Follow WeChat Download Audiophile APP Follow the audiophile class related suggestion '+ data.data.username +' '; dom + =' Our company specializes in the production and sales of all kinds of terminals, copper terminals, nose wire ears, cold pressed terminals, copper joints, but also according to customer requirements for customization and production, our raw materials are produced and sold by ourselves, we have their own raw materials processing plant, high purity T2 copper, quality and quantity, come to me to order it! Cable Terminals Taixing Longyi Terminals Co.,Ltd. , https://www.longyicopperlugs.com Recently, I want to make several Yagi directional antennas in various frequency bands. I have read several books about Yagi directional antennas and summarized the following experiences (laws), which are all things in the book, which may not be correct. I hope you all can correct me.
Since the indicators of the lead antenna are easier to meet at the low end of the low frequency band and change faster at the high end, the design frequency is usually selected at a frequency slightly higher than the center frequency.
1. The number of vibrator elements is mainly determined according to the given gain, and the gain directed to the antenna is mainly determined by the antenna length L / λ. Therefore, the antenna length can be determined first according to the required gain value, and then based on The common distance between the director and the reflector is used to determine the number of vibrators; or it can be selected directly based on empirical data. In general, the number of directional dipoles leading to the antenna is 6-12. If the number of directional directors is increased, there is no significant effect on increasing the gain. For the requirement of high gain, the antenna array method can be used to solve it.
2. Passive oscillator size selection Passive oscillator size selection should mainly be considered from two aspects of directivity and impedance characteristics. Selection of the distance between the lead oscillators. Since the gain is mainly determined by L / λ, if the number of the guided vibrators is fixed, it is more advantageous to obtain a larger distance, but when> 0.4λ, the antenna gain decreases rapidly, so it is generally taken as (0.15 to 0). 4) λ. The distance between the first director and the active vibrator should be slightly smaller than the distance between other vibrators, such as ≈0.1λ, the gain is slightly increased. The length of the director is usually in the range of ≈ (0.42 ～ 0.46) λ. The greater the number of vibrators, the shorter the optimal length of the director. If the working frequency band is required to be wider, the length of the director should be shorter.
The distance between the reflector and the active oscillator is usually in the range of (0.15 to 0.23) λ. The distance between the reflector and the front and back radiation ratio of the pattern and the input impedance has a greater influence. The smaller distance can effectively suppress the backward radiation. But the input impedance is low and it is difficult to match the impedance of the feeder, so it is necessary to compromise. The reflector length is usually (0.50 to 0.55) λ. If the requirements on the front-to-back ratio are high, the form of a transmission network can be used.
The passive vibrator is generally made of aluminum tube, and the radius of the conductor is usually selected in the range of (1/200 ～ 1/300) λ. The thickness of the vibrator does not have much influence on the directivity, but has a certain influence on the impedance characteristics. The thicker the vibrator, the lower the characteristic impedance is, which is beneficial to broaden the impedance bandwidth.
The steering antenna has two forms: uniform structure and non-uniform structure. The former is the case where the director is of equal length and equal spacing, while the latter is the case where the director is of unequal length and unequal spacing. The far director, the shorter its length, the greater the interval. They can all be adjusted to their "best" status. Comparing the two, it is generally said that the main lobe of the uniform structure is narrower and the side lobe level is higher; the main lobe of the non-uniform structure is wider and the side lobe level is lower, but if properly adjusted, the side lobe can be significantly reduced Do not broaden the main lobe too much or reduce the antenna gain. The latter is relatively flexible.
3. The selection of the size of the active vibrator has a basic requirement for the active vibrator to be well matched with the feeder. For this reason, the active vibrator should be designed to have a resonant length and transform its input impedance to a value equal to or close to the characteristic impedance of the feeder .
Yagi directional antennas are generally fed by coaxial cables. When the active vibrator adopts a half-wave symmetrical vibrator, due to the influence of the passive vibrator, its input impedance value is low. Therefore, it is necessary to try to increase the input resistance of the active vibrator. The common method is to use a folded vibrator. Appropriate selection of the length of the folded oscillator, the diameter ratio of the two conductors and the distance between them can effectively increase the input resistance of the active oscillator. Combined with the adjustment of the reflector and the dimensions of several nearby oscillators, a satisfactory standing wave ratio can be obtained. Secondly, because the equivalent radius of the folded oscillator is thickened, it is also beneficial to broaden the impedance frequency bandwidth. Of course, the active vibrator can also adopt the form of a symmetrical vibrator with an additional matching device.
Regarding the feeding to the antenna, if coaxial cable is used for feeding, in order to ensure the symmetry of the antenna, it is necessary to add a balanced-unbalanced converter at the feeder and antenna interface, such as U-shaped tube matcher, T matching and Broadband transmission transformers, etc. 
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