Imperial Journal of Interdisciplinary Research (IJIR) Vol-2, Issue-8, 2016 ISSN: 2454-1362, http://www.onlinejournal.in A Review on Fundamental of Antenna Rachna Devi1 & Naveen Rawat2 1PG Student, Department Of Electronics and Communication Engineering 2Assistant Professor, Department Of Electronics and Communication Engineering Prannath Parnami Institute, Chaudharywas, Hisar, Haryana 112413, India Abstract— Antennas are useful for many applications elements or surfaces with no electrical connection to due to their broadband characteristics and relative the transmitter or receiver, such as parasitic simplicity. It has long been known that the antenna elements, parabolic reflectors or horns, which serve has broadband characteristics and good radiation to direct the radio waves into a beam or other efficiency. The design considerations in reducing the desired radiation pattern. size of top loaded conical antenna by using posts with [1.1] Fundamentals of Antenna : lumped resistive loading are presented. The antenna Different types of application requires antenna with designed is compact in size, Size reduction, different parameters. Like for cellular mobile bandwidth and gain enhancement. communication a circular polarized antenna is requires with high gain and for satellite Keywords— GPS , LMR , communication in downlink a high directive antenna is required. The selection and the performance of an I. INTRODUCTION antenna is characterize on the basis of some An antenna is an electrical device which parameters these are Bandwidth, Polarization, changes electric power into radio waves, and vice radiation, Pattern, Efficiency, Gain. These parameters versa. It is generally used with a radio are described in brief below: transmitter or radio receiver. In transmission, a radio Radiation Patterns: transmitter supplies a high frequency alternating Also known as Antenna Pattern or Far-Field Pattern. electric current oscillating at radio frequency to the Radiation pattern of an antenna is graphical antenna's workstations, and the antenna radiates the representation of radiated power at as fix distance energy from the current as electromagnetic from the antenna as a function of azimuth and waves (radio waves). At reception, an antenna elevation angle. So the antenna pattern shows that captures some of the power of an electromagnetic how the power is distributed in the space. For wave in order to produce a small voltage at its simplicity the radiation pattern can be drawn in 2D terminals that is applied to a receiver to be amplified. plane for different azimuth and elevation angle Antennas are vigorous components of all equipment referred as azimuth plane pattern and elevation plane that uses radio. They are used in systems such pattern [22]. It is good to plot the radiation patterns in as radio broadcasting, broadcast television, two-way Cartesian (rectangular) coordinates, especially when radio, communications receivers, radar, cell phones, antenna radiation pattern consists of different side and satellite communications, as well as other lobes and where these side lobes levels plays an devices such as garage door openers, wireless important role. There are different types of antenna microphones, Bluetooth-enabled devices, wireless patterns described below: computer networks, baby monitors, and RFID tags on a. Omnidirectional Antennas: merchandise. Omnidirectional antenna can be referred as an Typically an antenna consists of an organization of antenna has radiation pattern uniform and equally metallic conductors, electrically connected to the distributed in one plane generally referred to receiver or transmitter. An oscillating current horizontal planes. Some applications like mobile, cell of electrons forced through the antenna by a phones, FM radios, walkie talkies, wireless computer transmitter will create an oscillating magnetic networks, cordless phones, GPS, many portable field around the antenna elements, while handheld devices and in base stations antenna the charge of the electrons also creates an required with the characteristics that can radiate oscillating electric field along the elements. These equally in a plane. Omnidirectional antenna has time-varying fields radiate away from the antenna radiation pattern like doughnut shaped. Slot antenna into space as a moving transverse electromagnetic and dipole antenna, whip antenna, discone antenna, field wave. duck antenna are some good example of low gain Antennas can be designed to transmit and receive omnidirectional antenna. Omnidirectional antenna radio waves in all horizontal directions equally, or with high gain can also be design by narrowing the preferentially in a particular direction. In the latter beam width of the antenna in the vertical plane will