-Precis-ion meastlfernent of the operating paramek'rs of uncooperoting rndars QUALITY ELINT William H Na nee Most of electronic intelligence is devoted to the inten ept and amlysis of radar signals in order to locate rad r sites and establish the general characteristics of radar systems This type of Elint usu lly called •radar order of battle has proved to be of great value in the Vit t Nam air war where the U S Air Force iind Navy both conduct Lu-gc• scale Elint opcratjons in support of air strike mission s Anothe category of Elint receiving wide recognition in the intellige nce c -ommunity is called precision parameter measuwments This technique involves either the me-asurement of radar signal characteristics to a very high order of accuracy or mca suremenls to detennine something about a radar's operation that will rcveaJ its detection and tracking capabi lities Of greatest importance a re measurements which will reveal a radar's vu h1erability to electronic countenneasures As advanced radar ystems with complex modes of operation have been evolved to achieve greater range ac-curacy and immunity to countermeasures electronics intelligence groups are being pressed harder and harder to develop equiprnent and techniques for meaningful measurernents of their pararneters Rather large-scale research programs are ing carried out to develop special receiving and rec ording systems and these often incorporate electrnnic computers to process the vast quantity of information bits in a typical radar signal Studies of tcclmical and operational feasibility are also undertaken to devise methods of deploying these systems in collection operations In 1962-63 the CIA Office of Elint expanded its program of precision measurements to determine the vulnerability of reconnaissance vehicles and to develop equipment for electronic countermeasures This program has been highly succes fol in a variety of projects developing a number of new approaches lo the collection of electronic intelligence One of the most interesting of these is the technique for accurately measuring the radiated power of an operating radar and i L 7 Quality Elint describi ng tl1e 6ne-grain structure of the radiation pattern A simplified review of this power-pattern tl'chnfri11e although it represents only one facet of the precision mc 'lSuremcnts program should give some insight into the tedmical and operational problems encouDtercd and some idea of the ccomplisbments of the p1ogr«m Power Mca mrcments 1957-1957 1ne first serious att1 rnpt to measure the radiated power of a radar for intelligence purposes was made by CIA in 1958 on the Soviet e arly-waming radar known as Bar Lock The Bar J_ oc k was a new version of the Soviet multi-beam S-band 1 family of radars which had undergone a rapid and V•tidespread leploymcnt in East Genna11y and olher areas peripheral to the USSR Intelligence indicated this new radar was deployed to detect and Lrack the U-2 aircfaft which were just beginning to make deep penetlations over the Soviet Union The Bar lock Rodar Estimates of the Bar Lock's radiated power output based largely upon photographic evidence ranged as high as 5 megawatts peak pulse power from each of its 5 transmitters Vith 5 megawatts in each beam the Bar Lr ck would have had ten times the power of previous similar rndars and would have significantly improved the '2 to 4 GHz or 2 000 to 4 000 roegacydcs per second 8 r f t Quality Elint I I I 1 detection and 1racking capabilities of the Soviet air defense system To meet this threat to the U-2 those responsible for the reconnaissance program demanded firmer information on the Bar Lock's power output and radiation pattern coverage A laboratory that provided scientific back-up to the U-2 program assembled powe1-measurcrnent cguipment crnde by present-day standards a mi installed it in a C-119 aircraft With little advance t c ting a sedes of flights was made through the air conidors to Berlin where Dar Lock signals were easily intercepted The resulting power measurements at various vertical angles in the antenna pattern were not of high accuracy because of uncontrolled errors in the equipment The data did indicate however somewhat less than one megawatt of vak power for i - ich Bar Lock trarismitter and this was later '011finne l by other sources Although not entirely successful in power measurement this project suggested solutions to many technical problems and opened the way for follow-on developments In 1963 a cor1tract was let with a major electronics laboratory for research on the technical problems of precision power-pattern measurement