Micro Strip Patch Antenna

little moorage Patch advanceChapter 1 entreThe project which we arrest chosen to do as our final year project for the under graduate program involves the characterization of sharp comb objet dart overture.In this project we have carried out simulations of different types of transmitting aerials, which include dipole, monopole and patch. The propose of designing all of these is to score acquaintance and experience in the designing of overtures for different gets by utilize commercially available CEM. The frequency band, which we have chosen as our relevant band, is the GSM-900 band, which is of wide use in the cellular ne twork. The purpose of choosing this band is to kick upstairs valuable kip downledge of this frequency band. transmitting aerials be a first harmonic part of every system in which wireless or shrive space is the medium of communication. Basically, an feeler is a transducer and is designed to transmit or start electromagnetic hustles. It is a transducer as it converts radio frequency galvanizingal currents into electromagnetic waves. Common applications of feelers include radio, television broadcasting, point-to-point radio communication, wireless networks and radar. A detailed pick out of antennas is discussed in chapter two and chapter three of this report.The CEM parcels that we have used for the designing include XFDTD provided by Remcom Inc. and CST Microwave Studio, which is a full wave, 3-Dimensional, Electromagnetic simulation softwargon and CST Microwave Studio. XFDTD utilizes a numerical electromagnetic write in code for antenna design, that is, the finite difference quantify domain technique (FDTD). Finite-difference time-domain (FDTD) is a popular computational electrodynamics mildew technique.The first antenna complex body part sculptural is the dipole. A dipole antenna consists of two conductors on the same axis with a fount at the center. It is also frameworked in XFDTD by fol confuseding the p rocedure provided by the softwargon and mentioned in the Appendix. The results atomic number 18 verified by comparing with analytical papers of (lambda/2) dipole. After completing this, the next goal is to model the micro strip (patch) antenna which is one of the main focuses of this project. It comprises of a metallic patch bonded to a nonconductor substrate with a metal layer bonded to the opposite side of the substrate forming a ground carpenters plane. This metal layer is very edit out. Hence, it can be fictive very easily using printed circuit techniques. Therefore, they argon inexpensive to manufacture and argon easily integrate able with microwave integrated circuits.The softw be poser is carried out in XFDTD and on CST Microwave Studio. The verification of the results with the experimental results entertained leads to the final phase and the conclusion of the project.1.1 PurposeThe purpose of this project is to take a crap knowledge and experience about computationa l electromagnetic, as it applies to antenna design. It was also our sole purpose to gain experience in fabrication and experimental characterization of micro strip patch antennas. To achieve these objectives we used two commercially available CEM softw ares, XFDTD and CST Microwave Studio, to design a micro strip patch antenna for 900 MHz. We also gained experimental experience by characterizing the return loss of this patch antenna using the vector network analyzer.1.2 Project Scope1.2.1 DescriptionWe go out study some basic types of antennas extending basic knowledge of antenna to complex antenna designs such as micro strip patch antennas and also modeled them on antenna design and simulation software. This report has been divided into a number of chapters each discussing a different stage of the project. They are briefly expound to a lower placeChapter 2 describes the fundamentals of antennas and thoroughly discusses the theory of fundamental parameters and quantities of anten na. In this chapter the basic concept of an antenna is discussed and its running(a) is explained. Some critical performance parameters of antennas are also discussed. Finally, some common types of antennas are also discussed for understanding purposes.Chapter 3 discusses the important characteristics of antennas as radiators of electromagnetic energy. These characteristics are normally considered in the furthermost sphere of influence as the antenna pattern or radiation pattern of an antenna is the three-dimensional plot of its radiation at outlying(prenominal) work. It also discusses the types of antenna patterns in detail. Some important mathematical equatings are also solved in this chapter for the better understanding of how an antenna works.Chapter 4 discusses in detail the modeling of the half(prenominal) wave dipole and micro strip patch antenna using XFDTD. It describes the modeling of the antenna, the feeding, and the resultant plots obtained. Furthermore it concludes with comparison of the