VC07 Ground receiver and rectification
Depth of coverage
At its target depth of L3. What the depth levels mean.
What this layer covers
Rectenna or optical receiver, RF or light to DC conversion, receiver site, land area, civil works, co-use of land
Where it ends
Ends at the DC or LV terminals of the receiver array
Deep area
This layer is studied in more depth than most. It belongs to the deep area Power electronics and ground segment.
Ground receiver: where it stands
The ground receiver has measured results, but only at small scale. It is a rectenna, a field of antennas that turns the beam back into DC electricity. By 1976 a rectenna had delivered 30 kW of DC over 1.6 km, converting over 82 per cent of the microwave power reaching it (CLM-1097). A 2022 US Navy laboratory array of about 4.45 m2 turned 73 per cent of 2,265 W into DC at about 1 km, in short pulses and with no stated uncertainty (CLM-1123, CLM-1125). Two NASA programmes in the 1980s aimed at frequencies above 2.45 GHz, and both ended with no working device (CLM-0940). A 2021 Frazer-Nash study summary calls the beam inherently safe because sunlight is more intense, but cites no exposure standard (CLM-0002). A 1980 DOE assessment said the risk from the added microwave exposure must be assessed before building (CLM-1007).
Scope. The ground receiver is a rectenna. It is a field of small antennas, each joined to a diode (an electronic part that lets current flow one way only), that turns the microwave beam back into direct current (DC). This section also covers optical receivers, the site and the civil works. It ends at the DC terminals of the array. The beam itself is covered separately.
What is settled. Small rectennas work, and the best figures are old. By 1976 an array at Goldstone, California, had converted over 82 per cent of the microwave power reaching it and delivered 30 kW of DC over 1.6 km (CLM-1097). In 1977 single elements, tested one at a time in a bench fixture rather than in an array, reached 90.5 per cent at 8 W input, but only 79.5 per cent at 50 mW (CLM-1096). In 2022 a US Naval Research Laboratory array of about 4.45 m2 turned 2,265 W of incident power into 1,649 W of DC, 73 per cent, at 9.7 GHz and about 1 km (CLM-1122, CLM-1123, CLM-1125). The 2022 figures are peak values in pulses of up to a microsecond, and the paper gives no numerical uncertainty (CLM-1123, CLM-1125). The authors say the 1970s power record still stands and its custom diodes no longer exist (CLM-1129). None of these tests approaches the gigawatt scale of a full design, such as the 1980 5 GW ground station (CLM-1097, CLM-1125, CLM-1077).
What is disputed. The design beam strength differs between documents. UK feasibility documents give the beam strength at the rectenna as about 230, 240 and 245 watts per square metre (W/m2) in different places, with no stated reason for the difference (CLM-0001, CLM-0002, CLM-0003). A 29 W/m2 figure in the same documents is electricity per unit of land, not beam strength. This site's own calculation reproduces it (CLM-0005).
A 2021 Frazer-Nash study summary calls the system "inherently safe" because the beam centre, at about 240 W/m2, is about a quarter of the intensity of the sun at the equator. It cites no exposure standard, a limit on how much radio energy people may absorb (CLM-0002). A full-text search of five main documents on CASSIOPeiA, a UK satellite design, and the UK studies found no named exposure standard and no restricted area around the receiver. A later or unread document could contain this work (CLM-0504). A 1980 US Department of Energy summary said a risk assessment must come before building (CLM-1007).
A 2008 review found that at 2.45 GHz the 230 W/m2 design beam may cause thermal self-focusing in the ionosphere, the charged upper layer of the atmosphere, but not at 5.8 GHz. In self-focusing, the beam's own heating concentrates it further. The review used one assumed electron density, which is well above a typical mid-latitude value in measured data (CLM-0105).
Costs and siting. Cost rests on 1980 numbers. A 1980 rectenna design paper put a 5 GW ground station at USD 2,578 million, in a cost table that gives no source (CLM-1077). An independent 1980 cost audit judged the rectenna's civil costs low by a factor of three to five (CLM-1079). A preliminary 1980 study priced an offshore version on towers at USD 36 billion, which it judged too expensive, and an unoptimised cable-hung version at USD 5.7 billion (CLM-1078). The 25 W diode of the reference design did not exist to test for lightning damage (CLM-1101).
A 1980 siting study gave a reference site of 12.0 km by 15.8 km at 35 degrees north, or 148.9 km2. That includes a buffer zone, a margin about 1 km wide around the field that keeps microwave levels outside it low (CLM-1102). The study found about 40 per cent of the land area of the continental United States nominally eligible. A closer check of 180 eligible map squares, each about 13 km across, reclassified 71 per cent of them. Leaving out terrain, the figure was 24 per cent (CLM-1103). A follow-on study found it "appears possible" to site 60 rectennas within 150 km of the load centres they would serve, if each supplied no more than 25 per cent of its load centre's projected baseload power, the steady part of demand. The mid-Atlantic region was the exception (CLM-1082).
Other receivers. Two NASA programmes in the 1980s aimed at rectennas above 2.45 GHz, and both ended with no working device. That was a judgement about 1980s fabrication methods, not a physical limit (CLM-0940).
Two items bear on use in space. A 1993 report titled "Construction and Testing of a Space Ready Rectenna" describes launch shock, vibration and fit tests and mentions no vacuum or thermal test (CLM-0948). A 1987 calculation capped a rectenna cooled only by radiation, as in space, near 2.33 kilowatts per square metre (kW/m2) of DC at an assumed 70 per cent efficiency. At 85 per cent, the same figures give 5.67 kW/m2. It is a rough sketch (CLM-0941).
