# antenna is a transducer which converts

The above figure shows the voltage distribution of full-wave dipole whose length is λ. Bursts of data sent in rapid succession tend to merge due to dispersion. The attenuation of electromagnetic waves under water is expressed in terms of skin depth. It is especially prevalent in wireline transmissions such as an optical fiber. If that particular direction is not specified, then the direction in which maximum intensity is observed, can be taken as the directivity of that antenna. The gain and directivity are improved by having an array of antennas. This term is derived from two Latin words, meaning literally “to lead across” or “to transfer.” Thus, a transducer is a device that transfers, or converts, energy from one form to another. An Antenna is a transducer, which converts electrical signals into electromagnetic waves and vice versa. Hence, without considering the losses, the area, which utilizes the maximum power obtained to the actual area, can be termed as effective area. This is mostly used in television receivers. The power from the transmission line travels through the waveguide which has an aperture, to radiate the energy. For a transmitter antenna, antenna’s input impedance should match with transmitter amplifier’s output impedance, along with the transmission line impedance. that signal by converting it into an electrical analog or digital output that can easily be read and understood. If the impedance of the antenna, the transmission line and the circuitry do not match with each other, then the power will not be radiated effectively. Such an antenna is called as half-wave dipole antenna. Traditional passive antennas are capable of this conversion in either direction. These are especially used for the microwave transmission or reception. The magnitude of currents in each element is same, but there is a phase difference between these currents. Let us now have a look at these types of aperture antennas. Omni-directional pattern (also called non-directional pattern): The pattern usually has a doughnut shape in three-dimensional view. The following scenario explains this. If one end of this wire is not connected, then the power in it tries to escape. The antenna is placed in the shape of an inverted V, with its two transmission lines or legs bent towards the ground making 120° or 90° angle between them. It converts electrical waves into radio waves and vice versa. The device, which converts the required information signal into electromagnetic waves, is known as an Antenna. After the antenna parameters discussed in the previous chapter, another important topic of consideration is the near field and the far field regions of the antenna. It helps convert waves that are magnetic to electricity and can also be used to convert electricity to magnetic waves. Larger amount of wave, than a parabolic reflector, can be handled. The following image shows another example of an antenna array. Signal multipath is the common problem for the propagation of electromagnetic waves going through Sky wave. The transducer is also a physical device, that converts one form of energy into an another form. Antenna (whether it transmits or receives or does both) can be connected to the circuitry at the station through a transmission line. Now, lets us look at the long wire antennas. The following image shows a waveguide. For example, a wire, which is connected to an antenna. A dipole antenna requires to be fed with 20 kW of power to produce a given signal strength to a particular distant point. When such a small loop antenna is mounted on top of a portable receiver, whose output is connected to a meter, it becomes a great direction finder. In hog-horn antenna, a parabolic cylinder is joined to pyramidal horn, where the beam reaches apex of the horn. A number of directors are placed to increase the directivity. This pattern resembles the broad-side array. As various levels of ionization are done at each level, having different gases, few layers with different properties are formed in the ionosphere. Hence, the frequency and length are inversely proportional to each other. The image of a helix antenna detailing the antenna parts is shown above. The feed is given through the feeder. The figure given above shows the radiational pattern for a bi-directional log-periodic antenna. The waveguide antenna has to be further modified to achieve better performance, which results in the formation of Horn antenna. An Antenna can be used either as a transmitting antenna or a receiving antenna. Transmitting antenna generates the radio frequency field that is transferred to receiving antenna which converts these radio frequency field in to alternating current by using transducer. The following figure shows the radiation pattern of half-wave folded dipole antenna, which is Omni-directional pattern. The actual size of the antenna does not matter. One type of Sensor is LED. The above equation gives us the energy per unit time, per unit area at any given instant of time, which is called as Poynting vector. The radiated power is a function of the angular position and the radial distance from the circuit. Here, the length of the dipole is less than even fiftith part of the wavelength. In simple words, antennas are transducers that change RF electrical signal into an electromagnetic wave of similar frequency. The above images show circular and square loop antennas. The figure depicts a clear form of the Yagi-Uda antenna. The center rod like structure on which the elements are mounted is called as boom. Low Frequency bands comprise of the radio, microwave, infrared