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GENERIC TYPES OF RADAR SYSTEMS AND TECHNIQUES 



Eclipsing. The relatively high duty cycle of a pulsed-doppler system 

 — typical values vary from 0.5 to 0.02 — introduces a strong possibility 

 that part or all of the received target pulse may arrive during a transmission 

 period. Since the receiver is turned off during transmission, target infor- 

 mation will be lost or "eclipsed." 



The basic problem is shown for a 0.33 duty cycle pulsed doppler radar in 

 Fig. 6-26. Eclipsing causes an effective change in the duty cycle for returns 



Transmitted Pulses 



o n 



o 



Range 



1.0 



Duty Ratio Correction Factor dj = Eclipsed Duty Cycle 

 djo = Normal Duty Cycle 



*- Range 



Idealized Range Correction Factor 



Ro= 7 Duty Cycle 



Probability of Detection (Single Scan) -No Eclipsing 



Fig. 6-26 Effect of Eclipsing on Pulsed-Doppler Blip-Scan Ratio. 



which overlap transmission periods. Since average power that registers in 

 the doppler filters is proportional to the square of the duty cycle, the 

 idealized range will vary as the square root of the duty cycle. The blip-scan 

 ratio is a function of idealized range as shown in the fourth figure. When 

 the blip-scan ratio with no eclipsing is corrected for the eclipsing effect, the 

 last curve in Fig. 6-26 results. As can be seen, the effect of eclipsing is to 

 cause "holes" in the blip scan curve in the regions of pulse overlap. In a 

 practical pulsed-doppler system the ratio of PRF to the useful range 