Optical receivers work at much higher intensity. A 2026 laboratory chip of 5.4 square millimetres turned 55.9 per cent of near-infrared laser light, invisible light of longer wavelength than red, into electricity at 271 kW/m2. It turned about 30 per cent at 1 kW/m2, a level the authors call eye-safe (CLM-1110). That bright case is about 1,200 times the 1978 microwave design peak of 230 W/m2 (simple division). The paper proposes no laser power satellite (CLM-1113).
Beam safety: the design numbers. The 1978 US reference design put 230 W/m2 at the centre of the receiving site. The design dropped to 10 W/m2 where the rectenna ends, and to 1 W/m2 at the outer boundary of the exclusion zone (CLM-0020). The UK study figures are 230 to 245 W/m2 (CLM-0001, CLM-0003). The main international guideline today, ICNIRP 2020, sets a screening level of 10 W/m2 for members of the public and five times that, 50 W/m2, for workers, averaged over 30 minutes and over the whole body (CLM-0008, CLM-1169). The UK beam centre is about 23 to 24.5 times the public level and 4.6 to 4.9 times the worker level (CLM-0010). For the UK design, averaging does not lower these figures, because the beam is steady and kilometres wide (CLM-0009). Going above a screening level does not by itself show harm (CLM-0010).
Every use of the 230 W/m2 figure traced in the sources examined goes back to the 1978 document, and none states independent grounds for it (CLM-0044). A 2013 review says it was chosen to avoid strong interaction with the ionosphere (CLM-0111). The 2019 CASSIOPeiA paper calls it an economic optimum and says under 1 kW/m2 is safe, citing no standard (CLM-0004, CLM-0013). A 2007 URSI paper sets 10 W/m2 as the design level at the rectenna edge (CLM-0049). A 2024 Chinese concept at 5.8 GHz simulates a first sidelobe of about 22 W/m2, about twice the public level (CLM-0141). Low confidence: a fenced zone with controlled access, sized so that the public level is met at its edge, could in principle let a centre of 230 to 425 W/m2 coexist with the public level (CLM-1467 (low confidence)).
Who would be exposed. A 1980 DOE and EPA assessment put people beyond the exclusion boundary well below 1 W/m2 in general. People entering the site could receive up to 230 W/m2, perhaps more with reflections, unless precautions were taken (CLM-0036). Under ICNIRP, the worker level applies only to trained adults exposed under controlled conditions, and a pregnant woman counts as a member of the public (CLM-1171). Shinohara says a future system has to meet the safety guideline beyond the site, while the status of the keep-out area inside it is still being discussed (CLM-0017). Near the centre of the transmitting antenna in orbit, the 1980 figure is 2,200 mW/cm2 (CLM-1008), which is 440 times the ICNIRP worker level. A 1978 workshop on radiation for space workers left microwaves out of its scope (CLM-1158).
Aircraft. A 1980 assessment argued that a metal fuselage would keep cabin levels generally much lower than the 230 W/m2 centre. This was reasoning about shielding, not a measured value (CLM-0153). A 1981 assessment took the crossing to last roughly half a minute to a minute, and judged the passengers' exposure insignificant. That was an assessment, not a test, and it assumed metal airframes (CLM-1204). The cabin measurements found are for an aircraft's own radar, not an outside beam. In 1974 the EPA found nothing above its meter's 2 W/m2 floor in two cockpits with the nose radar on (CLM-1363). Low confidence: a 1971 US Air Force survey measured crew areas of EC-121 aircraft in flight at more than 30 dB under the 10 mW/cm2 limit (CLM-1364 (low confidence)).
Birds and insects. A 1978 review judged it unlikely that a bird crossing the middle of the beam would live. It reached that view by reasoning, not by experiment (CLM-1155). In 1980 field work, small birds at 25 mW/cm2 showed only mild changes in behaviour, and a first estimate put the level that kills half of resting birds in winter near 150 mW/cm2, based on a handful of birds (CLM-1066). Low confidence: Canadian tests in 1966-69 used mostly pulsed 9 to 16 GHz beams on caged birds. Exposed from above, the birds reacted within seconds to minutes (CLM-1295 (low confidence), CLM-1292 (low confidence), CLM-1293 (low confidence), CLM-1294 (low confidence)). Exposed from below, they barely reacted (CLM-1294 (low confidence), CLM-1292 (low confidence), CLM-1293 (low confidence)). A 2007 URSI working group suggested capping the beam centre near 25 mW/cm2 with birds in mind, and assumed that 5.8 GHz acts the same as 2.45 GHz (CLM-0460). In chambers, honey bees exposed for half an hour to 3 to 50 mW/cm2 of continuous 2.45 GHz showed no effect, in tests on one species only (CLM-1147). A single colony kept for four weeks at 1 mW/cm2, the expected edge level, stayed within normal variation (CLM-1149). The programme said other species must also be tested (CLM-1153).
