Antenna array DEFINITION + An antenna array is a system of similar antennas oriented similarly to get greater directivity in a desired direction. An antenna array is a combination of two or more antenna elements that can be placed in a specific geometry Elements Individual antennas of an antenna array system are called elements Uniform linear array In which the elements are fed with currents of equal magnitude with uniform progressive phase shift along the line. Antenna Array types Based on the geometrical arrangement antenna arrays are of 3 types 1. Linear antenna arrays Ina linear antenna array, antenna elements are placed along one axis 2.Planar antenna arrays e.g., square, rectangle, circle etc 3.Conformal antenna arrays e.g., a sphere, cylinder, paraboloid, etcAdvantages of antenna arrays 1.Higher directivity + te 2.Lower side lobes 3.Narrow beam : = 4.Steerable beam(radiation direction change). In an array of identical elements, there are at least five controls that can be used to shape the overall pattern of the antenna. These are: 1. The geometrical configuration of the overall array (linear, circular, rectangular, spherical, etc.) . The relative displacement between the elements . The excitation amplitude of the individual elements . The excitation phase of the individual elements . The relative pattern of the individual elements Uk WN Antenna types based on radiation patterns 1.Broad side array 2.End fire array 3.Collinear array 4.Parasitic arrayAn antenna, when individually can radiate an amount of energy, in a particular direction, resulting in better transmission, how it would be if few more elements are added it, to produce more efficient output. It is exactly this idea, which led to the invention of Antenna arrays. An antenna array can be better understood by observing the following images. Observe how the antenna arrays are connected.An antenna array is a radiating system, which consists of individual radiators and elements. Each of this radiator, while functioning has its own induction field. The elements are placed so closely that each one lies in the neighbouring one's induction field. Therefore, the radiation pattern produced by them, would be the vector sum of the individual ones. The following image shows another example of an antenna array.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. The antennas radiate individually and while in array, the radiation of all the elements sum up, to form the radiation beam, which has high gain, high directivity and better performance, with minimum losses. NahrantananAdvantages The following are the advantages of using antenna arrays — 5 The signal strength increases 5 High directivity is obtained 5 Minor lobes are reduced much ® High Signal-to-noise ratio is achieved ® High gain is obtained 5 Power wastage is reduced 5 Better performance is obtained Disadvantages The following are the disadvantages of array antennas - 5 Resistive losses are increased 5 Mounting and maintenance is difficult 5 Huge external space is requiredApplications The following are the applications of array antennas Used in satellite communications Used in wireless communications Used in military radar communications Used in the astronomical studyTypes of Arrays The basic types of arrays are - ® Collinear array Broad side array End fire array Parasitic array Yagi-Uda array & Log-peroidic array & Turnstile array & Super-turnstile arrayArray factor ¢ The array factor is the ratio of the magnitude of resultant field to the magnitude of the maximum field. Ed |Emaxl But Es =2 a Nae Le — me) rae 2 A.F. = rr fe]Principle of Pattern Multiplication Antenna & Wave Propagation 1. The principle of pattern multiplication states that “the radiation pattern of an array is the product of the pattern of the individual antenna with the array pattern of isotropic point sources each located at the phase centre of the individual source.” 2. The array pattern is a function of the location of the antennas in the array and their relative complex excitation amplitudes. 3. The phase centre of the array is the reference point for total phase pattern. 4. Advantage: It helps to sketch the radiation pattern of array antennas rapidly from the simple product of element pattern and array pattern.5. Disadvantage: This principle is only applicable for arrays containing identical elements. 