An Assessment of Potential Health Effects from Exposure to PAVE PAWS Low-Level Phased-Array Radiofrequency Energy (2005) / Chapter Skim
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5 PAVE PAWS Exposure Conditions
5 PAVE PAWS Exposure Conditions
Pages 53-93
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From page 53... ...
The carrier frequency varies from 420 MHz to 450 MHz. Signal bandwidths at the input to the final amplifiers range from ~ kHz for the narrowest pulse to 125 Hz for the widest pulse.
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From page 54... ...
All modules are excited simultaneously; beam scan is provided by phase shift. Sidelobe levels are held 20 dB below the main beam by tapering: the inner subaTrays have all active elements, while middle subaTrays have some passive elements, and outer subarrays have more passive elements.
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From page 55... ...
In Figure 5-2b the rise time is approximately I microsecond, with a gradual nse and gradual leveling off Finally Figure 5-2c shows fall time, which is much slower, roughly 12 microseconds, and therefore no abrupt changes are evident. Note that the nse-time bandwidth is narrow (roughly 2 MHz)
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From page 56... ...
rise time taken from RF monitor example in T.O. 3 IP6-2FPS 115-51, Chapter 6.
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From page 57... ...
Although it has been implied that the measured radial fields (radial waves) represent a new and unexpected phenomenon, they are just the result of mulupath and simple geometry.
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From page 58... ...
. -2 O s FIGURE 5-3c Radial field amplitude (from 3-96 c of the waveform report)
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From page 59... ...
In the far-field of a large phased array or reflector antenna, the contributions from all parts of the antenna arrive at the main beam peak simultaneously (broadside beam for a phased array)
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From page 60... ...
Since those with the smallest projected separation contribute first, the array of projected separations is ordered in ascending order by a well-known subroutine called HEAPSORT, Because the excitation phases associated with the main beam position affect the phase of the buildup, the x and y coordinates are sorted in consonance with the projected separations. The delay time across the array is roughly 74 nanoseconds; the delay for the worst case mentioned above is 60 nanoseconds.
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From page 61... ...
The PP waveform buildup near normal (from Figure 3-46b in the waveform report) is shown in Figure 5-7.
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From page 62... ...
62 ASSESSMENT OF POTENTIAL IIEALTII EFFECTS FROM PA VE PAWS / FIGURE 5-5a PAVE PAWS wavefor n buildup. ~ Croup, az = 60 degrees, el = 0 degrees.
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From page 63... ...
PAVE PAWS EXPOSURE CONDITIONS 63 FIGURE 5-6 Array buildup; 60 degrees off normal. FIGURE 5-7 Array buildup; near normal to array face.
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From page 64... ...
Third, noise and interference were much worse for the D-dot measurements; all measurements discussed here were made with the TEM horn. Fourth, these results agree with the buildup calculations of Figures 5-7a and 5-7c, of the Air Force Phase IV waveform report; the discrete nature of the buildup can only be glimpsed at the very beginning, when the waveform has very small amplitude, and is heavily corrupted by noise and interference.
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From page 65... ...
Turning now to the waveform decay, Figure 5-11 (from Figure 3-56b in the Air Force Phase IV wave form report) shows the array at wide angle, Figure 5-12 (from Figure 3-53e in the Air Force Phase IV wave form report)
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From page 66... ...
66 ASSESSMENT OF POTENTIAL IIEALTII EFFECTS FROM PAVE PAWS FIGURE 5-10 Dish buildup; 46 degrees off normal narrow-band. FIGURE 5-11 Array fall-off; 60 degrees off nm~nal.
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From page 67... ...
PAVE PAWS EXPOSURE CONDITIONS 67 FIGURE 5-12 Array fall-off; near normal to a ray face FIGURE 5-13 Dish fall-off; 46 degrees off normal.
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From page 68... ...
A precursor is a modification of the Incident waveform that arrives at a given depth in the dispersive medium before or dunug the incident waveform. Sommerfeld precursors arrive before, and tend to contain frequencies higher than the signal carrier frequency.
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From page 69... ...
Each of these spectral components decays exponentially in a linear lossy medium; if the wideband applied waveform has sufficient lower frequency energy, the resulting precursor will decay more slowly than the exponential decay of the carrier. Because the spectral components of lower frequencies decay more slowly with penetration distance, the mix (spectrum)
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From page 70... ...
Albanese are corrupted by interference. The spatial variation in Figure 5-14 matches almost exactly the leading edge of the related Phase IV waveform in Figure 5-15; Figure 5-14 should be volts/meter, as in Figure 5-15.
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From page 71... ...
FIGURE 5-17 Leading edge, 540 meters from PAVE PAWS.
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From page 72... ...
The granularity maximum delay is 60 nsec; the waveform buildup is completely covered by Figure 5-18 but nothing attributable to the discrete delay is visible. Jim Tomlin, for the PPHSG, has smoothed the waveform data, and has calculated and plotted delta slopes (see Figure 5-19)
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From page 73... ...