Long-term, low-level exposure. This is the largest gap. In 1978 a review of the literature found no study lasting anywhere near the 30-year working life of a power station (CLM-1154). In 1981 OTA judged that the health risk of chronic exposure below 1 mW/cm2 could not be analysed with the data then available (CLM-1284). Most of these animal studies are short and small. Pregnant squirrel monkeys showed infant deaths in a first study, which a larger second study had not confirmed by 1980 (CLM-1067). Four rabbits exposed 23 hours a day for 180 days showed no lesions, but a weaker lymphocyte response (CLM-1304). Low confidence: pregnant rats at 0.5 mW/cm2 for 20 hours a day had more pup deaths in the first week, with 8 mothers per group (CLM-1300 (low confidence)). Two mouse papers disagree. Low confidence: one reported mice 4 to 6 per cent heavier after short hourly exposures, at a density it gave as 0.02 W/cm2 (CLM-1342 (low confidence)). A 1973 paper from the laboratory that ran the original test found no growth difference at 10 mW/cm2, and says the earlier density was misreported (CLM-1361). Low confidence: a 1986 review reported preliminary 1984 results from a five-year US Air Force rat study at pulsed 2.45 GHz, with more malignant tumours at an absorption level that the 1982 US standard accepted. The review judged the findings far from definitive (CLM-1333 (low confidence)). None used the higher frequency of recent designs.
Standards then and now. The US guideline was 10 mW/cm2, or 100 W/m2, in 1974 (CLM-0024). The 1982 revision set 50 W/m2 above 1500 MHz for the public and workers alike (CLM-1298). So the same 230 W/m2 centre went from 2.3 times the US limit in 1974 to 4.6 times in 1982, and is 23 times the ICNIRP public level now (simple division). Soviet limits were far lower. A comparison of about 1976 gives 1 uW/cm2 for the Soviet public (CLM-1297), while the 1980 DOE assessment gives 5 uW/cm2 for 24-hour exposure (CLM-1006). Low confidence: Soviet limits were 100 to 1,000 times below US ones, according to a paper of about 1970 (CLM-1322 (low confidence)). OTA worked out that a site with its boundary at 0.1 mW/cm2 needs about 174 km2, but almost 1,700 km2 if the edge had to meet 0.01 mW/cm2, which OTA called the Soviet standard. That is the Soviet worker value; the Soviet public value is ten times lower (CLM-1283).
What is missing. No cited source measures the level inside an aircraft crossing an outside beam, reports birds tested in flight, or reports a study of lifetime exposure. The harmonic levels (unwanted emissions at multiples of the beam frequency) later quoted for the rectenna come from one 1977 bench element at 5 W, measured at its input, not radiated from an array (CLM-1095). The 1977 report contains no measurement of harmonics radiated from an array (CLM-1095).
Read next. Beam intensity at the rectenna. Efficiency of power beaming at range. Receiver land per gigawatt. The ionosphere limit: tested or not? QST-017 (Why 2.45 GHz, and what the radio rules say). The beam. Getting the power into the grid. Rules, spectrum and law. Environment and lifecycle impact.
Records
113 of the 127 records tagged to this layer are published. The rest are not yet published. A record is published only after a second reader has checked it and it has passed every publication check. What the gate checks.
| Record | In plain language | Tier | Confidence |
|---|---|---|---|
| CLM-0001 | The UK government's own feasibility study describes a system beaming microwaves at about 230 watts per square metre onto the ground. | T4 | HIGH |
| CLM-0002 | The summary report says the beam is strongest at the middle of the receiving site, at about 240 watts per square metre, and argues that this makes it safe because sunlight is stronger. | T4 | HIGH |
| CLM-0003 | The report gives the receiving site as an ellipse roughly 7 km by 13 km, and states a beam strength of 245 watts per square metre. | T4 | HIGH |
| CLM-0005 | A second figure of 29 watts per square metre appears in the same report, but it measures electricity produced per unit of land, not beam strength. The two are different things and must not be compared. | T0 | HIGH |
| CLM-0010 | At its strongest, the beam is around 23 times the level the international guideline sets for the general public, and around 5 times the level set for workers. | T0 | MED |
| CLM-0015 | An independent Japanese authority on power beaming records the American reference design's beam strength as 23 milliwatts per square centimetre at the receiving site, which is 230 watts per square metre. | T2 | MED |
| CLM-0017 | One author, writing in an unpublished draft, says the exposure guideline must be met outside the receiving site, and that what applies inside the site is still under discussion. | T2 | MED |
| CLM-0020 | The original 1978 design set the beam at 230 watts per square metre in the middle of the receiving site, about one twenty-third of that at its edge, and about one two-hundred-and-thirtieth of that at a fenced boundary further out. | T3 | HIGH |
| CLM-0036 | The 1980 American assessment said people living or working near the receiving site, outside its exclusion boundary, would generally be exposed to much less than 0.1 milliwatts per square centimetre, and that anyone entering the site for work could be exposed to up to 23, the level at the centre of the site, unless precautions were taken. It treated space workers as a separate case with much higher exposure. | T3 | HIGH |
| CLM-0048 | An international scientific body reviewed the proposed figures, found them ranging from 230 to 1,000 watts per square metre, and chose 300 on health grounds, with 10 at the edge of the receiving site. | T2 | HIGH |
| CLM-0049 | The stated design intent in a 2007 URSI white paper is that the beam would be shaped to fall to 10 watts per square metre by the edge of the receiving site, which the paper gives as the human safety limit in most countries. | T2 | HIGH |
| CLM-0067 | According to a 2007 international report, Japanese designs of the time chose their beam strength on cost and land grounds; the report does not give the ionosphere as the reason. | T2 | HIGH |
