9-4] REQUIREMENTS IN ANGLE TRACKING ACCURACY 479 



where ai ~ 0.15— ; L is target length subtended to the radar; R is the range 

 K 



to the target; Wo is the noise "bandwidth"; 1 < Wo < 15. 



Amplitude Noise Inputs. The magnitude of the pulse-to-pulse 

 amplitude noise appearing at the antenna track input will be reduced 

 considerably by the AGC in the receiver if it has a bandwidth 10 cps or 

 more.^ At relatively short ranges, it is much smaller in magnitude than the 

 glint noise. However, the amplitude noise may still appear as an angle 

 track input signal after it passes through the AGC circuits and receiver 

 filter. In the angle track loop it is further attenuated by the angle track 

 demodulators which transmit narrow frequency bands of noise only at odd 

 harmonics of the carrier frequency.® However, there is a possibility that 

 noise could cause saturation of the track loop input amplifier. Therefore, 

 the dynamic range of the amplifier must be made large enough to prevent 

 saturation by noise most of the time even with steady state bias errors. 



9-4 REQUIREMENTS IN ANGLE TRACKING ACCURACY 



Generally, the antenna angular position and antenna space velocity must 

 be measured for use in a weapons control computer. Position is measured 

 with resolvers or potentiometers and rates are usually obtained from gyros 

 on the antennas. As discussed in Paragraph 2-27 the errors in measurement 

 have two essential components — bias errors and random errors. To 

 provide maximum system accuracy, all units including the tracking loop 

 must be designed to provide a proper relationship between the bias and 

 random errors that are generated in the physical equipment. 



Maximum Dynamic Lag or Bias Errors. The output of the track- 

 ing system, the antenna tracking line, must follow the sight line in space 

 with a maximum permissible space error of 0.525° total as specified in 

 Paragraph 2-27, Table 2-4, assuming that a particular attack, a lead 

 collision course, is being flown. The errors may be different for other types 

 of attacks. This is referred to as a bias error since it is predictable from a 

 given target flight path, attack course, and tracking loop configuration. 

 This space error of 0.525° is equivalent to 0.372° per channel. In a similar 

 manner, the line-of-sight bias rate error is specified as less than 0.2° /sec 

 total or 0.14°/sec/deg /sec /channel. These particular errors and the 

 random errors below will be used in an example to illustrate the relationship 

 between the errors and the design of angle track loops. 



^See Paragraph 8-18. Reference: J. H. Dunn and D. D. Howard, "The Effects of Automatic 

 Gain Performance on the Tracking Accuracy of Monopulse Radar Systems," Proc. IRE, 

 47, 430-435 (1959). 



^Assuming that an averaging type demodulator rather than a keyed demodulator is used, 

 because of the noisy signal. 



