Bright Sword starts with the grenade flat.

Chapter 527 The principle of electromagnetic wave radar.

The infinite electromagnetic waves in radio radar are naturally a kind of light, so naturally they are only as fast as the speed of light. Of course, perhaps radar does not need to worry about signal delays caused by distance during planetary warfare, after all, the space on the planet is there.

But when you go under the starry sky, which is several light years away, or even dozens or hundreds of light years away, you have to consider the problem of electromagnetic wave signal delay caused by distance.

After all, radio radar is a radio technology instrument used to detect and measure the position of a target. If its scope of use is narrowed down, it is a radio technology instrument used to measure the position and distance of passive active targets, such as aircraft or spacecraft.

The origin of radio radar is actually to imitate bats, which hide in dark places during the day and fly out at night to look for food.

However, how is it able to fly in the dark without hitting obstacles such as trees or houses?

For many years, humans on Blue Star believed that this was because bats' eyes had the same night vision capabilities as cats' eyes. However, even wild animals such as cats could not move around in a cave where there was no light at all.

As humans conducted in-depth research on bats, they finally uncovered this secret of bats.

It turns out that a sound that humans on Blue Planet cannot hear is emitted from the mouth of a bat. The number of oscillations per second is between 25,000 and 70,000, while the number of vibrations per second that humans' ears can sense is about 160,000 to 20,000, which is beyond the range of human ears. That's why it's called ultrasonic wave.

However, bats have special hearing organs that can sense this kind of ultrasonic wave. When they fly in the dark, they often emit ultrasonic waves from their mouths. When this sound wave encounters an obstacle in a certain direction, it will immediately reflect back from that direction. A part of it will be reflected into the bat's ears, and it will know that there is an obstacle in that direction, so it will avoid it in time.

Bats can also rely on experience to know that if the echo is fast, the obstacle is close, and if the echo is slow, the obstacle is far away. In other words, it judges the distance of the obstacle based on the speed of the echo, and the direction of the obstacle based on the direction of the echo.

So inspired by bats, humans on Blue Planet knew that ultrasound has the property of reflection and can be used to measure distance.

Therefore, ordinary sound waves, light waves, and even radio waves all have reflective characteristics, and radar does not use sound waves, but radio waves.

The radar transmitter sends out pulsed radio waves. If any object is encountered on the path of the radio waves, it will be reflected back. Water, earth, railways, urban buildings, aircraft and ships - all of these reflect radio waves differently. Some of the reflected radio waves return to the radar station. The second part is reflected from farther objects. All these signals are received by the receiver and displayed on the radar display.

Of course, the reason why airplanes are equipped with radar instead of sonar is that the speed of radio waves is many times faster than that of sound waves, at 300,000 kilometers per second.

Such a speed is naturally much faster than the speed of sound waves. An interesting example is that if you listen to a concert in a studio, before you hear the singer's voice, the sound waves have already been transmitted to a considerable distance through the radio station. A listener who is a thousand kilometers away from the singer can even hear the beautiful singing through the radio before the audience on the scene. However, although this speed can far surpass the sound on the planet, it is still too slow for the starry sky that is many light years away. Therefore, it is urgent to develop a superluminal radar. However, it is so easy to develop a superluminal radar with a large detection range and small delay. It is precisely because of this that Liu Xiu rushed to the battlefield in such a hurry.

Of course, radio radar is not just radio. If it is just radio, it would be no different from radio broadcasting. The most critical technology of radio radar is directional emission.

The so-called directional emission is to emit pulsed electromagnetic energy with a narrow beam at a specific moment.

It has an important advantage, which is the ability to save energy. The radar station can "see" far with low power and with good effect. For example, when a person is reading in a large room at night, he does not need to use a lamp to illuminate the entire room. He only needs a desk lamp to shine the light on the book, or even a small number of light bulbs will be enough so as not to hurt his eyes.

Although the rest of the room is dark at this time, it does not hinder reading. On the contrary, it makes us see the book more clearly.

This is also the way radar works. Since it concentrates energy in a small space, it is the best way to "illuminate" the target.

How narrow should the radar beam be? After all, the narrower the radar beam, the more energy is concentrated in it, and the more accurate the direction of the detected target is.

Suppose an enemy aircraft appears in the area illuminated by the radar, how long will it take to sweep the space around the radar station with a narrow needle-shaped beam? Will it be possible to prevent the enemy from escaping? The time it takes is probably a lot. During this time, any aircraft can escape the radar's search area.

That is to say, a "needle" beam is not suitable. There is a reasonable limit to the narrowing of the beam, which lies in the ability to meet the various requirements of the radar to the same extent. The solution to this problem is completely different for radar stations with different missions. The beam of an air defense sentry radar station should be wide, while the beam of a radar station aimed at artillery should be narrow. In many cases, in order to meet the needs of the special work tasks of the radar station, the beam often has a special shape.

From this point of view, the basic principle of radar is the directional emission of electromagnetic waves, its reflection on the conductor, and first of all, the correct knowledge of the propagation speed of radio waves. Obviously, to deeply understand and master radar technology, it is an indispensable foundation.

Usually, radio broadcasts use medium waves or short waves. Radars generally work on ultra-short waves or microwaves. Radars that work in the ultra-short wave band are called ultra-short wave radars or meter wave radars; radars that work in the microwave band are generally called microwave radars. Microwave radars are sometimes further subdivided into decimeter wave radars, centimeter wave radars, millimeter wave radars, etc.

So why can't radar work on medium or short waves like radio stations? This is determined by the working principle of radar. Clairvoyance can only "see" the target by the reflection of radio waves on the target. There is a rule for wave reflection: the larger the target, the stronger the reflection. Therefore, the shorter the wavelength of the radio wave used by radar, the stronger the reflection will be on other targets such as aircraft or missiles.

Therefore, radar must work in the ultra-short wave or microwave band to effectively play a role and detect the target. At the same time, the radar antenna is an important part of the radar. If the radar works in the medium wave band, to achieve directional transmission, dozens or even hundreds of metal rods that can excite radio waves must be arranged to form an array antenna, which will be a very large antenna, which is neither economical nor difficult to achieve in practice. Therefore, the wavelength of radar operation cannot be too long.

(End of this chapter)