and visible portions of the spectrum. a) S1 is true & S2 is false b) S2 is true & S1 is false c) Both S1 & S2 are true d) Both S1 & S2 are false. The cumulative effect of this produces a varying field effect which gets radiated in the same pattern produced on it. Multipath propagation is a term, which describes the multiple paths a signal travels to reach the destination. It is also known as secondary hyperboloid reflector or sub-reflector. It depends upon the values of diameter of helix, D and its turn spacing, S. Drawbacks of this mode of operation are low radiation efficiency and narrow bandwidth. The energy radiated by the Sun, not only heats this region, but also produces positive and negative ions. This is another type of feed used. It is a measure of depth to which an EM wave can penetrate. Following these points, the parabolic reflectors help in producing high directivity with narrower beam width. The image of the model of a lens antenna is shown. The following are the applications of Parabolic reflector antenna −. The frequency range, in which the collinear array antennas operate is around 30 MHz to 3GHz which belong to the VHF and UHF bands. The light does not pass through the plane but through the remaining portion. The following are the disadvantages of Lens antenna −, Lenses are heavy and bulky, especially at lower frequencies, Costlier compared to reflectors, for the same specifications, The following are the applications of Lens antenna −, Especially used for Microwave frequency applications. The feeder is the folded dipole. In the Earth’s atmosphere, the propagation of wave depends not only on the properties of the wave, but also on environment effects and the layers of earth’s atmosphere. Therefore, the radiation pattern produced by them, would be the vector sum of the individual ones. Take a look at the following illustration. The single element present at the back of the driven element is the reflector, which reflects all the energy towards the direction of the radiation pattern. This radiation should be effective with minimum losses. ROLE OF ANTENNA Antennas are the basic components of any electrical system and are the connecting link, which radiate or receive electromagnetic waves between transmitter, free space and receiver. When the antenna acts as a transmitting antenna, the energy from the feed radiates through a horn antenna onto the hyperboloid concave reflector, which again reflects back on to the parabolic reflector. It is also known as Hertz antenna. The fields radiated by the radial currents tend to cancel each other in the far field so that the far fields of the capacitor plate antenna can be approximated by the infinitesimal dipole. If the radiation is equal in all directions, then it is known as isotropic radiation. The first and third elements are fed out of phase and therefore cancel each other’s radiation. The image shows a slot antenna, which explains well about its working. It is true that when a HF field exists across a narrow slot in a conducting plane, the energy is radiated. In this type, the feed is located at the vertex of the paraboloid, unlike in the parabolic reflector. The directional pattern of the Yagi-Uda antenna is highly directive as shown in the figure given below. The given figure is a three dimensional radiation pattern for an Omni directional pattern. The length of the dipole, Δl << λ. In the case of an antenna, these two forms are (1) conductor-bound voltage and current signals and (2) electromagnetic waves. Therefore, the terms Energy and Power are associated with these electromagnetic waves and we have to discuss them. We have studied both the arrays. The antenna is one type of transducer. Its constructiion is similar to it, but uses a capacitor plate. Traditional passive antennas are capable of this conversion in either direction. When the same antenna is used for reception, the electromagnetic waves strike the reflector, gets reflected on to the concave hyperboloid and from there, it reaches to the feed. This is better understood with the help of the following diagram. Critical frequency for a layer determines the highest frequency that will be returned down to the earth by that layer, after having been beamed by the transmitter, straight up into the sky. S is the turn spacing (centre to centre). Definition− “The Effective length is the ratio of the magnitude of voltage at the open terminals of the receiving antenna to the magnitude of the field strength of the incident wave front, in the same direction of antenna polarization.”. If these minor lobes are eliminated and this energy is diverted into one direction (that is towards the major lobe), then the directivity of the antenna gets increased which leads to antenna’s better performance. The following are the applications of half-wave dipole antenna −. A parasitic element is an element, which depends on other’s feed. The dipole that is connected to the feed is known as a driven element. However, all of them are seldom used because of the limitations and disavantages they have in their working conditions. Definition − “Effective area is the area of the receiving antenna, which absorbs most of the power from the incoming wave front, to the total area of the antenna, which is exposed to the wave front.”