results obtained with the simulations already available in the software.Chapter 5 discusses the theory, calculations involved and the fabrication of the micro strip (patch) antenna in detail. The calculations for the dimensions of the rectangular patch in detail are in this chapter. Also, this chapter describes the results obtained through simulation of the model on the software CST Microwave Studio.Chapter 6 discusses conclusions drawn from the whole project.Chapter 2Antenna FundamentalsIn this chapter, the basic concept of an antenna is discussed and its working is explained.Next, some critical performance parameters of antennas are discussed. Finally, some commontypes of antennas are introduced. The treatment for these is taken from the reference 4, 6 and 9.2.1 IntroductionAntenna is a metallic structure designed for radiating and receiving electromagneticenergy. An antenna acts as a transitional structure between the guiding devices (e.g. waveguide, trans mission system line) and the free space. The official IEEE definition of an antenna as given byStutzman and Thiele 9 is as followsThat part of a transmitting or receiving system that is designed to radiate or receive electromagnetic waves.2.2 How an Antenna radiates?In order to understand how an antenna radiates, we have to first know how radiation exits. Aconducting wire radiates because of time-varying current or an accele proportionalityn or subnormality of charge. If there is no motion of charges in a wire, no radiation will occur, since no flow of current occurs. Radiation will not occur even if charges are moving with uniform or constant velocity along a straight wire. Also, charges moving with uniform velocity along a curved or bent wire will produce radiation. If charge is oscillating with time, then radiation will occur even along a straight wire as explained by Balanis 4.The radiation pattern from an antenna can be further understood by considering a voltage source conne cted to a two-conductor transmission line. When a sinusoidal voltage source is applied across the transmission line, an galvanizing automobile automobile field is generated which is sinusoidal in nature. The bunching of the electric lines of force can indicate the order of magnitude of this electric field. The free electrons on the conductors are forcefully dis set by the electric lines of force and the motion of these charges causes the flow of current, which leads to the introduction of a magnetic field.Due to time varying electric and magnetic fields, electromagnetic waves are created which travel between the conductors. When these waves approach open space, connecting the open ends of the electric lines forms free space waves. As the sinusoidal source continuously creates electric disturbance, electromagnetic waves are generated continuously and these travel through the transmission line, the antenna and are radiated into the free space.2.3 Near and Far Field RegionsThe field patterns of an antenna, change with distance and are associated with two types of energy radiating and reactive energy. Hence, the space surrounding an antenna can be divided into three portions.Figure 2.1 Field regions around an antennaThe three regions that are depicted in above figure are described as2.3.1 Reactive Near-Field RegionIn this region the reactive field dominates. The reactive energy oscillates towards and away from the antenna, thus appearing as reactance. In this region, energy is stored and no energy is dissipated. The ou shapeost boundary for this region is at a distance (2.1)where R1is the distance from antenna surface, D is the largest dimension of the antenna and is the wavelength.2.3.2 radiate Near-Field RegionThis region also called Fresnel region lies between the reactive near-field region and the far field region. In this region, the angular field distribution is a bureau of the distance from the antenna. reactive fields are smaller in this field as co mpared to the reactive near-field region and the radiation fields dominate. The outermost boundary for this region is at a distance(2.2)where R2is the distance from the antenna surface.2.3.3 Far-Field RegionThe region beyond is the far field region also called Fraunhofer region. The angular field distribution is not dependent on the distance from the antenna in this region. In this region, the reactive fields are absent and lone(prenominal) the radiation fields personify and the function density varies as the inverse square of the radial distance in this region.2.4 The Hertzian DipoleA Hertzian dipole or minute dipole, which is a piece of straight wire whose length L and diameter are both very small, compared to one wavelength. A uniform current I is assumed to flow along its length. Although such a current element does not exist in real life, it serves as a building seal off from which the field of a practical antenna can be calculated (Sadiku 6).Consider the Hertzian dipole s hown in figure. We assume that