and for the development of measuring equipmcot Before the end of the year a prototype system was 10 vn agai_nst the acquisition radar for a U S Nike Ajax and produl'1cd good results At the same time the procedures to be used in ov rscas deployment were being simulated and studied a nd a special laboratory Vas set up to pr0 ess and analyze tl1e nnique data to be c-ollected The first two oveneas deployments took place in 1963 against the Soviets' Tall King radar in the Far East and Fan Song in Europe and both were successful 'The appended Table lists the projects that followed produciHg precision data on the majority of the radar types used in the Soviet Chinese and North Vietnamese air defense systems Antenna Pattern M east rements ·1nc total raclic1 frequency power fed to a radar antenna is essentially determined by the type of output tube used in the transmitter the characteristics of tl e pulse train and the losses by attenuation in the system The function of the antenna is to concentrate this power in the desired lirection and its ability to do so is called gain The relative distribution of the energy in all directions is called the antenna radi ition pattern generally consisting of a main beam plus side and b ck lohes This antenna pattern and the level of power 9 Quality flint radiated are critical parameters in e-stabli hing the performance of the radar Thc se parameters are piiority requirements for intelligence and ECM purposes The accurate and comprehensive mcasun ment of a radar antenna pattern is a tedious pnx'Css even for the designer Test ranges with elaborate instrumentation are necessary to insure that the finished antenna has a beam of the desired shape and that the side and back lobes are properly mppressed Moreover the patterns seen on the test ninges are not always maintained in operational use because envirom ntal and ground effects at the site c m make signi£cant changes i11 the pattern The objectives of Elint power-pattern measurements a re to obtain piecise data on the rniiximum beam power the totaJ radi al ed power the «ntenna gain and variation in gain side md back lobe distribution around the antenna ·n1is requires the use of an airborne measming platform to avoid ground effects and to make me Lrnrements at various angles of elevation In theory the E int approach is tl1e same as that used on the antenna test range tlie power density is measured and then converted to r idiated power on tJie basis of the known geometric relationship between the radar antenna and the measurement system In p1 ac ice the El int operation has all of the problems encountered on the test range phL additional ones iDtrinsic to intelligence collection the target radars are noncooperative and may not radiate at tLe time and in the direction desired all of the imtrnmentation to measure power density and locate tlie aircraft's position must be ca1ried in the aircraft These handicaps increase the number of potential sources of error which must be eliminated minimized or calibrated ·n1e primary sources of error for power density measurements lie in uncertainties in the gain of the receiving antenna losses in the trari5mission foe characteristics of the receiver and the sou1ces used for calibration Errors in the geometric data may be associated with the position altitude and attitude of the aircraft the locatfon of the target atmospheric conditions or ground effects Speci al Equipment The design of the rneasuru1g equipment is centered upon the nc-ed for very accurate measurement of individual pulse amplitude and the use of calibration signals from laboratory standard power meters 10 r I t Quality £ int t ''· ' · · «_ _ Test range for cintenna design 1 The Yerticle boom on the left holds the mock-up nose section of a C-97 aircraft i I L_ 11 Ouofity int Dming collection operations provisfon is made for the acc-u rate calibration of the receiving antennas the tiansrnission Ii Des and the rec-eiving and recording systems with respect to attenu tion losses or other enors which n i y degrade the data A description of the labo1atory-tyfie receiving equipment calibration sources imd data enccxlers would be comprehensible only to cledronic spc--dalists A brief disClission of antenna problems however should give some idea of the development w 1rk behind pow - r-pr ttem measurement systems 1ne pattern of the receiving anle1111 is critical l e- fmse the angle at which tJ e ' nergy arrives is c-onst mtly changed by the movement of the aircrnft including its 101 pitch end yaw In order that the precise gain of the n c eiving antenna may be knov •n