Methods for balancing antennas. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Antennas. Measurements, setup and matching

 Comments on the article

Many HF and VHF antennas, in particular television ones, belong to the class of symmetrical antennas. When such antennas are fed through a coaxial feeder, their operation largely depends on the performance of transitional baluns. However, often radio amateurs, when making an antenna, do not make such devices at all or design them incorrectly, based on erroneous recommendations that are found in some popular books on antenna devices.

This article describes methods for balancing antennas and the properties of some balancing devices, as well as recommendations for their implementation.

Direct connection of a coaxial feeder to a symmetrical antenna (for example, to a dipole) breaks the symmetry of the currents in it and leads to the appearance of a current on the outer surface of the feeder screen, that is, it causes the appearance of an antenna-feeder effect. On fig. 1a shows such a connection of a dipole with a feeder. In this case, the output voltage of the feeder is applied not only to the input terminals 1-2 of the symmetrical vibrator, but also to one terminal 2 and the shielding shell 3 of the feeder.

Ris.1

The voltage between the terminals of the vibrator causes symmetrical currents in it, closing from one half of the vibrator to the other, as shown in fig. 1, but with solid arrows. The voltage between the right half of the vibrator and the cable sheath induces an additional current, shown by dashed arrows. The appearance of this current leads to the emission (reception) of electromagnetic energy by the feeder, which breaks the symmetry of the currents in the antenna and, as a result, distorts the radiation patterns.

On fig. 1, b shows the equivalent circuit of a symmetrical antenna with a directly connected coaxial feeder, where the antenna is shown as a load resistance Rn of the output terminals of the generator or consumer (transmitter or receiver). As can be seen from the diagram, one of these terminals will be connected not only to the load resistance Rn, but also to the ground through the capacitor C, the plates of which are the antenna vibrator and the shielding of the feeder. Thus, the symmetry of the antenna is broken. Therefore, to connect a coaxial feeder with a symmetrical antenna, special adapter devices are used, also called baluns, due to which the electrical symmetry of each half of the antenna relative to the shielding of the feeder is achieved.

Transition device type "locking cup" shown in fig. 2a.

Ris.2

In this device, the input terminals 1-2 of the antenna vibrator are directly connected to the inner and outer conductors of the coaxial cable, which is placed inside the metal cup B along its axis so that the walls of the cup and the shielding sheath B of the cable form a coaxial line with a characteristic impedance r (formulas for calculating wave impedances of coaxial and two-wire lines are given in the journal "Radio" N 11 for 1962). The input impedance of this line between points 2 and 3 is:

When l=l/4, the value of Z2,3 is large, the current from point 2 to point 3 will not flow, and the currents on both sides of the antenna will be equal. If the length l of the glass B is different from l / 4, then Z2,3 will not be large and, as can be seen from the equivalent circuit in Fig. 2b, the symmetry is broken: at point 2, part of the current will branch off to the ground and the voltages between the ground and points 1-2 will no longer be equal and out of phase. Therefore, the operating frequency band of such a balancing device is small. Usually it does not exceed 10% of the value of the fundamental frequency for which the device is designed.

Ris.3

The frequency band of a balancing device with a glass can be increased by introduction of the second segment of the coaxial line with the same wave resistance as the glass (Fig. 3a). In this case, as can be seen from the equivalent circuit (Fig. 3,b), the resistances of points 1 and 2 relative to the ground will be equal, regardless of their value, that is, Z1,2=Z2,3. Due to this, the antenna power will be symmetrical over a wide frequency band. The difference between the devices shown in Fig. 3 and Fig. 4 lies in the fact that in the latter two elements (B and B') are placed side by side, forming a two-wire line closed at the end.

The input impedance of this balun is

where r' is the wave impedance of the two-wire line.

Balancing device fig.4 simple in design, operates in a wide frequency band and is most often used in amateur practice. One of the conductors of this balancing device is the shielding shell of the coaxial feeder (element B), as the second (element B') either a piece of cable from which the feeder is made, or a tube of equal diameter can be taken. The main advantage of this device over the previous one (Fig. 3) is half the length.

Fig. 4 In Fig. 2,3 and 4: A - the inner core of the coaxial cable,
B and B'-outer braid of the cable, B and B'- metal cups.

Scheme of balancing device type "U-elbow" shown in Fig.5, a. Here the central wire of the main coaxial feeder is connected to terminal 1 of the left half of the vibrator. From the same point, voltage is supplied to terminal 2 of the right half of the vibrator through a piece of cable with a length of l/2, where l is the wavelength in the cable (taking into account shortening). The phase of the voltage during the passage of a section of cable with a length of l / 2 shifts by 180 °, therefore, the required anti-phase voltage is supplied to the vibrator terminals. The shielding sheaths of the cables are interconnected.

