FENN, TEMME, DELANEY, AND COURTNEYThe Development of Phased-Array Radar Technology

VOLUME 12, NUMBER 2, 2000 LINCOLN LABORATORY JOURNAL 321

The Development ofPhased-Array Radar TechnologyAlan J. Fenn, Donald H. Temme, William P. Delaney, and William E. Courtney

Lincoln Laboratory has been involved in the development of phased-arrayradar technology since the late 1950s. Radar research activities have includedtheoretical analysis, application studies, hardware design, device fabrication, andsystem testing. Early phased-array research was centered on improving thenational capability in phased-array radars. The Laboratory has developed severaltest-bed phased arrays, which have been used to demonstrate and evaluatecomponents, beamforming techniques, calibration, and testing methodologies.The Laboratory has also contributed significantly in the area of phased-arrayantenna radiating elements, phase-shifter technology, solid-state transmit-and-receive modules, and monolithic microwave integrated circuit (MMIC)technology. A number of developmental phased-array radar systems haveresulted from this research, as discussed in other articles in this issue. A widevariety of processing techniques and system components have also beendeveloped. This article provides an overview of more than forty years of thisphased-array radar research activity.

affordable array radar with thousands of array ele-ments, all working in tightly orchestrated phase co-herence, would not be built for a very long time. Inretrospect, both the enthusiasts and the skeptics wereright. The dream of electronic beam movement wasachievable, but it has taken a long time to achieve thedream, and it is not yet fully realizedwe still need toreduce the cost of phased-array radars. We are cer-tainly encouraged, however, by the progress in mod-ern solid state phased arrays.

The Beginning

Lincoln Laboratory started working on phased-arrayradar development projects around 1958 in the Spe-cial Radars group of the Radio Physics division. Theinitial application was satellite surveillance, and thelevel of national interest in this work was very highafter the Soviet Unions launch of the first artificialearth satelliteSputnik Iin 1957. The Laboratoryhad played a key role in the development of the Mill-stone Hill radar under the leadership of Herbert G.

T was certainlynot new when Lincoln Laboratorys phased-array radar development began around 1958.Early radio transmitters and the early World War IIradars used multiple radiating elements to achieve de-sired antenna radiation patterns. The Armys bedspring array, which first bounced radar signals off themoon in the mid-1940s, is an example of an early ar-ray radar. A new initiative in the 1950s led to the useof rapid electronic phasing of the individual array an-tenna elements to steer the radar beam with the flex-ibility and speed of electronics rather than with muchslower and less flexible mechanical steering. Many in-dustrial firms, government laboratories, and aca-demic institutions were involved in developing meth-ods for electronic beam steering. In fact, this researcharea in the 1950s could be characterized as one thou-sand ways to steer a radar beam. Bert Fowler haswritten an entertaining recollection of many of theseefforts from the 1950s to the present [1].

Many skeptics at that time believed a workable and

FENN, TEMME, DELANEY, AND COURTNEYThe Development of Phased-Array Radar Technology

322 LINCOLN LABORATORY JOURNAL VOLUME 12, NUMBER 2, 2000

Weiss, a radar visionary. At that time, the MillstoneHill radar was one of the few radar instruments in theworld with satellite detection and tracking capability.Weiss, along with others in the U.S. Air Force, fore-saw that the United States would soon need the capa-bility to detect all satellites passing over its territory.The volume of radar surveillance needed to accom-plish this task was clearly enormous, which meantthat radars of great power, antenna aperture, andbeam agility would be required.

One approach to solving this surveillance problemwas to build a large planar array of some five thou-sand UHF elements. Weisss intuition told him thenation was not yet equipped with the capability toproduce reliable low-cost components that would al-low engineers to implement a radar with five thou-sand individual transmitters and receivers. The coun-try, however, did have some big UHF klystrons in theMillstone Hill radar transmitter (2.5-MW peakpower, 100-kW average power), and klystrons such asthese could be incorporated into a phased-array radarof sorts. Thus began a search of a variety of hybridmechanically scanned and electronically scanned an-tenna-array configurations that would use a few ofthese big klystrons.