6. The principle of pattern multiplication is true for any number of similar sources. 7. Total phase pattern is the addition of the phase pattern of the individual sources and that of the array of isotropic point sources. The resultant pattern of an array of non-isotropic identical radiators is given by E=[f (8, @) x F (6, @)] * [fp (8, b) + Fr (8, b)] where, f (8, db) = element field pattern fp (8, @) = element phase pattern F (6, #) = array factor of isotropic elements Fp (8, @) = phase pattern of the array of isotropic elements. The angles 6 and @ respectively represent the polar and azimuth angles.Applications A few of the applications of the Yagi antenna are: e Yagi UDA antennas are employed in TV signal reception as this antenna holds good receiving capability. ¢ Used in defense applications. e Employed in the astronomical domain. e Also used in radio astronomy.__/ Yagi-Uda Antenna Yagi-Uda antenna is the most commonly used type of antenna for TV reception over the last few decades. It is the most popular and easy-to-use type of antenna with better performance, which is famous for its high gain and directivity Frequency range The frequency range in which the Yagi-Uda antennas operate is around 30 MHz to 3GHz which belong to the VHF and UHF bands. Folded dipole ty) Reflector Dipole Director ose. O4SA O55 | 035k 025AAdvantages, Disadvantages and Applications of Yagi-Uda Antenna Advantages The following are the advantages of Yagi-Uda antennas “ High gain is achieved. High directivity is achieved. + Ease of handling and maintenance. Less amount of power is wasted. Broader coverage of frequencies. Se ate ot ee ae Se % Disadvantages The following are the disadvantages of Yagi-Uda antennas * Prone to noise. Prone to atmospheric effects. Applications The following are the applications of Yagi-Uda antennas Mostly used for TV reception. « Used where a single-frequency application is needed.Applications A few of the applications of the Yagi antenna are: e Yagi UDA antennas are employed in TV signal reception as this antenna holds good receiving capability. ¢ Used in defense applications. e Employed in the astronomical domain. e Also used in radio astronomy.A folded dipole is an antenna, with two conductors connected on both sides, Folded Dipole Antenna 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. The directivity of Folded dipole Antenna is bi-directional. The input impedance is higher. 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. If the Radii of the 2 conductors are equal, then equal currents in both the conductors, in the same direction, i.e currents are equal in magnitude and phase in the 2 dipoles. The total power developed in folded dipole is equal to that developed in the conventional dipoles, therefore the input or terminal impedance of folded dipole is greater than that of the conventional dipole. It can be proved that the input impedance at the terminals of a folded dipole antenna is equal to the square of number of conductors comprising the antenna times the impedance at the terminals of a conventional dipole.120° 60" 150 oo 180" o 210" 30° 0 —“300" 270 Side view 7 Advantages ‘The following are the advantages of half-wave folded dipole antenna — = Reception of balanced signals. * Receives a particular signal from a band of frequencies without losing the quality. A folded dipole maximizes the signal strength. High input impedance Wide band in frequency Acts as built in reactance components network Disadvantages The following are the disadvantages of half-wave folded dipole antenna — * Displacement and adjustment of antenna is a hassle. * Outdoor management can be difficult when antenna size increases. Applications The following are the applications of half-wave folded dipole antenna — "Mainly used as a feeder element in Yagi antenna, Parabolic antenna, turnstile antenna, log periodic antenna, phased and reflector arrays, etc. "Generally used in radio receivers. \ "Most commonly used in TV receiver antennas.Two point sources with current of equal magnitude but with opposite phaseTwo point sources with current of equal magnitude but with opposite phase 7 W ny P ae iz eg) oy Rearranging the term in above equation } y we get, ee ae fe cere \ iv Pee By Trigonometric