outlined in the following steps.
	<ol>
		<li>Identify parts of the trace by placing markers on the trace. Select Marker/Analysis | Marker | Marker 1 and press OK.</li>
		<li>Select Marker/Analysis | Marker Search | Max to find the insertion loss of the trace filter. The knob on the front panel can also be used to identify maxima and minima while sweeping the marker across frequency points.</li>
		<li>Select Marker/Analysis | Marker &#60; Marker 1, then select delta marker and coupled markers. The value of this marker as shown on the screen should read 0 dB. This will set a reference value for the other markers.</li>
		<li>Select Marker/Analysis | Marker&#8230; | Marker 2 | ON | coupled markers. Click inside the stimulus box to highlight the frequency, then move the knob until the reading of Marker 2 on the screen shows -3 dB.</li>
		<li>Select Marker/Analysis | Marker&#8230; | Marker 3 | ON | coupled markers. Click inside the stimulus box to highlight the frequency and move the knob until the reading of Marker 3 on the screen shows -3 dB.</li>
		<li>Compare the measured values to those of the manufacturer&#8217;s filter specifications.</li>
	</ol>
	</li>
</ol>

<ol><li>Commerce Spectrum Management Advisory Committee. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=%221755-1850+MHz+Airborne+Operations%3A+Air+Combat+Training+System+Sub-Working+Group+Final+Report%22">1755-1850 MHz Airborne Operations: Air Combat Training System Sub-Working Group Final Report</a>. , (2014).</li>
<li>Hammerschmidt, C. A., Johnk, R. T., McKenna, P. M., Anderson, C. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Best+Practices+for+Radio+Propagation+Measurements%5BTitle%5D)+AND+%22U.S.+Dept.+of+Commerce%22%5BJournal%5D)">Best Practices for Radio Propagation Measurements.</a> U.S. Dept. of Commerce. , NTIA Technical Memo TM-19-535 (2018).</li>
<li>Molisch, A. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aMolisch%2C+A+%22Wireless+Communications+-+2nd+edition%22">Wireless Communications - 2nd edition</a>. , J. Wiley & Sons, Ltd. Hoboken, NJ. (2010).</li>
<li>Anderson, C. R. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=%22Design+and+Implementation+of+an+Ultrabroadband+Millimeter-Wavelength+Vector+Sliding+Correlator+Channel+Sounder+and+In-Building+Multipath+Measurements+at+2.5+%26+60+GHz%22">Design and Implementation of an Ultrabroadband Millimeter-Wavelength Vector Sliding Correlator Channel Sounder and In-Building Multipath Measurements at 2.5 & 60 GHz</a>. , Virginia Polytechnic Institute and State University. Master's Thesis (2002).</li>
<li>Network Analyzer Basics. Keysight Technologies. , Available from: 
 <a target="_blank" href="http://literature.cdn.keysight.com/litweb/pdf/5965-7917E.pdf">http://literature.cdn.keysight.com/litweb/pdf/5965-7917E.pdf</a> (2019).</li>
<li>Rytting, D. Network Analyzer Error Models and Calibration Methods. , Available from: 
 <a target="_blank" href="http://emlab.uiuc.edu/ece451/appnotes/Rytting_NAModels.pdf">http://emlab.uiuc.edu/ece451/appnotes/Rytting_NAModels.pdf</a> (2019).</li>
<li>Rytting, D. Advances in Microwave Error Correction Techniques, Hewlett-Packard. RF & Microwave Measurement Symposium and Exhibition. , Available from: 
 <a target="_blank" href="http://na.support.keysight.com/faq/adv-ocr.pdf">http://na.support.keysight.com/faq/adv-ocr.pdf</a> (2019).</li>
<li>Kerns, D. M., Beatty, R. W. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aKerns%2C+DM+%22Basic+Theory+of+Waveguide+Junctions+and+Introductory+Microwave+Network+Analysis+%28Monographs+on+Electromagnetic+Waves%29%22">Basic Theory of Waveguide Junctions and Introductory Microwave Network Analysis (Monographs on Electromagnetic Waves)</a>. , Pergamon Press. (1967).</li>
<li>Engen, G. F. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aEngen%2C+GF+%22Microwave+Circuit+Theory+and+Foundations+of+Microwave+Metrology%22">Microwave Circuit Theory and Foundations of Microwave Metrology</a>. , Peter Peregrinus, Ltd. London, UK. (1992).</li>
<li>Witte, R. A. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aWitte%2C+RA+%22Spectrum+and+Network+Measurements%22">Spectrum and Network Measurements</a>. , Noble Publishing Corporation. Atlanta, GA. (2001).</li>
<li>Jargon, J. A., Williams, D. F., Hale, P. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Developing+Models+for+Type-N+Coaxial+VNA+Calibration+Kits+within+the+NIST+Microwave+Uncertainty+Framework%5BTitle%5D)+AND+%2287th+ARFTG+Microwave+Measurement+Conference%22%5BJournal%5D)">Developing Models for Type-N Coaxial VNA Calibration Kits within the NIST Microwave Uncertainty Framework.</a> 87th ARFTG Microwave Measurement Conference. , Francisco, CA. (2016).</li>
<li>Keysight Electronic Calibration Modules. Keysight Technologies. , Available from: 
 <a target="_blank" href="https://literature.cdn.keysight.com/litweb/pdf/N7550-90002.pdf?id=2852836">https://literature.cdn.keysight.com/litweb/pdf/N7550-90002.pdf?id=2852836</a> (2019).</li>
<li>Smith, P. H. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aSmith%2C+PH+%22Electronic+Applications+of+the+Smith+Chart%22">Electronic Applications of the Smith Chart</a>. , Electromagnetics and Radar, SciTech Publishing, Inc. Raleigh, NC. (2006).</li>
<li>K&L Microwave. , Available from: 
 <a target="_blank" href="http://www.klfilterwizard.com/klfwpart.aspx?FWS=1222001&PN=8FV50-1802_fT95-O_2fO">http://www.klfilterwizard.com/klfwpart.aspx?FWS=1222001&PN=8FV50-1802_fT95-O_2fO</a> (2019).</li>
<li>Mini-Circuits. , Available from: 
 <a target="_blank" href="http://www.minicircuits.com/WebStore/dashboard.html?model=BW-N10W50_2B">http://www.minicircuits.com/WebStore/dashboard.html?model=BW-N10W50_2B</a> (2019).</li>
<li>Utiflex Flexible Microwave Cable Assemblies Brochure. , Available from: 
 <a target="_blank" href="https://rf.cdiweb.com/datasheets/micro-coax/UtiflexCableAssemblies.pdf">https://rf.cdiweb.com/datasheets/micro-coax/UtiflexCableAssemblies.pdf</a> 5(2019).</li>
<li>Smith Chart Explanation. , Available from: 
 <a target="_blank" href="https://commons.wikimedia.org/wiki/File:Smith_chart_explanation.svg">https://commons.wikimedia.org/wiki/File:Smith_chart_explanation.svg</a> (2019).</li>
<li>Camell, D., Johnk, R. T., Novotny, D., Grosvenor, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Free-Space+Antenna+Factors+through+the+Use+of+Time-Domain+Signal+Processing%5BTitle%5D)+AND+%22IEEE+Intl.+Symp.+Electromag.+Compat%22%5BJournal%5D)">Free-Space Antenna Factors through the Use of Time-Domain Signal Processing.</a> IEEE Intl. Symp. Electromag. Compat. , (2007).</li>
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<li>Grosvenor, C., Camell, D., Koepke, G., Novotny, D., Johnk, R. T. Electromagnetic Airframe Penetration Measurements of a Beechcraft Premiere 1A. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aGrosvenor%2C+C+%22NIST+Technical+Note+1548%22">NIST Technical Note 1548</a>. , (2008).</li>
</ol>

