What Is a Folded Dipole Antenna?

Dipole antennas are generally round-rod omnidirectional antennas. The omnidirectional antennas are covered by a horizontal 360-degree signal. Different omnidirectional antennas have different sizes of vertical transmission angles.

Symmetric array antenna structure: The symmetrical dipole antenna is composed of two arms, and the two arms of the antenna are composed of two equal-length equal-thickness wires. Structural parameters: The radius of the wire is a, the length is l, and the total length of the oscillator is L = 2l. The gap between the two arms is small and can be ignored in theory.

A dipole antenna (symmetrical oscillator) is a linear conductor whose midpoint is disconnected and connected to feed power.

In a wireless communication system, it is necessary to convert guided wave energy from a transmitter into radio waves, or to convert radio waves into guided wave energy. A device used to radiate and receive radio waves is called an antenna. The modulated high-frequency current energy (or guided wave energy) generated by the transmitter is transmitted to the transmitting antenna via the feeder, which will be converted into some kind of polarized electromagnetic wave energy and go out in the required direction. After reaching the receiving point, the receiving antenna converts the energy of a certain polarized electromagnetic wave from a specific direction in space into modulated high-frequency current energy and sends it to the input of the receiver via the feeder.
In summary, the antenna should have the following functions: The antenna should be able to convert as much of the guided wave energy as electromagnetic wave energy. This first requires that the antenna is a good electromagnetic open system, and secondly that the antenna is matched with the transmitter or receiver; the antenna should make the electromagnetic waves focus on the determined direction as much as possible, or accept the incoming wave to the maximum direction, that is, the direction It is directional; the antenna should be able to transmit or receive electromagnetic waves with a prescribed polarization, that is, the antenna has a proper polarization; the antenna should have a sufficient operating frequency band.

These four points are the most basic functions of the antenna. Based on this, several parameters can be defined as the basis for designing and evaluating the antenna. A system that connects an antenna with a transmitter or receiver is called a feeder system. The form of the feeder line is divided into a wire transmission line, a coaxial line transmission line, a waveguide or a microstrip line, etc. depending on the frequency. Therefore, the so-called feeder line is actually a transmission line.

Although the radio experiment was successful in 1906, the formal establishment of radio stations in the United States, the Soviet Union, France, Germany, and Italy was still in the early 1920s. Medium wave broadcasting antenna type. Initially, T-type, , and umbrella antennas were used. Later, cable or self-supporting tower antennas were used to enhance radiation along the ground. Later, the top load was increased to reduce the height of the tower. In terms of short-wave broadcasting, A short-wave communication antenna was introduced, and a horizontal in-phase antenna array was adopted to adapt to the requirements of the ionosphere with the change of day and night, season, and sunspot number, and a broadband horizontal antenna array and traveling wave antenna were developed.

In the 1930s, due to the development of radar and microwave technology, ultra-short wave and microwave antennas such as horn antennas, parabolic antennas, dielectric antennas, and slot antennas were successively born. After the Yagi antenna was successfully developed in 1926, it began to be used in this period, and it has not declined so far.

After the Second World War, and in the 1950s, television broadcasts and microwave relays developed greatly. Bat-wing antennas, various dipole antennas with reflective surfaces, periscope antennas, and high-power slot antennas were born. The medium and short wave antennas are basically fixed.

In the 1960s and 1970s, there was a great development in antenna technology. Developed a double-reflection antenna, a new feed, and a beam waveguide. FM and TV antennas are also basically fixed. Microstrip antennas, slot antennas, and active antennas have developed. The frequency reuse of reflective antennas, orthogonal polarization, near-field measurement, and off-focus offset caused by multiple beams have been valued.

In the 1980s, there were not many new types of radio and television antennas, but some new technologies came out in terms of matching devices and directional pattern control, especially in the vertical pattern shaping design of decimeter wave television transmitting antennas. The radiant energy covers the service area more reasonably, and can suppress the radiation that interferes with the neighboring areas. In the calculation method, due to the development of computer technology, a numerical calculation method suitable for the calculation of antenna electrical parameters has appeared. Microstrip Array Plane Antennas for Satellite Broadcasting Receiving Begin Commercial Availability ^[3]

The bat-wing antenna is a kind of orthogonal vibrator antenna, that is, it is composed of two mutually orthogonal symmetrical vibrators, and the feed current amplitude of the symmetrical vibrators is equal to 90 ° and the phase difference is 90 °, which is also called a rotating field antenna. Because the vibrator looks like a batwing, it is called a batwing antenna. It is widely used as a rice wave TV transmitting antenna. The horizontal pattern is approximately a circle, but the diameter of the antenna support rod should be kept between 0.1 and 0.15. If it is too thick, the horizontal pattern will appear frog-shaped. The input impedance is about 150 ohms, and the input reactance is not greater than ± 10 ohms. Bat-wing vibrators and antenna struts are generally made of steel pipe, and the surface is galvanized to prevent corrosion. The advantages of this antenna are: when the standing wave ratio is less than or equal to 1.1, the bandwidth is 25%; the power capacity is large; the vibrator is directly welded to the brace, and the structure is firm; the vibrator surface is composed of a horizontal vibrator (with a spacing of about 0.1 wavelength), and The wind area is small. The main disadvantage is that when the number of layers is increased to increase the gain, the struts need to be thickened, but the diameter of the struts is restricted by the horizontal pattern, so it is difficult to achieve high gains ^[4] .