Antenna Theory: Dipole Antenna

Dipole Antenna

Goals

In this experiment, dipole antenna and influence of reflector to dipole antenna will be examined by using CST Studio. The aim of this experiment is to understand fundamental characteristics of dipole antenna.

1. Introduction

The term "dipole" alludes to the truth that a dipole receiving wire has two posts or objects – two conductive components. An electromagnetic wave or radio flag is transmitted outwards from the radio wire due to current streaming through these two conductive components and the related voltage [1].

Figure 1. Basic Dipole Antenna [1]

As can be seen, the fundamental receiving wire comprises of two isolated conductors and a transmitting parcel. Ordinarily, both are on the same pivot, and the dipole receiving wire is part within the center. A transmitter's control can be included to be transmitted, or an antenna's control can be joined to a recipient. Ordinarily, a middle feeder interfaces the recipient or transmitter to the dipole receiving wire, permitting control to be exchanged from one point to another.

The bolster impedance, center working recurrence, and whether or not the dipole receiving wire is resounding are all decided by the length of the emanating components. As a result, the dipole length is one of the foremost basic dipole radio wire parameters [1].

Figure 2. Basic Half Wave Dipole Antenna [2]

The radio-frequency (RF) voltage source is connected to the dipole antenna's center between the two parts. A radio flag or electromagnetic wave is created by the voltage and current streaming through the two conductive components and transmitted outwards from the receiving wire. At the dipole antenna's center, the current is most prominent and the voltage is most reduced. At the dipole antenna's closes, on the other side, current is least and voltage is most noteworthy. The essential dipole antenna's radiation design is delineated within the chart underneath. It is opposite to the antenna's pivot [2].

Figure 3. A Basic Dipole Antenna's Radiation Pattern [2]

Take note that the antenna's radiation design could be a graphical representation of the antenna's radiation properties as a work of space, i.e., the antenna's radiation design depicts how it emanates vitality out into space.

To sum up this section, a dipole radio wire may be a shape of transducer that changes over electrical signals into RF electromagnetic waves and emanates them on the transmitting side whereas too changing over RF electromagnetic waves into electrical signals on the getting side [2].

1.1. Dipole Antenna Design

Numerous dipole radio wires can be planned to work on the radio recurrence spectrum's HF (tall recurrence), VHF (exceptionally tall recurrence), and UHF (ultra-high recurrence) groups [2].

To design a 1 MHz dipole antenna. First we will deal with the length of the antenna.

1.1.1. Selection of Length of the Dipole Antenna

The wavelength of a radio wave, or any other wave, is contrarily relative to the recurrence, as we all know. It is given by:

and

Where c is the velocity of light and it is 3 x 10⁸. We can convert the formula by doing some operation.

Our new formula is

The length of the antenna at a half-wavelength is now given by,

In this way, the esteem increased by a calculate K to the essential length of the radio wire yields the commonsense λ/2 length of the radio wire.

As a result, we obtained

The value of K is determined by the conductor thickness and operating frequency. For antenna wire with a frequency of up to 30 MHz, this value of K is true [2].

1.2.Selection of the Feed Impedance or Radiation Resistance

The proportion of voltage and current at the bolster point decides the bolster impedance of a dipole. It's as a rule nourished when the voltage is at its most reduced and the current is at its most noteworthy. To guarantee the greatest exchange of vitality from the feeder, or source/load, the bolster impedance of the dipole radio wire ought to be the same as that of the source or stack. By coordinating the bolster impedance to the source or stack impedance, the receiving wire can work to its greatest effectiveness.

The radiation resistance or an input bolster impedance of a perfect dipole receiving wire in free space can be roughly displayed by a 73 Ω impedance and beneath commonsense conditions it changes from 60 Ω to 70 Ω. The receiving wire impedance can be changed by changing the length or shape of the wires. Since a few sorts of coaxial cable have a 75 Ω characteristic impedance, the dipole receiving wire can be encouraged with 75 Ω two wire coaxial cable, which could be a great fit for a half-wave dipole receiving wire.

In expansion, depending on the control dealing with capabilities, the half-wave dipole can be bolstered with a transmission line with impedances of 300 and 600 open wire line with collapsed dipoles [2].

1.3.Dipole Antenna Types

The half wave dipole, which gets its title from the truth that its length compares to an electrical half wavelength, is the foremost common sort of dipole receiving wire. In any case, there are various other sorts of dipole radio wires accessible. The various types or variations of the dipole antenna are used in a variety of applications, demonstrating that the dipole is a very versatile and useful antenna [1].

1.3.1. Half wave dipole antenna

The half-wave dipole receiving wire is the foremost commonly utilized receiving wire. This sort of dipole radio wire is thunderous, meaning it works at a recurrence of half a wavelength. Since of the impact of the wire along which the wave is traveling, the electrical half wavelength within the receiving wire is altogether shorter than a half wavelength in free space.

Figure 4. Half Wave Dipole Antenna [3]

The half wave dipole is regularly middle bolstered. This gives a moo impedance bolster point which is simple to oversee. As the receiving wire is adjusted, i.e. not one or the other side connected to ground, it is essential to utilize either adjusted feeder, or in case an unequal feeder such as coaxial cable is utilized, at that point a balun - an adjusted to lopsided transformer ought to be utilized [1].

