Log-Periodic Antenna

btty038

Log-Periodic Antenna [Copy link]

Log-Periodic Antenna

The purpose of log-periodic antenna is nothing more than communication transmission, receiving and transmitting communication signals. However, there are many types of communication signals, such as long wave, medium wave and short wave. The log-periodic antenna is a communication antenna that can receive and send medium and short wave signals. It can be used for point-to-point communication, as well as for scientific and technological digital signal determination. It has a wide range of uses. For example, it can be used as a cable TV antenna, receive radio signals, send scientific and technological signals of digital base stations, and be used for the effectiveness of radiation measurement facilities radar. To see the radiation, we must first look at the radiation type. Radiation determines the distribution of radiation energy and is the most important factor in all antenna characteristics. It includes omnidirectional and directional types. The log-periodic antenna can be used at a variety of frequencies and elevation angles, and the installation accessories are perfect, the waterproof performance is good, and it is an omnidirectional antenna, but this also means that the radiation intensity is relatively large. In fact, if the radiation to the human body is taken into account, it can be basically completely ignored, because general antenna facilities are in high altitudes or special locations, far away from the human body. If you consider radiation to want to know the transmission effect, then the log-periodic antenna is a good choice. In the article, you said that you live on the top floor and it is right above my window. This is not good, because it is too far from your house, and the medium and short waves have strong penetration, and the radiation is still relatively large. It is best to ask it to move away from your window. It is also unethical to put the antenna next to someone else's window. He should first consider a location somewhere on the roof that is very far away from the residents! The logarithmic periodic antenna mainly receives medium and short wave signals. It is suitable for medium and short wave communications, using sky wave signals, with high efficiency and close to the expected value of transmission. Compared with other high-gain antennas, the logarithmic periodic antenna has stronger directivity, but it has greater attenuation for useless directional signals. This does not matter, because it is a useless signal, so it is useless. It is good to only efficiently receive useful signals. Antenna formed by a logarithmic periodic structure. The logarithmic periodic structure is a system composed of many units of different sizes but similar shapes. The size and position of each unit satisfy the following formula (d in the figure) where i=1, 2, 3, ..., corresponding to the three-dimensional serial number of the unit; n is the unit serial number; Rn is the coordinate of the nth unit; τ (<1) is called the proportional factor. If the geometric shapes of two antennas are similar, but the size differs by τ times, when the operating frequency also differs by τ times and their radiation resistance is much larger than the loss resistance, then the electrical parameters of the two antennas are the same. This is the similarity principle. According to this principle, the electrical parameters such as the input impedance and directivity of the logarithmic periodic antenna should be repeated periodically according to the logarithm of the frequency, and the repetition period is lnτ. Within the frequency band (f, τf), the electrical parameters of the antenna are variable, but when τ is close to 1, this change is very small. Experiments show that even if τ is not close to 1, this change is not large, so the logarithmic periodic antenna has a very wide frequency band. There are many structural forms of logarithmic periodic antennas, and the figure shows four common ones. The form shown in Figure d is the most widely used, which is the logarithmic periodic dipole antenna, referred to as LPD antenna. It is composed of multiple symmetrical oscillators and two transmission line conductors in the form shown in the figure. The length and position of the oscillators of this antenna meet the requirements of the logarithmic periodic structure. The diameter of the oscillator plays only a minor role in the radiation of the antenna. In order to facilitate the production, the requirements of the logarithmic periodic structure can be appropriately relaxed. For a certain working frequency, only a part of the structure of the logarithmic periodic antenna plays the main radiation role. Taking the logarithmic periodic dipole antenna as an example, the structures that play the main radiation role are the oscillators with a length of approximately λ/4, because their current is much larger than the rest. This part of the oscillators is called the effective area. When the working frequency changes from low to high, the effective area will move from the long oscillator to the short oscillator. The lower limit of the passband of the antenna is determined by the longest oscillator, and the upper limit is determined by the shortest oscillator. In the entire passband range, the input impedance and directivity of the antenna remain basically unchanged. The maximum radiation direction of the logarithmic periodic dipole antenna is the direction of the arrow in Figure d. Logarithmic periodic antennas are mainly used in the ultra-short wave band, and can also be used as short-wave communication antennas and medium-wave and short-wave broadcast transmission antennas. In addition, logarithmic periodic antennas can also be used as feed sources for microwave reflector antennas. Since the effective area moves with the change of the working frequency, the deviation between the effective area and the focus in the entire working frequency band must be within the tolerance range during installation. Speaking of this, I mentioned the term sky wave to you again. In fact, there are three transmission modes of radio waves: ground wave (surface wave) propagation, direct wave propagation and sky wave propagation. The details are as follows: Radio waves propagating along the interface between the earth and the air are called surface waves, or ground waves for short. Its propagation path mainly depends on the electrical characteristics of the ground. During the propagation process of ground waves, the energy is gradually absorbed by the earth and weakened quickly (the shorter the wavelength, the faster the weakening), so the propagation distance is not far. However, ground waves are not affected by climate and have high reliability. Ultra-long wave, long wave, and medium wave radio signals are all propagated by ground waves. Short-wave short-distance communication also uses ground wave propagation. Direct wave propagation: Direct waves, also known as space waves, are radio waves that propagate in a straight line from the transmitting point to the receiving point. The propagation distance of direct waves is generally limited to the line of sight range. During the propagation process, its intensity decays slowly. Ultrashort wave and microwave communications use direct wave propagation. When direct wave communication is carried out on the ground, the field strength at the receiving point consists of two paths: one path is from the transmitting antenna directly to the receiving antenna, and the other path is reflected from the ground and reaches the receiving antenna. If the height and direction of the antenna are not properly set up, it is easy to cause mutual interference (such as TV ghosting). Sky wave propagation: Sky waves are electromagnetic waves radiated by antennas to high altitudes and then refracted by the atmospheric ionosphere and returned to the ground. The ionosphere only reflects electromagnetic waves in the shortwave band, so sky wave propagation is mainly used for shortwave long-distance communication. From the working principle of sky waves, it can be seen that sky waves need to be extremely radioactive. As mentioned at the beginning, the logarithmic periodic antenna uses sky wave transmission, so there is still the same conclusion as before: strong radioactivity.

btty038

Upload a log-periodic antenna filled out online

hqli126

The log-periodic antenna uses sky wave transmission and has strong radiation.

btty038

hqli126 Published on 2021-8-15 08:19 The log-periodic antenna uses sky wave transmission and has strong radiation

The log-periodic antenna is similar to the Yagi antenna. The director and reflector increase the directivity. The same applies to receiving and transmitting.

LIJIARU

btty038 posted on 2021-8-11 21:53 Upload a log-periodic antenna filled out online

A 100mhz-500mhz log-periodic antenna is needed later

LIJIARU

btty038 Published on 2021-8-16 21:17 The log-periodic antenna is similar to the Yagi antenna. Through the director and reflector, the directivity of reception and transmission is increased...

btty038 posted on 2021-8-11 21:53 Uploaded a log-periodic antenna filled in online Need a 100mhz-500mhz log-periodic antenna

btty038

LIJIARU posted on 2021-12-6 15:10 I need a 100mhz-500mhz log-periodic antenna in the future

This size is a bit like a building. The wavelength is too long. They all use active antennas. Small size