184 



t°C 



DIELECTRIC CONSTANT. ABSORPTION AND SCATTERING 



Table 20. Temperature variation of the dielectric jiropertics of \vater.'ii>"' X = 10 cm. 



Refractive index 



Absorption index k 



Ex-perimental 



Calc 



9.72 cm X = 10 cm 



Calc 



Experimental 



X = 9.72 cm X = 10( 



calc 



calc CT mhos/ra 



Table 50 refers to 10-eiii waves for which measure- 

 ments were made in the temperature range to 

 40 C.*^'^'' In one series of measurements the wave- 

 length was 9.72 cm. hut this is considered close 

 enough to have tlie corresponding data included with 

 the 10-cm waves. 



Tlie preceding table indicates that the agreement 

 between calculated and measured values of n and k 

 is satisfactor}-. It is to be noted here that the experi- 

 mental results on S band were obtained by the stand- 

 ing wave ratio method, those at K band with the reilec- 

 tion-transmission method. 



Using ec^uations (105) and (106), the temperature 

 variation of the refractive and absorption index, or 

 real and imaginary parts of the complex dielectric con- 

 stant, can be computed at any wavelength provided 

 that the relaxation time at the temperature in ques- 

 tion is known. 



In Tal)les 21 and 22, the temperature variation of 

 the indices n and k are given. These results were com- 

 puted with the aid of formulas (105) and (106). 



It is thought^*-''^ that until more extensive experi- 

 mental results become available the computed values 

 can be regarded as representing the best information 

 available on the dielectric constant of water in the 

 millimeter and centimeter range. Figure 25 represents 

 the best available information on water at 20 C. 



Table 21. Temperature variation of the dielectric 

 properties of water. ^8,39 x = o.50 cm. 



as 



2.4 

 22 



?.o 



.6 k 

 .6 



0.1 0.2 0.3 0.4 05 0.7 1.0 2.0 3.0 4.0 5.0 7.0 IQD 



A IN CM 



Figure 25. Refraction and absorption indices for 

 water. 



Ice 



A certain numl)er of measurements on the dielectric 

 constants of ice were made in the centimeter wave- 

 length I'ange. The British workers*^ used the resonator 

 Q method at 3 and 9 cm. The latest results on both 

 these wavelengths are collected on the accompanying 

 graph (Figure 26). The temperature range extends 

 from about — 50 C to C. The refractive index turns 

 out to be constant in this range. It was found to be 

 equal to 1.75 at 3.01 cm and 1.72 at 9.18 cm. The 

 absorption index increased in this temperature range 

 from about 0.0001 to 0.0010. 



Table 22. Temperature variation of /(, k, t,, e, and a-.'^i^^ 

 X = 3.2 cm. 