it is located at the radical of a coordinate system and that it carries a uniform current. i.e. I=I cost. The decelerate magnetic vector potential at the field point, imputable to dipole is given by(2.3)Where I is the retarded current given by(2.4)Where =/u=2/, and u=1/ the current is said to be retarded at point under consideration because there is a propagation time delay r/u or phase delay.By heterotaxy we may also write A in phasor form ast(2.5)Transforming this vector in Cartesian to spherical coordinates yieldsWhere simply(2.6)We find the E field using(2.7)(2.8)Where,A close observation of the field equations reveals that we have terms varying as The 1/ term is called the electrostatic field since it corresponds to the field of an electric dipole. This term dominates over other terms in a region very close to the hertzian dipole. The is called the inductive field, and it is predictable from the from the Biot Savart law. The term is important o nly at near field, that is, at distances close to the current element. The 1/r term is called the far field or radiation field because it is the only term that remains at the far zone, that is, at a point very far from the current element.Here, we are mainly concerned with the far field or radiation zone (r1), where the terms in can be neglected in favor of the 1/r term. Thus at far field,(2.9)The radiation terms of and are in time phase and orthogonal just as the fields of a uniform plane wave. The near and far zone fields are determined respectively to be the in equalities We define the boundary between the near and far zones by the value of r given by . where d is the largest dimension of the antenna.The time amount power density is obtained as)(2.10)Substitution yields time average radiated power asButAnd hence above equation becomesIf free space is the medium of propagation, =120 and(2.11)This power is equivalent to the power dissipated in a fictitious subway system by curren tThat is,(2.12)Where is the root mean square value of I. From above equations we obtainOr(2.13)The resistivity is a characteristic property of the hertzian dipole antenna and is called its radiation resistance. We observe that it requires antennas with large radiation resistances to deliver large amounts of power to space. The above equation for is for a hertzian dipole in free space.2.5 Half Wave Dipole AntennaThe Half Wave dipole is titled after the fact that its length is half of the wavelength i.e. . It is excited through a thin wire fed at the midpoint by a voltage source connected to the antenna via a transmission line. The radiated electromagnetic field overdue to a dipole can be obtained if we consider it as a chain of hertzian dipoles (Sadiku 6)./2 I zx yIFigure 2.3 Half Wave DipoleThe magnetic Vector potential P due to length dl of the dipole carrying a phasor current is(2.14)We have assumed a sinusoidal current distribution because the current must vanish at the ends o f the dipole. Also note that the actual current distribution on an antenna is not precisely known. It can be determined by using Maxwells equations subject to the boundary conditions on the antenna by a mathematically complex procedure. The sinusoidal current assumption approximates the distribution obtained by solving the boundary value problem and is commonly used.OYXZFigure 2.4. Magnetic field at point oIf r , thenHence we can substitute in the denominator of the first equation where the magnitude of the distance is needed. In the numerator for the phase term, the difference between and is significant, so we will replace by . We maintain the cosine term in the exponent plot neglecting it in the denominator because the exponent involves the phase constant while the denominator does not. So,(2.15) apply the following integrating equation,Applying this equation gives on (2.15)Since and the above equation becomes,Using identity = 2cos x, we obtain(2.16)We use in conjunction with the fact that to obtain electric and magnetic fields at far zone as(2.17)The radiation term of and are in time phase and orthogonal.We can obtain the time-average power density as(2.18)The time average radiated power can be determined asIn the previous equations has been substituted assuming free space as the medium of propagation. The last equation can be written asChanging the variables, and using partial fractions reduces the above equation toReplacing with in the first integrand with in the second results in(2.19)Solving the previous equation of yields value of . The radiation resistance for the half wave dipole antenna is readily obtained from the following equation and comes out to be.