The National Astronomy andIonosphere Center (NAIC),operated by Cornell Universityfor the National ScienceFoundation, has its laboratoryat Arecibo in Puerto Rico. TheObservatory's main instrumentis a radio/radar telescope thatutilizes a giant reflector anten-na 1,000 feet in diameter, thelargest in the world by a con-siderable margin. A 40th anniversary celebration of the 1963inauguration of this Observatory was held at the site in PuertoRico on 1 November 2003. About 135 invited guests enjoyednearly daylong ceremony.

My associationMy association with the Arecibo

antenna goes back 45 years ago whenthe idea of such a large instrumentwas but a dream in the mind ofWilliam E. Gordon, a professor of Electrical Engineering atCornell University. He wanted to build powerful radar requir-ing a very large antenna in order to measure the backscatterfrom the earth's ionosphere. With a diameter of about 1,000feet, it would transmit (and receive) with a very narrow sta-tionary beam at 430 MHz, pointing straight up through theionosphere.

At that time I was working at Wiley Electronics Co, inPhoenix, Arizona. Our company had successfully devel-oped a line source feed for a scanning microwaveradiometer using a spherical reflector. Along with theowner of the company, Carl Wiley, we described theantenna design at a meeting of people from AssociatedUniversities interested in large scanning antennas for radioastronomy in New York on 12December 1958. Two members of thegroup were from Cornell: HenryBooker, eminent electromagneticist,and radio astronomer Marshall Cohen.They invited us to give the same pre-sentation to Professor Gordon and hisgroup at Cornell, which we did the fol-lowing week. Based on the presenta-tion, we were invited to submit a pro-posal in response to an open bid for a1,000-foot aperture spherical reflectorthat would satisfy Dr. Gordon's require-ments. Our bid was not accepted, butthe concept of a spherical, rather thana paraboloidal reflector was retained.

Nearly five years later, in November1963, the Arecibo IonosphericObservatory (AIO) became operationalbut its performance was disappointing.The reason was due to deficiencies inthe radiation characteristics of thesquare, slotted waveguide line feed.During 1969-1971, under a contractfrom Cornell and Thomas Gold,Director of AIO, I was able to design acircular waveguide line source that

overcame those deficiencies How did I get the assign-

ment? Now at NorthAmerican Rockwell inAnaheim (CA), I hadobtained a contract todesign, build and test a scalemodel of an improved linefeed after a meeting (inabout 1967) of a panel ofexperts who were trying to

understand why the original square waveguide feedworked so poorly.

(I had studied the problem analytically (on my owntime) for several years and found there were two prob-

lems. Both problems related to thefact that the waveguide had a squarecross section and utilized transverseslots in all four sides to allow radia-tion to leak out. Further analysis indi-cated that the two problems would

not exist if the waveguide had a circular cross section andif the four slots were replaced by six rectangular shapedholes. I got some IR&D money from the company, built ascale model of a short section of the feed, tested it andshowed experimentally that it worked as I had predicted.)

The panel members listened to my presentation withinterest but also with some skepticism until I showed theexperimental results. They were the clincher for the techni-cal experts. But it took much longer to win support fromthe funding agency, DARPA.

My thought process in attacking the problem was:Analyze the performance data for the original feed to deter-mine the nature of the problems; synthesize a new structurethat could overcome them and then analyze the new struc-

Arecibo Observatory40th Anniversary

celebration

Allan W. Love

APRIL/MAY 2004 0278-6648/04/$20.00 © 2004 IEEE 41

Looking back

Fig. 1 This view shows the Gregorian dome near the left end of the feedarm while the 430 MHz circular line feed is near the right end.

42 IEEE POTENTIALS

ture to predict its performance. Finally, build a scale modeland make experimental measurements to verify the theory.

The one-way gain of the antenna increased by 3.8 dBand the two-way radar gain by 9 dB due to improved polar-ization characteristics. The former efficiency of 22% became53%, and that percentage increased to 72% in 1974 after thefirst upgrade in which the original mesh surface wasreplaced by aluminum panels.

