Airport Passenger Screening Using Millimeter Wave Machines Compliance with Guidelines (2017) / Chapter Skim
Currently Skimming:
6 Committee-Led Measurements of Advanced Imaging Technology Millimeter Wave Scanners at U.S. Airports
6 Committee-Led Measurements of Advanced Imaging Technology Millimeter Wave Scanners at U.S. Airports
Pages 67-107
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 67... ...
Thus the primary focus of this study was to collect realistic emission data within the primary emission operating band of 24 to 30 GHz over a wider area than is typically occupied by a human during ProVision scanner operations. These measurements were compared to the published maximum permissible exposure (MPE)
|
From page 68... ...
, to provide technical design advice, test planning, test execution, data reduction, and technical reporting for the ProVision scanner measurements performed at four air ports selected by the committee from a longer list of TSA-chosen airports -- Dayton International Airport (DAY) in Ohio, Cincinnati/Northern Kentucky International Airport (CVG)
|
From page 69... ...
The remainder of this chapter summarizes the test plan and technical details of the RF measurement approach, measurement results, measurement uncertainty, and prediction results. PROVISION ATD AND PROVISION 2 BACKGROUND Characterizing the RF emissions of ProVision machines is not trivial with signal strengths close to the noise levels.
|
From page 70... ...
During each vertical scan, each element in the transmit array sequentially radiates a linear-frequency modulated (LFM) ramp or chirp waveform that begins at 24 GHz and ends at 30 GHz.
|
From page 71... ...
Power density emissions or field characterization measurements out of the operational frequency band (executed on a single ProVision scanner at DAY airport)
|
From page 72... ...
Due to the extremely limited space within the ProVision units, a typical Cartesian X-Y field probe scanner was not employed because it simply would not fit within the chamber. Instead, the team designed a FIGURE 6.2 Left: The field probe instrumentation set-up inside of a ProVision ATD unit at Dayton (DAY)
|
From page 73... ...
As the project developed, extensive "off vertical" field probe measurements for ±15 degrees and ±30 degrees were collected, mostly in Dayton. Most of the measured power levels significantly decreased off the vertical line due to the mast being at a fixed location directly in front of the rig, and many measurements showed power levels below the measurement sensitivity of the equipment.
|
From page 74... ...
FIELD PROBE POWER MEASUREMENT SYSTEM The ProVision RF power density emissions were collected by a NARDA V637 standard gain horn antenna. The antenna was mounted to a short, curved section of waveguide, then to a waveguide to coax adaptor.
|
From page 75... ...
The Schottky diode device is simply not sensitive enough for the power density emissions of the ProVision unit in the 24 to 30 GHz range, and therefore all DAY airport data using the Schottky diode detector was indistinguishable from random noise. For the subsequent three measurements (CVG, MEM, and TYS airports)
|
From page 76... ...
in the CVG, MEM, and TYS airport set-ups. A schematic view of the DAY airport field probe system that matches the physical layouts of Figures 6.2 and 6.5 is shown in Figure 6.6.
|
From page 77... ...
In the subsequent three airports, the team repeated the rear reference antenna case as used at DAY airport. The team also acquired data using a front-pointed reference antenna positioned several inches above the primary probe antenna, which allowed slightly higher time-domain sampling of the results (see Figure 6.8)
|
From page 78... ...
Ultimately, the team measured the incident power density at an initial Scan Plane 1 position and repeated the forward tests with the antenna extension removed, effectively moving the antenna 30.48 cm farther away from the front array. Because this induces more "spread loss" as the wave propagates away from the array, the power density emissions at the Scan Plane 2 center position were substantially weaker than the Scan Plane 1 emissions.
|
From page 79... ...
After a two-stage amplifier, the signal was then directed through a frequency doubler and a WR-28 waveguide bandpass filter, resulting in a linear FM output from 24 to 30 GHz, precisely the sweep time of the L3 ProVision system. This laboratory simulator was driven by an external sweep FIGURE 6.9 The radio frequency (RF)
|
From page 80... ...
Upon testing the field probe system with the simulator, the TSA agreed that a ProVision machine in DAY airport could be used for the first measurement. The DAY airport field test measured the power density emissions for the three scan planes in Figure 6.2, as well as two additional scan planes, defined here as Scan Planes 4 and 5.
|
From page 81... ...
FIELD PROBE CALIBRATION The overall purpose of this measurement effort was to produce calibrated field power density measurements versus frequency in SI units that are widely recognized in RF and millimeter wave measurement standards worldwide. Normally, incident power density is either reported as E-field strength (volts per meter, or V/m)
|
From page 82... ...
value had to be "backed out" based on the overall RF (or millimeter wave) "trail of signal custody" from the field probe receive horn, through the various cables and modules, to the Keysight 8990B time-domain power meter.
|
From page 83... ...
= Ka band solid state amplifier Gain. The incident power density Pd, is found from the classical equation Prcv ( f )
|
From page 84... ...
Based on Equations 6.8 and 6.10, as long as the NARDA receive probe antenna is greater than 11.5 cm from the ProVision transmit array, Equation 6.7 is valid to calculate incident power density. Finally, the incident E-Field in free space is simply from Equation 6.7: Ei ( f )
|
From page 85... ...
Committee-Led Measurements 85 FIGURE 6.13 Far-field range of NARDA V637 versus frequency. FIGURE 6.14 NARDA V637 horn antenna used for probing the ProVision scanner.
|
From page 86... ...