(2.20)Chapter 3Antenna CharacteristicsIn the previous chapter we have discussed the basics of antennas and the main(a) types of antennas. Now we will discuss the important characteristics of antennas as radiators of electromagnetic energy. These characteristics are normally considered in the far field and are as follows. And have been set from the references 4, 6 and 9.3.1 Antenna PatternsThe Antenna Pattern or Radiation Pattern of an antenna is the three-dimensional plot of its radiation at far field. There are two types of Radiation Patterns of antennas. The Field and the Power Pattern.3.1.1 Field PatternWhen the amplitude of the E-field is plotted, it is called the Field Pattern or the Voltage Pattern. A three dimensional plot of an antenna pattern is avoided by plotting separately the normalized versus for a constant which is called an E-Plane pattern or vertical pattern and the normalized versus for called the H-plane pattern or horizontal pattern. The normalization of is with respect to the supreme value of the so that the upper limit value of the normalized is unity as explained by Sadiku 6.For Example, for the hertzian Dipole, the normalized comes out to be,(3.1)Which is independent of From this equation we can obtain the E-plane pattern as the polar pattern of b y varying from 0 to 180 degrees. This plot will be symmetric about the z-axis. For the H-plane pattern we set so that , which is a circle of radius 1.3.1.2 Power PatternWhen the square of the amplitude of E is plotted, it is called the power pattern. A plot of the time-average power, for a fixed distance r is the power pattern of the antenna. It is obtained by plotting separately versus for constant and versus for constant.The normalized power pattern for the hertzian dipole is obtained from the equation.(3.2)3.2 Radiation IntensityThe Radiation intensity of an antenna is delimitate as(3.3)Using the above equation, the total average power radiated can be show as(3.4)(3.5)Where d= is the differential solid angle in atomic number 38 (sr). The radiation intensity is measured in watts per steradian (W/sr).The average value of is the total radiated power divided by that is,(3.6)3.3 Directive GainThe directive gain of an antenna is a measure of the concentration of the radiated power in a particular managementIt can also be regarded as the ability of the antenna to direct radiated power in a given pedagogy. It is unremarkably obtained as the ratio of radiation intensity in a given direction to the average radiation intensity, that is(3.7)may also be expressed in terms of directive gain as(3.8)The directive gain depends on antenna pattern. For the hertzian dipole as well as for the half wave dipole is maximum at and minimum at . Hence they radiate power in a direction government note to their length. For an isotropic antenna, . However, such an antenna is not in reality but an ideality.The directivity D of an antenna is the ratio of the maximum radiation intensity to the average radiation intensity. D is also the maximum directive gainSo,(3.9)Or,(3.10)For an isotropic antenna, D=1, which is the smallest value that D can have. For the hertzian dipole, as derived in equation (3.7)For half wave dipole,Where, =120 and(3.11)3.4 Bandwidth (Impedance Bandwidth)By de finition Bandwidth of an antenna is the difference between the highest and the lowest operational frequency of the antenna.Mathematically,(3.12)If this ratio is 10 to 1, then the antenna I classified as a broadband antenna.Another definition for Bandwidth isWhere,.3.5 GainWe define that G is the actual gain in power over an ideal isotropic radiator when both are fed with same power. The reference for gain is the input power, not the radiated power. This efficiency is defined as the ratio of the radiated power () to the input power ().The input power is transformed into radiated power and surface wave power while a small portion is dissipated due to conductor and dielectric losses of the materials used. The power gain of the antenna as(3.13)The ratio of the power gain in either specified direction to the directive gain in that direction is referred to as the radiation efficiency of the antenna i.e.(3.14)Antenna gain can also be specified using the total efficiency instead of the rad iation efficiency only. This total efficiency is a combination of the radiation efficiency and efficiency conjugate to the impedance matching of the antenna. Hence, from equation 3.14(3.14(a))3.6 PolarizationThe definition for polarization can be quoted from Balanis 4 asPolarization of a radiated wave can be expressed as that property of an electromagnetic wave describing the time-varying direction and relative magnitude of the electric field vector specifically, the figure traced as a function of time by the extremity of the vector at a fixed location in space, and in the sense in which it is traced, as observed along the direction of propagation. Polarization then is the curve traced by the end point of the arrow representing the instantaneous electric field. The field must be observed along the direction of propagation.3.7 Return LossThe Return Loss (RL) is the parameter which indicates the amount of power that is lost to or consumed by the load and is not reflected back as wave s are reflected which leads to the formation