Vishal Digital Electronics Pvt. Ltd., Vitthalpur, Sikhar, Mirzapur

A  short dipole  is a simple wire antenna. One end of it is open-circuited and the other end is fed with AC source. This dipole got its name because of its length. Frequency range The range of frequency in which short dipole operates is around 3KHz to 30MHz. This is mostly used in low frequency receivers. Construction & Working of Short Dipole The  Short dipole  is the dipole antenna having the length of its wire shorter than the wavelength. A voltage source is connected at one end while a dipole shape is made, i.e., the lines are terminated at the other end. The circuit diagram of a short dipole with length L is shown. The actual size of the antenna does not matter. The wire that leads to the antenna must be less than one-tenth of the wavelength. That is L &lt; &#x03BB; 10 " role="presentation"> L < λ 10 L < λ 10 Where L  is the length of the wire of the short dipole. λ  is the wavelength. Another type of short dipole is infinitesimal dip...

If the length of the dipole, i.e. the total wire, equals the full wavelength  λ , then it is called as  full wave dipole . If a full wavelength dipole is used either for transmission or for reception, let us see how the radiation will be. Construction & Working of Full-wave Dipole The full-wave dipole with its voltage and current distribution is shown here. Both the positive and negative peaks of the wave induce positive and negative voltages respectively. However, as the induced voltages cancel out each other, there is no question of radiation. The above figure shows the voltage distribution of full-wave dipole whose length is  λ . It is seen that two half-wave dipoles are joined to make a full-wave dipole. The voltage pattern when induces its positive charges and negative charges at the same time, cancel out each other as shown in the figure. The induced charges make no further attempt of radiation since they are cancelled. The output radiation will be zero for a fu...

A folded dipole is an antenna, with two conductors connected on both sides, and folded to form a cylindrical closed shape, to which feed is given at the center. The length of the dipole is half of the wavelength. Hence, it is called as  half wave folded dipole antenna . Frequency range The range of frequency in which half wave folded dipole operates is around 3KHz to 300GHz. This is mostly used in television receivers. Construction & Working of Half-wave Folded Dipole This antenna is commonly used with the array type antennas to increase the feed resistance. The most commonly used one is with Yagi-Uda antenna. The following figure shows a half-wave folded dipole antenna. This antenna uses an extra conducting element (a wire or a rod) when compared with previous dipole antenna. This is continued by placing few conducting elements in parallel, with insulation in-between, in array type of antennas. The following figure explains the working of a half-wave folded dipole antenna, whe...

The dipole antenna is cut and bent for effective radiation. The length of the total wire, which is being used as a dipole, equals half of the wavelength (i.e., l = λ/2). Such an antenna is called as  half-wave dipole antenna . This is the most widely used antenna because of its advantages. It is also known as  Hertz antenna . Frequency range The range of frequency in which half-wave dipole operates is around 3KHz to 300GHz. This is mostly used in radio receivers. Construction & Working of Half-wave Dipole It is a normal dipole antenna, where the frequency of its operation is  half of its wavelength . Hence, it is called as half-wave dipole antenna. The edge of the dipole has maximum voltage. This voltage is alternating (AC) in nature. At the positive peak of the voltage, the electrons tend to move in one direction and at the negative peak, the electrons move in the other direction. This can be explained by the figures given below. The figures given above show the work...

Wire antennas are the basic types of antennas. These are well known and widely used antennas. To have a better idea of these wire antennas, first let us have a look at the transmission lines. Transmission Lines The wire or the  transmission line  has some power, which travels from one end to the other end. If both the ends of transmission line are connected to circuits, then the information will be transmitted or received using this wire between these two circuits. If one end of this wire is not connected, then the power in it tries to escape. This leads to wireless communication. If one end of the wire is bent, then the energy tries to escape from the transmission line, more effectively than before. This purposeful escape is known as  Radiation . For the radiation to take place effectively, the impedance of the open end of the transmission line should match with the impedance of the free-space. Consider a transmission line of a quarter-wave length size. The far end of it...

Antennas have to be classified to understand their physical structure and functionality more clearly. There are many types of antennas depending upon the applications applications. Type of antenna Examples Applications Wire Antennas Dipole antenna, Monopole antenna, Helix antenna, Loop antenna Personal applications, buildings, ships, automobiles, space crafts Aperture Antennas Waveguide (opening), Horn antenna Flush-mounted applications, air-craft, space craft Reflector Antennas Parabolic reflectors, Corner reflectors Microwave communication, satellite tracking, radio astronomy Lens Antennas Convex-plane, Concave-plane, Convex-convex, Concaveconcave lenses Used for very highfrequency applications Micro strip Antennas Circular-shaped, Rectangularshaped metallic patch above the ground plane Air-craft, space-craft, satellites, missiles, cars, mobile phones etc. Array Antennas Yagi-Uda antenna, Micro strip patch array, Aperture array, Slotted wave guide array Used for very high gain applic...

Antennas radiate Electromagnetic energy to transmit or to receive information. Therefore, the terms  Energy  and  Power  are associated with these electromagnetic waves and we have to discuss them. An electromagnetic wave has both electric and magnetic fields. Consider the wave at any instant, which can be viewed in both the vectors. The following figure shows the representation of electric and magnetic field components in an Electromagnetic wave. The electric wave is present vertical to the propagation of EM wave, while the magnetic wave is horizontally located. Both the fields are at right angles to each other. Poynting Vector Poynting vector describes the energy of the EM Wave per unit time per unit area at any given instant of time.  John Henry Poynting  first derived this vector in 1884 and hence it was named after him. Definition  − “Poynting vector gives the rate of energy transfer per unit area” or “The energy that a wave carries per unit time ...