| CLM-0101 | The 1978 contract required the researchers to report fixes if ionospheric disturbance pushed the pilot-beam phase error past 2 to 3 degrees, and a 1981 NASA report allowed 10 degrees of phase error for the whole pointing system. The requirement to hit the receiver within about 300 metres from geostationary orbit was stated in 2007, not in the 1978 design, which left that number open. | T3 | MED |
| CLM-0105 | A third party looked at the 230 watt per square metre design figure and said self-focusing may happen at 2.45 gigahertz but not at 5.8 gigahertz. | T2 | HIGH |
| CLM-0108 | A 2004 ESA review found that during the October 2003 solar storm, just under 20 per cent of a space solar power beam would have been absorbed before reaching the ground. In quiet conditions the loss is under 0.3 per cent. | T3 | HIGH |
| CLM-0109 | In normal conditions the ionosphere takes essentially none of the beam. In a severe solar storm it could take a little under a fifth of it. | T0 | MED |
| CLM-0126 | The 1982 source behind the disputed 10 per cent absorption figure actually says absorption is 0.002 per cent, and never mentions solar activity at all. | T3 | HIGH |
| CLM-0401 | A 2004 review calculated that, under some of the most extreme conditions measured during a large solar storm in October 2003, only just over four fifths of a microwave power beam would get through the ionosphere and atmosphere to the ground, against more than 99.7 per cent normally. The storm lasted more than a day, but conditions varied, so a loss that large probably (our inference) did not last throughout. The standard 1978 efficiency figures include no allowance for it. | T3 | MED |
| CLM-0461 | The ionosphere absorbs about one part in a hundred thousand of the beam. It is not a meaningful loss. | T0 | MED |
| CLM-0500 | The same formula for how much microwave power a beam can carry before it destabilises the upper atmosphere gives 425 watts per square metre at one textbook set of conditions and a typical 189 across thousands of real radar measurements. That is not two methods disagreeing; it is one method fed different starting numbers. | T2 | MED |
| CLM-0501 | A 2024 Chinese satellite design concept plans to beam down microwaves twice as strong as CASSIOPeiA's own typical figure, and its designers do not appear to have considered the upper-atmosphere stability question at all. | T2 | MED |
| CLM-0504 | None of the main CASSIOPeiA-related documents in the register mentions any named safety or exposure standard, or describes any restricted area around the receiving site, anywhere in nearly 300 pages. | T2 | HIGH |
| CLM-0511 | The first real, built, and measured version of CASSIOPeiA's beam-steering hardware converts electricity to radio power at 42%, against about 80% for the amplifier alone and 65% for the amplifier with its circulator, once every real component is counted rather than just the amplifier chip. | T2 | HIGH |
| CLM-0512 | The small prototype achieved a beam strength close to what a real system would use, but only over an area the size of a small table, using about 672 watts of radio power. | T2 | MED |
| CLM-0516 | Public money funded a real piece of hardware that was built and tested, not just another report -- a rare outcome in this field -- even though what it found was not entirely flattering to the design. | T3 | MED |
| CLM-0539 | A UK consultancy, working for the European Space Agency and using the same design as its reference point, actually published a full weight breakdown -- something the original 2019 paper never did. It comes out lower than the headline claim, at about 0.70 kilowatts per kilogram rather than 1, even though it leaves out several categories of weight altogether. It also rates one of the satellite's power-conversion stages as barely more than an idea on paper, and its input notes say the lightest case for the radio equipment is an expert's judgement, not something anyone has measured or built. | T4 | MED |
| CLM-0782 | UK rules limit the overhead line between a generating unit and the grid to 5 km for units producing at least 2000 gigawatt-hours a year and 20 km otherwise. A 2 gigawatt plant counted as one unit would cross that threshold even if it ran only about 11 per cent of the time, but the rules define a generating unit as any apparatus which produces electricity, and counted that way a receiving site made of many converters would fall under the 20 km limit. Which reading applies is not settled. | T0 | HIGH |
| CLM-0869 | The 1978 reference report gives two different figures, 88 and 89 per cent, for how much of the beam lands inside the same 5 km circle on the ground. | T3 | HIGH |
| CLM-0870 | Recomputing the 1978 design from its own stated parameters reproduces its beam, its power and its own intercept figure of 95 per cent; the 88 per cent quoted elsewhere in the same report matches a different term in another breakdown of the same losses, and on the knowledge base's arithmetic the two breakdowns agree to about 0.3 per cent. | T0 | MED |
| CLM-0872 | A 1978 efficiency diagram has two of its numbers in the wrong boxes, which its own intermediate figures reveal and its bottom-line total cannot. | T0 | HIGH |
| CLM-0938 | A 1988 NASA paper says a rectenna built on mylar reached 85 per cent efficiency. The 1987 final report of the contract it cites says mylar managed 70 per cent, and that 85 per cent needed a different plastic. | T3 | HIGH |
| CLM-0939 | The 85 per cent figure that later papers quote flat was one component on a bench, in moving air, with an error bar, at one power level. The array number beside it was an estimate, not a measurement. | T3 | HIGH |
| CLM-0940 | Two NASA efforts to build rectennas at much higher frequencies than the standard 2.45 GHz ended without a working device. One concluded the approach it had chosen would not work; the other simply ran out without completing anything. | T3 | HIGH |
| CLM-0941 | In space there is no air to carry away the waste heat, so a rectenna's output is limited by how much waste heat it can radiate. The report puts that ceiling at about 2.33 kW of DC per square metre. | T3 | MED |
| CLM-0946 | A rectenna under test emitted a spurious signal. The cause was the resistor they hung on its output, not the rectenna itself, and swapping the resistor made it stop. The diode's own harmonics were measured separately and plotted. | T3 | HIGH |
