RADAR ANTENNAS 



311 



The objective was to obtain as long range early warning as possible with 

 moderate accurracy of location. Emphasis was placed on detection of low 

 flying planes. 



The objectives for the set indicated that the antenna should be built 

 as large as reasonable and placed as high as reasonable for a portable set. 

 Some latitude in choice of frequency was permitted at first. For rugged- 

 ness and reliability reasons which seemed controlling at the time, the fre- 

 quency was pushed as high as possible with vacuum tube detectors and 

 R.F. amplifiers. This was finally set at 1080 mc. 



Fig. 59— AN/TPS-IA Antenna. 



The antenna as finally produced was 15 ft. in width and 4 ft. in height" 

 The reflecting surface was paraboloidal. The mouth of the feed horn was 

 approximately at the focus of the generating parabola. The feedhorn 

 was excited by a probe consisting of the inner conductor of the coaxial 

 transmission line extended through the side of the horn and suitably shaped. 

 To reduce side lobes and back radiation the feedhorn was dimensioned to 

 taper the illumination so that it was reduced about 10 db in the horizontal 

 and vertical planes at the edges of the reflector. Dimensions of probe and 

 exact location of feed, etc. were determined empirically to secure acceptable 

 impedance over the frequency band needed. This band, covered by spot 

 frequency magnetrons, was approximately ±2.5% from mid frequency. 



Figure 59 shows the antenna in place on top of the set. 