The authors have nothing to disclose.

It is important to allow the VNA to warm to RT for at least 0.5 h (although, 1 h is better) before calibrations are performed, which allows all internal components to come to RT and results in more stable calibrations. One calibration can last several days without a large loss of accuracy; however, the calibration is checked daily using a calibration standard to ensure integrity of the measurement. Inspection of all system components is essential so that bad connectors do not damage the precision of the VNA. It is best to use low loss cables with the VNA. The integrity of the calibration must be checked before the measurement of any system component or DUT. Any measurement outside the specifications provided here should be repeated or may require a new calibration. Finally, using the manufacturer&#8217;s specifications to check the measured DUT values is a necessary part of validation.
Using the VNA as a measuring instrument has its limitations. If the DUT or system has losses so large that the measured S-parameters fall below the noise floor of the VNA, it cannot be measured with the VNA. It is possible to lower the noise floor by decreasing the IF bandwidth and increasing the sweep time. This will slow down the measurement acquisition time; thus, there is a trade-off when adjusting these parameters. The VNA cannot handle input powers greater than 30 dBm, so using internal or external attenuation when measuring amplifiers is required. The VNA has a source and receiver located in the same instrument, so it has been used as a radio propagation measurement system. Because the source and receiver are located in the VNA, the transmitting port must be joined in some manner to the receiving port. Typically, this is done with cables; however, cables add loss, decreasing the dynamic range of what can be measured. Furthermore, separation distances become limited.
The other method by which losses can be measured is use of a signal generator and power meter. The power meter is a scalar measurement device, so it can only measure a signal&#8217;s magnitude. It cannot monitor the phase of the signal, which results in less accurate measurements of the signal. The VNA measures both the magnitude and phase (of real and imaginary components) of a measured signal relative to a well-known input signal, which is a higher quality measurement.
VNAs are a versatile option for many types of measurements. The instrument can be used to measure radiated radio signals using antennas on the transmitting and receiving ports18. Time domain analysis can be used to monitor signals over time and determine where a break occurs in a cable. It can measure many frequencies during a sweep, which can be used to understand attenuation losses over many frequencies either in a conducted19 or radiated environment20. Understanding the various parameter settings of the VNA results in well-characterized DUTs/systems, and measurements obtained with the DUT/system can be used with a high degree of confidence.

