398 REGULATORY CIRCUITS 



rms value- of ar = 0.8 times the estimated radius of gyration of the reflec- 

 tivity distribution of the target about its center of reflectivity. These 

 results relate to average noise power. By nature, wide fluctuations from 

 sample to sample may be expected with the actual value dependent upon 

 sample time. Examples of spectral power distributions are shown later. 



3. The range noise power spectra for a variety of aircraft targets in 

 normal flight show that the significant power is below 10 cps and, in general, 

 one-half the range noise power lies below 1 cps. The frequency components 

 of range noise are a function of rates of target motion in yaw, pitch, and roll 

 and are influenced by air turbulence, angle of view, maneuvering of the 

 target, and the target type. 



4. The influence on the noise values incident to the specific type of range 

 tracking system employed has not been extensively investigated, but the 

 values shown are believed to be typical for fire-control design purposes 

 (assuming good system engineering and performance). 



The measured spectral range noise power distributions for an SNB twin- 

 engine aircraft, for two SNB aircraft, and for a PB4Y patrol bomber are 

 shown in Fig. 8-2. The curves represent mean values while the upper and 

 lower maximum excursions from the mean are shown by the arrowed lines. 

 The analysis was based upon 80-sec samples with the indicated mean value 

 for (Tr taken over the number of runs shown. The broad frequency range of 

 the radar range input noise power clearly emphasizes the requirement of 

 range tracking bandwidth minimization consistent with tracking error 

 specifications. 



Angle Tracking Noise. The general shape of the dispersion versus 

 range for the various noise factors entering into angle tracking is shown in 

 Fig. 8-3. The various noise components shown are uncorrected. The 

 rms total output noise for conical scanning or sequential lobing radar is 

 greater^'^ than for monopulse^ (simultaneous lobe comparison) radars 

 because of the high-frequency amplitude noise at the lobing frequency. For 

 prediction of system performance, at least one point on each characteristic 

 must be determined by measurement. In the case of external angle noise, • 

 the following facts have been established. 



1. Amplitude noise is an amplitude modulation of the echo caused by the 

 vector summation of echoes from the complex multielement reflecting 



2D. D. Howard and B. L. Lewis, Tracking Radar External Range Noise Measurements and 

 Analysis, NRL Report 4602, August 31, 1955. 



3J. E. Meade, A. E. Hastings, and H. L. Gerwin, Noise in Tracking Radars, NRL Report 

 3759, 15 November 1950. 



■•J. E. Meade, A. E. Hastings, and H. L. Gerwin, Noise in Tracking Radars, Part II: Dis- 

 tribution Functions and Further Power Spectra, NRL Report 3929, 16 January 1952. 



5R. M. Page, "Monopulse Radar," paper presented at the 1957 Institute of Radio Engineers 

 Convention, IRE Convention Record, Part 8, Communications and Microwaves, p. 132. 