1.3.2. Multiple half waves dipole antenna

Figure 5. Multiband Dipoles

Although the half wave dipole antenna is the most common, an odd multiple of half wavelengths long dipole antenna may also be used. The radiation pattern is somewhat different in this mode, but it still works well. Once more, this sort of receiving wire is by and large middle encouraged and once more this gives a moo nourish impedance. It is worth noticing that as it were by having an odd number of half wavelengths does a point of current greatest and voltage least happen at the middle to supply a moo impedance nourish point which empowers simple bolstering of the receiving wire. In the event that you need to utilize the radio wire at its principal recurrence of reverberation and after that at three or more times that figure, you'll be able utilize this shape of receiving wire to form a multi-band dipole [1].

1.3.3. Folded dipole antenna

Figure 6. Folded Dipole Antenna Design [5]

This sort of dipole airborne or dipole radio wire is collapsed back on itself, as the title recommends. In parallel with the first dipole components, a half wave conductor is connected, with one conclusion associated to the other, coming about in a DC brief circuit. The extra conductor permits the collapsed dipole to have the next nourish impedance and more extensive transfer speed whereas keeping up the length between the closes of half a wavelength, which can be useful in certain cases [1].

1.3.4. Short dipole

From all of the receiving wires, the brief dipole radio wire is the foremost fundamental. A brief dipole receiving wire is one in which the wire length is less than half the wavelength. The nourish impedance of a brief dipole receiving wire starts to rise, and its reaction gets to be less subordinate on recurrence changes. The brief dipole antenna's show dissemination is generally triangular [2].

Figure 7. Short Dipole Antenna [2]

A short dipole will require special feed arrangements to accommodate the much higher feed impedance. Over a broad bandwidth, however, the antenna will appear to have identical characteristics. In comparison, the efficiency level of a dipole antenna, which is larger in terms of wavelength range, may be considerably lower [1].

1.3.5. Non-resonant dipole

Figure 8. Non-Resonant Dipole Antenna [6]

A dipole radio wire can be bolstered with a tall impedance feeder and worked absent from its thunderous recurrence. It can presently run over a much more extensive transfer speed as a result of this [2].

1.4.What are the Applications of a Dipole Antenna?

Dipole Antenna has a variety of uses, including

·         The dipole radio wire is broadly utilized in radio and telecommunications.
·         An radio wire can be utilized either as a transmitting receiving wire or a getting receiving wire.
·         A transmitting radio wire is utilized to changes over electrical signals into electromagnetic waves and transmits them. Whereas a getting receiving wire is utilized to changes over electromagnetic waves into electrical signals. In two-way communication, the same dipole radio wire can be utilized for both transmission and reception.
·         A half-wave dipole radio wire is utilized in radio and tv recipients.
·         A Collapsed dipole receiving wire is utilized in Yagi-Uda receiving wires for earthbound tv (TV) gathering utilizing the adjusted line of Z0 = 300 Ω since a collapsed dipole receiving wire encompasses a tall input impedance and subsequently it is effectively coordinating with the impedance of the transmission line.
·         The Collapsed dipole receiving wire is utilized in wideband operations such as FM and TV (Tv) broadcast.
·         Coastal zones, open security, open communication, and mechanical applications all utilize VHF and UHF recieving wires for arrive versatile communication.
·         For the FM broadcast band 88 MHz to 108 MHz, an FM dipole receiving wire is utilized as an FM broadcasting- receiving wire.
·         Partisan communications, radio space science, and distinctive shapes of radio contact joins all utilize allegorical reflector radio wires [2].

1.5. Farfield Formulas of the half wave dipole antenna

Half-wavelength dipole antenna is used as a most common type of dipole antenna. Because it radiates about 73 Ω, that means it is easy to feed it via 50 or 75 Ω transmission line. The farfields of the half wave dipole antenna’s formules are given below.

The farfield representation of half wave dipole antenna is given as below picture.

Figure 9.The farfield representation of half wave dipole antenna[7]

Some additional formulas are also given below and power, resistance and directivity parameters of the half wave dipole antenna is written.

H.O, Antenna Theory [7]

Method

1- Half Wave Dipole Antenna

In the first question of this experiment, a half-wavelength dipole antenna was drawn using CST Studio. The total length (L) of the antenna is 55.3mm, the radius is 0.5mm. It is made of PEC. Figure 9 shows initial version of the Dipole Antenna.

Figure 10.Initial Version of Dipole Antenna

Another cylinder was created to create the gap and it is seen Figure 10. Dimension of it is same previous the other but, its length is 2mm.

Figure 11. Another Cylinder to Create Gap

The middle of the dipole antenna was removed by performing the Boolean subtract processing. Feeding to the antenna was made between the gap using discrete port. Figure 11 shows it.

Figure 12. Gap which been Middle of Dipole Antenna

The last version of dipole antenna is seen Figure 12. According to theory, radiation resistance of the half-wave dipole should be 73 Ohm, but port impedance is 50 Ohm in simulation.

Figure 13. The last version of dipole antenna

2- Half Wave Dipole Antenna with Reflector

Second question of experiment, same processes were made previous question. In addition to schematic, a reflector was added. It is made of PEC. Wide and length of reflector is 120 mm, height of reflector is 0.02mm. Distance between dipole antenna and reflector is 28 mm. In this part, effect of distance between dipole antenna and reflector will be examined. It is shown Figure 13.