The Gregorian feed domeThe Gregorian feed dome, 86 feet in overall diameter and

weighing 90 tons, houses two reflectors, a secondary, 72 feetin diameter and a tertiary, 26 feet in diameter. These mirrorsserve to transform the aberrant rays from the spherical pri-mary into a bundle that converges to a single focal point.Here, there is a turret carrying a number of simple pointsource feeds (e.g. horns) that can be rotated into a positionsuch that the phase center of a chosen horn coin-cides with the focal point of the rays from the ter-tiary mirror. The system permits very widebandoperation over several discrete frequency bandsranging from about 600 MHz to 10 GHz. This farsurpasses the narrow bandwidth of the circularline feed. It is interesting to note that the moreusual multiple mirror configuration is named aftera man of the clergy, the Abbe Cassegrain. Thishas led many to think that the alternate versionwas named after Pope Gregory. This is not thecase; it was named after the Scottish mathemati-cian James Gregory.

Figure 1 shows the Gregorian dome near the leftend of the feed arm while the 430 MHz circular linefeed is near the right end. Project Serendip IV of theSearch for Extraterrestrial Intelligence (SETI) makesuse of a second line feed at 1.4 GHz. This feed isshorter and smaller than the 430 MHz line feed andis not visible in the photograph. Figure 2 is a phototaken from the center of the main reflector looking

nearly straight up to the platform above. The “black hole”is the mouth of the dome, which serves to protect the

internal mirrors from the elements and to act as ashield against external radio interference.

The telescope The Arecibo telescope (shown in Fig. 3) is truly

a marvel of mechanical engineering. Its reflectorsurface is composed of 38,788 accurately shapedaluminum panels each 3 by 6 feet, supported by anetwork of steel cables and tie-downs beneath it.Its diameter is 1,000 feet, the depth at the centeris 167 feet and its total area exceeds 18 acres, bigenough for 26 football fields. But the really impres-sive feature of the reflector is that it conforms tothe surface of a sphere of radius 870 feet to within0.087 inches (2.2 mm) root-mean-square deviation,and it maintains that accuracy over all 18 acres ofits surface and throughout diurnal changes in ambi-ent temperature.

The platformThe reflector is a purely static structure but the triangular

platform (see Figs 1 and 2) above it is a combination of staticand dynamic elements whose mechanical characteristics areat least as impressive, probably more so, than those of thereflector. It weighs 900 tons and is suspended in mid-air 450feet above the reflector. The Golden Gate bridge is suspend-ed by cables between two towers; the Arecibo platform iscentrally suspended by cables that pass over three towers,the tallest being 365 feet. Six steel cables, each 3.25 inches indiameter, pass over each tower and are fastened to largeconcrete anchor blocks set in the ground. A bow-shapedstructure 328 feet long, called the azimuth arm, turns on acircular track attached to the bottom of the platform. It pro-vides azimuth angle scanning. To the lower part of theazimuth arm is fastened another track in the form of a circu-lar arc. On this track ride both the Gregorian dome and acarriage house that carries the 97-foot long circular line feed.This arrangement provides for zenith angle scanning. Once

Fig. 3 Aerial shot of the Arecibo Observatory

Fig. 2 Photo taken from the center of the main reflectorlooking nearly straight up to the platform above

again, the most impressive feature of this structure is itsstability and the “millimeter” precision in positioning that ismaintained during scanning.

The celebrationThe anniversary event began shortly after 11 AM with

guided tours of the whole area, including a peak under-neath the edge of the huge 1,000-foot diameter main reflec-tor and the noise-reducing ground screen that surrounds it.Noticing that the reflector 's surface was not at all shiny butlooked a dull gray in color, I asked Frank Drake, a formerhead of the Observatory and later Director of NAIC, if therehad ever been an attempt to clean the surface. He said,"No, chiefly because we haven't figured out a good way todo it." Obviously, the surface had oxidized over the years,creating a thin dielectric layer. Fortunately, the layer is notlossy enough to cause a noticeable increase in antenna skytemperature. The same situation applies to the circular wave-guide feed.

