296 GENERIC TYPES OF RADAR SYSTEMS AND TECHNIQUES 



kinds of information, regardless of how it might be split up between range, 

 angular, and velocity coordinates: 



(Total interrogation rate) N = Nr = Aft. (6-5) 



2. The transmission periodicity fr is defined as the fundamental repetition 

 frequency of the radar signal. (In a pulse radar, for example, /r would be 

 equal to the pulse-repetition frequency or PRF.) This quantity governs the 

 radar's ability to split up information between range, angle, and velocity 

 coordinates. 



The transmission periodicity defines the maximum unambiguous range 

 interval as follows: 



/?.ax = 7^- (6-6) 



Target returns from greater ranges will be ambiguous because they will 

 enter the receiver after the transmitter has begun another transmission 

 cycle. 



The total number of separate range intervals covered by the radar is then 



The transmission periodicity also defines the maximum relative velocity 

 interval that may be measured without ambiguity. This may be derived as 



(A^)rn,ax--^ (6-8) 



where (AF)r^ax = maximum relative velocity interval (cm /sec) 



X = wavelength (cm). 



For higher velocities, the total doppler spread becomes higher than the 

 sampling frequency/.. Thus the sampling process will create measurement 

 ambiguities regardless of how the total doppler spread is split between 

 opening and closing velocities. 



3. The angular scanningjrequency is defined as the rateA^a at which signal 

 information is collected from separate portions of the angular space volume. 

 This quantity defines the minimum possible bandwidth of any received 

 signal and it may be expressed: 



A^.=/. = ^ (6-9) 



where i^s = total solid angle scanned 



^o = solid angle subtended by antenna pattern or instantaneous 

 field of view. 