This paper shows indirectly the association between signal rise time (in nsec) amd precursor formation.
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From page 74... ...
The coaxial test cell was designed for a 50 ohm match with air; the water, salt, and sugar solutions produced major mismatches resulting in quite apparent ringing, All of the measurements were wideband, and had frequency spectra centered above 1000 MHz, where dielectric constant £ and conductivity ~ changes with frequency are significant. Precursors were observed only in those few wideband experiments that were designed to create strong dispersion (waveguide and Goubau line)
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From page 75... ...
. The wideband waveforms decay at the carrier rate for several meters, then more slowly, However the band-limited signal decays at the carrier rate at all penetrahon distances.
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From page 76... ...
They are grouped into precursor measurements, precursor calculahons, related papers on precursors, pulse propagation in lossy media, and publications by Professors Oughstun and others. SUMMARy The PAVE PAWS phased array contains a large number of elements per face (1792)
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From page 77... ...
There are extensive calculations, and several measurements, that show that wideband signals produce observable precursors. Typical precursor wide bandwidth is 10,000 MHz, a factor of 2000 times the PAVE PAWS bandwidth.
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From page 78... ...
The PAVE PAWS instantaneous bandwidth is never more than 5 MHz, although the carrier frequency changes as the beam moves between 420 MHz and 450 MHz. Thus this narrow bandwidth signal is not expected to produce measurable precursors, ANNEX 5-2: PAPERS ON PRECURSOR MEASUREMENTS 1.
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From page 79... ...
A single-step function with a rise time of roughly 500 picoseconds was the applied signal. For the frequency spectrum of the waveform, roughly 4000 MHz wide, distilled water, if sufficiently pure, has dielectric constant and conductivity similar to those of muscle tissue.
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From page 80... ...
The source signals were of poor quality. The coaxial test cell was designed for a 50 ohm match with air, the water, salt, and sugar solutions produced major mismatches with resulting quite apparent nngung.
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From page 81... ...
," NSWC report JPOSTC-CRF-005-03, Dablgreen, VA, Sept. 2001 The test cell was a 1.4 m-long coaxial transmission line with recirculated deionized water.
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From page 82... ...
Sherman, Electromagnetic Pulse Propagation in Causal Dielectric, Springer, 1997 This treatise shows in detail the difficulties in obtaining approximate solutions to wave propagation in dispersive media. Crudely, the signal is represented in the complex phase plane by a pole, and the precursors by branch points.
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From page 83... ...
Signal bandwidth was approximately 10 GHz; the widest PAVE PAWS bandwidth is 5 MHz, or 2000 times smaller. PAVE PAWS precursors will be too small to be measurable.
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From page 84... ...
Because of the Harrow bandwidth of the I microsecond waveform, all spectral (Founer) components decay essentially exponentially, producing the classic "shin depth." Figure 5-A3.3 shows waveform decay over a ammeter depth; this waveform decays exponentially just like all narrow-band waveforms.
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From page 85... ...
PAVE PAWS EXPOSURE CONDITIONS ,5r :> 85 s 502 — I moor — ~ meets — s me s.o. 506 s 08 s 1 Me, micomsec FIGURE 5-A3.2 Leading edge of I usec signal at various depths; baselines are offset for clarity.
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From page 86... ...
Penn, and R Medina, "Short-Rise-Time Microwave Pulse Propagation through Dispersive Biological Media," J
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From page 87... ...
At 1.5 m distance the rise time affected the precursor amplitude, with longer rise time reducing the amplitude. However, at this distance the main signal is very small and the precursors are also small.
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From page 88... ...
AppL Phys., Vol. 45, March 1974, 1171-1175 Propagation of a single Gaussian type pulse (slow rise time and fall time)
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From page 89... ...
The aim was to see if precursors could help in the inverse problem Note, the inverse problem is: given the response, find the details of the scatterer or the details of the medium. Pulse Propagation in Lossy Media Researchers from Harvard have published papers on pulse propagation in sea water, a highly lossy medium.
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From page 90... ...
and K.E. Oughstun, "Dispersive Pulse Propagation in a DoubleResonance Lorentz Medium," J
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From page 91... ...
and J.E.K. Laurens, "Asymptotic Description of Electromagnetic Pulse Propagation in a Linear Dispersive Medium," in UltraWideband, Short-Pulse Electromagnetics, }1.
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From page 92... ...
and K.E. Oughstuo, "Electromagnetic Pulse Propagation Across a Planar interface Separating Two Lossy, Dispersive Dielectrics," in Ultra-llideband, Short-Pulse Electromagnetics 3, C
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From page 93... ...
and K.E. Oughstun, "Ultrawideband Electromagnetic Pulse Propagation in Triply Distilled Water," Ultra-Wideband, Short-Pulse Electromagnetics 4," Heyman et al, Eds., Kluwer Academic/Plenum Publ., 1999,265-276 27.
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