1-4] FUNCTIONAL CHARACTERISTICS OF RADAR SYSTEMS 15 



by a rearward-looking antenna on the missile t\ ^tsec after transmission. 

 The missile, by measuring the time difference between these two signals, 

 can obtain the range to the target; thus 



Rft = Ct2 



Rfm = ctx. 



Since Rmt = R/t — Rfm 



then Rmt = c{t2 - /i) (1-13) 



where c = speed of propagation in yd/jusec = 328 yd/Msec. 



The relative velocity between the missile and the target can be obtained 

 by analogous means, using the frequency difference between the direct 

 and reflected signals. This frequency difference is caused by the doppler 

 effect. 



Information Relay. From a systems standpoint, it is often desirable 

 to display and utilize radar information at a different location from the 

 point of collection of the information. Typical of such an application is 

 the air surveillance system shown in Fig. 2-15. Data are collected by a 

 number of airborne early warning (search radar) systems located in such 

 a manner as to provide the required coverage. It is desirable to assemble, 

 correlate, and assess the data at a central location (Fleet Center) in order 

 to provide a complete picture of the tactical situation. From this analysis, 

 instructions and data can be relayed to the operating elements. This type 

 of operation is typical of airborne, ground, or ship-based combat information 

 centers (CIC). 



Jamming. Radars may also be used to transmit microwave energy 

 with the object of confusing or obscuring the information that other radars 

 are attempting to gather. Jamming is of two fundamental types: (1) 

 "brute force" and (2) deceptive. 



Brute force jamming attempts to obscure as completely as possible the 

 information contained in other radar signals by overpowering these signals. 



Deceptive jamyning, on the other hand, endeavors to create mutations 

 in the information contained in other radar signals to render them less 

 useful tactically. 



Both types of jamming are aided by their one-way transmission char- 

 acteristic as contrasted with the two-way transmission characteristic of 

 active radar. This feature allows a jammer to operate successfully with 

 a few watts of transmitted power against a radar transmitting hundreds 

 of thousands of watts of peak power. 



