This paper quotes some information written by netizens to supplement my understanding of antennas. I am a radio enthusiast. Not long ago, I invented an adjustable yagi antenna, which has been successfully applied. Now we are doing the promotion of this antenna. Although the antenna style is different, but the principle is the same, I am limited to just an enthusiast. Please correct me if there is any mistake in the description! 1894, when assembling the electromagnetic wave receiver in popov, Russia, it was accidentally found that a metal wire was connected to the detector, which could significantly improve the receiving sensitivity, enhance the receiving ability and increase the communication distance.
This wire became the first antenna in the world. In fact, the main working part of the antenna is the solid metal conductor. So what kind of conductor can give the antenna excellent performance?
Here, I rank that electromagnetic characteristic of ordinary metal materials from high to low,
Silver (Ag), copper (Cu), aluminum (Al) and iron (Fe)
Of course, there are also some newly invented liquid metals, such as gallium (Ga), which is the latest invention of eagle sauce. Gallium alloy is sealed in a section of insulating material, and then connected to the transmitting or receiving equipment through the feeder line to become a liquid antenna.
Many friends ask why the best antenna is not made of gold (Au). The answer is that although gold is golden, its electromagnetic performance is far inferior to that of silver. More than 100 years of industrial production practice has proved that I didn't invent it.
A few months after the unexpected harvest in popov, the Italian Marconi connected a large piece of metal to one end of the spark gap of the transmitter and hung it on a tree. The other end of the spark gap was connected to the earth. The intensity of radio waves emitted by the transmitter has increased several times, and the transmitting and receiving distance has reached several kilometers. The application of radio waves across the English Channel was successfully realized in 1899.
(If you cross and want to make a radio station, remember to take these two. )
Insert a picture to illustrate this point.
The coaxial cable marked in the above picture is also common in our life. Closed-circuit signal lines for home TV implemented by the Ministry of Radio, Film and Television in 1980s and 1990s. This kind of cable and the flat cable in the picture below are collectively called feeder, but the impedance values are different. In the original CCTV system, the "characteristic impedance" of the coaxial cable used was 75 ohms. In the field of radio, this kind of radio system connected by feeder with 75 ohm characteristic impedance is collectively called 75 system, and the characteristic impedance of flat cable is 300 ohm. Now our daily wireless Internet access (commonly known as WiFi) uses a 50-system, which is connected by a 50-ohm characteristic impedance feeder.
Note: When the flat cable is connected to the transmitter, the impedance must be reduced by electronic components to match the transmitter and receiver. It is the ohm values 50, 75 and 300 mentioned here, but it is not the resistance value of the wires in the DC circuit.
Another breakthrough in antenna development was created by diogenes dipole according to the principle of seesaw balance. One wire is connected to the shell of the transmitter, the other wire is connected to the output end of the transmitter, and the two wires are symmetrically arranged to form a dipole antenna.
1923, according to the principle that objects with different weights can keep balance on the seesaw by adjusting the fulcrum, scientists invented the Windom antenna, which was published by Loren Windom(W8GZ) in 1929 in the American magazine QST.
The old man in the picture below is Mr Roland Winton, the inventor of Winton antenna.
Before World War II, with the enhancement of the processing capacity of electronic components. The antenna is getting smaller and smaller (the geometric size of the antenna is determined by the working frequency, and the working frequency is determined by the transmitting and receiving frequencies of the radio station). During World War II, most electronic tubes operated at more than ten megahertz. Take 15MHz as an example, the wavelength is 20M, and the length of antenna active vibrator is about 5M. Why 5M? Because the length of the active vibrating arm is usually at least 1/4 wavelength.
