312 BELL SYSTEM TECHNICAL JOURNAL 



The characteristics of this antenna are summarized below: 



Gain 27.3 db. 



Horizontal Half Power Bcamwidth 4.4° 



Vertical Half Power Beamwidth 12.6° 



Vertical Beam Characteristic Symmetrical 



Polarization Horizontal 



Impedance (SWR over ±2.5% <4.0db 

 band) 



16. Airborne Rad.vr Antennas 



16.1 The AX APS-4 Anten)ia^ 



AN/APS-4 was designed to provide the Navy's carrier-based planes 

 with a high performance high resolution radar for search against surface 

 and airborne targets, navigation and intercej^tion of enemy planes under 

 conditions of fog and darkness. For this service, weight was an all im- 

 portant consideration and throughout a production schedule that by \"-J 

 day was approaching 15,000 units, changes to reduce weight were con- 

 stantly being introduced. In late production the antenna was responsible 

 for 19 lbs. out of a total equipment weight of 164 lbs. The military require- 

 ments called for a scan covering 150° in azimuth ahead of the plane and 30° 

 above and below the horizontal plane in elevation. To meet this require- 

 ment a Cutler feed and a parabolic reflector of 6.3" focal length and 14|" 

 diameter was selected. Scanning in azimuth was performed by oscillating 

 reflector and feed through the required 150° while elevation scan was per- 

 formed by tilting the reflector. Beam pattern was good for all tilt angles. 

 In early flight tests the altitude line on the B scope due to reflection from 

 the sea beneath was found to be a serious detriment to the performance of 

 the set. To reduce this, a feed with elongated slots designed for an elliptical 

 reflector was tried and found to give an improvement even when used with 

 the approximately round reflector. The elliptical reflector was also tried, 

 but did not improve the performance sufficiently to justify the increased 

 size. 



As will be noted in Fig. 60, the course of the mechanical development 

 brought the horizontal pivot of the reflector to the form of small ears pro- 

 jecting through the ])arabola. No appreciable deterioration of the beam 

 {)attern due to this unorthodox expedient was noted. 



The equipment as a whole was built into a bomb-shaped container hung 

 in the bomb rack on the underside of the wing. Various accidents resulted 

 in this container being torn ofT the wing in a crash landing in water or 

 dropped on the deck of the carrier. After these mishaps, the equipment 

 was frequently found to be in good working order with little or no repair 

 required. 



» Written by F. C. Willis. 



