]fTCRO\VAVE RADAR TESTING 439 



In developing test equipment, an offhand approach might have been to 

 provide speciaUzed equipment for testing each radar under specific condi- 

 tions. Since this would have made the total burden of development, manu- 

 facture and field maintenance well nigh intolerable, a coordinated plan was 

 followed whereby (with minor exceptions) each test set was made capable 

 of widespread application in testing as many radars under as varied condi- 

 tions as possible. 



Broadbanding 



Generality of application required the designing of test equipment for 

 broad frequency bands, bands as a rule much wider than those of the radars 

 themselves. It was necessary, therefore, not only to develop new micro- 

 wave testing techniques, but to advance the art still further to render the 

 testing components as far as possible insensitive to frequency. 



Precision 



A radar itself is an instrument of considerable precision. The test equip- 

 ment used for checking the radar performance in the field has to have still 

 higher accuracy. It is noteworthy that the measuring accuracy realized 

 throughout the microwave range is comparable with that obtainable at 

 lower frequencies where many years of background exist. 



Packaging — Size and Weight 



Light weight and compactness are of paramount unportance where a 

 test set has to be carried any distance by the maintenance man, where it 

 is used in cramped quarters in a plane, truck or submarine, or where it has 

 to be taken up ship ladders or through small hatchways. To permit portable 

 use under such conditions, the design objective was established of a weight 

 not exceeding about 30 lbs. (exclusive of transit case), combined with a rug- 

 gedness adequate for all conditions of use. Through rigorous attention to 

 both mechanical and electrical design, this objective has been realized (in 

 many cases with considerable margin) except for a few sets intended prima- 

 rily for bench use. Figure 3 illustrates the use of lightweight test equipment 

 in maintaining airborne radars. 



Environmental Influences 



Military usage requires that the test equipment be capable of efficient 

 operation at any ambient temperature between a minimum of the order of 

 -40° to -55° C and a maximum of the order of +65° to +70° C, as well 

 as at any relative humidity up to 95%. In addition the set must withstand 

 continued exposure to driving rain, dust storms and all other conditions en- 

 countered in tropical, desert or arctic climates. Often the test set in its 