Note: If the electromagnetic performance of the antenna does not match the transmitter, the standing wave ratio will be too high, which will not only lead to low transmission efficiency, but also cause damage to the electronic components of the transmitter. The author makes an explanation, assuming that the power of the transmitting station is 10W, then the power transmitted through the antenna should also be 10W in an ideal state. But in fact, the power emitted by the antenna can't reach 10W. Assuming that the antenna parameters require that the standing wave ratio must be less than or equal to 1.5, assuming that the antenna standing wave ratio parameter is exactly 1.5, then 20% of the energy will be transmitted back to the transmitter through the feeder, and only 80% of the energy will be transmitted through the antenna. Once the standing wave ratio is greater than 1.5, I'm sorry, long-term full-load use of the radio station will burn out and the electronic components must be replaced.
Winton antenna is widely used in the main battle planes of major countries participating in World War II, such as Japanese A6M2 Zero Fighter, Soviet LaGG-3 Fighter, British MK 1 Spitfire Fighter, German Fw 190 Transparent Paper Fighter, Italian MC205 Hunting Fighter and American F6F Hellcat. These antennas can only be used for communication between aircraft or between aircraft and ground command system.
The zero and fire breathing in the picture below, as well as the wires between the upright post and the tail wing of the Me-262 cockpit, are all antennas, but many friends mistakenly think that they are steel cables or connecting cables of the rudder to strengthen the structure of the aircraft.
In the 1920s, another important development of antenna was that Yagi antenna was invented by Hidetsugu Yagi and Ota Taichi of Japan. Yagi antenna is a directional transmitting antenna, which consists of an active vibrator (usually a folded vibrator), a passive reflector and several passive directors connected in parallel. Yagi antenna has strong directivity and higher gain than dipole antenna, and can be used for direction finding and long-distance communication. In the 1980s, among flower growers, Yagi antenna was once a brilliant "branch" on the roofs of many high-rise buildings. Since Japan has been mentioned, I have to tell this story:1In February 1942, the Japanese army, which was rampant in Southeast Asia, occupied Singapore and found two new telecommunications radio weapons at the British military base, which were made of iron bones and copper wires and marked with the word "Yagi". The Japanese looked at each other, wondering what secret weapon it was. As a huge secret, it was transported to Tokyo, and officials and experts from Japan's domestic weapons headquarters looked at each other, wondering what it was, especially Yagi-what was it?
Only after the war did the Japanese realize that it was a high-frequency directional antenna in the military aerial radar device, and the truth of Yagi made them vomit blood: it was the Roman phonetic alphabet of the surname Yagi when Hidetsugu, a Japanese electrical engineer, applied for a patent in Germany, Britain and the United States. Before and after the Meiji Restoration, the Black Book of American Missionaries was founded and spelled into Roman characters through the pronunciation of Japanese pseudonyms. Eight spell "Ya" and wood spell "Ji".
As early as 1925 and 65438+February, Hidetsugu Yagi applied for a patent in Japan for the theory and technical structure of the high-frequency directional antenna he invented, and in western countries the following year. After several years of scientific practice, it has been proved that with the great invention of Yagi antenna, it is possible to develop high-performance radar. However, this is the story of "flowers inside the wall, fragrance outside the wall". At that time, the Japanese government and the Japanese scientific community simply didn't understand the value and importance of this invention. On the contrary, the western countries are rewarded with treasure. It can be said that this is a modern version of the "urban cannon." Look at the picture below. Yagi antenna was used in German aircraft during World War II, but Hans set up Yagi antenna array, which increased the distance between the enemy and us.
In the mid-1930s, in addition to the above antennas, there was a tile-shaped, flat-plate or hemispherical parabolic antenna with feed. This kind of antenna has a large electromagnetic wave reflection surface, which can be a hollow net or a whole surface. It is fed with medium gain and has strong directivity and gain. At that time, this kind of antenna was mainly used for radar detection. We see in movies that the radar antenna used by warships or radar stations to detect planes and ships is a parabolic antenna. (262) We talked about parabolic antennas in the first program of Military Power 20 16. Do you remember the x and c signals? ), and some multi-element yagi arrays used on ships, because the transmission frequency was low at that time, the antenna size could not be reduced. Only large vehicles such as ships can carry parabolic antennas and yagi array antennas. Small vehicles such as airplanes and tanks can only use dipole antennas or Winton antennas, but these antennas have a certain coverage blind area and can only be used for communication. If they are used to attack the enemy, there is a big loophole. My rabbit's homemade air police 200 early warning aircraft, the barrel antenna it carried had the problem of covering the blind area, and finally it was replaced by air police 2000 with a back plate.
