10-9] RADOMES 533 



radome designer with sufficient flexibility, the specification on boresight 

 error shift should not be the same for the entire radome; rather, it should 

 be matched to the tactical problem. The generation of radome requirements 

 on bases such as these is a tedious and time-consuming system study task. 

 However, it is easier than trying to design a complete radome to meet a set 

 of rigid specifications that actually are necessary for only a small portion of 

 the radome's area. It is becoming more and more necessary to approach 

 the radome problem in this manner because aerodynamic considerations 

 require radome shapes of increasingly poor geometrical properties so far as 

 the transmission of electromagnetic energy is concerned. In fact, histori- 

 cally the radome problem has advanced somewhat as follows. 



History of Development. The earliest radomes were dielectric 

 material made of organic composition in a single half-wavelength layer. 

 The form was hemispherical. This shape made possible good accuracy, 

 since by reason of symmetry a hemisphere will not affect the antenna 

 boresight. The half-wavelength thickness minimizes reflective losses at 

 least one frequency, and a strong low-loss dielectric material need only 

 be found. 



Typically, radome material has a dielectric constant between 4 and 7 with 

 a loss tangent less than 0.02. The principal radome problem is that strong 

 dielectric materials inevitably have a high dielectric constant. Thus, the 

 transition reflections in and out of the dielectric are large and the bandwidth 

 is narrow. To increase bandwidth, various sandwich arrangements have 

 been used with materials of differing dielectric constants to arrange for 

 reflection cancellation at more than one frequency. ^^ 



At the same time, aircraft speeds increased, requiring a special high- 

 density, protective coating on the outside surface of the radome to protect 

 against raiil erosion. Further, the hemisphere is no longer satisfactory 

 aerodynamically, and progressively sharper structures were required. A 

 typical radome for a transonic aircraft is shown in Figure 10-10-a. 



Still it was found possible to maintain good system accuracy through 

 radomes of conical symmetry by carefully and experimentally compensating 

 the radome by large dielectric rings suitably fastened to the inside of the 

 radome.^'' 



At this point in the history comes the transition to missiles, which 

 changes the requirements considerably. For aerodynamic reasons, the 

 required shape is definitely ogival. Further, aerodynamic heating precludes 

 the use of most organic plastics. In Fig. 10-10-b, the temperature expected 

 at the nose of a missile is shown as a function of speed. Some help has come 



^^Radome Design Criteria for Precision Guidance Radar, p. 41, Final Report, Contract 

 AF33(038)-12283. N. M. Weiderborn and A. F. Kay, McMillan Laboratory Report No. 1276. 



I'^H. A. Schetne, "The Use of Dielectric Rings in Reducing Radome Error, Proceedings of the 

 OSU-WADC Radome Symposium, Vol. II, June 1956. 



