Value chain · CLM-1095
In plain terms
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.
The claim as recorded
The -25 dB, -40 dB and "<-70 dB" second, third and fourth harmonics that Arndt and Leopold quoted for the rectenna are Brown's 1977 measurements on a single RXCV rectenna element "at 5 watts" of input, taken at the element's input terminals in a ground-plane test fixture with the dipole replaced by a matched 50 ohm line and with no stub lines, and the fourth-harmonic figure is the instrument floor: "no 4th harmonic was observed" with "equipment to 4th harmonic was -70 dB from fundamental". Computer simulation of the same element gave -27.5 dB and -37.4 dB. Adding the inter-element transmission-line section of the two-plane construction, which doubles as a second-harmonic filter, took the measured second harmonic from -25 dB to -50 dB; an open-circuited stub resonant at the third harmonic took the third from -40 dB to -55 dB; and a metallic shield over the rectifier tank circuit reduced the second and third harmonic power that an unshielded element radiated, "easily detected by monitoring equipment fifty feet away", to a level the equipment could not detect, while improving efficiency by nearly 1 per cent.
Evidence behind this: T3-NASA contractor report, not peer reviewed: the contractor's own bench measurement on one element, with the measurement conditions and the instrument floor stated.
Scope and limits
ONE ELEMENT, AT ITS INPUT TERMINALS, WITH THE DIPOLE REPLACED BY A MATCHED LINE: the page itself says the 50 ohm line "is an accurate simulation of the properties of the dipole antenna only at the fundamental frequency" (normalised, PDF 69), so these are not radiated levels and not array levels. The second-harmonic reduction by the inter-element line was later found "so critical as not to be practical" in the two-plane foreplane (normalised, PDF 69) and the summary calls the maximum reduction nominal. No measurement of harmonic radiation from an array through its dipoles exists in the document ("far field", "radiated from the array" zero). 1977 diodes and circuits. The same p.71 paragraph goes on to say the fourth harmonic was later observed in the rectifier tank circuit with a special probe, so the -70 dB floor is the input measurement only.
What it assumes
The measurement frequency is the contract's 2450 MHz (PDF 59 states the objective at 2450 MHz; the harmonic table does not restate it).
Where it comes from
PDF 71 / printed 61, render read: the table "HARMONIC LEVEL WITH RESPECT TO FUNDAMENTAL", columns "Measured at Input on Ground - Plane Fixture" and "Predicted at Input Computer Simulation": 2nd Harmonic -25 dB (at 5 watts) and -27.5 dB; 3rd Harmonic -40 dB (at 5 watts) and -37.4 dB; 4th Harmonic <-70 dB (at 5 watts) with the footnote "Sensitivity of equipment to 4th harmonic was -70 dB from fundamental. However, no 4th harmonic was observed." ("no 4th harmonic was observed" raw; "equipment to 4th harmonic was -70 dB from fundamental" raw). Same page, normalised: "For both the experimental case and the simulated case the input to the rectenna element was terminated in a 50 ohm line"; raw: "stub lines were being used when the measurements were made" (the page reads "In the experimental case no stub lines were being used"); normalised: "It is therefore concluded that the fourth harmonic is down by at least this factor from the fundamental". PDF 70 / printed 60, Table 3-3 render read: experiments 1 to 7 on the RXCV element with diode 40593CPX1G No. 13 on the ground-plane fixture at 4.07 to 5.12 W absorbed (experiment 2 reads 3.980 W at the render, its first digit damaged) and 86.30 to 88.73 per cent DC output; experiment 5 "-25 dB" second and "-55 dB" third harmonic relative to incident power; experiment 6, with the transmission line section "which doubles as 2nd harmonic filter", "-50 dB" and "-55 dB (-40 dB with filter removed)". PDF 71 section 3.5, raw: "easily detected by monitoring equipment fifty feet away"; normalised: "The addition of the shield reduced any radiation to a level that the monitoring equipment could not detect"; the shield's efficiency gain of nearly 1 per cent is Table 3-3 experiment 2 (86.30 to 87.19 per cent). PDF 117 / printed 107, normalised: "result in a reduction of third harmonic output energy from 40 dB to 55 dB" and "there could be a two to three percent drop in efficiency at a point of adjustment of the electrical length of this line extremely close to the one found optimum for the reduction of harmonic energy".
Basis: dB relative to the fundamental at the element input; watts of microwave input to one element
Related records
- Answers question
- QST-007 not published in this release
Cite this
energyaperture.com/c/clm-1095
CLM-1095, Energy Aperture, as of 1977-08.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-558
- CLM-1096In 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...CLM-1097By 1976 a rectenna had delivered thirty kilowatts over a mile at 82 per cent, a certified bench system had turned DC into microwaves and...CLM-1098The 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...