After touring the Operations Center, photographers fromCornell University took photographs of guests and dignitariesassembled on the large deck in front of the building. Figure 1is an aerial photograph that portrays this magnificent scenefrom a different viewpoint. At the base of the tower in theforeground is a triangular shaped building that houses aVisitor Center and an Auditorium.

Many pictures were taken of guests,among them being Fig. 4, which showastrophysicist Frank Drake and myself,with the platform in the background.Responding to a question by the pho-tographer, Frank answered, "Allanbuilt a line feed that still works per-fectly, yet it has never had a bath andit has never melted." The last state-ment refers to the fact that the feedradiates 2.5 megawatts of peak powerat 430 MHz.

The patio of the Visitor Center wascrowded between 1 and 2 PM where alight lunch was served and old friendsexchanged greetings while protectedfrom the rain by a large canopy over-head. Here I met Bill Gordon, known asthe father of the Arecibo Observatory,shown at the left in the photograph ofFig. 5, along with Marshall Cohen andHerb Carlson, Chief Scientist at the AirForce Office of Scientific Research. Inaddition, I was fortunate to meet for thefirst time and talk to Dale Corson,President Emeritus of Cornell and co-author with Paul Lorraine of the well-known textbook, ElectromagneticFields and Waves. Others that I metwere Marshall Cohen, Hal Craft, former-ly head of the Observatory, RobertBrown, currently Director of NAIC atCornell and Sixto Gonzalez, who hadjust been named director of theObservatory, and is a native born PuertoRican. Also on the list were old friends

Mike Davis and Donald Campbell, the latter being AssociateDirector of NAIC, Head of the Solar System Studies Group andProfessor of Astronomy at Cornell University.

Another friend attending the celebration, Tor Hagfors, wasDirector of NAIC in the late 1980s, leaving Cornell in 1992 to

APRIL/MAY 2004 43

Just some of what has been accomplished

Some of the major discoveries and accomplishments radio scientists have made

using the Arecibo Observatory over the last 40 years.

• 1964. Incoherent radar backscatter measurements led to significant advances

in our understanding of earth's ionosphere. Rotational and surface studies of the

planet Venus were initiated.

• 1965. Radar observations of the planet Mercury established its rate of rotation

around its polar axis as 59 earth-days, which is about two-thirds of the planet's

88-day orbital period around the Sun. An interesting corollary is that on Mercury

there are only three days every two years.

• 1974. The first pulsar in a binary system was detected. This led to further confir-

mation of Einstein's general theory of relativity and a Nobel Prize for astronomers

Russell Hulse and Joseph Taylor (1993).

• 1980s. Detailed mapping of the distribution of galaxies in the universe was car-

ried out and "superclusters" of galaxies were discovered that constitute the

largest physical objects in our universe. The first pulsar with a millisecond period

(1.6 ms) was discovered, followed by precise measurement of the rotation rates

of hundreds of other such fast-spinning neutron stars. Radar measurements

through the dense cloud cover around Venus with a resolution of 1.5 kilometers

were used in pre-Magellan mission planning.

• 1990s. The first planets outside of our solar system were found in orbit around

Pulsar B1257 + 12. Ice in craters in the polar regions of Mercury was detected.

• 2000. Detailed radar imagery of Saturn's moon, Titan, revealed lakes of liquid

hydrocarbons.

• 2003. Asteroid Hermes, rediscovered by optical astronomers after being lost for

66 years, was shown by Arecibo astronomers to be a binary object.

The web site <www.naic.edu> has many links that record the history of the obser-

vatory and describe the remarkable scientific achievements made by the radio

scientists who have used it over the last 40 years.

Fig. 4 From left: Frank Drake astrophysicist and Allan Love (the author)

44 IEEE POTENTIALS

become Director of the Max Planck-Institut fur Aeronomie inGermany. During his tenure at NAIC, he initiated the studiesthat led to the design of the very successful Gregorian feedsystem. In this effort, he was aided by an advisory panel con-sisting of Lynn Baker, Per-Simon Kildal, Sebastian vonHoerner, myself and a very capable mechanical engineer,Paul Stetson. His calculations showed that the whole plat-form could be raised up eight feet to accommodate and opti-mize the Gregorian system. I was disappointed that none ofthem was able to be present. One person, unfortunately, wasabsent: Merle LaLonde, who had been Chief Engineer in theearly years of the construction and operation of theObservatory. Sadly, Merle died very suddenly in April 1977 inhis mid-forties.