| CLM-0948 | The "space ready" rectenna was tested for surviving the rocket launch and fitting into its container. Its report describes no vacuum or heat testing. | T3 | HIGH |
| CLM-0953 | The rectenna was squashed to fit its container, which spoiled the impedance match between it and the incoming beam. The report accepts this on two grounds: the mismatch protects the circuit from high power, and efficiency was not being measured anyway. | T3 | HIGH |
| CLM-0970 | A 1992 computer model of the same thin-film receiving antenna, sitting in space with nothing but radiation to cool it, found its diodes would overheat well before the sheet itself ran out of cooling capacity. The usable power per square metre came out about nine times lower than the simpler sheet-only estimate. | T3 | HIGH |
| CLM-0992 | The receiving field on the ground makes its own harmonics: the diodes that turn microwaves into electricity also generate signals at two, three and four times the frequency and send some of it back out. Early measurements put the strongest of these at about three hundred times weaker than the main beam. | T3 | MED |
| CLM-0993 | Space Solar has won a 1.3 million pound research contract from the research agency ARIA to help solar-powered high-altitude aircraft keep flying through the winter at UK latitudes by beaming them microwave power from the ground, at 5.8 GHz, into an antenna built into the wing. The programme's goal is a few hundred watts to a small payload for a week at a time. | T5 | HIGH |
| CLM-1007 | The 1980 assessment worked out that a full American deployment would raise the microwave background everywhere in the country to about twenty times what people were then typically exposed to, though it said the two could not be compared directly because the frequencies differ. It said a risk assessment had to be done before building. No such assessment is held. | T3 | HIGH |
| CLM-1008 | The 1980 documents give the beam's strength at the satellite, on failure, and above and below the receiving panels. The summary and the detailed report disagree by about twenty times on how much reaches the ground under the panels, which is the number the conclusions about ground animals and plants rest on. | T3 | HIGH |
| CLM-1054 | The programme reckoned a receiving site would give off about as much heat per square metre as a suburb, a tenth of what the sun puts into the ground, enough for a degree of local warming in still air; one of its two reports prints the figure a hundred times too small, and the climate report suspects that the structure's roughness and reflectivity matter more than the heat. | T3 | MED |
| CLM-1077 | The ground station was seven million panels holding thirteen billion little antennas, costed at about two and a half billion dollars, about 1.7 million tonnes of steel and nearly seven million cubic yards of concrete, and built by three thousand people in two years. | T3 | HIGH |
| CLM-1078 | Put on stilts in fifty metres of North Atlantic the 1980 rectenna cost fourteen times its land price; strung from cables without its ground screen it came down to about twice, and Europe had a dozen shallow patches of sea to put one in. | T3 | MED |
| CLM-1082 | Two-fifths of the lower forty-eight states were nominally open to ground stations and sixty of them could be placed near the cities they served; the gallium for one satellite was sixteen times the world's yearly output; and the ground-station dipoles would come off the line at six hundred a second. | T3 | HIGH |
| CLM-1089 | The higher industrial band would have shrunk the receiving field to a fifth or a third of its size, at the price of a satellite that could not shed its heat, a bigger electricity bill, and a beam that rain could knock out. Every time the programme costed it the answer was the same and 2.45 GHz stayed. | T3 | HIGH |
| CLM-1090 | The programme's two printed tables of how much beam the weather eats do not agree. One has the ionosphere numbers the wrong way round, and its rain and hail figures are a million times too small for the unit printed over them. The other is internally consistent. | T3 | HIGH |
| CLM-1092 | The famous 23 milliwatts per square centimetre is measured face-on to the beam, which is how the receiving panels are tilted, and is the same number the beam carries through the upper atmosphere. Spread over flat ground at the reference site in the southern United States, where, if the satellite is due south of the site, the beam comes in at about 50 degrees above the horizon, the same beam delivers about a quarter less per square metre of ground, 17 to 18 rather than 23. | T0 | HIGH |
| CLM-1093 | Working the 1978 antenna design forward gives 25 mW/cm2 straight down from the satellite. The report prints 23. That drop can be explained by the extra distance to a site in the southern United States, or by the report's own allowance for phase errors and failed tubes, but not by both, and each explanation alone is worth the same 7 per cent. The report's own labelling suggests the errors were included, in which case the figure at the actual site is about 21.5. | T0 | MED |
| CLM-1095 | The three harmonic numbers the register has carried since the 1978 conference paper come from one rectenna element on a bench at five watts, measured at its input with the antenna replaced by a matched line; the fourth is the meter's floor, not a reading. Filters and a metal shield on the element cut the second and third by 25 and 15 decibels. | T3 | HIGH |
| CLM-1096 | In 1977 one rectenna element converted 90 per cent of eight watts of microwaves to DC but only 80 per cent of fifty milliwatts, and the report says why: at low power the diode's own losses dominate. The 85 per cent the programme wanted at low power was not reached. | T3 | HIGH |
| CLM-1097 | By 1976 a rectenna had delivered thirty kilowatts over a mile at 82 per cent, a certified bench system had turned DC into microwaves and back at 54 per cent, and 199 elements had run four months without a failure, which the maker converted into a 27-year mean time between failures at 90 per cent confidence. | T3 | HIGH |
| CLM-1098 | The 1977 plan for a cheap rectenna was two flat planes, the front one doing all the work inside a metal shroud that is also the structure, wired in series to reach a thousand volts for the inverters; a five-element piece was built and worked, and the report says the next thing to build is a thousand-volt section. | T3 | HIGH |