of standing waves. This occurs when the transmitter and antenna impedance do not match. Hence, the RL is a parameter to indicate how well the matching between the transmitter and antenna has taken place.The RL is given as(3.15)For perfect matching between the antenna and transmitter, RL = and = 0 whichmeans no power is being reflected back, whereas a = 1 has a RL = 0 dB, which implies thatall incident power is reflected. For practical applications a RL of -9.54 dB is acceptable.Chapter 4 clay sculpture of Half-Wave Dipole Micro Strip Patch Antenna Using XFDTD4.1 IntroductionFor the purpose of modeling and simulation of antennas we have used modeling softwares, which are widely used in industries. These softwares are specially used for the purpose of electromagnetic (EM) modeling, which refers to the process of modeling the interaction of electromagnetic fields with physical objects and the environment.The first such software brought i nto use is XFDTD. It is a three-dimensional full wave electromagnetic solver based on the finite difference time domain method. It is fully three-dimensional. Complex CAD objects can be imported into XFDTD and have and editing can be done within XFDTD using the internal graphical editor. It is a powerful software which offers a lot of options to its users.This software has been initially used for modeling of basic antennas to get familiarity with interface and working of the software. Dipole is one of such basic antennas with a simple structure as the name suggests dipole antenna consists of two wires on the same axis with a source applied at the center point.In this chapter, we begin with the analysis of a half-wave dipole antenna by derivation of field equations and the MATLAB plot. After the analysis the modeling is done using XFDTD. Finally, all the results are matched by plotting the data in MATLAB.4.2 Derivation of Vector Magnetic PotentialWe begin with the derivation done in chapter 2 for of the radiated fields for a half-wave dipole antenna in equation 3.11 which gives us the following expression for(4.11)4.2.1 MATLAB Plots of Half Wave Dipole AntennaThe expression can be plotted in MATLAB using the following codeclear alltheta = 0360*pi/180F = cos((pi/2)*cos(theta))./(0.0000001 + sin(theta))Pn = F./max(F)Pn=abs(Pn)title (POLAR PLOT OF HALF WAVE DIPOLE )polar(0,1) hold onpolar (theta,Pn,r)The MATLAB generated plot of normalized electric field for half-wave dipole for above code is as followsFigure 4.1 MATLAB plot for Normalized Electric Field4.3 Modeling of Half Wave Dipole Using XFDTD4.3.1 IntroductionXFDTD is a full wave, 3D, Electromagnetic Analysis Software. XFDTD used solid, dimension based modeling to create geometries. To create geometry, library objects and editing functions may be used. Modeling of half-wave dipole antenna was carried out in XFDTD to test the softwares capability of generating far field radiation pattern. And also to get in d epth knowledge of XFDTD sooner using it for the modeling of patch antennas, which is the foremost objective of this project.4.3.2 Validity of ModelAs in the previous section the electromagnetic theory of half-wave dipole was analyze and its mathematical equations for normalized radiated field was derived and plotted. This plot will be our reference plot while doing the modeling of half-wave dipole.4.3.3 Modeling of Half Wave DipoleAs we know the length of a half-wave dipole antenna should be half the wavelength of the operating carrier wave frequency. Thus the dipole modeled in XFDTD has the following specifications aloofness of 30cmFrequency used 1 GHzThin wire was used to create the dipoleSource was attached in the middleFigure below shows the geometry of dipole being modeled in XFDTD.Figure 4.2 XFDTD geometry of Half-Wave Dipole4.3.4 ResultsThe far fields of dipole antenna were calculated by XFDTD and plots were obtained for far field versus both Phi and Theta, as shown in Figur e 4.3 Figure 4.4. The results matched with the theoretically established results.Figure 4.3 Far Field vs. Theta Figure 4.4 Far Field vs. Phi4.3.5 Plotting XFDTD Results in MATLABThe data for far fields from XFDTD was exported and matched with the theoretical results in MATLAB for the purpose of confirming the results. Help was taken from the XFDTD reference manual to learn how to export far field data.The XFDTD file was copied and the addendum was changed to .dat and name was changed to XFTDT.dat Next this file was read by MATLAB using the MATLAB code providedangle1, a1, c1, d1, e1 = textread(XFDTD.dat,%f %f %f %f %f, 361)angle1=angle1*pi/180q=find(c1c1(q)=-9c1=c1+9m=max(c1)c1=c1./mpolar(angle1,c1,g)The MATLAB result is shown n figure below.Figure 4.8 XFDTD radiation pattern in MATLABThe experimentally produced curve qualitatively matches with our theoretical calculations. The shape of the curve is confusable to the theoretical description, whereas the scale is different. For the purpose of confirming this result, the data of