A short dipole antenna is a type of antenna made by sending a signal through a wire in the middle. The actual antenna length, however, is often far shorter than one-tenth of a wavelength. Also, the wire size of the real antenna has low radiation resistance and is used in narrow-band applications.
Moreover, you can get more advantages from its field pattern as it provides a high impedance to the feeder. But it’s important to keep an eye on the short dipole voltage at higher power levels; if it’s not controlled properly, it could become a problem.
But what is the structure of these antennas and how does it works on the actual fields? Keep on reading to get a clear idea of this.
What is Short Dipole Antenna?
From the name, it’s visible that this antenna will be short in actual size, and this is one of the simplest types of antenna that you can find. So basically, the dimension of this antenna is less than half of the wavelength, that is, (<λ/2).
In this dipole aerial, one end is open-circuited and the other end is connected to an AC circuit. However, the current distributions in the antenna are triangular, like the figures given below.
The current flows of this antenna heavily rely on the frequency and the operating frequency will range between 3KHz to 30MHz. But the antenna impedance will rise and the responses won’t depend on the operation frequency.
Compared to other half-wave dipole antenna current distributions of the short dipole, the radiation pattern is a circle here, which means the dipole will be vertical. Moreover, radiation resistance (considered relative to the feed point) is the same as the resistive (real) component of the feed point impedance if ohmic losses in the conductors are disregarded.
Why is Short Dipole Antenna important?
This short-dipole antenna element refers to the wire’s physical length, which is shorter than the normal dipole.
However, these active antennas receive electromagnetic waves from free space and require the antenna to convert those waves into circuit voltages for processing, to convert voltages back into free space.
Despite their basic field expressions, their performance and complexity keep rising due to the discovery of better computational analytical methods.
It also acts as a receiver and transmitter of the magnetic field, with both linear and vertical polarizations. In addition, these antennas are favored for broadband satellite communication due to their strong gain across a large frequency range.
Types Of Short Dipole Antenna
There are different types of Short dipole antenna available. However, the most common ones are Vertical Antenna, the Dipole Antenna, and the Yagi Antenna.
- Vertical Antenna (GP)
These are basically used for short-range communication, for example, ground wave transmission. The focus field of GP is ground; while arranging the GP network, you have to be extra careful.
Moreover, Gp has a 21-29M band of frequencies and a height of 5-10 meters. That means they are easy to mount. In some situations, a horizontally positioned antenna could not be as wind resistant as a vertically installed one.
- Dipole Antenna (DP)
This dipole is a straightforward antenna configuration, hence the acronym. It has many antennas constructed upon it. However, it’s more challenging to install. Thus, two rods is the bare minimum required for usage as supports.
A total of 3 rods are needed to hold up the antenna because of the center feed and the feeder itself. Since its impedance is higher than 50, it can’t be transmitted over a standard 50 feeder.
In order to communicate, the DP antenna relies heavily on electromagnetic waves in the sky. The long-distance communication effect is powerful, and the setup is straightforward. Most radio enthusiasts use it because it is constructed as mast radiators.
- Yagi-Uda Antennas
These antennas have a reputation due to their high antenna gain and directivity. They have three major current elements: electric dipole, directors, and reflectors. It has fixed transmission frequencies.
More gain can be obtained by pointing the beam in different angular directions with different numbers of directors.
Structure Of Short Dipole Antenna
When a voltage is delivered to the junction of the antenna’s two halves, electromagnetic or radio waves are produced by the voltage source, and current flow through the two conductive elements and radiates away from the transmitter. However, the coaxial feeder is one of the important parts used for coaxial transmission.
This antenna current is highest, and voltage is lowest at its center. The ends of the antenna wire have the lowest current and the highest voltage, respectively. In this form, short dipole transmitters are now dispersed.
Radiation Resistance Of Short Dipole Antenna
The antenna’s radiation resistance is a crucial specification. Without it, you can’t determine the total feed point current and, by extension, the required matching. That’s why you need to figure out how much radiation this rather common dipole can withstand.
The power levels of their total feed inductance are made up of the antenna’s series inductance, capacitive coupling, radiation resistance, and Ohmic losses. These components must have vector potential to determine the overall current flows.
It’s already clear that short dipole antennas behave under natural resistive losses and it is shorter than the actual size. Therefore, capacitive reactance will play a pivotal role as the reactive component. This means that the antenna’s impedance will be a bit complicated because of the electrostatic repulsion.
You can use a balanced feeder instead of a coaxial feeder between the antenna and the matching circuit. However, the former is the simpler alternative.
Tips About Short Dipole Antenna
There are certain facts that you need to be careful about while buying or building this antenna. So let’s check them out.
- It’s crucial to place the loading coils at the correct points along the antenna wire. The most efficient placement of coils is close to the dipole’s ends; however, this requires coils with enormous inductances. That’s why you must set this dipole’s loading coils away from the central feed point as the source current.
- The maximum radiation of the dipole will depend on the wire’s quality. It’s best to use solid copper. However, copper-clad steel wire is not as preferable.
- The diameter of the wire used in the coil design plays a role in current sources. As resistance absorbs radian frequency energy as heat rather than signal, the antenna arrays need a smaller wire size. The accurate coils would be made from thin copper tubing, but this would present mechanical challenges when building the dipole.
- Although air-wound coils are ideal, they aren’t always mechanically possible. That’s why having a form to wind the designed coil impedance-matching around is necessary. The insulating characteristics of the form material are important.
- In conclusion, coils are the “high-Q” parts of the loaded dipole. They were created to operate at a specific frequency so that they can measure the correct input feed impedance. To put it another way, the efficiency and efficacy of a “loaded” dipole antenna diminish drastically when it’s used at a frequency different from its resonant frequency.
How strong is the short dipole’s resistance to radiation?
A radiation resistance of 802(L/)2, or four times the right side of Equation 10.6, has been proposed for an “electrically-short dipole.”
What is the directional gain of a short dipole antenna?
The short dipole antenna supplied in the center has a directivity that is entirely field component dependent. And the computed value is 1.5 (1.76 dB), which is relatively low compared to theoretically optimal antennas.
What effect does distance have on a dipole?
Unlike the spherically symmetric Coulomb potential, the non-spherical dipole potential diminishes exponentially with distance, with a rate of (1/distance)^2. As distance goes up, the dipole field gets weaker, and the effects of dipoles become quickly insignificant.
How does the electricity move through a dipole antenna?
The charge and current that are carried by a dipole cause fields to be generated that are perpendicular to one another and produce these fields. When voltage is given to an antenna, it causes the elements to take on either a positive or negative charge.
Now you have an idea about a short dipole antenna and its structure, importance and where it’s used. However, among others, this one is the basic antenna that’s used for feeding sources to larger antennas.