Dipole Antenna

Dipole Antenna Types (Hertzian Dipole, Small Dipole & Halfwave Dipole)

Types of Dipole Antenna

• Based on size of Dipole, we have three types of Dipole Antenna

Hertzian Dipole Antenna

• Hertzian Dipole Antenna is shortest form of Dipole Antenna. It has a length lower then λ/50

• Hertzian Dipole is in minimum use with the Dipole Antenna category.

• It has lower radiation Efficiency.

• It has higher Losses.

• It has a Larger region of reactive field.

Small Dipole Antenna

• Small Dipole Antenna is smaller form of Dipole Antenna. It has a length of λ/50 < l < λ/10

• Small Dipole is used with a few applications only [Narrowband Applications, Tuner Circuits, Effective with low Frequency Applications].

• It has lower radiation Efficiency.

• It has higher Losses.

• It has a Larger region of reactive field.

Dipole Antenna

• Basic Dipole Antenna has a length of λ/2

• Basic Dipole Antenna is widely used with many applications [Yagi Antenna, Tower Antenna, Dipole Arrays Etc.].

• It has higher radiation Efficiency in the dipole antenna categories.

• It has minimum Losses in the dipole antenna categories.

• It has a minimum region of reactive field in the dipole antenna categories.

How Dipole Antenna Radiate EM waves in Space?

Radiation by Dipole Antenna

• Here, Radiation of the Half wave Dipole Antenna is shown, so length of Dipole is L= λ/2

• For The Half Wave Dipole Antenna, Radiation resistance is 73 Ω.

Two Wire Transmission Line

Flaring with Two Wire Transmission Line

Dipole Antenna with Two Wire Transmission Line

In Dipole with Transmission line of 75Ω, minimum Reflection & maximum radiation is acheived.

Electric Field & Magnetic Field of Halfwave Dipole Antenna

E and H Fields of Dipole Antenna

• Here, Radiation of the Half wave Dipole Antenna is shown, so length of Dipole is L= λ/2

• For The Half Wave Dipole Antenna, Radiation resistance is 73 Ω.

Radiation Resistance of Halfwave Dipole Antenna

Radiation Resistance of Hertzian Dipole Antenna

Radiation Resistance of Small Dipole Antenna

Feeding Methods of Dipole Antenna (Center Fed, Off Center Fed, Delta Matching & Inverted L Dipole)

• There are in general four popular feeding methods for Dipole Antenna 1. Centre Feed

2. OFF Centre Feed

3. Delta Matching

4. Inverted L Type

Center Feed Dipole Antenna

• Here, Feeding is given at the center of the Dipole Antenna.

• Feeding can be given by the following transmission line.

i. Coaxial Transmission Line

ii. Two Parallel Wire Transmission Line

iii.Microstrip Transmission Line Transmission Line is of 750 for center feed Halfwave Dipole Antenna.

• For a halfwave Dipole Antenna, the radiation resistance of the Dipole is 73Ω.

Off Center Feed Dipole Antenna

• When the 75Ω cable is not available, then instead of feeding dipole at the center, it is fed OFF the center.

• OFF center fed is done to get impedance matching.

• By Shifting the Center by 13%, an impedance of 600Ω is obtained.

• OFF center feed Dipole has an issue of cross-polarization due to the Asymmetric fed mechanism.

Delta Matching Dipole Antenna

• In this Method, Two wires are fanned gradually.

• Radiation Resistance increases gradually with Delta Matching Dipole Antenna.

• Symmetric Feeding, So less Cross Polarization.

• For 600Ω transmission line,

Inverted L Type Dipole Antenna

• In this Method, the vertical Section and Horizontal section of the wires are connected to form an inverted L shape.

• Given Feeding is not symmetric with respect to feeding, hence it results in higher cross- polarization.

• It is used for a Narrow Range of frequencies.

Monopole Antenna (Basics, Virtual Ground, Working, Structure & Performance)

Basics of Monopole Antenna

• Monopole Antenna has only a single pole.

• Single pole is fed with respect to ground by the source.

• The Physical Length of the Monopole Antenna is λ/4.

• The Virtual Length of the Monopole Antenna is λ/2.

• The working of the Monopole Antenna is identical to the Dipole Antenna, where the Monopole has the second imaginary pole with respect to the ground.

• Replica Happens due to perfect reflection.

• Monopole has lower radiation efficiency with respect to the dipole antenna.

Folded Dipole Antenna (Basics, Modes, Radiation Resistance & Applications)

Basics of Folded Dipole Antenna

• It consists of two parallel Dipoles connected at the ends forming a narrow wire loop. The length of the Dipole is L = λ/2 and the separation between the two dipoles is d, which is much smaller than A and L.

• It has a higher input impedance than Half-Wave Dipole.

• It has a higher bandwidth than Half-Wave Dipole.

• It is utilized for 300Ω transmission Line.