The Institute for Telecommunication Sciences (ITS) is the research laboratory of the National Telecommunications and Information Administration (NTIA), an agency of the U.S. Department of Commerce. ITS has been active in radio propagation measurements since the 1950s. Spectrum sharing, the new paradigm for federal and commercial spectrum users, requires that two disparate systems share the same radio frequency spectrum at the same time. As spectrum sharing scenarios increase, so does the need for accurate and reproducible radio propagation measurements that provide a better understanding of the radio environment, which multiple services must share. The goal of the described procedure is to ensure that any components constituting such a system are well-characterized by an accurately configured VNA.
While demand for spectrum increases, it is not always possible to rapidly free spectrum that is currently used by federal agencies for commercial purposes. For example, in the Advanced Wireless Services (AWS)-3 band (1755&#8211;1780 MHz), spectrum sharing arrangements are being developed between military services and commercial wireless carriers1. These arrangements allow commercial wireless carriers to enter the AWS-3 band prior to completing the transition of military services out of the band.
The Defense Spectrum Organization (DSO) has been tasked with managing the AWS-3 transition. A key part of the transition involves developing new propagation models to evaluate the potential for RF interference between military and commercial wireless systems that share the band. The DSO has tasked ITS and others with performing a series of channel sounding measurements to build new models that better calculate the impact of foliage and man-made structures in the environment (collectively known as clutter). Improved propagation modeling that considers clutter will lead to fewer restrictions on commercial transmitters in the vicinity of military systems.
In situ measurements of RF spectrum activity provide insight into the physics of RF wave propagation and validate existing and new radio propagation models. Both of these components are essential to supporting and preserving interference-free spectrum sharing. Channel sounding techniques, in which a known test signal is transmitted from a specific location to either a mobile or stationary receiver, provide data that estimates radio channel characteristics in different environments. The data are used to develop and improve models that more accurately predict propagation losses or attenuation of the signal. These losses may be due to blocking and reflection by buildings and other obstacles (i.e., trees or terrain in urban canyons). These obstacles produce multiple, slightly variant, propagation paths resulting in signal loss or attenuation between the transmitting and receiving antenna.
ITS measurement techniques produce accurate, repeatable, and unbiased results. The DSO has encouraged ITS to share its institutional knowledge with the wider technical community. This knowledge includes how to optimally measure and process RF propagation data. The recently published NTIA Technical Memorandum TM-19-5352,3,4,5 describes a set of best practices for the preparation and verification of radio propagation measurement systems. As part of these best practices, a VNA is used to accurately measure the component losses or gains of a measurement system. The gains and losses are then used to calculate the signal attenuation between two antennas.
The protocol presented here addresses the best practices for calibrating a VNA5 prior to testing in laboratory or field applications. These include warm-up time, selection of RF connector type, making proper connections, and performance of appropriate calibration steps. Calibration should be conducted in a controlled lab environment prior to data collection in the context of a specific propagation measurement scenario. Additional considerations may be relevant to specific propagation measurement environments, which are outside the scope of this protocol.
The VNA is used to measure device characteristics of components and sub-assemblies when assembling other measurement systems. Power amplifiers, receivers, filters, low noise amplifiers, mixers, cables, and antennas are all components that can be characterized by a VNA. Prior to testing and/or calibrating a system, a list of all required components of the system is prepared, and all system components are assembled. Each component of a system is measured separately by inserting them between the VNA cables. This ensures that all components are operating within the manufacturer&#8217;s specifications. Once the components have been checked, the system is assembled, and losses throughout the entire system are measured. This ensures that reflections and transmissions between components are properly characterized.
A VNA measures scattering parameters (S-parameters), which are complex-valued quantities with both magnitude and phase. An S-parameter is a ratioed measurement of either the 1) reflected signal to the incident signal (reflection measurement) or 2) transmitted signal to the incident signal (transmission measurement). For a two-port device, four S-parameters (S11, S21, S12, and S22) can be measured. The first subscript refers to the port where the signal is received, and the second refers to the port where the signal is transmitted. Thus, S11 means the transmitted signal originated at port 1 and was received at port 1. Additionally, S21 means that the transmitted signal originated again at port 1 but is received at port 2. S11 measures the amount of signal that is reflected by the device under test (DUT) at port 1 with reference to the original signal that was incident at port 1. S21 measures the amount of signal that is transmitted through the DUT and arrives at port 2 with reference to the incident signal at port 1. S11 is a measure of the reflection coefficient of the DUT at port 1, and S21 is a measure of the transmission coefficient of the DUT from port 1 to port 2.
A calibration of the VNA is required to remove the systematic errors from components up to (and including) the measurement reference plane, which is typically at the end of the VNA measurement cables. A calibration removes system errors by measuring &#8220;perfect&#8221; known standards (open, shorts, loads, thru/line) and comparing it to the value that the VNA measures. Through a series of error corrections, a corrected value for the DUT is displayed. There are currently 12 error terms6,7 that are characterized during calibration. For more information, refer to original S-parameter measurements that were made on six-port network analyzers8 supported by classical microwave circuit theory9,10.
The most common types of S-parameter reflection measurements are return loss, standing wave ratio (SWR), reflection coefficient, and impedance matching. The most common types of S-parameter transmission measurements are insertion loss, transmission coefficient, gain/loss, group delay, phase or phase delay, and electrical delay. Transmission loss measurements are emphasized in the described protocol.
Measurement of gains and losses of system components using a VNA is well-understood. However, important steps are often skipped, such as cleaning connectors and using a proper torque wrench. This protocol provides all necessary steps and explanations of why some are particularly important. It will also serve as a prelude to a future article describing how to perform RF propagation measurements, including the calculations of signal attenuation.

