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English: Yagi-Uda antenna; Yagi antenna explains: a stimulated unit, a reflection

Unit and one or more elements to the end-fire array. Note: in fact the reflection unit can consist of a few unit

Or a reflective surface. The last century twenty's, Tohoku University Japan's Yagi Xiuji and Uda Ta

Two the invention of the antenna, is called "the Yagi Uda antenna ", referred to as " Yagi antenna ".

Advantage

Yagi antenna is good with. It has good directivity, a dipole antenna with high gain. Use it to measure

To good effect, long distance communication. If matched with elevation and azimuth rotation control device,more free

Desire and includes a space vehicle, all directions on the radio contact, this feeling is from the vertical antenna

Not to be.

Composition and structure

Typical Yagi antenna should have three pairs of vibrator, the entire structure is the "King" - shaped. Feederconnected with said

An active vibrator, or the main oscillator, ranked three on the vibrator, " Wang " intermediate cross. Slightly longer than an active vibrator

A little known reflector, it is in an active vibrator side, plays a weakened from this direction coming from theradio or

The transmitting antenna to the wave function; active vibrator is slightly shorter than the known director, it is located in an active vibrator of another

Side, it can enhance the side came to the direction or emitted wave. A director can have

Many, each root length than its adjacent and close to the active vibrator of the slightly shorter. Toimplement more

The direction, more sharp, gain is higher, but in fact more than four or five director, the " good " by

And less obvious, and large volume, weight, on the strength of material requirements increase, the problems of increasing cost

It is highlighted gradually. Typically have a five element Yagi ( namely three director, a reflector and a

An active vibrator ) will be enough. Each director and reflector are used a metal rods. Regardless of

The number of " unit ", all oscillators, are in spaced parallel fixed on a " beam ".

Beam is made of metallic materials. These oscillators with beam midpsoint insulation? Don't. Originally, radio

" Walk" in these approximately half wavelength length of vibrator, vibrator midpsoint is located in theinduction signal

Of zero voltage, zero ground " land ", a little problem. But there is a benefit, the space sense

Electrostatic can just through these contact points, the antenna metal vertical rod and then leads into thebuilding lightning protection grounding grid to.

Editor this paragraph working principle

Yagi antenna works like this ( to three unit receiving antenna as an example ): director is slightly shorter than the two

Quarter-wavelength, master oscillator is equal to 1/2 wavelengths, wavelength reflector slightly longer than1/2, two between the oscillators

From the 1/4 wavelength. At this time, director of the induction signal is " tolerance ", current leads the voltage by 90°; LED

Device induced electromagnetic wave to the master oscillator radiation, radiation signal after 1/4wavelength distance to lag

From the air directly to the main oscillator signal 90 °, exactly offsets the front caused by the " lead", both photograph

The bits are the same, then a signal superposition, strengthened. The reflector is slightly longer than the 1/2 wavelength, is sensitive, current

Lag 90°, coupled with the radiation to the master oscillator process lag 90 °, and from the orientation of the reflector is directly added to the Lord

The vibrator signal is a difference of 180°, the offset effect. A direction to strengthen, weaken a direction

, have a strong orientation of. Firing process is.

Principle of antenna

An active vibrator is a key unit. There are two common forms: folding vibrators with straight vibrator. Thestraight vibrator

It is the 1/2 wavelength dipole, folded dipole is its deformation. An active vibrator feeder is connected withthe place shall be

With the main beam to maintain good insulation, and the folding vibrator midpsoint still and beams. Imitation of a pair of antennas,

But also need to make appropriate adjustments. What? Why to want to move? This needs us to know theantenna

The principle. Antenna is an important feature, that is " input impedance ". In resonant condition, the antenna such as

A resistor is connected in the feeder terminal. Common feeder impedance is 50 ohms, if the antenna input impedance is 50 ohm, then

To " match", the radio signal can be output from all the antenna emitting; if not " matching ",