| CLM-1099 | Boeing's 1977 sum gave the ground receiver 85 per cent, said it was probably a little low, and drew the trade that sets a rectenna's size: spreading the power evenly across the transmitter needs the smallest transmitter but wastes the most power outside the receiver's edge, and tapering the power towards the transmitter's edge makes the transmitter bigger and wastes less. | T3 | HIGH |
| CLM-1100 | Boeing thought the receiving elements could be spaced almost twice as far apart as Raytheon's, halving their number, and that the receiver might lie flat on the ground rather than tilted at the satellite, but said the rectenna had had little attention and both ideas needed analysis. | T3 | MED |
| CLM-1101 | Lightning will hit a ten-kilometre receiver often, so Rice designed a grounded conductor into its structure at every bay, costing under one per cent of the collecting area; a single diode survives an ordinary strike, but the forty-thousand-volt strings they are wired into do not, and need the same surge protection as any transmission line. | T3 | HIGH |
| CLM-1102 | The receiving station the siting maps were drawn for is an oval twelve kilometres wide and, in the middle of the United States, sixteen long once its safety margin is added, about 150 square kilometres, with two and a half million panels on it; further north it gets longer because the satellite sits lower in the sky. | T3 | HIGH |
| CLM-1103 | Mapped at the scale of one receiver per cell, two-fifths of the country was not ruled out; look closer and seven in ten of those cells fail too, mostly on terrain; take out farmland and a quarter is left. The study still found enough room in every region, with the caveats that its own numbers imply. | T3 | HIGH |
| CLM-1104 | The siting maps kept receivers 150 km from radio telescopes, 100 km from NASA's deep-space stations, 60 km from air traffic radars and 50 km from nuclear plants, on asserted distances; because those places are mostly excluded for other reasons too, the electromagnetic rules only cost about seven per cent of the country. | T3 | MED |
| CLM-1105 | The first look, in 1978, used a coarser grid and a bigger site than the 1980 study, ruled out half to five-sixths of the country depending on how many rules were applied, and declined to name sites; three million acres is a small fraction of America but a tenth of its cities. | T3 | HIGH |
| CLM-1110 | The best near-infrared laser-to-electricity receiver so far turns 56 per cent of the light into electricity, but only when the light is 271 kilowatts per square metre, a thousand times brighter than the microwave design beam. At the level the authors call eye-safe, about 270 times lower, it turns about 30 per cent into a couple of milliwatts, while also carrying gigabit data. | T1 | HIGH |
| CLM-1111 | Before this paper, the best near-infrared laser receivers reached about half efficiency, and only under very bright light; at gentler light they manage a fifth to a bit under a half. Receivers for shorter-wavelength light do better, nearly 69 per cent, but the paper prefers the near-infrared band on eye-safety and atmospheric grounds. | T2 | MED |
| CLM-1112 | The paper says this colour of infrared is good because the air lets it through and the eye-safety rules allow more of it, but it cites other papers for both and never gives a number for either. | T1 | HIGH |
| CLM-1113 | This paper does not describe a laser power satellite, though two NASA-funded designs for one exist from 1978-80. It does show how a laser receiver behaves: it needs light about a thousand times brighter than the microwave beam to work well, and even at the level the authors call eye-safe it is about a third as efficient as the microwave receiver. | T0 | MED |
| CLM-1122 | About twenty thousand postage-stamp-sized antenna-plus-diode cells, each with an off-the-shelf microwave diode, wired into tiles, then panels a metre square, then four panels side by side: a bit over four square metres in all. | T1 | HIGH |
| CLM-1124 | One 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 hundred watts per square metre, a little over half the highest level tested. | T1 | HIGH |
| CLM-1125 | Four 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 transmitter; the main doubt is whether the probe antenna used to measure the arriving power sees the ground reflections the same way the receiver does. | T1 | HIGH |
| CLM-1126 | They deliberately fried each of the four panels with ever-stronger pulses. A bare panel gave up at 672 watts out; clamping its voltage with a Zener let it take about 30 per cent more incoming power before failing, and shorting it outright about 50 per cent more, which is the best any clamp could do. | T1 | HIGH |
| CLM-1128 | A 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 flowing during each pulse; the receiver sat well inside the dish's near field, where the beam is uneven, and turned an estimated 60 per cent of the power reaching it into DC. | T1 | MED |
| CLM-1129 | The authors say the 1975 record still stands at twenty times their power, that the custom diodes which set it no longer exist, and that going bigger needs three things nobody has yet built for this job: many small combined transmitters instead of one big tube, a tougher diode, and the electronics to feed a rectenna into a grid. | T2 | MED |
| CLM-1135 | Modern power beaming, by the review's dating, starts in 1963 with a radar tube, a horn five and a half metres away and a single vacuum-tube rectifier: 100 watts out for about 670 in. The same year the rectenna was invented by giving every little dipole its own diode. | T2 | MED |
| CLM-1141 | In 2002 a metre-wide rectenna moved along an exhibition floor in Houston, tracked by a self-steering 5.8 GHz beam, converting 82 per cent of what hit it to DC in front of ten thousand people. | T2 | MED |
| CLM-1172 | A 2025 UK government study tried two places for the receiving station, Aberdeen and southern England near London. Southern England came out better, because the grid there can take the power almost all the time while Aberdeen's connections would lose a quarter of it. | T4 | MED |