<table><tbody><tr><td>12 inch-pound torque wrench</td><td>Maury Microwave</td><td></td><td>TW-12</td></tr><tr><td>8 inch-pound torque wrench</td><td>Keysight Technologies</td><td></td><td>8710-1764</td></tr><tr><td>Attenuators</td><td>Mini-Circuits</td><td></td><td>BW-N10W50+</td></tr><tr><td>Cable 1</td><td>Micro-Coax</td><td></td><td>UFB311A &amp;ndash; 36 feet</td></tr><tr><td>Calibration Standard Set (1) (manual)</td><td>Keysight Technologies</td><td></td><td>Economy Type-N Calibration kit, 85054 D</td></tr><tr><td>Calibration Standard Set (2) (E-cal)</td><td>Agilent Technologies</td><td></td><td>Electronic Calibration Kit, N4693-60001, 10 MHz to 50 GHz</td></tr><tr><td>Cleaning Swab</td><td>Chemtronics</td><td></td><td>Flextips Mini</td></tr><tr><td>Compressed Air</td><td>Techspray</td><td></td><td>Need ultra filtered</td></tr><tr><td>Filter 1</td><td>K&amp;amp;L Microwave, Inc.</td><td></td><td>8FV50-1802-T95-O/O</td></tr><tr><td>Isopropyl Alcohol</td><td>Any brand</td><td></td><td></td></tr><tr><td>VNA</td><td>Keysight Technologies</td><td></td><td>There are many options available for a researcher &amp;ndash; please consult the website</td></tr></tbody></table>

calibration of vector network analyzer for measurements in radio frequency propagation channels

In situ measurements of radio frequency (RF) spectrum activity provide insight into the physics of radio frequency wave propagation and validate existing and new spectrum propagation models. Both of these parameters are essential to supporting and preserving interference-free spectrum sharing, as spectrum use continues to increase. It is vital that such propagation measurements are accurate, reproducible, and free of artifacts and bias. Characterizing the gains and losses of components used in these measurements is vital to their accuracy. A vector network analyzer (VNA) is a well-established, highly accurate, and versatile piece of equipment that measures both magnitude and phase of signals, if properly calibrated. This article details the best practices for calibrating a VNA. Once calibrated, it can be used to accurately measure components of a correctly configured propagation measurement (or channel sounding) system or can be used as a measurement system itself.

