6-3] 



MONOPULSE ANGLE TRACKING TECHNIQUES 



303 



antenna difference pattern null is therefore the familiar error signal curve 

 of Fig. 6-6, with zero signal on target, and polarity of error signals indicating 

 error sense. The output of the sum amplifier provides indication of the 

 presence of a target, an indication which is maximum when on target. The 

 balance point representing zero angle error is not significantly affected by 

 relative shifts in gain or phase between the two amplifiers. The sensitivity 

 to angle error, represented by the slope of the error curve as it passes 

 through zero, is influenced by relative phase shift between the two ampli- 

 fiers, becoming zero at 90° relative shift. Since it is a cosine function, 

 however, it is insensitive to phase shift near correct phase, a relative shift 

 at 25° producing a decrease in angle error sensitivity of only 1 db. 



A system diagram illustrating the 

 monopulse principle for angle error 

 indication is shown in Fig. 6-7. A 

 conventional hybrid ring (see Para- 

 graph 10-1 5) is used for deriving sum 

 and difference signals from the two 

 antennas. The transmitter is con- 

 nected to both antennas by suitable 

 TR circuitry in the sum channel, so 

 that the transmitter radiation pat- 

 tern corresponds to Fig. 6-4. The 

 output of the sum amplifier is recti- 

 fied and applied in a conventional 

 manner as a video signal to a radar A 

 scope, giving indication of presence 

 of target and target range. Also the 

 outputs of the two amplifiers are mul- 

 tiplied in the phase-sensitive or prod- 

 uct detector to give an error signal 

 whose sign corresponds to error sense. 

 This error signal, which is a video sig- 

 nal, is added to the time base signal 



and the combination applied to the indicator deflection system orthogonally 

 to the output of the sum amplifier. The resulting indication presents targets 

 as pips perpendicular to the time base line for targets which are in align- 

 ment with the antenna difference pattern null and which "lean" forward or 

 backward from the perpendicular as angle of arrival deviates to one side or 

 the other from the pattern null. It is apparent that the direction in which 

 the signal pip points is related to the direction of arrival of signal energy 

 relative to the antenna pattern null and is independent of the amplitude of 

 the signal. The length of the signal pip indicates signal amplitude. Sensi- 

 tivity of the indicator to angle of arrival is a function of relative attenuation 



Fig. 6-7 Single-Coordinate Monopulse 

 System. 