this curve is also exported into MATLAB to be compared with previously simulated results.4.4 Modeling of Micro Strip Patch Antenna Using XFDTD4.4.1 IntroductionAfter gaining confidence on the design of dipole antenna by comparing its results with the simulations and the results obtained from MATLAB, we use the same computational software for the modeling of micro strip patch antenna.4.4.2 Validity of ModelFor the modeling of micro strip patch antenna, a paper of IEEE Application of Three-Dimensional Finite-Difference Time humanity Method of the Analysis of Planar Micro strip Circuits is reproduced. This paper is used as a reference so that the results could be compared in order to bar the validity. The result of our exercise confirms the results of the IEEE paper this takes us to design a micro strip antenna of our desired parameters. This training will help us gain the expertise over the computational software, which can be used for the modeling of multiple different antennas.4.4.3 Modeling of Micro Strip Patch AntennaThe antenna is designed for the frequency range from 0 GHz (dc) to 20 GHz. The dimensions used for the antenna centers it at 7.8 GHz. Although its results at the higher frequencies are also examined for the accuracy, the parameters for the antenna are given belowDuroid substrate is used with =2.2Thickness is 1/32 inch=0.794mmLength = 12.45mmWidth = 16mmTransmission line feed is used and is placed at 2.09mm away from the left corner.With these specifications the center frequency comes out to be 7.8 GHz and this can be verified from the link www.emtalk.com/mpaclac.phpFigure 4.5 shows the geometry of micro strip patch modeled in XFDTD.Figure 4.5 Geometry of the micro strip patch antenna4.4.4 ResultsThe S11 plot of micro strip patch antenna was calculated by XFDTD, as shown in Figure 4.6 Figure 4.7 is the plot of the IEEE paper. This gives us the comparison between the two.Figure 4.6 obtained from t he XFDTDFigure 4.7 Results of S11 parameters from published IEEE PapersChapter 5Micro Strip Antennas5.1 IntroductionThese days there are many commercial applications, such as mobile radio and wireless communication, where size, weight, cost, performance, ease of installation, and aerodynamic profiles are constraints and low profile antennas may be required. To meet these requirements micro strip antennas can be used. These are low profile antennas and are conformable to planar and non-planar surfaces. These are simple and inexpensive to manufacture using modern printed circuit technology. They are also mechanically robust and can be mounted on besotted surfaces. In addition, micro strip antennas are very versatile in terms of resonant frequency, polarization, pattern and impedance as explained by Balanis 4.5.1.1 Basic CharacteristicsMicro strip antennas consist of a very thin metallic strip or patch placed a small fraction of a wavelength above a ground plane. The micro strip patch is designed so its pattern maximum is normal to the patch hence making it a broadside radiator. This is accomplished by properly choosing the mode or field configuration of excitation beneath the patch. End-fire radiation can also be accomplished by judicious mode selection. For a rectangular patch, the length L of the element is usually . The conducting micro strip or patch and the ground plane are separated by the substrate (Balanis 4).There are numerous substrates that can be used for the design of micro strip antennas and their dielectric constants are usually in the range of . The substrate that we are using in our designs has a value of 4.6.Often micro strip antennas are also referred to as patch antennas. The radiating elements and the feed lines are usually photo etched on the dielectric substrate. The radiating patch may be square, rectangular, thin strip, circular, elliptical, triangular or any other configuration.Arrays of micro strip elements with single or multiple fee ds are used to achieve greater directivities.5.1.2 Feeding MethodsThere are numerous methods that can be used to feed micro strip antennas. The four most common and popular are the micro strip line, coaxal probe, aperture span and proximity coupling. In our designs we have selected coaxial probe as our method of feeding the Micro strip antenna. Following is a brief explanation of coaxial feeding as explained by Balanis 4.Coaxial-line feeds, where the inner conductor of the coax is attached to the radiation patch while the outer conductor is connected to the ground plane are widely used. The coaxial probe feed is also easy to fabricate and match, and it has low spurious radiation. However is has narrow bandwidth and it is more difficult to model.5.2 impertinent PatchThe rectangular patch is one of the most widely used configurations of Micro strip antennas. It is very easy to analyze using either the transmission line model or the cavity model, which have higher accuracy for thin s ubstrates as explained by Balanis 4. In our desig