When verifying whether a component is operating correctly, it is important to consult the manufacturer&#8217;s specifications, which can be found on their respective websites. Here, the filter (Figure 10) was measured after consulting its specifications14. As shown in Figure 11, the insertion loss was identified, as well as the 3 dB points. The measured insertion loss after calibration, as shown by marker 1, had a magnitude of 0.83 dB. The negative sign indicates that it was a loss. The insertion loss in the reference is specified to be 0.8 dB adjusted (dBa). The measured 3 dB bandwidth of the filter changed from 1749 MHz to 1854 MHz. When subtracted, this yielded a value of 105 MHz, which is close to the typical value of 104.5 MHz.
There are 10 dB attenuators built to withstand an input power of 50 W, as described by the manufacturer&#8217;s specifications15. The attenuation specification for this attenuator is 10 dB &#177; 0.5 dB. At some point, an input power greater than 50 W was input into the attenuator, which damaged the attenuator. A calibrated VNA was used to check the quality of this component. Again, it is important to measure each component before all field measurements for quality assurance. Measurement of the DUT is shown in Figure 12. In comparison, measurement of a good 10 dB attenuator is shown in Figure 13. It should be noted that the measured value was 9.88 dB at 1750 MHz, which is within the specified range of -9.5 to -10.5 dB across the entire bandwidth of 1700&#8211;1900 MHz.
Finally, cable loss is another important measurement frequently performed in radio frequency measurements. Specifications for the measured cable can be found on page 5 of the data sheet16. The attenuation per foot (dB/ft) was 0.05 dB at 1 GHz, or 0.16 dB/m. A measured cable with a length of 36 feet/11 m had a specified loss of ~1.8 dB, according to the manufacturer. The measured loss is shown in Figure 14. At a frequency of 1750 MHz, the measured loss was -1.88 dB (which, when rounded up to the nearest tenth of a decibel, is a magnitude of 1.9 dB).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/60874/60874fig01.jpg" /> 
Figure 1: Turning on the VNA.&#160;The red circle represents the location of the VNA power button. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60874/60874fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/60874/60874fig02.jpg" /> 
Figure 2: High quality, phase-stable cables attached to two VNA ports.&#160;The cables are attached to the front panel of the VNA using an 8 in.lbf. torque wrench. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60874/60874fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/60874/60874fig03.jpg" /> 
Figure 3: Cleaning connectors.&#160;(A) Cleaning of the inner conductor, (B) cleaning of the outer conductor and threads, and (C) gently blow drying the connector using compressed air. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60874/60874fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/60874/60874fig04.jpg" /> 
Figure 4: A 12 in.lbf. torque wrench for type N connectors.&#160;This wrench is used to tighten connections between the VNA cables and DUT. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60874/60874fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/60874/60874fig05.jpg" /> 
Figure 5: Type N calibration kit.&#160;Shown here is a calibration kit containing open, short, load, and thru standards used to calibrate errors in the VNA. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60874/60874fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/60874/60874fig06.jpg" /> 
Figure 6: Type N calibrations standards.&#160;Photographs of the male and female calibration standards used in the calibration. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60874/60874fig06large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/60874/60874fig07.jpg" /> 
Figure 7: Electronic calibration module.&#160;A photograph of an electronic calibration module. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60874/60874fig07large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/60874/60874fig08.jpg" /> 
Figure 8: Thru calibration check after calibration on a log-magnitude plot as a function of frequency in GHz.&#160;The value of the thru is 0.01 dB at a frequency of 1.8 GHz. This shows the value of the thru as a function of frequency in GHz after calibration. The thru is used as a calibration check to ensure that the calibration is valid. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60874/60874fig08large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/60874/60874fig09.jpg" /> 
Figure 9: Smith Chart explanation.&#160;Real and imaginary impedance value locations for standard impedances are shown in the left-hand figure, and impedance magnitude values are shown in the right-hand figure17. This Smith Chart drawing shows both the real and imaginary impedance on the left and impedance magnitude on the right. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60874/60874fig09large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/60874/60874fig10.jpg" /> 
Figure 10: RF filter inserted between ports 1 and 2.&#160;A photograph of an RF filter inserted between ports 1 and 2 at the end of the VNA cables during measurements. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60874/60874fig10large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 11" class="xfigimg" src="/files/ftp_upload/60874/60874fig11.jpg" /> 
Figure 11: Measured insertion loss and 3 dB points for RF filter with specifications provided in Figure 9.&#160;This is a screenshot from the VNA during measurement of the RF filter that is shown in Figure 10. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60874/60874fig11large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 12" class="xfigimg" src="/files/ftp_upload/60874/60874fig12.jpg" /> 
Figure 12: Measurement of 10 dB attenuator not within its specifications.&#160;The measured value is -22.70 dB at 1.7 GHz and its specification is 10 dB &#177; 0.5 dB. Also shown is measurement of a 10 dB attenuator that is no longer within its specifications. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60874/60874fig12large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 13" class="xfigimg" src="/files/ftp_upload/60874/60874fig13.jpg" /> 
Figure 13: Measurement of 10 dB attenuator within its specifications.&#160;The measured value was -9.88 dB. Also shown is measurement of a 10-dB attenuator that is within its specifications. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60874/60874fig13large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 14" class="xfigimg" src="/files/ftp_upload/60874/60874fig14.jpg" /> 
Figure 14: Measurement of 36 ft (11 m) coaxial cable with a 0.05 dB/ft specified attenuation value.&#160;Loss through the length of the cable was expected to be ~1.8 dB, which is consistent with the measured value of -1.9 dB at 1.87 GHz. Also displayed is measurement of a cable showing that the measured loss is within the manufacturer&#8217;s specifications. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60874/60874fig14large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

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Calibration of Vector Network Analyzer for Measurements in Radio Frequency Propagation Channels

This protocol describes best practices for calibrating a vector network analyzer prior to use as an accurate instrument, intended to measure components of a radio frequency propagation measurement test system.

In situ measurements of radio frequency (RF) spectrum activity provide insight into the physics of radio frequency wave propagation and validate existing ...