nd used in the C3kulations for absolute power it i s highly desirable to have smooth L_ ·' --- · _ - _ -- __ · · oo L _oo' Figure 1 Typical omnidireciionol pot1err•s pos5ible from aircraf1 - mounted antennas above 1 000 MHz 554 79 2-68 Cl A 12 ''' rQuality flint « _ '- Figvre 2 The lowed antenno-corrying vehicle us d for power-pattern measure- ments below l 000 MHz The RC-135 oircrof1 hos a special A - frame boom slruclure for lol'nc hing and recovering the vehicle in flight The specially developed towing coble serves os the RF transmission line bet -een the antenna ond the receiving system in the oircrcft It ubo carries the electric oble to Ontrol 1he vehicle from the aircraft -8480 2-68 CIA omni-directional rcce1vmg patterns with equal gain over a wide sector Airborne omni-antenna patterns are difficult to achieve because of interfereuce from Ll-ie aircraft strncture whose complex shape breaks the pattern into shr11-p peaks and dc cp nulls A speci 11 test range was established for this program to find interference-free locations on ain raft surf aces which would yield patterns with smooth contours M xkups of complete aircraft nose sections and v-ringtips were tested and in some c-a ses new antenna elements were developed ' t 1 'When the desired paHems were obtained the antenna elements were carefully transferred from the moekups to the real aircraft Even with these meticulous efforts good patterns could be developed only for the liigher frequencies and only off the nose and wingtips of ceitain aircraft as shown in Figure 1 This limitation has often been a handicap in t-ollection operations In the radio frequencies lwlow 1 000 MHz where some important Soviet rc1dars operate it proved impossible to produce good patterns t k · 13 Quality E int from antennas mounted on the aircraft To solve tlie problem at these frequencies a new phase of resr 1rch was bcgun---thc development of ac-ro lynamic antenna- anying vehicles to be towed behind the ain rnft Auk1mas mou11ted iu these vehicles could be de signed to produce a s1rnxith c-ardioid pattern v ith the one harp null pointed toward the towing aircraft Thi s null eliminates intei frrence from Vie lircraft leaving patterns that are ideal for po V T measwements i tk ugh the towing of the nntenna greatly incn ases the co1npk- rity of the system it ha 5 proved to be a good teclmical solution to the receiving pattern problem at the lower radio frcque ndes A typical configurnJion is shown in Figure 2 The collrct - l data consist of measurements of pulse Bmplitude taken from different portions of tl e rndiation pattern as the radar antenna 1otates or cans and the airciaft moves through the pattern Mcasmements are recorded digitally reduced and read out on continuous-dJart paper rolls which display the varying amplitudes making up the pattern The chart paper format is of sufficient accuracy to allow a11trnna specialists to ma kc direct me isuremenls from the di 1Jhy Successive scan patterns together with geometric and other calib1ation data as shown in Figure 3 are processed by computer to make' lll three-dirnemional radiation patterns -········································· _ -a -' I ' 4 J r J _ 1-- --- _ · i • ' C i'·- J - I 0 - s -- Figure 3 An exai ple of the c hcrt paper roll readout of the antenna i •ollern do1o 5848 l 2- 8 CIA Collection Operatfon s Ideally tbe flight path for power-pattern mcas-urcment is a radial patJ1 from the bo1izon to directly over the radar site If the radar Quality flint antenna is making 360-degree scan rotations the radial flight will yield continuous measurements around it at increasing angles of elevation This provides data from which the complete three-dimensional radiation pattern can he desc ribcd Such flight p i ths of course are not often possible wmetiines the data are limited to elevations of 15 degrees or Jess Fortuni tcly tl- e Jower angles of a radar pattern are of greatest importance for iutelligence that is where target detection and tracking begin Each of the deployments shown in the Table wa s the result of 1 onths of preparation which included calibration and installation of t1Je equipment det 1iled phuming of the mission operator trniriing imd t 1e coordin ition of a multitude of technical and operational Wdtkrs The radar types were selected on tl1e basis of intelligence p1iority and the paiticufar tr _rget sites on the basis of air access ·with preference to isolated areas where oilier radar would not offer interference The location of the site was known beforehand tl1e target signals were identified by direction-finding equipment which