Ris.5

Author: Ing. K. Kharchenko; Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Antennas. Measurements, setup and matching.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

The existence of an entropy rule for quantum entanglement has been proven 09.05.2024

Quantum mechanics continues to amaze us with its mysterious phenomena and unexpected discoveries. Recently, Bartosz Regula from the RIKEN Center for Quantum Computing and Ludovico Lamy from the University of Amsterdam presented a new discovery that concerns quantum entanglement and its relation to entropy. Quantum entanglement plays an important role in modern quantum information science and technology. However, the complexity of its structure makes understanding and managing it challenging. Regulus and Lamy's discovery shows that quantum entanglement follows an entropy rule similar to that for classical systems. This discovery opens new perspectives in the field of quantum information science and technology, deepening our understanding of quantum entanglement and its connection to thermodynamics. The results of the study indicate the possibility of reversibility of entanglement transformations, which could greatly simplify their use in various quantum technologies. Opening a new rule ... >>

Mini air conditioner Sony Reon Pocket 5 09.05.2024

Summer is a time for relaxation and travel, but often the heat can turn this time into an unbearable torment. Meet a new product from Sony - the Reon Pocket 5 mini-air conditioner, which promises to make summer more comfortable for its users. Sony has introduced a unique device - the Reon Pocket 5 mini-conditioner, which provides body cooling on hot days. With it, users can enjoy coolness anytime, anywhere by simply wearing it around their neck. This mini air conditioner is equipped with automatic adjustment of operating modes, as well as temperature and humidity sensors. Thanks to innovative technologies, Reon Pocket 5 adjusts its operation depending on the user's activity and environmental conditions. Users can easily adjust the temperature using a dedicated mobile app connected via Bluetooth. Additionally, specially designed T-shirts and shorts are available for convenience, to which a mini air conditioner can be attached. The device can oh ... >>

Energy from space for Starship 08.05.2024

Producing solar energy in space is becoming more feasible with the advent of new technologies and the development of space programs. The head of the startup Virtus Solis shared his vision of using SpaceX's Starship to create orbital power plants capable of powering the Earth. Startup Virtus Solis has unveiled an ambitious project to create orbital power plants using SpaceX's Starship. This idea could significantly change the field of solar energy production, making it more accessible and cheaper. The core of the startup's plan is to reduce the cost of launching satellites into space using Starship. This technological breakthrough is expected to make solar energy production in space more competitive with traditional energy sources. Virtual Solis plans to build large photovoltaic panels in orbit, using Starship to deliver the necessary equipment. However, one of the key challenges ... >>

Random news from the Archive 868MHz wireless PIR sensor on the new CC1310 radio 24.01.2016 Texas Instruments' new reference development is a wireless stand-alone IR sensor with a detection range of moving objects at a distance of up to 9 meters. Thanks to the use of a multi-core radio system on a chip, the sensor can operate up to 10 years from a single CR2032 battery. High technical parameters are obtained thanks to the latest wireless microcontroller CC1310F128RGZT with Cortex M3 core and built-in 868 MHz radio. An analog PIR sensor Murata IRS-B210ST01-R1 ​​is used as a sensitive element. For primary signal processing, nano-consuming components were used: an LPV521 operational amplifier (0,375 μA) and a TLV3691 comparator (75 nA). The consumption of the device in Standby mode (with an active IR sensor) is only 1,65 μA. The average current consumption in the active mode of operation is 1,2 mA for 104 ms when data is processed and the packet is sent over the air. The operating temperature range of the device -30...60°C is determined by the type of CR2032 battery used. Due to the fact that both the microcontroller and the radio are on the same chip, the overall size of the board is very compact (35x75 mm), including the PCB antenna. Measured at the office, the range was up to 220 meters when received on a CC1111 USB dongle connected to a laptop.

Other interesting news:

▪ Dangerous fungal clouds

▪ Sound without speakers

▪ 512 GB SSD from Samsung in BGA chip format

▪ Huawei NetEngine 9000 Petabit Backbone Router

▪ Miniature board Tah for controlling electronic devices via Bluetooth

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ site section Preamplifiers. Article selection

▪ article Eat to live, not live to eat. Popular expression

▪ article Why do clouds have different shapes? Detailed answer

▪ article Electrician for the maintenance of electrical equipment of power plants. Standard instruction on labor protection

▪ article Choosing your first metal detector. Encyclopedia of radio electronics and electrical engineering

▪ article Semiconductor solar panels. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024