Introduction to radar related contents

I am looking at radar related knowledge recently , Today, let's talk about radar , I hope it will be helpful to the small partners in related fields ！
Radar is an electromagnetic sensor , It is used to detect and locate reflective objects . Its work can be summarized as follows ：
**(1)** Radar radiates electromagnetic energy by lifting antenna , Make it spread in the air .
**(2)** Part of the radiated energy is reflected by a reflector at a certain distance from the radar ( The goal is ) to intercept .
**(3)** The energy intercepted by the target is re radiated in many directions .
**(4)** Part of the re radiated ( Echo ) The energy is returned to the radar antenna , And received by radar antenna .
**(5)** After amplification by the receiver and proper signal processing , At the output of the receiver, a decision is made as to whether the target echo signal exists . here , The location of the target and other information about the target are obtained .
A common waveform of radar radiation is a series of narrow rectangular like pulses .
Some radars need to detect targets at distances as short as a baseball field from home plate to pitcher ( To measure the speed of the ball ), Other radars work at distances to the nearest planet . therefore , The radar may be small enough to hold in your hand , Or big enough to occupy the space of many football fields .
The radar target may be an aircraft 、 Ships or missiles ; It may also be human 、 bird 、 insect 、 rainfall 、 Clear air turbulence 、 Ionized medium 、 Surface features ( Vegetation 、 mountains 、 road 、 The river 、 The airport 、 Architecture 、 The fence 、 Electric poles, etc )
ocean 、 Ice layer 、 Iceberg 、 buoy 、 Underground features 、 A shooting star 、 Aurora 、 Spaceships and planets . In addition to measuring the target distance and angular direction , The radar determines the relative velocity of the target by determining the change rate of the range with time or extracting the radial velocity from the Doppler frequency shift of the echo . If the position of the moving target is measured over a period of time , Then the target track or track can be obtained , The absolute speed and moving direction of the target can be determined , So we can predict its future position . A properly designed radar can determine the size and shape of the target , You can even identify different types of targets .
notes ： The article is excerpted from 《 Radar manual 》 Volume 3