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1-15 RADAR ACCURACY Radar accuracy is a measure of the ability of a radar system to determine the correct range, bearing, and, in some cases, height of an object. The degree of accuracy is primarily determined by the resolution of the radar system. Some additional factors affecting accuracy are pulse shape and atmospheric conditions. Pulse Shape In the case of a pulse radar, the shape and width of the rf pulse influences minimum range, range accuracy, and maximum range. The ideal pulse shape is a square wave having vertical leading and trailing edges. However, equipments do not usually produce the ideal waveforms. The factors influencing minimum range are discussed first. Since the receiver cannot receive target reflections while the transmitter is operating, you should be able to see that a narrow pulse is necessary for short ranges. A sloping trailing edge extends the width of the transmitter pulse, although it may add very little to the total power generated. Therefore, along with a narrow pulse, the trailing edge should be as near vertical as possible. A sloping leading edge also affects minimum range as well as range accuracy since it provides no definite point from which to measure elapsed time on the indicator time base. Using a starting point at the lower edge of the pulse’s leading edge would increase minimum range. Using a starting point high up on the slope would reduce the accuracy of range measurements at short ranges which are so vital for accurate solution of the fire-control problem. Maximum range is influenced by pulse width and pulse repetition frequency (prf). Since a target can reflect only a very small part of the transmitted power, the greater the transmitted power, the greater the strength of the echo that could be received. Thus, a transmitted pulse should quickly rise to its maximum amplitude, remain at this amplitude for the duration of the desired pulse width, and decay instantaneously to zero. Figure 1-12 illustrates the effects of pulse shapes. Figure 1-12.—Pulse shapes and effects. Atmospheric Conditions Electromagnetic wavefronts travel through empty space in straight lines at the speed of light, but the REFRACTIVE INDEX of the atmosphere affects both the travel path and the speed of the