In order to transmit electromagnetic signals farther, humans added a secondary reflector to the original parabolic antenna to make Cassegrain antenna. I won't mislead people here. It is easier to understand by looking at the schematic diagram below.
The feed signal is reflected by two paraboloids. The following is the practical application of this antenna, most of which are equipped on the second and third generation jet fighters.
In World War II, Hans arranged several Yagi antennas in an array at a certain distance. The group assembled the JU88 as a night fighter, and of course, the 262 deity was not spared.
The picture below shows Me262 with Yagi array antenna.
Scientists have found that since "group buying" has so many benefits, everyone plays with antenna arrays!
When the German JU88 was used and the Yagi array, which could not be moved mechanically, was converted into a night battle, Eagle Sauce found another way and began to play "pot". 1944 P-6 1 "Black Widow" came out, and the method of installing antenna was more practical and beautiful. Install the parabolic antenna on the nose and add a protective cover.
Not only is it small, but it can also be done. A small mechanical rotation increases the enemy's range, and its performance is naturally much higher than that of the non-rotating Yagi array.
note:
The protective cover of the antenna should be made of materials that can easily penetrate electromagnetic waves, otherwise it will affect the standing wave ratio of the antenna feeding system and further reduce the service life of radio equipment. When making antenna protective cover, I found that PE (polyethylene) is the easiest to get in our daily life.
After decades of development, eagle sauce has been exploring antenna technology, and finally phased array radar was born.
The antenna part of phased array radar is exposed after the fairing is removed in the above picture.
The following figure is a schematic diagram of phased array.
Through the lag and lead control of electromagnetic wave emission time of each vibrator by integrated circuit, the scanning angle can be changed, so that simple electromagnetic scanning can replace clumsy mechanical scanning, and the antenna can be made smaller, with wider detection range and longer distance.
With the popularization of computer electromagnetic simulation technology, friends can now sit at home and develop antennas virtually.
The figure below shows the computer electromagnetic simulation calculation. When a fighter plane is illuminated by radar, it will reflect and diffract radar waves.
This can not only help our engineers to design the shape of the aircraft, but also help us to know what kind of special coating is covered on the surface of the aircraft model through computer analysis, thus reducing the probability of being discovered by radar. Of course, the electromagnetic parameters of this coating should be input into the software database in advance. However, the probability of finding this model plane in the picture is quite high.
In addition to the above purposes, electromagnetic simulation can also help friends design some simple and practical antennas, such as Yagi antenna mentioned in the last article, and of course it also includes Biling antenna, four-leaf clover antenna, copper antenna and so on. If you have high processing accuracy, you can also challenge to make your own phased array. Below are some simulation screenshots of Yagi antenna that I successfully applied for.
Isn't it great? Note that the handmade items I made are in the 2.4GHz band (WiFi working band), and the 2.4GHz band is also the working band of microwave ovens. It is not good to leave home WiFi on for a long time. Throw a brick and wait for the jade of the army god first!
This article quotes the article: 1. Lessons from Japan's "Cat's Eye Magic" PK radar in World War II: Author: Mao Xinhua Release date: 201September 5 18. On May 6, 2065438+06, the Phoenix Network program also mentioned the bureau seat. 2. Understand the structure and installation method of the antenna on World War II aircraft-airborne Winton antenna. 3. Tracking the radio communication antenna of World War II aircraft-CQ Modern Communication Magazine hopes to adopt it.