Figure 1 is a drawing of the favored hybrid con-cept, which featured a cylindrical receiver reflector140 ft high by 620 ft long [2]. Three rotating verticallinear arrays formed multiple receive beams in eleva-

tion angle, which were mechanically scanned acrossthe cylindrical reflector. The klystron transmitterswere coupled to three horizontal linear arrays that didnot use the reflector, nor did they electronically scan.They formed a fan beam in elevation angle, whichwas scanned across a large portion of the sky as a re-sult of the mechanical drive in a large center hub(hence this massive machine was given the irreverentnickname centrakluge). Average power output froma group of 900-MHz klystrons was to be one mega-watt. This hybrid array concept had great power,great receiving aperture, and a rapid wide-angle scancapability. It was configured to survey huge volumesof space, so that one installation could detect all satel-lites passing over the United States up to an orbital al-titude of three thousand nautical miles.

The Laboratorys focus at the start of this develop-ment effort was to find efficient ways to build thelong linear phased arrays for the receivers. A variety ofbeamforming schemes were investigated, includingbeamformers at intermediate frequencies (where highlosses could be tolerated), radio-frequency (RF) di-ode-switched phase shifters (where losses needed tobe kept very low), and RF multibeam beamformers.

This hybrid electronic-scan/mechanical-scan ap-proach had critics who argued that it could track sat-ellites only in a track-while-scan mode, and it couldnot track high-interest satellites outside of its some-what restricted vertical search window. The nation

FIGURE 1. Drawing of a proposed 1950s-era hybrid phased-array radar that combined mechani-cally scanned and electronically scanned antenna-array configurations.

FENN, TEMME, DELANEY, AND COURTNEYThe Development of Phased-Array Radar Technology

VOLUME 12, NUMBER 2, 2000 LINCOLN LABORATORY JOURNAL 323

seemed to favor the five-thousand-element, fullphased-array approach, an option that was encour-aged by a significant U.S. Air Force effort on elec-tronic scanning array radar (ESAR) at the BendixCorporation. Also, many engineers in the defensecommunity of that era really wanted the nation tobuild a full planar phased-array radar.

The increase in national interest in ballistic missiledefense shifted everyones focus toward planar phasedarrays because the challenges and intricacies of activemissile defense would demand every ounce of radarbeam agility, flexibility, power aperture, and wide-angle scan that the radar community could muster.Therefore, interest in linear arrays fadedplanar ar-rays were what was neededbut the nation was still along way from achieving the dream of an affordableplanar phased array.

The Early Years

By 1959, a cadre within the Special Radars group atthe Laboratory had formed around a phased-array vi-sionary, John L. Allen, to push the development ofphased arrays for a wide variety of military missions,with ballistic missile defense as the mission for whichsuch radars were most obviously needed. Allens goalwas to conduct a broad development effort on arrays,starting from array theory and extending to practicalhardware developments, in order to improve the na-tional capability in phased arrays to a point where wehad reliable and reasonable-cost array components, avariety of beam-scanning techniques, and a soundunderstanding of array theory. The work had to havea practical orientation, and the Laboratorys efforthad to connect with and influence the wide diversityof array research going on in industry and govern-ment laboratories.

Thus in 1959 the Laboratory launched a broad at-tack on new developments in theory and hardware,and through the ensuing five years the phased-arrayeffort functioned very much as an intellectual openhouse to share insights with other researchers and as aclearinghouse to help industry try out its ideas. TheLaboratory developments were chronicled in a seriesof yearly reports entitled Phased-Array Radar Stud-ies, which were best-sellers in the array community[36].

The Sixteen-Element Test Array

The strong emphasis on making phased arrays intopractical devices led to the construction of a 900-MHz, sixteen-element linear-array fixture as an arraytest bed, where array components, such as antenna el-ements, low-noise amplifiers, intermediate-frequency(IF) amplifiers, mixers, transmitters, and beamform-ing techniques could be tried, tested, and exercised.The array test bed was mounted as a feed looking intoa parabolic cylinder reflector, and this whole antennastructure was mounted on a rotating pedestal andhoused in a radome on the rooftop of LincolnLaboratorys C Building, as shown in Figure 2. A widevariety of embryonic phased-array receiver and trans-mitter components were developed and tested in thissixteen-element array over the first five years of theLaboratorys program.

FIGURE 2. Sixteen-element linear-array test-bed facility atLincoln Laboratory in 1960. Phased-ar