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20.7K Views.  Institute for Telecommunication Sciences. Het maken van goede metingen is moeilijk. Deze procedure zal helpen bij het ontwikkelen van goede meetpraktijken. Wanneer dit protocol wordt gevolgd, zullen de VNA's RF-apparaten en -systemen nauwkeurig debuggen en karakteriseren.VNA's zijn de meest nauwkeurige manier om een RF-apparaat of -systeem te meten. De theorie achter deze techniek is goed ingeburgerd en het volgen van dit protocol zal consistente en herhaalbare resultaten opleveren. Het aantonen van de procedure zal Savio Tran...

Video: Calibration of Vector Network Analyzer for Measurements in Radio Frequency Propagation Channels

Calibrated Passive Sampling - Multi-plot Field Measurements of NH3 Emissions with a Combination of Dynamic Tube Method and Passive Samplers

Agricultural ammonia (NH3) emissions (90% of total EU emissions) are responsible for about 45% airborne eutrophication, 31% soil acidification and 12% fine dust formation within the EU15. But NH3 emissions also mean a considerable loss of nutrients. Many studies on NH3 emission from organic and mineral fertilizer application have been performed in recent decades. Nevertheless, research related to NH3 emissions after application fertilizers is still limited in particular with respect to relationships to emissions, fertilizer type, site conditions and crop growth. Due to the variable response of crops to treatments, effects can only be validated in experimental designs including field replication for statistical testing. The dominating ammonia loss methods yielding quantitative emissions require large field areas, expensive equipment or current supply, which restricts their application in replicated field trials. This protocol describes a new methodology for the measurement of NH3 emissions on many plots linking a simple semi-quantitative measuring method used in all plots, with a quantitative method by simultaneous measurements using both methods on selected plots. As a semi-quantitative measurement method passive samplers are used. The second method is a dynamic chamber method (Dynamic Tube Method) to obtain a transfer quotient, which converts the semi-quantitative losses of the passive sampler to quantitative losses (kg nitrogen ha-1). The principle underlying this approach is that passive samplers placed in a homogeneous experimental field have the same NH3 absorption behavior under identical environmental conditions. Therefore, a transfer co-efficient obtained from single passive samplers can be used to scale the values of all passive samplers used in the same field trial. The method proved valid under a wide range of experimental conditions and is recommended to be used under conditions with bare soil or small canopies (&#60;0.3 m). Results obtained from experiments with taller plants should be treated more carefully.

Calibrated Passive Sampling - Multi-plot Field Measurements of NH3 Emissions with a Combination of Dynamic Tube Method and Passive Samplers

Ammonia emissions are a major threat to the environment by eutrophication, soil acidification and fine particle formation and stem mainly from agricultural sources. This method allows ammonia loss measurements in replicated field trials enabling statistical analysis of emissions and of relationships between crop development and emissions.

Agricultural ammonia (NH3) emissions (90% of total EU emissions) are responsible for about 45% airborne eutrophication, 31% soil acidification and 12% ...

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Implementation of a Reference Interferometer for Nanodetection

A thermally and mechanically stabilized fiber interferometer suited for examining ultra-high quality factor microcavities is fashioned. After assessing its free spectral range (FSR), the module is put in parallel with a fiber taper-microcavity system and then calibrated through isolating and eliminating random shifts in the laser frequency (i.e. laser jitter noise). To realize the taper-microcavity junction and to maximize the optical power that is transferred to the resonator, a single-mode optical fiber waveguide is pulled. Solutions containing polystyrene nanobeads are then prepared and flown to the microcavity in order to demonstrate the system&#8217;s ability to sense binding to the surface of the microcavity. Data is post-processed via adaptive curve fitting, which allows for high-resolution measurements of the quality factor as well as the plotting of time-dependent parameters, such as resonant wavelength and split frequency shifts. By carefully inspecting steps in the time-domain response and shifting in the frequency-domain response, this instrument can quantify discrete binding events.

A reference interferometer technique, which is designed to remove undesirable laser jitter noise for nanodetection, is utilized for probing an ultra-high quality factor microcavity. Instructions for assembly, setup, and data acquisition are provided, alongside the measurement process for specifying the cavity quality factor.

A thermally and mechanically stabilized fiber interferometer suited for examining ultra-high quality factor microcavities is fashioned. After assessing ...

Using Microwave and Macroscopic Samples of Dielectric Solids to Study the Photonic Properties of Disordered Photonic Bandgap Materials

Recently, disordered photonic materials have been suggested as an alternative to periodic crystals for the formation of a complete photonic bandgap (PBG). In this article we will describe the methods for constructing and characterizing macroscopic disordered photonic structures using microwaves. The microwave regime offers the most convenient experimental sample size to build and test PBG media. Easily manipulated dielectric lattice components extend flexibility in building various 2D structures on top of pre-printed plastic templates. Once built, the structures could be quickly modified with point and line defects to make freeform waveguides and filters. Testing is done using a widely available Vector Network Analyzer and pairs of microwave horn antennas. Due to the scale invariance property of electromagnetic fields, the results we obtained in the microwave region can be directly applied to infrared and optical regions. Our approach is simple but delivers exciting new insight into the nature of light and disordered matter interaction.

