What Is a Helical Antenna?
A helical antenna is an antenna having a spiral shape. It consists of a metal conductive wire with good electrical conductivity. It is usually fed by a coaxial line. The coaxial line of the coaxial line is connected to one end of the spiral line. The outer conductor of the coaxial line is connected to a grounded metal mesh (or board). connection. The radiation direction of a spiral antenna is related to the circumference of the spiral. When the circumference of the spiral is much smaller than one wavelength, the direction of the strongest radiation is perpendicular to the axis of the spiral; when the circumference of the spiral is one order of wavelength, the strongest radiation appears in the direction of the axis of the spiral.
- Chinese name
- Helical antenna
- Foreign name
- helical antenna
- A helical antenna is an antenna having a spiral shape. It consists of a metal conductive wire with good electrical conductivity. It is usually fed by a coaxial line. The coaxial line of the coaxial line is connected to one end of the spiral line. The outer conductor of the coaxial line is connected to a grounded metal mesh (or board). connection. The radiation direction of a spiral antenna is related to the circumference of the spiral. When the circumference of the spiral is much smaller than one wavelength, the direction of the strongest radiation is perpendicular to the axis of the spiral; when the circumference of the spiral is one order of wavelength, the strongest radiation appears in the direction of the axis of the spiral.
Definition of helical antenna
- A helical antenna is a type of antenna that can send and receive polarized electromagnetic signals that rotate in space. Such antennas are commonly used in ground stations for satellite communications. Use unbalanced feeders, such as coaxial cables
- Helical antenna
- Helical antenna
- From the outside, a helical antenna looks like a helix is mounted on a flat reflective screen. The length of the helical portion should be equal to or slightly longer than one wavelength. The reflector is round or square, and the maximum internal distance (diameter or edge) of the reflector must be at least three quarters of a wavelength. The radius of the spiral part is between one-eighth and one-quarter wavelength, and the inclination angle of one-quarter to one-half wavelength must also be guaranteed. The minimum size of the antenna depends on the frequency of the low-frequency signal used. If the helix or reflector is too small, the efficiency of the antenna is severely reduced. In the axial part of the helical antenna, the energy of the electromagnetic wave is the largest. A helical antenna usually consists of multiple helical sections and a reflector. You can move an entire group of antennas simultaneously or vertically to track a satellite. If the satellite is not in orbit,
- Helical antenna
Classification and application of helical antenna
- When D / = 0.25 0.46 (that is, the circumference of a spiral is about one wavelength), the antenna has the maximum radiation along the axis.
- Effect of helical antenna radius (perimeter) on pattern
- Normal mode spiral antenna (D / <0.18) is essentially a thin wire antenna. In order to shorten the length, it can be wound into a spiral. Therefore, its characteristics are similar to monopole thin-line antennas, with a figure-eight pattern and a narrow frequency band. It is generally used as a communication antenna for low-power radio stations.
- Edge-fired spiral antenna is a normal mode spiral antenna. It is a metal conductor placed on the center axis of the spiral. When the circumference of a spiral is l = M (M = 2, 3, ... integer), the maximum radiation is also generated in the normal direction of the spiral. This antenna can be used as a television transmitting antenna.
- The equiangular spiral antenna is also a normal mode spiral antenna. The two arms of the antenna are unfolded on a plane or cone according to a specific curvature change. Because the shape of this antenna is determined only by the angle and does not include the linear length, the characteristics of the antenna are not affected by frequency changes, so it has an extremely wide frequency band. The maximum radiating direction of a planar equiangular spiral antenna is the normal direction on both sides of the plane, and it radiates circularly polarized waves.
Spiral antenna pocket antenna production
- Design and production of antennas for pocket communication machines
- Helical antenna
- Pocket communication machines are widely used in various sectors of society due to their small size, light weight, and ease of use. This type of machine is widely used in helical antennas. Generally, the finished helical antennas are wound and sealed with conductive metal wires. . Under its working principle:
- The general antenna structure shown in Figure 1. D is the diameter of the helical antenna, L is the length of the helical antenna, is the pitch, and I and II are the two corresponding points on the helix.
- Generally, it can be considered that the electromagnetic wave moves at a constant speed of the light speed C along the metal spiral.
- A spiral is performed from point to , the time required is
- t = D / C
- For a helical antenna, its axial electromagnetic wave only travels a pitch , and its axial equivalent velocity
- = / t = / C (D)
- This relationship can also be explained in the form of FIG. 2. From Figure 2:
- = Csin = C / D C
- It can be seen from the above formula that is always less than or equal to C. Therefore, the helical antenna can slow down the electromagnetic wave movement speed. It is a slow-wave system, and its equivalent wavelength is equivalently smaller than the working wavelength . For a helical antenna, it should resonate at its 1/4 equivalent wavelength, so it can be reduced
- Helical antenna
- For a communication machine working at a certain center frequency, the number of coils N that it needs to be wound can be approximated by the following formula:
- Pitch: = L / N
- Required metal wire length: = ND
- Desirable for general communication
- L = 20 ~ 40cm
- D = 10 ~ 20mm
- The following table is a design example of some common frequency spiral antennas. Other frequencies can also be similarly designed.
- f is the working center frequency;
- Helical antenna
- L is the length of the helical antenna;
- N is the number of spiral turns;
- is the required wire length.
- The above N and are approximate values for actual production.
- It can be wound with 0.5 ~ 1.5mm diameter enameled wire or silver-plated copper wire or aluminum wire on the plexiglass or other insulating material with a diameter of D, and make small holes at both ends of the rod to facilitate the fixing of the metal wire. A thick metal rod or plug is welded on the bottom end to fix it on the rod to facilitate connection with the machine; the outside of the entire helical antenna can be sealed with a rubber tube or other material, and a rubber cap or other material can be used to seal the top end It is beautiful and generous, and it is also resistant to rain and corrosion, and is durable. If the above-mentioned metal wire is not available, multiple strands of fine insulated wires can also be used instead. The effect is the same, except that it is more difficult to fix when winding.
- The above spiral antenna can also be used on various small remote control equipment and other similar machines.
- In order to compare the difference between a slow wave antenna and a conventional whip antenna, and explain the advantages of the small size of the slow wave antenna, we can make a calculation on the whip antenna.
- The setting parameters are as follows:
- Frequency f = 27MHZ
- Wave speed c = 3 × 108M (Note: 108 should be the power of 10)
- The antenna should resonate at 1/4 operating wavelength. The length of the whip antenna can be calculated according to the formula:
- L = 1 / 4 = 1/4 c / f = 1/4 (3 × 108/27 × 108) = 2.78m (Note: 108 should be the power of 10)
- According to the above table, it can be seen that if a spiral antenna is used, a slow-wave antenna with a center frequency of 27 MHz has an appearance length of only 40 cm and a size of about one-seventh that of a rod antenna.