. Isotropic radiation is the radiation from a point source, radiating uniformly in all directions, with same intensity regardless of the direction of measurement. Inter modulation noise − Caused by signals produced at frequencies that are sums or differences of carrier frequencies. The frequency range of operation of a Rhombic antenna is around 3MHz to 300MHz. However, if two people want to communicate who are at longer distances, then we have to convert these sound waves into electromagnetic waves. According to the standard definition, “An arrangement in which the principal direction of radiation is perpendicular to the array axis and also to the plane containing the array element” is termed as the broad side array. The functioning of an antenna depends upon the radiation mechanism of a transmission line. The radiation pattern for small, high-efficiency loop antennas is shown in the figure given above. However, a portion of the radiation, called the sky wave, is radiated outward and upward to the ionosphere in the upper atmosphere. If the dipole is vertical, the pattern will be circular. If the length of the dipole, i.e. The spacing between the elements and the length of the elements according to the wavelength are also to be kept in mind while designing these antennas. For example, a wire, which is connected to an antenna. Antenna has the capability of sending or receiving the electromagnetic waves for the sake of communication, where you cannot expect to lay down a wiring system. The above diagram represents a waveguide, which acts as an antenna. The mathematical expression for aperture efficiency is as follows −. The following figure shows the geometry of parabolic reflector. The physical structure and electrical characteristics, when observed, are repetitive in nature. These non-resonant antennas are non-periodic in nature. This can be termed as Flaring. A Waveguide is capable of radiating energy when excited at one end and opened at the other end. This becomes a problem with small dimension paraboloid. This line is transposed between each adjacent pair of dipoles. The standard definition of a parabola is - Locus of a point, which moves in such a way that its distance from the fixed point (called focus) plus its distance from a straight line (called directrix) is constant. The individual national governments allocate spectrum for applications such as AM/FM radio broadcasting, television broadcasting, mobile telephony, military communication, and government usage. These resultant patterns are known as Horizontal pattern and Vertical pattern respectively. The dipole lengths and seperations are related by the formula −. The following are the advantages of Aperture antenna −, The following are the disadvantages of Aperture antenna −, The following are the applications of Aperture antenna −. Half-wave folded dipole antennas are used where optimum power transfer is needed and where large impedances are needed. They are plotted on logarithmic or commonly on dB scale. Consider an infinite plane conducting screen is taken and pierced with apertures of desired shape and size and this will be the screen of slot antenna. A receiving antenna is one, which converts electromagnetic waves from the received beam into electrical signals. Normally, its impedance is around 72Ω. An antenna is a transducer; that is, a device which converts signals in one form into another form. It is usually used with a radio transmitter or radio receiv… An antenna is an electrical device which converts electric energy into radio waves, and vice versa. Therefore, Energy transferred in time (dt) per area (A) is −. Fig 1 shows the dipole when the charges induced are in positive half cycle. When a wave is refracted, it is bent down gradually, but not sharply. Its construction is simple with small size and weight. If one end of the wire is bent, then the energy tries to escape from the transmission line, more effectively than before. converts electrical power into electromagnetic waves and vice versa It is desirable for many applications such as mobile communications, radio receivers etc. The radiation of an isotropic antenna, fills this space. In the case of an antenna, these two forms are (1) conductor-bound voltage and current signals and (2) electromagnetic waves. The terminal impedance is quite desirable for the radiation. The maximum radiation for an inverted V-antenna is at its center. The above images show super-turnstile antenna. This thesis explores the top-loading design technique to reduce the size of traditional antennas. The function of radial distance is also indicated as Φ. At the same time, standard incandescent light bulbs lose a considerable amount of energy as heat, and, hence, they function … The radiated energy, which is being wasted in such forms needs to be utilized. The isotropic radiation is nothing but Omni-directional radiation. Consider a transmission line of a quarter-wave length size. This antenna works in UHF range. All of these have to be studied in order to form an idea of how a wave propagates in the environment. It means that, the waves come out of the focal point and strike the Paraboloidal reflector. The sky wave propagation is well depicted in the above picture. The sole functionality of an antenna is power radiation or reception. The instrumentation is very big and common involves being in our daily life in the instrument system. The device or tube, if bent or terminated to radiate energy, then it is called as waveguide. The figures show the Omni directional radiation pattern in H and V planes as explained above. The antennas of different specifications can be used for these purposes. The tangent line at 0° indicates vertical polarization, whereas the line with 90° indicates horizontal polarization. In addition, the signal is filtered to avoid distortion and amplified for clear output. As discussed in detail in [3], an antenna is a transducer. If this antenna is designed for right-handed circularly polarized