| CLM-1173 | A 1980 European survey for offshore receiving stations looked only at the North Sea and the Channel, left the Atlantic and Mediterranean for later, and listed distance to the grid among its siting factors, though it chose the areas on its offshore factors alone. Because the beam's footprint stretches north to south at those latitudes, coasts running east to west fitted badly. | T3 | MED |
| CLM-1191 | The study sized its transmitting and receiving antennas with a standard beam formula, assumed about half the transmitted power would be caught on the way down, and found that above 35 GHz the antennas are small enough that they stop mattering much to the total mass, and that going beyond 100 GHz gains little. | T3 | MED |
| CLM-1197 | The company beams at 10 GHz and claims its beam loses nothing in space on the way down, where the other designs in its own table lose between a sixth and a half. | T4 | MED |
| CLM-1198 | The first project's receiving site is a circle 2 km across, with two hours of batteries on the ground. | T4 | MED |
| CLM-1200 | A 2025 UK study says Virtus Solis counts the power its receiving site catches in a way the other designs do not: on their common method, a receiver that collects only the central spot of the beam can catch at most about 84 per cent of it. | T4 | MED |
| CLM-1203 | Caltech's receiving station on the ground is a circle about 1.6 kilometres across, just large enough to catch the whole central spot of the beam. Batteries keep its output steady through the short eclipse seasons and the dips while the craft turn. | T2 | MED |
| CLM-1229 | A lunar lander company said in late 2025 that it would carry a power-beaming receiver to the Moon for a start-up planning orbital power missions from 2028. | T6 | MED |
| CLM-1232 | In 1978 a NASA contractor designed a satellite that would turn sunlight into an infrared laser beam and send it, by way of a mirror satellite high above the equator, to a ground station about 30 m across. The ground station would use the beam as heat to run turbines. On paper, about 5 to 6 per cent of the sunlight collected in space would reach the grid as electricity. | T3 | MED |
| CLM-1233 | The design's beam would be very intense at the receiver, about two thousand times stronger than sunlight, so the site would need a fenced zone a few hundred metres across. At the fence, the study says, the infrared light would be far below the eye-safety limit of the day. A passing jet would warm slightly, but a slow light aircraft might be harmed. | T3 | MED |
| CLM-1234 | A second NASA-funded study in 1980 imagined the standard power satellite with its microwave transmitters swapped for about twenty very large infrared lasers. On paper, about one-seventh of the electricity made on the satellite would reach the grid, a bit more on mountain sites. The receivers would again turn the beam into heat. | T3 | MED |
| CLM-1240 | In 1999 a US national laboratory sent infrared light from a bank of laser diodes across a lab room onto ordinary solar cells and got a few watts out, enough to turn a small motor. The beam was patchy and the run was cut short, so less than one per cent of the electricity put in came out at the far end. | T3 | LOW |
| CLM-1242 | TerraSpark says it will first use wireless power on the ground, where cables are hard to lay, and move parts of the system into space later. The article suggests Luxembourg could become a financial centre for such projects. It gives no dates. | T6 | MED |
| CLM-1250 | In a 2015 ground test in Japan, a 1.8 kW microwave beam sent over 55 m delivered about a third of a kilowatt when the steering corrected a deliberate panel misalignment, and about 90 W, roughly a quarter of that, when it did not. | T5 | MED |
| CLM-1283 | In 1981 the US Congress's technology office worked out that keeping the edge of a receiving site to the Soviet limit would make each site about ten times bigger, close to 1,700 square kilometres. That limit is ten times stricter than the American design boundary. | T3 | MED |
| CLM-1286 | The 1981 congressional assessment listed who would be exposed to the beam and how strongly. Levels ran from a ten-thousandth of a milliwatt per square centimetre for the public to about 2 watts for workers at the satellite's antenna, and it said no one could yet say what was safe for workers. | T3 | MED |
| CLM-1287 | In 1978 a draft plan for the US satellite power programme proposed that every lab test rats the same way, at fixed microwave levels from far below to just above the beam-centre level of the later reference design, for at least four hours a day, and later for 23 hours a day. | T3 | MED |
| CLM-1288 | The 1978 draft plan said long-term low-level studies would decide whether the satellite was safe for the public, but that in the two to three years available most effort would go to checking earlier alarming reports, with three-fifths of the money on health. | T3 | MED |
| CLM-1289 | The 1978 plan aimed to find, by stepping the dose up or down, the lowest microwave level that changed anything in mice, rabbits, birds and plants, and to use the rabbit result to inform human safety standards. | T3 | MED |
| CLM-1292 | In 1966 Canadian researchers found that caged birds under a pulsed radar-band beam at roughly the strength proposed for a power beam's centre reacted within seconds, but only when the beam came from above. | T1 | LOW |
| CLM-1293 | A year later the same laboratory found chickens under a pulsed beam at a strength about twice the proposed beam centre went lame on one side or fled within seconds, and barely reacted when the beam came from beneath. | T1 | LOW |
| CLM-1294 | The fullest of the four papers: caged birds under a pulsed beam above them reacted within seconds at about twice the proposed beam-centre strength and more slowly at lower strengths, pigeons stayed drowsy for half an hour after two minutes, and birds lit from below barely noticed. | T1 | LOW |
| CLM-1295 | Wiring a chicken's muscles showed the beam made one side tense and the other go slack within moments, and the bird was back to normal seconds after it was switched off. | T5 | LOW |