case, an antenna may also include additional result in concentrating of energy in horizontal plane. Imperial Journal of Interdisciplinary Research (IJIR) Page 49 Imperial Journal of Interdisciplinary Research (IJIR) Vol-2, Issue-8, 2016 ISSN: 2454-1362, http://www.onlinejournal.in Therefore a narrow beam width antenna has a high characteristics. Bandwidth can be described on the gain and different type of omnidirectional antenna basis of gain, axial ratio bandwidth, and Impedance with various gains can be design. A 0dBd gain or VSWR bandwidth .Impedance bandwidth related antenna radiates more efficiently in vertical plane. to Q factor can be described as b. Directional Antennas: As the name suggest directional antennas concentrate their radiation in a particular direction. They are also BW = known as Beam Antenna. They are useful in some point to point application like satellite communication, in base station antenna to transmitting energy in a particular sector. Yagi, horn, log-periodic antenna and panel antenna are some example that have directional radiation pattern. c. Isotropic radiator: An Isotropic antenna has the radiations distributed uniformly in all direction. An isotropic antenna radiates all the power given. It is an imaginary antenna does not exist practically. It is used as a reference to compared with the other antennas. Figure 1: Bandwidth The Fraunhofer distance is related to antenna’s larger dimension and can be calculated as: TYPES OF ANTENNA: Antennas can be classified in several ways. One way is the frequency band of operation. Others include Where physical structure and electrical/electromagnetic R= distance from antenna design. The antennas commonly used for LMR both D= larger dimension of antenna at base stations and mobile units represent only a λ= wavelength in free space very small portion of all the antenna types. Directivity: Dipoles and Monopoles : Directivity of an antenna shows that how much the The vertical dipole or its electromagnetic equivalent, antenna is able to radiate in a particular given the monopole could be considered one of the best direction. It is a major requirement when antenna is antennas for LMR applications. It is omnidirectional working as a receiver. Directivity in its simple form (in azimuth) and, if it is a half-wavelength long, has a can be described as the comparison of maximum gain of 1.64 (or G = 2.15 dBi) in the horizontal plane. radiation intensity to average radiation intensity As A center-fed, vertical dipole is illustrated in figure 2(a). Although this is a simple antenna, it can be Directivity = difficult to mount on a mast or vehicle. The ideal Gain: vertical monopole is illustrated in figure 2(b). It is Antenna Gain is also referred as Power gain or half a dipole placed in halfspace, with a perfectly simply Gain. This combines of antenna efficiency conducting, infinite surface at the boundary. and directivity. When it is calculated with efficiency Eantenna and directivity D it is referred as Power Gain. Power Gain = Eantenna . D When the directivity with a particular direction is given it is known as Directive Gain. Directive Gain (θ,π) = Eantenna. D (θ,π) Antenna polarization: Polarization of an antenna is polarization of the electromagnetic waves radiated from the antenna. Polarization on a wave is the orientation or path traces by the electric field vector as a function of time. Polarization can be categorized in three parts : a. Linear polarization Figure 2. The vertical dipole and its electromagnetic equivalent, b. Circular polarization the vertical monopole c. Elliptical polarization A monopole over an infinite ground plane is Antenna Bandwidth: theoretically the same (identical gain, pattern, etc., in Antenna bandwidth is another important parameter of the half-space above the ground plane) as the dipole antenna can be described as the range of frequencies in free space. In practice, a ground plane cannot be over which antenna justify some desired Imperial Journal of Interdisciplinary Research (IJIR) Page 50 Imperial Journal of Interdisciplinary Research (IJIR) Vol-2, Issue-8, 2016 ISSN: 2454-1362, http://www.onlinejournal.in infinite, but a ground plane with a radius (usually one or two) reflector elements and one or approximately the same as the length of the active more (usually two or more) director elements. Figure element, is an effective, practical solution. The flat 5 shows a Yagi antenna with one reflector, a folded- surface of a vehicle’s trunk or roof can act as an dipole active element, and seven directors, mounted adequate ground plane. for horizontal polarization. Omnidirectional Base antenna: For base-station installations (where an omnidirectional pattern is desired), there are two Figure 5. The Yagi antenna — (a) three