identity, E, seed 7 2 But Phase angle = W = B dcos@Two point sources with current of equal magnitude but with opposite phase Maxima direction ¢ The total field is maximum when a ed Merb alla ¢ Hence condition for maximum field is given by Paw xe oC") Va aT ea ) Sol, ¢ Consider Spacing between point source d = ees or) Sei oe’) = sin-+(+1) aaa CL , Where n = 0,1,2... If n =0, thenBem Sei meleca-M Uae me equal magnitude but with opposite phase ir me Lieve Cela) (a) 3 ¢ The total field is minima when sin Meal ite ¢ Hence condition for minima field is given by Paw 4 :xelels\) ae i ore * Consider Spacing between point source d = . (1 _ : sin(=cosd) =0 ae sin71(0) =+ nz, Where n = 0,1,2... If n =0, then orc =0 Din = 90° or 270°Two point sources with current of equal magnitude but with opposite phase Half power point direction ¢ The condition for Half power point is given by a ed) 9g eae aes eo) a = eo) = +(2n+1)5, Where n = 0,1,2... If n =0, then = COSB ppp =e n ook Dippp = 60° or 120°Two point sources with current of equal magnitude but with opposite phas Field patternTwo point sources with current of equal magnitude and with same phase Let the distance between point P and point sources A, and A, lol om eur ]aleM Om a=s) 01-100 NYZ-1VA As these radial distances are extremely large as compared & with the distance of separation between two point sources d, we Can assume, rn ore f The radiation from the point source A, will reach earlier at point P than that from point source A, because of the path Ola cnaceTwo point sources with current of equal magnitude and with same phase * Hence Path difference is given by, Path difference = d cos@ ¢ Path difference can be expressed in terms of wavelength as, Path difference = d a Phase angle =W = 2n(Path difference) (o[exe)17) er iv ) p= an uO But Phase shift = £8 = ais W =f dcos@ radTwo point sources with current of equal magnitude and with same phase oPTwo point sources with current of equal magnitude and with same phaseTwo point sources with current of equal magnitude and with same phaseTwo point sources with current of equal magnitude and with same phase Maxima direction But B = i cos(* or) iat po ei cos-1+1=+n1, Where n = 0,1,2... If n =0, then is 2 (of0)1 Ed 0) Dimax = 90° or 270°Two point sources with current of equal magnitude and with same phase Minima direction core cong = 0 y ot omen Oe aaCAne ees Vise Ren ae (On ae man Onder ne > COS 5 COSO @.,,, = 0 minTwo point sources with current of equal magnitude and with same phase Half power point direction * The condition for Half power point is given by oo aed =+ a eye cos(= oe) ae ee < NI a 3 =cos71(+4) = 7 _ - cos@ = cos (+ 7 = a CAS Ore Where n = 0,1,2... If n =0, then sid ue paca — rm" eh is 7 Dippy = 60° or 120°Two point sources with current of equal magnitude and with same phase atalem e-1aclaalReflector length = 0.495*A Dipoe length = 0.473*A Director length = 0.440*} Reflector to Dipole spacing = 0.125*) Dipole to Director spacing = 0.125*} A=e/f A-Wavelength in meters c-Velocity of propagation in air(3*10“8m/s) f-Carrier frequency in MHzYagi Antenna Calculator Operating Frequency in MHz (input1) : Reflector Length Output#1): 0.1649999999999¢ Dipole Length Output#2): 0.1576666666666¢ Director length Output#3): 0.1466666666666¢ Reflector to Dipole Spacing (Output#4): 0.0416666666666¢ Dipole to Director Spacing (Output#5): 0.0416666666666¢EXAMPLE 1: Consider an array of four elements (isotropic or non-directional): Fig: Array of four elements « Elements are spaced at A/2. « Elements 1 and 2 are considered as one unit, 3 and 4 are considered as one unit. e Since the elements are identical, both the units have the same radiation pattern. ¢ The unit pattern is the pattern of two elements spaced at A/2, given below:d=2/2, a= Fig: Pattern of two isotropic elements spaced M2 * The units represented by A and B are separated by A. These two units are considered to be one unit whose radiation pattern is shown below: IK— *»§—4 Fig: Pattern of two isotropic elements separated by A¢ Therefore, the resultant pattern is given by the product of unit pattern (A/2 spacing) of 1 and 2 elements or 3 and 4 elements and a group pattern (A spacing) of A and B. e e x | Unit pattern Group pattern Resultant pattem Fig: Resultant pattern of four isotropic elements spaced at A/2