86 A i r p o r t P a s s e n g e r S c r e e n i n g U s i n g M i l l i m e t e r W av e M a c h i n e s FIGURE 6.15 NARDA V637 far-field gain. FIGURE 6.16 NARDA V637 computational electromagnetic (CEM)
|
From page 87... ...
DATA PROCESSING For each of the RF airport measurements, the field probe data at each test point consisted of a series of linear FM pulses that was maximized when the field probe antenna was electrically aligned with the ProVision scanner element directly in line with the field probe. An actual raw time-domain linear FM pulse train measured in MEM is shown in Figure 6.18.
|
From page 88... ...
ProVision Memphis International Airport (MEM) power meter data; in this case, Scan Line 106.
|
From page 89... ...
The field probe device is placed inside the ProVision ATD scanner chamber, and the unit is positioned with the front antenna extension installed, which places the NARDA receive horn 28.7 cm from the transmit array.3 While the L3 ProVision system scans from top to bottom, the field probe is positioned from bottom to top. Because it takes ~3 µs for the ProVision unit to complete a single line scan, the time-domain instrument in DAY airport was adjusted to display 3.5 µs of time response.
|
From page 90... ...
With this method, the entire field probe apparatus, which weighed over 150 lb and was not easily moved, did not have to be repositioned. However, for Scan Plane 3, the entire field probe was picked up and rotated 180 degrees, and the rear array was characterized at 29 cm from the rear ProVision array.
|
From page 91... ...
Committee-Led Measurements 91 FIGURE 6.21 Data from Figure 6.20 rotated 90° with time as abscissa and power as ordinate. FIGURE 6.22 Raw P8990B data (Dayton International Airport [DAY]
|
From page 92... ...
Now it is easy to see the individual linear chirp waveforms for this case. How ever, the data are still not calibrated and Figure 6.23 represents P8990B(f)
|
From page 93... ...
of the Keysight 8990B measurement RF network, the "raw" data acquired by the 8990B must be "calibrated" using Equation 6.7. FINAL CALIBRATION ADJUSTMENT AND NOTIONAL POWER DENSITY DATA PLOT As discussed above, it was straightforward to convert the time domain power meter measurements to an equivalent frequency domain power meter measurement because the ProVision linear chirp waveform is very precise and repeatable by design.
|
From page 94... ...
FIGURE 6.26 Sample power density (Pd) in dBm/cm2, (Dayton International Airport [DAY]
|
From page 95... ...
FIGURE 6.27 Dayton International Airport (DAY) Scan Plane 1 power density data versus height plus average of all waveforms.
|
From page 96... ...
This occurs because the system signal-to-noise figure varies more in this region, inducing more calibration offset. The average value of the measured power density fell right between the expected radiated power limits of the DAY airport unit tested with an approximate upper limit of −50 dBm/cm2 (or 0.0001 W/m2)
|
From page 97... ...
FIGURE 6.28 Dayton International Airport (DAY) Scan Plane 2 power density data versus height plus average of all waveforms.
|
From page 98... ...
FIGURE 6.29 Dayton International Airport (DAY) Scan Plane 3 power density data versus height plus average of all waveforms.
|
From page 99... ...
All of the DAY airport results reported above were produced with the rear reference antenna as described earlier. In subsequent airport measurements in CVG, MEM, and TYS airports, adjustments were made with the front reference antennas, and time base window adjustments -- to allow a denser number of points in the curves above that -- provide a slightly higher sampling of the power density in the frequency domain.
|
From page 100... ...
. NOTE: CVG, Cincinnati/Northern Kentucky International; DAY, Dayton International Airport; MEM, Memphis International Airport; TYS, McGhee Tyson Airport.
|
From page 101... ...
. NOTE: CVG, Cincinnati/Northern Kentucky International; DAY, Dayton International Airport; MEM, Memphis International Airport; TYS, McGhee Tyson Airport.
|
From page 102... ...
This gives an average exposure of 3.7 × 10−5 W/m2, which is about 270,000 times less than the 10 W/m2 recommended limit. The committee notes that making a direct comparison to the IEEE exposure recommendation for millimeter waves is somewhat problematic, because this recommended maximum exposure value (10 W/m2)
|
From page 103... ...
When the noise limit of the Keysight P8990B is plotted versus the predicted levels that were based on the angle and distance of the measurement, it is clear why there was no signal response in this configuration. At CVG airport, the BRC/ARA team attempted to measure the power density in the ProVision exit door adjacent to the TSA operators position (Scan Plane 4)
|
From page 104... ...
FIGURE 6.33 Attempt in Dayton International Airport (DAY) to measure Scan Plane 4 and 5 with Pro Vision in center.
|
From page 105... ...
FIGURE 6.35 Cincinnati/Northern Kentucky International (CVG) Scan Plane 4, transient sweep, center of exit door aperture versus minimum specific power.
|
From page 106... ...
The BRC/ ARA team used a wideband spectrum analyzer at the DAY airport to test for subharmonic emissions. A standard 2 to 18 GHz dual-polarized horn antenna was positioned in close vicinity of the ProVision scanner in an attempt to detect frequency harmonics of the original millimeter wave (24 to 30 GHz)
|
From page 107... ...
Finding 6.1: The committee-led measurements at airports indicate that even an "out of position" person will receive an average pulsed power density during a scan that is 270,000 times below the applicable standard exposure limit of 10 W/m2 and most likely will receive even less standing correctly in the center of the portal. Finding 6.2: The committee-led measurements at airports indicate that even at the entry position of the portal, the power density is several million times below the acceptable limit, even for a continuous signal.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.