Between 2 and 3 PM, guests moved into the Auditoriumto hear tributes from a number of speakers. The first was awelcoming address from the Observatory's new Director,Sixto Gonzalez. This was followed by remarks form RichardBarvainis, of the National Science Foundation, Division ofAstronomical Science and then Cornell's Provost forResearch, Dr. Robert Richardson. Further tributes came fromdignitaries and representatives of the government of PuertoRico and from Chancellor Dr. Gladys Escalona of theUniversity of Puerto Rico, Rio Piedras. Some speeches tend-ed to be rather long since they were given first in Spanishand then in English.

The last one was a very interesting and informative talkby Robert Brown, appointed Director of NAIC in May 2003.He had formerly spent a number of years with the NationalRadio Astronomy Observatory (NRAO) in Charlottesville,West Virginia. According to Dr. Brown, "The celebrationwill not only be for the longevity of the radio/radar tele-scope, but also for the way it has adapted to the manner inwhich astronomers do science today. The telescope hasgreatly changed the way it serves its user community; thesedays an astronomer is far more likely to be operating thetelescope remotely from a distant institution than actuallybe on the island," he said.

At this point, there was a welcomed break duringwhich we could stretch our legs and take in theexhibits on display in the area adjoining theAuditorium. Of special interest to me was an artist'srendition of binary asteroid, Hermes, with Earth in thebackground. It had been lost for 66 years and wasrediscovered only last October. Radar astronomers atArecibo then were able to identify it as actually twoobjects, roughly the same size, and very close togeth-er, in rotation around each other. Taken together, theywould cover an area about the size of Disneyland. Atthis approach, they were distant from earth by onlyabout 1.6 times the earth-moon distance.

It was back to the Auditorium at about 4 PM tohear the keynote address, "The Story of Arecibo," byProfessor Gordon. He began by noting that expertscriticized his plan in 1958, saying that to build amantenna with an aperture 1,000 feet in diameter couldnot be done. He went on, using slides and pho-

tographs, to show how, over the next five years, it actuallywas done. It was a fascinating story, starting with bulldoz-ers moving earth around to create a huge bowl in which alake soon began to form due to the tropical rain that seemsto fall every afternoon in the summer. Pumps had to beinstalled to pump the water over the rim and into a nearbyravine, and non-porous material was removed to restorenatural drainage. I thought of the outrageous scene in theJames Bond movie, Goldeneye, that shows the wholeArecibo site, towers, platform, reflector and buildings, risemagically out of a lake as the water recedes. For a shorttime, years ago, there really was a lake there after all!

Dr. Gordon noted that it was originally hoped the tele-scope would last for 10 years. He then emphasized thatnow, 40 years later, it is operating better than it ever didbefore and that its sensitivity has increased by orders ofmagnitude. This is due to the two upgrades, the first com-pleted in 1974 and the second, completed in 1997. Heended his story by saying, “If you dream, have big dreams.And have talented supporters to help you.”

The first 40 years have been exciting and fruitful onesfor the Arecibo Observatory. No one knows what the futurewill bring. But we can be sure there will be many surprisesand unexpected discoveries. It has been a rewarding expe-rience for me to have played a small part in its success.

About the authorAllan Love retired at the end of 1990 after 35 years in

the aerospace industry but continues to do part time con-sulting in that field of Electromagnetrics. He is a LifeFellow of the IEEE, a Past President of the Antennas andPropagation Society, and a contributing editor to IEEEPotentials magazine. He lives in Irvine, California.

Fig. 5 From left: Bill Gordon, known as the father of theArecibo Observatory along with Marshall Cohen andHerb Carlson, Chief Scientist at the Air Force Officeof Scientific Research.

A version of this article is also being pub-lished by the IEEE Antennas and PropagationSociety Magazine.