Definition
English: YAGI-UDA Antenna; YAGI Antenna
Interpretation: Composed of a substantial unit, a reflection unit, and one or more leading units Terminal shot. Note: The actual reflecting unit can be composed of some units or a reflective surface.
("China Encyclopedia" and Electronics and Computer ")
Advantages
Eight wooden antennas is really easy to use. It has a good direction, which has a high gain than the dipole antenna. Use it to measure, long-distance communication effect is particularly good. If the elevation angle and azimuth rotation control device are again contained, it is more likely to contact the radio in each direction including the space aircraft, which is not available from the upright antenna.
Composition Structure
Typical eight wooden antennas should have three pairs of vibrators, the entire structure is "king" glyphs. It is called an active vibrator, or the main vibrator, and the middle of the "Wang" word is horizontal. A reflector than the active vibrator, it plays an electric wave that weakens from this direction or the radio wave transmitted from this antenna, which is slightly shorter than the active vibrator. The leader, which is located on the other side of the active vibrator, which enhances the radio waves emitted from the direction of this side or in this direction. The leader can have many, and each length is slightly shorter than that of its adjacent and close to the active vibration. The more the guide is, the more the direction is, the higher the gain, but it actually exceeds the four and five leaders, this "benefit" increase is not obvious, and the volume is large, the weight is increased, the material strength requirement Increased, cost increases, etc. Usually there is a five-unit eight wooden (ie, three leaders, a reflector and an active vibrating) are enough.
Each leader and reflector are made of a metal rod. No matter how many "units", all the vibrators are fixed in a "big beam" in a certain spacing. The beam is also made of metal materials. Does these vibrators are insulated from the beam? do not want. It turned out that when the radio wave "walking" on the vibrator of these approximately half wavelength lengths, the midpoint of the vibrator is located in the zero point of the induction signal voltage, and the zero point is "ground", and there is no problem. And there is also a benefit that static electricity induced in space can pass through these contact points, the metal thread of the antenna, and then onto the main lightning network of the building.
Working principle
The working principle of the eight-timber antenna is such (as an example of three unit antennas): the leader is slightly shorter than one-half wavelength, the main scorch is equal to the second One wavelength, the reflector is slightly longer than one-half, and the two-vibrator is quarter. At this time, the guide is "capacitive" in the induction signal, the current advance voltage is 90 °; the electromagnetic wave induced by the guide will radiate to the main vibration, and the radiation signal passes through a quarter wavelength to lag 90 ° happens. The "exceeded" caused by the front, the same phase is the same, so signal iterations are strengthened. The reflector is slightly longer than one-half wavelength, inductive, current lag 90 °, and then radiates 90 ° during radiation to the main vibration, and the two are just 180 °, and it has been canceled. One direction is strengthened, and one direction weakens, there is strong directionality. The process of transmitting is also available.
Antenna principle
Active vibrator is a key unit. There are two common morphology: the ivotary and direct zones. Directivilation is actually one-half of the wavelength dipolar, and the deformation of the oscillator is. The active vibrator is in contact with the feeder to maintain good insulation with the main beam, and the midpoint of the oscillator is still connected with the lamination.
imitation a pair of antennas, but there is always an appropriate adjustment. What does it? Why do you want to adjust? This requires us to understand the principles of the antenna.
an important feature of antennas, that is, "input impedance". In the resonant state, the antenna is like a charged end in the feeder. The usual feed line impedance is 50Ω. If the antenna input impedance is 50Ω, then "match", the signal output by the radio can be fired from the antenna; if not "match", a part of the power will reflect the power amplifier circuit of the back Radio. .
The input impedance of one-half wavelength dipole antenna is about 67 Ω, and the input impedance of one-half wavelength alficitivity is higher than that of the former. When the leader, the reflector, the impedance relationship is complicated. In general, eight woods should be much lower than that only basic vibrators, and the pitch of eight woods is high, and the impedance is low, and the antenna efficiency is lowered. According to information, the leader is lowered by 0.15 wavelengths and the main scorpion spacing, and the impedance is high at 0.2-0.25, and the efficiency is improved. At this time, the change in impedance ranges from 5 to 20 Ω.
The characteristic impedance of the album antenna of the classic osmium antenna is about 300Ω, (the vibrator is about a quarter of the wavelength), such as a common television receiving antenna. When the spacing of the fragrant is divided, or the "long side" diameter of one-half is greater than the diameter of the "Short Side" of the two quarter-wavelengths, and its input impedance is higher.
Transfer
Our communication machine output is 50Ω designed, with a 50Ω cable feeder. How can Baimu Antennas can meet the impedance match with the feeder? Obviously, this issue cannot be considered. Then there are a variety of matching methods. The "hairpin" matching of the short-wave section eight wood is to pick up a U-type conductor at the feed, which plays a inductor, and the capacitance of the antenna itself is parallel to increase the antenna impedance; there is a classic "Gamma" matches, famous HB9CV antenna, etc. The simplest approach is to wire around the feeder from the antenna feeder to a coil that is about 15 cm in a seven-loop diameter, I think this is the same as the principle of matching the hairpin.
There is also a question to note: Eight wooden antennas is "balanced output", and its two feed points have the same characteristics to "ground", but the usual transceiver antenna port is "not The balance ", the core wire is the hot end, the outer conductor ground. Although we can also report the feeder core wire to one of the two feed points of the antenna, another feed feed outside the outer conductor layer, but this will destroy the original direction characteristics of the antenna, and also on the feeder Generate unnecessary emission. A good eight wood should have a "balance-imbalance" conversion.
Precautions
There is a friend asking, the vibrator of the antenna when erate is good or vertical with the earth or the earth? The answer is, accept, send the party to keep the same "posture" is good. When the vibrator is horizontal, the emission electric waves have its electric fields and the large land parallel, called "horizontal polarization waves", the vibrator "vertical polarization wave" transmitted when the vibrator is vertically transmitted. Both the transceivers should maintain the same polarity. In the U / V band, people use the upright antennas, and the eight-timbenes must have a few more obedients, so that the vibrator is vertically in the earth. The short-wave section eight wood antennas are mostly horizontal, and such a large substitute may not be able to achieve the vertical stand!
has a friend asking, what is the impact of the diameter of the vibrator? The answer is that the diameter affects the length of the vibrator, and the diameter is slightly shorter length. The diameter is large, the antenna Q is low, and the operating frequency bandwidth is large.
There are friends asking, and the equivalent is "flat" in the girder, and how many sides are good with other vibrators in a plane? Or is it equivalent to the larger and beam of the vibrator, only its long side and other vibrators are kept on a plane? Classic Iribrevian Eighthwat Antenna is the former. According to the previously described working principle, if the lying oscillator is flat between the leader and the reflector, the oscillator has two "insert", which is more complicated more complicated?
But the words have to come back. Many results of amateur radio, especially a wide variety of antennas, and "success" or "unsuccessful" is often determined by its own satisfaction, "compared to the past". Several antennas mentioned again in this journal, some are 50Ω feeders directly connected to the oscillator, and the oscillator is equipped with the "Merical" brothers. How is it best? Still try it yourself. Connected to a standpoint, try to adjust the length of each vibrator, how to match between the units, etc., it is likely to have new discovery.
By the way, you must take the antenna seriously when debugging, and there is at least two or three meters away from the ground.