waves, then it will not receive left-handed circularly polarized waves and vice versa. Hence, this is the infinitely small dipole, as the name implies. Micro strip antennas are low-profile antennas. A pictorial representation of the electromagnetic spectrum is given in the following figure. To have a better understanding, consider the following figure, which represents the radiation pattern of a dipole antenna. The power radiated by an antenna, will be effectively radiated, if the antenna impedance matches the free space impedance. The far end of it is kept open and bent to provide high impedance. Transducers are used for conversion of electric waves into radio waves. Following are the types of antennas according to the frequency of operation. Figure 1 illustrates the doughnut shaped pattern in 3D and Figure 2 illustrates the figure-of-eight pattern in 2D. The following illustration shows two individuals communicating with each other. The smaller the radius, the larger the amplitude of the reactance. The other name for Super-turnstile antenna is the Batwing Antenna. Antennas radiate Electromagnetic energy to transmit or to receive information. The frequency range used for the application of Parabolic reflector antennas is above 1MHz. The emission of radiation to a maximum possible extent is nothing but the radiation intensity. It is important to consider the isotropic radiation even though it is impractical. The layer above ionosphere has very low amount of air particles and density of ionization is also quite low. The evolution of wireless technology has made this whole process very simple. Transducers and sensors are two type of devices that can provide energy. The figure clearly distinguishes the virtual height (height of wave, supposed to be reflected) and actual height (the refracted height). The following types of Lens Antennas are available −, Di-electric lens or H-plane metal plate lens or Delay lens (Travelling waves are delayed by lens media), Metallic or artificial dielectric type of lens, The following are the advantages of Lens antenna −. R is the distance between the feed and the dipole. These wires are generally used with capacitor plates on both sides, where low mutual coupling is needed. A Horn antenna may be considered as a flared out wave guide, by which the directivity is improved and the diffraction is reduced. The dipole antenna is one type of transducer which converts electrical signals into RF electromagnetic waves and radiates them at the transmitting side and to convert RF electromagnetic waves into electrical signals at the receiving side. The following figure depicts the layers present in both day time and night time in the earth’s atmosphere. The waves of higher frequencies are transmitted and received using this wave propagation technique. In a LVDT, the two secondary voltages. The following diagram shows the broad side array, in front view and side view, respectively. The elements, which are added do not possess an electrical connection between them to the driven element or the feed. The capacitor plates can be simply conductors or the wire equivalents. In figure 1, it is seen that collinear array is formed using folded dipoles, while in figure 2, the collinear array is formed by normal dipoles. ${P_{input}}$ is the input power for the antenna. $\hat{S}$ is the instantaneous Poynting vector (W/m2). Different types of antennas are manufactured depending upon the frequency range in which they are operated. The radiation pattern of a horn antenna is a Spherical Wave front. Non-resonant Antennas are those for which resonant frequency does not occur. Wireless communication is based on the principle of broadcast and reception of electromagnetic waves. Antennas with isotropic, cosine, and custom response patterns; dipole antennas; microphones with omnidirectional and custom response patterns; sonar transducers; polarization Position Transducers are also types of Input Transducers. Wire antennas are the basic types of antennas. The elements are placed so closely that each one lies in the neighbouring one’s induction field. The radiation patterns can be field patterns or power patterns. This type of horn antenna, flares out in only one direction. $\varepsilon_{A}$ is Aperture Efficiency. Thus, they play a very important role in finding the characteristics of the system. The full-wave dipole with its voltage and current distribution is shown here. This antenna works in high frequency range. Simply, gain of an antenna takes the directivity of antenna into account along with its effective performance. Each type of polarization has its own advantages and disadvantages. It means VSWR (voltage standing wave ratio, discussed in basic parameters chapter) value increases. This is otherwise called as Radiation Efficiency Factor of the antenna. These are well known and widely used antennas. When the walls of a circular wave guide are flared, it is known as a conical horn. It has lesser directivity. Now-adays, antennas have undergone many changes, in accordance with their size and shape. This mode of radiation is obtained if the dimensions of helix are small compared to the wavelength. The operational frequency range of a wave guide is around 300MHz to 300GHz. Axial or end-fire or beam mode of radiation. Hence, ionization is not proper. This D layer is responsible for the day time attenuation of HF waves. Hence, of all the types of reflector antennas, the simple parabolic reflectors and the cassegrain feed parabolic reflectors are the most commonly used ones. The features of small loop antennas are −. 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