| CLM-1325 | In 1979 American and British radiation officials worked out that the then-standard limit of 10 milliwatts per square centimetre was safe at 2.45 GHz (the frequency planned for power satellites; our context, not on the page), about nine times below the level that warms the body by 1 C (our arithmetic). They said it was too loose at much lower frequencies, where the body absorbs more. | T2 | MED |
| CLM-1326 | A 1980s US federal health review of animal studies put the onset of harm at about 2 watts absorbed per kilogram of body, mostly from heating. Below about a tenth of that it found few effects and none it judged harmful, though a cancer-promotion result at 2-3 W/kg was unconfirmed. | T3 | MED |
| CLM-1330 | A 1964 Polish study found that workers exposed for longer to weak radio and microwave fields reported more headaches, sleep problems and similar complaints, and argued that safety limits based only on heating were too lax. | T2 | LOW |
| CLM-1333 | By 1986 one early long-term rat study had hinted at more tumours at the level US rules called safe, but it was unconfirmed. Eastern European reports of nerve symptoms had not been confirmed by careful studies, and experts said there was no theory to predict any non-heating effects. | T2 | LOW |
| CLM-1334 | In 1978 the US environment agency calculated that the American safety limit of the time could, at some radio frequencies, heat parts of the body far more than normal metabolism does. It found that a cautious heat-based limit would land close to the much stricter Soviet limit. | T3 | MED |
| CLM-1335 | In the 1970s most city dwellers in the US received radio-frequency exposure more than a hundred times below even the strictest heat-based limits the note considered; only people next to big transmitters came close. | T3 | MED |
| CLM-1339 | A 1950s experiment found that 3 GHz microwaves have to be about four times stronger than infra-red heat before skin starts to hurt, because most of the microwave heat goes deeper than the nerves that sense pain. Pain began at about half a watt per square centimetre. | T1 | MED |
| CLM-1348 | People feel microwave warmth only at fairly high strengths: tens of milliwatts per square centimetre for a second or so on the forehead, and less if more of the body is exposed. Pain needs tens of times more. So feeling nothing does not mean a person is below the limit. | T2 | MED |
| CLM-1408 | In the late 1970s, US studies sketched receiving stations raised on posts or legs so the ground beneath could still be farmed or built on. They noted a trade-off: panels close to the ground are easier to reach for repairs. | T3 | MED |
| CLM-1409 | A 1977 NASA study of how to hold up the receiving station's panels was told the ground underneath had to stay farmable, with a metal mesh of small diamond-shaped holes. It compared eleven ways of building it, some raised about 5 metres, high enough for farm machines underneath, and found the more usable the land below, the more the structure costs. | T3 | MED |
| CLM-1410 | US government studies around 1980 thought crops might be grown under a receiving station, because its mesh lets most sunlight through and warms the ground only slightly. They also said it would make farming and repairs harder, needed design changes and had not been studied properly. One later survey suggested raising the station and screening the ground from microwaves, or building greenhouses under it. | T3 | MED |
| CLM-1411 | In 1978 nobody knew whether animals could graze, or crops be grown, under or around a receiving station, because research on what its microwaves do to people and animals was not finished. | T3 | MED |
| CLM-1412 | A 2022 study for the European Space Agency describes the receiving station as a fairly open grid of small antennas about 10 centimetres apart, which might let the land underneath be used for something else. It says the basic layout goes back to Raytheon and NASA in the late 1970s. | T4 | MED |
| CLM-1413 | A 1977 NASA-funded report says the metal mesh behind a receiving station's antennas can be about three-quarters open to light while letting through only about half a per cent of the microwave power. The 1978 reference design used a steel mesh about that open. | T3 | MED |
| CLM-1454 | The 2020 international limit for public exposure, 10 watts per square metre, is about 19 to 42 times lower than the beam strengths at which one theory says the beam might start to focus itself in the upper atmosphere (42 times uses a 2008 estimate, 19 times uses measured conditions), and 23 times lower than the 230 that a 2019 CASSIOPeiA paper gives as a typical peak. Those atmospheric figures are estimates, not hard limits. A 2026 international radio report that takes CASSIOPeiA as its example says the beam can be designed to fall below the public limit at the edge of the receiving site, with a safety zone over the beam's footprint; it gives no figure for the beam's strength at that edge, and a diagram in it shows the receiving site taking 245 watts per square metre. | T3 | MED |
| CLM-1467 | Keeping people out of the area where the beam is strong is a plausible way for a strong beam to meet the 2020 international limit for public exposure, and international exposure guidance accepts limiting access as a way to comply. Other designs have worked this out: a 2013 Japanese review plans a no-entry area 3.5 kilometres across, and a 2007 international study sizes a 4-kilometre receiver this way. A 1977 US study set aside 204 square kilometres for one receiving site, without saying in its cost table what fixed that size, and costed buying and preparing that land. A 2026 international radio report that takes CASSIOPeiA as its example says the beam can be designed to fall below the public limit at the edge of the receiving site, with a safety zone matching the beam's footprint, about 3.5 to 6.5 by 7 to 13 kilometres in the UK. A diagram in it shows the receiving site taking 245 watts per square metre, but the report gives no figure for the beam's strength at the edge and no cost for the zone. A 2021 UK cost model for a CASSIOPeiA design includes the land for the receiving site but names no safety zone. | T4 | LOW |
| CLM-1474 | One UK study designs small power satellites that beam to receivers in Scotland, Canada and Japan, switching between them as they move along their orbit. Each satellite beams to one receiver at a time, and the UK receiver comes first when both are in view. | T4 | MED |