A part of power will be reflected back to the radio power amplifier circuit. 1/2 wavelength dipole antenna input impedance

About 67Ω, 1/2 wavelength folded vibrator input impedance is higher than that of the former 4 times. When a director, reflection

Converter, impedance relations become complicated. In general only basic Yagi oscillator low impedance,

And each unit is spaced Yagi impedance high impedance, and low efficiency, at the same time the antenna.Data presentation,

Director and principal oscillator pitch 0.15 wavelength impedance minimum, 0.2 - 0.25 of high resistance,improve the efficiency of. When the resistance

Anti range in about 5 - 20Ω. Classic folded dipole Yagi antenna characteristic impedance of approximately300 ohms,

( oscillator pitch of about 1/4 wavelengths ) such as the common television receiving antenna. Folded dipole at spaced stenosis

1/2 wavelength, or " the long side of the two " diameter greater than a wavelength of about 1/4 " short "diameter,

The high input impedance.

Transmission

Our communication machine output are at 50Ωdesign, with 50 Ωcable feeder. Yagi antenna how can

Feeder to match the input impedance? Obviously, take no account of this problem. So there are variousmatching method.

Shortwave band Yagi used " hairpin " match, in the feed and connected with a U type conductor, it plays an electric

The sensor, and the antenna itself capacitor forming a parallel resonant so as to improve the impedance of the antenna; and the classic "

Gamma " match, the famous HB9CV antenna etc.. The simplest approach is to close to the antenna feedpoint around the feeder

About six or seven of a circle having a diameter of about 15 cm coil hanging in there, I think this and hairpinmatching principle should be

The same to you. There is also a problem to the attention of: Yagi antenna is " balanced output ", the two feed points on

" To " show the same characteristics, but usually the transceiver antenna port is " unbalanced", the core wire is a hot end,

The outer conductor to ground. Although we can to pay no heed to the feeder line connected to theantenna core at one of two feeding point,

Another point is connected with the outer conductor of feeder layer, however, this will destroy the originaldirection of antenna characteristics, but also in the feeder will

Unwanted emission. A good pair of Yagi, there should be " a balance-unbalance conversion ".

Matters needing attention

A friend asked, Yagi antenna erection of the vibrator is parallel or perpendicular to the earth and the earth and good? Answer.

Collecting, transmitting both maintain the same " posture " as well. Vibration level, emission of the electric field parallel with the earth,

Called " the horizontally polarized wave ", vibrator and vertical emission is a " vertically polarized wave ".Both the receiver should

Keep the same polarization. In U/V band, people use a vertical antenna, Yagi antenna of course will be

The minority is subordinate to the majority, let the vibrator perpendicular to the earth. Shortwave band Yagi antenna is horizontally arranged, and, like this

The huge monster afraid to vertical frame can not be realized! A friend asked, vibrator diameter on antenna performance what

Impact? The answer is diameter influence oscillator length, diameter is shorter. Large diameter antenna,low Q value,

Working frequency bandwidth is bigger. Have a friend asked, folded dipole is " flat " on the girder, several of its

Edge and other oscillator in a plane? Or a folded dipole is perpendicular to the face and beams, only the long edge and its

The oscillator remains on a plane is good? Classic folded dipole Yagi antenna is the former. According tosaid in front of the

The principle of work, if the folded dipole lying in between the director and the reflector, a folding vibratorhas two side " plug

Foot ", in which the phase relationship is more complex with many? Not to have to say. Amateur radio of Xu

The results, particularly the various antenna, is after the actual test to come, " success" or " not successful "

It is often to his own satisfaction, "compared to the past " to determine the. This print again presents severalantenna,

There are 50 Ωfeeder connected directly to the folding vibrator, folding vibrator firmly flatly lying in the "device" brothers when

In. What is the best? Or yourself to try. After the last standing wave form, try to adjust a

The length of vibrator, the distance between the units, and how to match and so on, is likely to have newdiscovery.