![]() ![]() Radar designers try to use the highest PRF possible commensurate with the other factors that constrain it, as described below. However, with the higher PRF the range that the radar can "see" is reduced. The higher the PRF that is used, then the more the target is painted. ![]() An echo from a target will therefore be 'painted' on the display or integrated within the signal processor every time a new pulse is transmitted, reinforcing the return and making detection easier. In order to build up a discernible echo, most radar systems emit pulses continuously and the repetition rate of these pulses is determined by the role of the system. As with everything else in a radar system, compromises have to be made to a radar system's design to provide the optimal performance for its role. (For simplicity, all further discussion will use metric figures.) If the radar pulse width is 1 μs, then there can be no detection of targets closer than about 150 m, because the receiver is blanked.Īll this means that the designer cannot simply increase the pulse width to get greater range without having an impact on other performance factors. For convenience, these figures may also be expressed as 1 nautical mile in 12.4 μs or 1 kilometre in 6.7 μs. ![]() A simple calculation reveals that a radar echo will take approximately 10.8 μs to return from a target 1 statute mile away (counting from the leading edge of the transmitter pulse ( T 0), (sometimes known as transmitter main bang)). While the radar transmitter is active, the receiver input is blanked to avoid the amplifiers being swamped (saturated) or, (more likely), damaged. Pulse width also determines the radar's dead zone at close ranges. At any range, with similar azimuth and elevation angles and as viewed by a radar with an unmodulated pulse, the range resolution is approximately equal in distance to half of the pulse duration times the speed of light (approximately 300 meters per microsecond). Pulse width also constrains the range discrimination, that is the capacity of the radar to distinguish between two targets that are close together. Therefore, pulse width constrains the maximum detection range of a target. The amount of energy that can be delivered to a distant target is the product of two things the peak output power of the transmitter, and the duration of the transmission. The pulse width must be long enough to ensure that the radar emits sufficient energy so that the reflected pulse is detectable by its receiver. If the pulse is not a perfect square wave, the time is typically measured between the 50% power levels of the rising and falling edges of the pulse. The pulse width ( τ ) (or pulse duration) of the transmitted signal is the time, typically in microseconds, each pulse lasts. ![]()
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