Value chain · CLM-1132
In plain terms
They then measured it: raising the receiver through five metres above the ground the received power jumped by about 70 per cent, close to the model's 87 per cent; the beam was as narrow as in free space side to side and a little wider up and down; and because the ground reflection varies across the receiver, they had to map the arriving power point by point rather than swing the transmitter past a fixed probe.
The claim as recorded
NRL 2022 measured the predicted ground bounce by "varying the height of the horn, boresighting the horn and reflector at each height, and measuring received power" at 1046 m: "A sharp increase in received power is evident in the 4.5" to "5.5 m range, as predicted by simulation", a measured 2.3 dB enhancement against the predicted 2.7 dB, which "nonetheless confirms the importance of terrain scattering in the design of terrestrial power beaming links"; measured half-power beamwidths were 0.50 degrees (elevation cut) and 0.40 degrees (azimuth) at 5.5 m receiver height against 0.51 simulated and 0.40 free space, and 0.40 / 0.42 / 0.41 at 11 m; vertical and horizontal polarisations "match closely, as expected for very low grazing angles"; and because a rotating-source measurement "cannot capture the true variation in terrain scattering across the receive aperture", the incident power had to be found by spatially sampling the receive plane with a translating horn (+/-1.5 m by 4 to 7 m), the paper calling itself "the first power beaming demonstration to exploit the effect of" ground bounce.
Evidence behind this: T1-peer-reviewed measurement of a predicted terrain effect with the instruments, geometry and comparison stated; no numerical uncertainty on the 2.3 dB.
Scope and limits
ONE SITE, ONE LINE OF SIGHT, ONE FREQUENCY, NO STATED UNCERTAINTY ON THE 2.3 dB; the enhancement is a property of this terrain at this geometry and the paper says the optimum "is not general". The Table 1 rows are vertical polarisation only by the authors' choice. The "first ... to exploit" claim is the authors' against their own review [1].
What it assumes
The predicted 2.7 dB in the comparison is the 2.73 dB of CLM-1131 rounded.
Where it comes from
PDF 8 / printed 35: the optimal receiver height at 1046 m standoff from the reflector is found, the paper says, by varying the height of the horn, boresighting the horn and reflector at each height, and measuring received power (R1); "A sharp increase in received power is evident in the 4.5" (normalised) to "5.5 m range, as predicted by simulation" (normalised); "is 2.3 dB, which although slightly less than the predicted value of 2.7 dB" (normalised); the result, it says, nonetheless confirms the importance of terrain scattering in the design of terrestrial power beaming links (R1); Table 1 (render read): 0.50 / 0.40 / 0.51 at h_RX = 5.5 m, 0.40 / 0.42 / 0.41 at 11 m, free space 0.40; the table note has measured quantities in green text and, for simplicity, vertically polarised results only (normalised); "Measured HPBW matches closely with simulated HPBW in the" (normalised) phi = 0 plane; increased variation in power density with height is, the paper says, clear in Fig. 19b, as predicted from the results in Fig. 18 (normalised); confirming, the paper says, the importance of spatially sampling the received field to determine the incident power at the receive aperture accurately (R2); Fig. 18 (render reading): measured points on the predicted curve, a peak near 5 m, a plateau 2.3 dB (measured) and 2.7 dB (predicted) lower from about 8 m out. PDF 7 / printed 34: the measured radiation patterns for vertical and horizontal polarisation match closely, as the paper expects for very low grazing angles (its [23]) (normalised); the simulation shows, it says, excellent agreement with the measured main beam shape for both vertical and horizontal polarisations (normalised); outside the main beam a large side lobe predicted in Fig. 17b is much reduced in the experimental results (normalised). PDF 6 / printed 33: terrain scattering, the paper says, affects the measurement strategy for characterising the power density, and therefore the efficiency, of a power beaming link (R2); the rotating-source approach of Fig. 13a samples every point of the radiation pattern along the same line of sight and so, it says, cannot capture the true variation in terrain scattering across the receive aperture (normalised); even for highly directive transmit sources, scattering from terrain can be significant, making it necessary, the paper says, to spatially sample the beam (R2) "to accurately determine the incident power" (normalised). PDF 2 / printed 29: prior terrestrial demonstrations at distances > 500 m, the paper says, minimised terrain scattering by significantly elevating the transmit aperture and rectenna array (its [1], [8], [9]) and by positioning the beam's target across a chasm on a mountainside ([8]) (R2); the paper calls itself the first power beaming demonstration to exploit the ground bounce effect (R1) "to enhance power density at the target location" (normalised). PDF 13: the conclusion states a 2.3 dB enhancement in power density at the target site, achieved by deliberate exploitation of a ground bounce over cluttered, irregular terrain (normalised). Recomputed: 10^0.23 = 1.70 and 10^0.27 = 1.86; 0.40 deg x 1,046 m = 7.3 m and 0.50 deg x 1,046 m = 9.1 m full half-power widths at the target.
Basis: dB of received power against receiver height; deg of half-power beamwidth; m
Cite this
energyaperture.com/c/clm-1132
CLM-1132, 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.