Value chain · CLM-1131
In plain terms
They ran a radio-propagation model over a map of the actual ground and found that, aimed just right, the beam plus its reflection off the ground would land nearly twice as much power on the receiver as the direct beam alone; a perfect mirror-flat ground would give almost four times, the theoretical best.
The claim as recorded
NRL 2022 models the 1046 m Blossom Point link with "The parabolic wave equation", a method "valid in the Fresnel region and therefore well-suited for power beaming applications", on USGS 1/3 arcsec terrain reduced to "a homogeneous 2-D cross section" with soil "uniform and dry with 0.67 S/m conductivity and a relative dielectric constant of 25.916", r_TX 2.7 m, h_TX 3.71 m, delta h 0.8 m, and finds that as the transmitter tilt passes through +/-0.1 degrees "the ground scattering actually improves the beam focus at the target location", "predicting a 2.73 dB increase in maximum power density" for tilts of -0.2 to +0.1 degrees over the line-of-sight plateau, against "> 4dB" over perfectly flat terrain and 5.75 dB over a perfectly conducting flat earth, "which approaches the theoretical limit of 6 dB"; the optimum receiver height is 5 m "with a slight downward tilt from the line of sight", and "This result is not general", being "sensitive to small variations in link distance".
Evidence behind this: T2-peer-reviewed numerical propagation model (split-step parabolic equation, PETOOL) with its inputs and approximations stated; the prediction is confirmed by the measurement in CLM-1132, which is where the T1 sits.
Scope and limits
A MODEL WITH ONE SOIL, ONE PROFILE AND NO SENSITIVITY: 0.67 S/m and 25.916 appear once each and are not varied, and the authors' own caveats are the homogeneous 2-D cross-section and "not general". Site- and distance-specific by the paper's statement. Measured value 2.3 dB (CLM-1132), 0.4 dB short. Terrestrial grazing geometry only.
What it assumes
The 2.73 dB is peak over the line-of-sight plateau (Fig. 11a, crop reading); the terrain is the Fig. 2 profile along one line of sight.
Where it comes from
PDF 5 / printed 32: the paper says a power beaming link can be designed to exploit scattering from terrain to reach a higher power density at the target location (normalised); the parabolic wave equation (its [21], [22]) is described as a numerical method for exploring propagation effects across terrain, valid in the Fresnel region and therefore well suited to power beaming (normalised); "= 2.7 m", "= 3.71 m", "= 0.8 m" (raw fragments; the layer drops the delta); "the soil is assumed to be uniform and dry with 0.67 S/m conductivity and a relative dielectric constant of 25.916" (normalised); the ground scattering, the paper says, actually improves the beam focus at the target location (normalised); the approximations it lists include reducing the terrain model to a homogeneous 2-D cross section (normalised); "predicting a 2.73 dB increase in maximum power density for" (raw); the results over perfectly flat terrain (R1) "show a > 4dB improvement is possible" (normalised); making the flat earth perfectly conducting in the simulation raises the ground bounce (R1) "effect to 5.75 dB, which approaches the theoretical limit of 6 dB [23]" (normalised); "a receiver height of 5 m is optimal over a" (normalised); indicating, the paper says, that the optimum geometry uses this height with a slight downward tilt from the line of sight (normalised); "This result is not general, however" (normalised); the optimal choice of receiver height and transmitter tilt can, it says, be sensitive to small variations in link distance (normalised; the page prints "tile" for tilt); "must be repeated or parameterized vs." (raw) d_TRX "if standoff distance is a design variable" (normalised); the Fig. 10 caption says that over this range the ground scattering enhances power density at the target location (normalised). PDF 2 / printed 29: the terrain data resolution is 1/3 arcsec in latitude and longitude (its [11]), with a height accuracy of 58 mm at 95 per cent confidence in the presence of vegetation ([12]) (R2). PDF 13: [21], [22] PETOOL (normalised); [23] M. Dolukhanov, Propagation of Radio Waves, Mir Publishers, Moscow, 1971 (normalised). Fig. 11 crop (render readings): Blossom Point peak 0 dB near -0.1 deg, plateau near -2.8 dB above +0.2 deg; flat earth peak near -0.2 deg, plateau near -4.5 dB; 3-dB height extent 7.2 m on the plateau narrowing to 3.6 m at the bounce (flat earth 2.2 m). Recomputed: 10^0.273 = 1.875; 10^0.575 = 3.76; 20 log10(2) = 6.02 dB.
Basis: dB of power density at the target relative to the line-of-sight plateau; m of receiver height; deg of transmitter tilt; S/m; relative permittivity
Cite this
energyaperture.com/c/clm-1131
CLM-1131, Energy Aperture, as of 2022-01.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-270
- CLM-1122About twenty thousand postage-stamp-sized antenna-plus-diode cells, each with an off-the-shelf microwave diode, wired into tiles, then...CLM-1123A five-metre dish and a 100 kW radar-type pulsed tube a kilometre away, bounced partly off the ground on purpose to get more power onto the...CLM-1124One panel the size of a sheet of paper turned about seven-tenths of the microwave power landing on it into DC, and did best at about three...CLM-1125Four square metres of receiver turned 73 per cent of the microwave power arriving at it into 1.65 kW of DC, measured a kilometre from the...CLM-1126They deliberately fried each of the four panels with ever-stronger pulses. A bare panel gave up at 672 watts out; clamping its voltage with...CLM-1127As flown, under two per cent of the microwave power fed to the dish came out of the receiver as electricity, because the beam had to be...CLM-1128A second test used a big radar dish in Massachusetts to light up a strip of LEDs on a tower over a kilometre away, with about a kilowatt...CLM-1129The authors say the 1975 record still stands at twenty times their power, that the custom diodes which set it no longer exist, and that...More on the source page.