114 



SITING AND COVERAGE OF GROUND RADARS 



coverage may be extended accordingly. The disad- 

 vantages of outlying sites presented by communica- 

 tion and supply difficulties, exposure to enemy 

 attack, etc., should be carefully considered. More 

 often, however, the success of the warning system 

 depends on effective long-range operation of radars 

 located relatively close to the defense area. The early 

 warning stations give periodic reports of the grid 

 position of an aircraft and its response to interro- 

 gation signals. 



The GCI radar is used to direct from the ground 

 the operation of friendly fighters against enemy 

 aircraft. It has a range of about 50 miles and is 

 capable of handling a large volume of traffic. In 

 addition to the grid position and identification of 

 the target it also determines the height. Surrounding 

 the defense area is a region whose width depends on 

 the time required to make an interception on an 

 incoming enemy plane. The siting objective of the 

 GCI stations is the continuous and effective cover- 

 age of the interception region. Close coordination is 

 maintained between early warning and fighter sta- 

 tions, and the coverage deficiencies of one station are 

 counteracted by favorable characteristics of the 

 other stations. 



The coast defense gunlaying radar is concerned 

 primarily with accurate location of ships. It has a 

 range up to 100,000 yd and must be sited fairly high 

 and within a few miles of the coast defense guns 

 which it directs. This radar supplies accurate data 

 on the azimuth and range of the target. 



The antiaircraft gunlaying radar is used primarily 

 for directing the guns. Long-range search features 

 are usually provided so that they may function also 

 as early warning radars, at least to a limited extent. 

 They are sited near the guns which are located to 

 meet artillery requirements. These units provide a 

 continuous flow of data to the gun director giving 

 the azimuth, elevation, and range with great accuracy. 



The searchlight control radar is a short-range high 

 angle set which is located near the light it directs. 

 It furnishes the azimuth, angular elevation, and 

 altitude of the target. 



15.2.3 



Radar Siting — Technical Aspects 



In the past some elaborate air warning systems 

 have been set up without a competent analysis of 

 terrain effects. This resulted in a waste of time and 

 money and in failure to adequately provide urgently 

 needed radar screens. This failure was caused in 



many cases by the use of prepared coverage diagrams, 

 furnished with the equipment, which were computed 

 for idealized sites. In mountainous regions where 

 only limited reflection areas occur and where the 

 sites are very much higher than those used in labora- 

 tory tests, such diagrams are likely to be very 

 misleading. A result of this experience is an unfor- 

 tunate tendency to explain variations from expected 

 coverage by resort to various abstruse speculations, 

 with weather not infrequently bearing the brunt 

 of the odium. 



It is the purpose of this report to provide an 

 engineering type of solution for the bulk of the 

 problems that arise in siting and in field computa- 

 tion of coverage. A more accurate analysis, with 

 increased attention to detail, probably is not war- 

 ranted at this time in view of the relatively rough 

 measurements which now are made in the field of 

 radar. 



The common early warning radar uses horizontal 

 polarization and operates in the VHF band. It must 

 be sited from several hundred to several thousand 

 feet high in order to obtain sufficiently low angles 

 for the range and low coverage desired. Suitable 

 sites of the required height may be far inland so 

 that an important part of the reflecting surface may 

 be rough land or sloping flat areas. Such features 

 and also cliff edges, ridges, hills or other obstacles, 

 nearby towers and structures will, in general, produce 

 a marked effect on the coverage pattern. 



The GCI radar uses horizontal polarization, 

 operates in the VHF band and should be sited on 

 a large, flat area. The determination of the height 

 of an airplane is accomplished by comparing signals 

 from two antennas of different heights. If reason- 

 able accuracy is to be attained the lobe structure in 

 the vertical plane must be known with considerable 

 precision. Best results are obtained by using a site 

 of the extent and flatness prescribed in the instruc- 

 tion manual. In practice it may be necessary to 

 operate on rough ground or limited areas. The ques- 

 tion may then arise concerning the benefit that will 

 be obtained by grading the surrounding areas, or 

 how much forest or vegetation should be removed 

 for acceptable operation. 



Similar problems arise in siting DF stations. Large 

 errors may be introduced by reflection from sloping 

 land or other terrain features. 



The effects described above, involving reflection 

 from limited areas or rough land or passage of waves 

 past an edge, may all be treated as problems of 