was part of the airborne system During collection runs tl c aircraft's position and altitude were recorded by special navigational instruments so that the exact geometric relationships between the radar and the measurement system would be kno- 'Jl Several of the projects were completed in fewer than six missions others required more than 40 to get the desired results TI1e power-pattern measurement program has been carried out with the full cooperation of U S Air Force organizations which have furnished the aircraft and crews and have also given the extensive suppoit required for airborne reconnaissance operations The flight missions have been conducted for the most part within the framework of world-v ide peripheral reconnaiss mce prog ams carried out i by the Strategic Air Command and other USAF elements Exceptions to established flight restrictions and security rules have been necessary on only a few X casions 1 As of this writing the most recent deployment was tlrnt listed as Project See Top in which a C-97 aircraft flew over the Gulf of Tonkin to make measurements of the SA-2 Fan Song radar during U S air stxikes ir the Haiphong-Hanoi area The antenna patterns recorded were used in the development of guida 1ce systems for new anti-radiation missiles designed to home on and destroy target radars 15 ° 0 Power Pattern MeMurement ProjPcte a C Projec Code Name Table Deployment Datee Aircrnft Used Target Ra da r I Frequcncy Bllnr I STR Location No Field Day Jul-Sep '63 C-97 Fan Song S C Cuba E Germ11 ny 1-65 New Breed I Jul-Aui '63 RB-47H Tall King VHF Sakhalin 2-65 New Breed II Jul-Aug '63 RB-47H Sr onn Rest A Knife Reet B VHF Se11 of Ja po n VHF Iron Lung Oct '63 RB-47H Spoon Re8t A VHF Cuba 4-65 New Breed III Sep-Oct '63 RB-47H Tall King Spoon Reet A VHF VHF Arctic above USSR 2--65 New Breed iV Jan '64 RB-47H Spoon Rest A Knife Reet B VHF Arctic above USSR 2-05 VHF W neaap I May-Sep '64 C-97 BG07 BG06 Fan Song A B C E S C E Germany Iron Lung I Jan-Sep '64 RB-47H SCR-' 270 ' BKEH KNB BK08 BKDQ Ttill King VHF Yellow a nd Ee et China Sea 5-65 Iron Lung II Feb-May '65 RB-47ll BK08 EKEN SCH -270 I nife Re t B Spoon Rest A B Tall King VHF Yellow and E11 8t China Sea 8-65 - - - - - - - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Wfff f1Hwl 1 ¥ ' tt· 1 M41tci afr ·zrt tr f®7Xf1'$ l iildaJcl ' i • wt tttz·tr lt M' M i t i i i r·-- l T11 blo Continued Project Code Nnmc Deployment Dates Aircrnft Used FreTarget Radar I quency Unnd Location STR No WincRnp II Jun-Aug '6 5 C-97 Fin t Face L Lend Off Aug-Sep '65 RB-47JI Bnck Net 8 Black Sea 1-66 High 1 1tch Jan-Mar '66 RB-47H Bnr Lock Big Mesh Token s Sea of Jnpa n Yellow and E11 et ChlnB 4-66 E Germany l 2-66 Sea Low Pitch Sep '66 RB-47H Bn ock Big Mesh Fan Song s Cuba Cross Field May-Oct '66 C-97 Fan Song C E C E Germany o-66 Top Hn t C-97 Bar Lock Big i lesh Fnn Song s E Germany • 7-66 Side Net Briar Patch C-135 Hen Houee VHF Barents Sea See Top C-97 Fan Son ··· s Gulf of Tcnkln 4-67 D C Q n _ i '-I - -· - - ··---- - ·- ---- ·- Quality Elinl A series of reports on the power-pattrm measurements have been dissemin ted throughout the intelligence community where the accuracy and significance of the data have been widely accepted Present Capabilities 'l1 e Offic--e of Elint power-pattern mcasure1ne11ts are unique there is i o other comparable program in the U S intelligence rommtmity or in the Elint organizations of allii d counbies Even the radar design and development laboratories have as yet produced no sirnllar selfcontained ai rb0rne measurement systems Because of tlie se 'unique capabilities the USAF Air Proving Grounds C 01nmand and other groups have several times ananged for the use of the OEL system to cornp rc the patterns of 5imulated Soviet radars with those of the real ones opei ating in the USSR Airborne instrurnenlotion required for pcwer-pot1ern m1 osurement 18 Quality Elinf As each project was c 1rried out improvements were made in the instrumentation to enhance the system's ac uracy and the convenience of its use Now instead of re-engineering the equiprnent for each new project as was required in the early days the use of ad2ptable equipment is being emphasized Receivers and recording Ccqujpment are now available along with the associated antenna configm tions and modified aircraft for quick-reaction deploy1nent against any rctdar in the normally used fr quency bands Additional instrnmentation is beL g incorporated for the predsion me•1surement of otter parameters in tlie signals such as radio frequency coherency intra-pulse modulation and pulse train diaracterisl ics 19