Our representative results include the first experimental demonstration of the existence of a complete and isotropic PBG in a two-dimensional (2D) hyperuniform disordered dielectric structure. Additionally we demonstrate experimentally the ability of this novel photonic structure to guide electromagnetic waves (EM) through freeform waveguides of arbitrary shape.

Disordered structures offer new mechanisms for forming photonic bandgaps and unprecedented freedom in functional-defect designs. To circumvent the computational challenges of disordered systems, we construct modular macroscopic samples of the new class of PBG materials and use microwaves to characterize their scale-invariant photonic properties, in an easy and inexpensive manner.

Recently, disordered photonic materials have been suggested as an alternative to periodic crystals for the formation of a complete photonic bandgap (PBG). ...

Fabrication and Characterization of Superconducting Resonators

Superconducting microwave resonators are of interest for a wide range of applications, including for their use as microwave kinetic inductance detectors (MKIDs) for the detection of faint astrophysical signatures, as well as for quantum computing applications and materials characterization. In this paper, procedures are presented for the fabrication and characterization of thin-film superconducting microwave resonators. The fabrication methodology allows for the realization of superconducting transmission-line resonators with features on both sides of an atomically smooth single-crystal silicon dielectric. This work describes the procedure for the installation of resonator devices into a cryogenic microwave testbed and for cool-down below the superconducting transition temperature. The set-up of the cryogenic microwave testbed allows one to do careful measurements of the complex microwave transmission of these resonator devices, enabling the extraction of the properties of the superconducting lines and dielectric substrate (e.g., internal quality factors, loss and kinetic inductance fractions), which are important for device design and performance.

Superconducting microwave resonators are of interest for detection of light, quantum computing applications and materials characterization. This work presents a detailed procedure for fabrication and characterization of superconducting microwave resonator scattering parameters.

Superconducting microwave resonators are of interest for a wide range of applications, including for their use as microwave kinetic inductance detectors ...

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials such as organo-lead halide perovskites is presented. The perovskite film thickness and absorption coefficient are initially characterized by profilometry and UV-VIS absorption spectroscopy. Calibration of both laser power and cavity sensitivity is described in detail. A protocol for performing Flash-photolysis Time Resolved Microwave Conductivity (TRMC) experiments, a non-contact method of determining the conductivity of a material, is presented. A process for identifying the real and imaginary components of the complex conductivity by performing TRMC as a function of microwave frequency is given. Charge carrier dynamics are determined under different excitation regimes (including both power and wavelength). Techniques for distinguishing between direct and trap-mediated decay processes are presented and discussed. Results are modelled and interpreted with reference to a general kinetic model of photoinduced charge carriers in a semiconductor. The techniques described are applicable to a wide range of optoelectronic materials, including organic and inorganic photovoltaic materials, nanoparticles, and conducting/semiconducting thin films.

A Time Resolved Microwave Conductivity technique for investigating direct and trap-mediated recombination dynamics and determining carrier mobilities of thin film semiconductors is presented here.

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials ...

Measurements of Soil Carbon by Neutron-Gamma Analysis in Static and Scanning Modes

The herein described application of the inelastic neutron scattering (INS) method for soil carbon analysis is based on the registration and analysis of gamma rays created when neutrons interact with soil elements. The main parts of the INS system are a pulsed neutron generator, NaI(Tl) gamma detectors, split electronics to separate gamma spectra due to INS and thermo-neutron capture (TNC) processes, and software for gamma spectra acquisition and data processing. This method has several advantages over other methods in that it is a non-destructive in situ method that measures the average carbon content in large soil volumes, is negligibly impacted by local sharp changes in soil carbon, and can be used in stationary or scanning modes. The result of the INS method is the carbon content from a site with a footprint of ~2.5 - 3 m2 in the stationary regime, or the average carbon content of the traversed area in the scanning regime. The measurement range of the current INS system is &#62;1.5 carbon weight % (standard deviation &#177; 0.3 w%) in the upper 10 cm soil layer for a 1 hmeasurement.

Here, we present the protocol for in situ measurement of soil carbon using the neutron-gamma technique for single point measurements (static mode) or field averages (scanning mode). We also describe system construction and elaborate data treatment procedures.

The herein described application of the inelastic neutron scattering (INS) method for soil carbon analysis is based on the registration and analysis of ...

Measurements of Waves in a Wind-wave Tank Under Steady and Time-varying Wind Forcing

This manuscript describes an experimental procedure that allows obtaining diverse quantitative information on temporal and spatial evolution of water waves excited by time-dependent and steady wind forcing. Capacitance-type wave gauge and Laser Slope Gauge (LSG) are used to measure instantaneous water surface elevation and two components of the instantaneous surface slope at a number of locations along the test section of a wind-wave facility. The computer-controlled blower provides airflow over the water in the tank whose rate can vary in time. In the present experiments, the wind speed in the test section initially increases quickly from rest to the set value. It is then kept constant for the prescribed duration; finally, the airflow is shut down. At the beginning of each experimental run, the water surface is calm and there is no wind. Operation of the blower is initiated simultaneously with the acquisition of data provided by all sensors by a computer; data acquisition continues until the waves in the tank fully decay. Multiple independent runs performed under identical forcing conditions allow determining statistically reliable ensemble-averaged characteristic parameters that quantitatively describe wind-waves&#39; variation in time for the initial development stage as a function of fetch. The procedure also allows characterizing the spatial evolution of the wave field under steady wind forcing, as well as decay of waves in time, once the wind is shut down, as a function of fetch.

This manuscript describes a fully computer-controlled procedure that allows obtaining reliable statistical parameters from experiments of water waves excited by steady and unsteady wind forcing in a small-scale facility.

This manuscript describes an experimental procedure that allows obtaining diverse quantitative information on temporal and spatial evolution of water ...

Effective Analysis of Human Exposure Conditions with Body-worn Dosimeters in the 2.4 GHz Band

A well-defined experimental procedure is put forward to evaluate maximum exposure conditions in a worst-case scenario whilst avoiding the uncertainties caused by the use of personal exposimeters (PEMs) as measuring devices: the body shadow effect (BSE), the limited sensitivity range, and the non-identification of the radiation source. An upper bound for exposure levels to EMF in several indoor enclosures has been measured and simulated. The frequency used for the study is 2.4 GHz, as it is the most commonly used band in indoor communications. Although recorded values are well below the International Commission for Non-Ionizing Radiation Protection (ICNIRP) reference levels, there is a particular need to provide reliable exposure levels within particularly sensitive environments. In terms of electromagnetic field (EMF) exposure, limits established in national and international standards for health protection have been set for unperturbed exposure conditions; that is, for real and objective exposure data that have not been altered in any way.

This study describes a protocol to measure exposure levels in the 2.4 GHz band, avoiding the uncertainties caused by the use of personal exposimeters as measuring devices. These alterations of the exposure levels should be taken into account, especially in compliance testing, where exposure limits are defined from non-perturbed data.

A well-defined experimental procedure is put forward to evaluate maximum exposure conditions in a worst-case scenario whilst avoiding the uncertainties ...

An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids

An analog, macroscopic method for studying molecular-scale hydrodynamic processes in dense gases and liquids is described. The technique applies a standard fluid dynamic diagnostic, particle image velocimetry (PIV), to measure: i) velocities of individual particles (grains), extant on short, grain-collision time-scales, ii) velocities of systems of particles, on both short collision-time- and long, continuum-flow-time-scales, iii) collective hydrodynamic modes known to exist in dense molecular fluids, and iv) short- and long-time-scale velocity autocorrelation functions, central to understanding particle-scale dynamics in strongly interacting, dense fluid systems. The basic system is composed of an imaging system, light source, vibrational sensors, vibrational system with a known media, and PIV and analysis software. Required experimental measurements and an outline of the theoretical tools needed when using the analog technique to study molecular-scale hydrodynamic processes are highlighted. The proposed technique provides a relatively straightforward alternative to photonic and neutron beam scattering methods traditionally used in molecular hydrodynamic studies.

An experimentally accessible analog method for studying molecular hydrodynamic processes in dense fluids is presented. The technique uses particle image velocimetry of vibrated, high-restitution grain piles and allows direct, macroscopic observation of dynamical processes known and predicted to exist in strongly interacting, high density gases and liquids.

An analog, macroscopic method for studying molecular-scale hydrodynamic processes in dense gases and liquids is described. The technique applies a ...

Optimizing Brillouin Optical Time-Domain Analyzers Based on Gain Spectrum Engineering

Demonstrated is a unique method for sensing performance enhancement in Brillouin optical time-domain analyzers (BOTDA). A Brillouin gain spectrum (BGS) is superimposed with two symmetric Brillouin loss spectra (BLS). This leads to a complex engineered spectrum shape that is more resistant to the sensing system noise. Instead of only one pump and probe interaction as in the conventional BOTDA setup, three optical probe waves are exploited, with one probe located in the BGS and the other two symmetrically in the BLS. Due to the resistance and insensitivity of the engineered spectrum shape to the noise, the sensing performance is enhanced by 60% and the measurand resolution is doubled.

A protocol for Brillouin optical time-domain analyzers based on gain spectrum engineering is presented. Enhancements in the sensing performance, including sensing range and measurand resolution are achieved and the excess Brillouin intensity noise is studied. The protocol introduces a new way to enhance distributed Brillouin sensing performance.

Demonstrated is a unique method for sensing performance enhancement in Brillouin optical time-domain analyzers (BOTDA). A Brillouin gain spectrum (BGS) is ...

Calibration of Vector Network Analyzer for Measurements in Radio Frequency Propagation Channels

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