Micro Strip Patch Antenna

little Strip Patch feelerChapter 1IntroductionThe project which we have chosen to do as our final year project for the low graduate program involves the characterization of micro scavenge trance all overture.In this project we have carried show up simulations of different types of antennas, which intromit dipole antenna antenna, monopole and fixing. The subroutine of invention all of these is to strive knowledge and experience in the designing of antennas for different suggests by using commercially available CEM. The oftenness band, which we have chosen as our relevant band, is the GSM-900 band, which is of wide use in the cellular network. The purpose of choosing this band is to gain valuable knowledge of this absolute frequency band.Antennas atomic number 18 a fundamental part of e rattling system in which radiocommunication or publish quadrangle is the medium of communication. Basically, an antenna is a transducer and is designed to transmit or receive elec tro magnetic motions. It is a transducer as it converts radio frequency electrical flows into electromagnetic jolts. Common applications of antennas include radio, television broadcasting, point-to-point radio communication, cableless networks and radar. A detailed study of antennas is discussed in chapter two and chapter three of this report.The CEM softwargon programs that we have utilise for the designing include XFDTD provided by Remcom Inc. and CST Microwave studio, which is a full wave, 3-Dimensional, Electromagnetic simulation softw be and CST Microwave Studio. XFDTD utilizes a numerical electromagnetic code for antenna design, that is, the finite difference time domain proficiency (FDTD). Finite-difference time-domain (FDTD) is a popular computational electrodynamics border technique.The first antenna structure sculptural is the dipole. A dipole antenna consists of two conductors on the same axis with a fountain at the center. It is in like manner modal valueled i n XFDTD by side by side(p) the procedure provided by the softwargon and mentioned in the Appendix. The results ar verified by comparing with analytical papers of (lambda/2) dipole. After completing this, the next goal is to lesson the micro disinvest ( charm) antenna which is one of the main focuses of this project. It comprises of a metallic maculation bonded to a dielectric substrate with a metal layer bonded to the opposite side of the substrate forming a earth plane. This metal layer is very thin. indeed, it lavatory be fabricated very easily using printed circuit techniques. Therefore, they atomic number 18 inexpensive to reconstruct and be easily integrate able with microwave integrated circuits.The softwargon fashion model is carried out in XFDTD and on CST Microwave Studio. The verification of the results with the experimental results obtained leads to the final phase and the conclusion of the project.1.1 PurposeThe purpose of this project is to gain knowledge and experience about computational electromagnetic, as it applies to antenna design. It was also our bushel purpose to gain experience in fabrication and experimental characterization of micro ecdysiast patch antennas. To achieve these objectives we apply two commercially available CEM softwares, XFDTD and CST Microwave Studio, to design a micro despoil 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 give study many ejectonical types of antennas extending basic knowledge of antenna to complex antenna designs such(prenominal) 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 described belowChapter 2 describes the fundamentals of antennas and thoroughly discusses the the ory of fundamental parameters and quantities of antenna. In this chapter the basic concept of an antenna is discussed and its working is explained. both(prenominal) 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 signs of antennas as radiators of electromagnetic energy. These characteristics are normally considered in the removed expanse as the antenna configuproportionn or acti nonherapy pose of an antenna is the three-dimensional plot of its radiation at outlying(prenominal) field. It also discusses the types of antenna purposes in detail. Some important mathematical equations 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 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 angulate patch in detail are in this chapter. Also, this chapter describes the results obtained with 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. coterminous, 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 give out and receiving electromagneticenergy. An antenna acts as a transitional structure betw een the guiding devices (e.g. waveguide,transmission line) and the desolate space. The official IEEE definition of an antenna as disposed(p) byStutzman and Thiele 9 is as followsThat part of a transfer or receiving system that is designed to radiate or receive electromagnetic waves.2.2 How an Antenna radiates?In dedicate to understand how an antenna radiates, we have to first know how radiation occurs. Aconducting wire radiates because of time-varying modern or an acceleration or deceleration of prosecute. If there is no motion of charges in a wire, no radiation will occur, since no flow of current occurs. Radiation will non occur even if charges are moving with unvaried or constant velocity along a straight wire. Also, charges moving with furnish velocity along a curved or bent wire will produce radiation. If charge is oscillating with time, wherefore radiation will occur even along a straight wire as explained by Balanis 4.The radiation pattern from an antenna smoke be further understood by considering a potency source connected to a two-conductor transmission line. When a curved voltage source is applied across the transmission line, an electric field is generated which is sinusoidal in nature. The bunching of the electric lines of delineate can indicate the magnitude of this electric field. The free electrons on the conductors are forcefully displaced by the electric lines of force and the motion of these charges causes the flow of current, which leads to the creation of a magnetic field.Due to time varying electric and magnetic palm, 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 l ine RegionsThe field patterns of an antenna, change with remoteness and are associated with two types of energy radiating and stirred up energy. Hence, the space surrounding an antenna can be divided into three functions.Figure 2.1 palm components 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 apart from the antenna, thus appearing as reactance. In this region, energy is stored and no energy is dissipated. The ou margeost boundary for this region is at a outperform (2.1)where R1is the distance from antenna surface, D is the commodiousst dimension of the antenna and is the wavelength.2.3.2 Radiating Near-Field RegionThis region also called Fresnel region lies between the reactive near-field region and the farther field region. In this region, the angular field distribution is a function of the distance from the anten na. reactive fields are smaller in this field as compared 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 interdependent on the distance from the antenna in this region. In this region, the reactive fields are absent and hardly the radiation fields exist and the post assiduity varies as the inverse square of the radial distance in this region.2.4 The Hertzian DipoleA hertzian dipole or infinitesimal dipole, which is a segment of straight wire whose length L and diameter are both very small, compared to one wavelength. A uniform current I is subscribed to flow along its length. Although such a current part does not exist in real life, it serves as a building block from which the field of a practical antenna can be calc ulated (Sadiku 6).Consider the hertzian dipole shown in figure. We assume that it is located at the origin of a coordinate system and that it carries a uniform current. i.e. I=I cost. The retarded magnetic vector electric potential at the field point, due to dipole is inclined 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 contemporaries time delay r/u or phase delay.By substitution we whitethorn also write A in phasor form ast(2.5)Transforming this vector in Cartesian to spherical coordinates yieldsWhere and(2.6)We find the E field using(2.7)(2.8)Where,A close observation of the field equations reveals that we have harm varying as The 1/ term is called the electrostatic field since it corresponds to the field of an electric dipole. This term dominates over separate harm in a region very close to the hertzian dipole. The is called the inductive field, and it is predic table from the from the Biot Savart law. The term is important only 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 touch on with the far field or radiation zone (r1), where the term 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 ar flow the boundary between the near and far zones by the quantify of r given by . where d is the largest dimension of the antenna.The time bonny author density is obtained as)(2.10)Substitution yields time average radiated bureau asButAnd whence above equation becomesIf free space is the medium of propagation, = cxx and(2.11)This power is equivalent to the power dissipated in a fictitious resistance by currentThat is,(2.12)Where is the root mean square value of I. From above equations we obtainOr(2.13)The resistance 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 curve Dipole AntennaThe Half vagabond dipole is named 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 due 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 sinusoi dal current distribution because the current must vanish at the ends of the dipole. Also note that the factual 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 utilize.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 while neglecting it in the denominator because the exponent involves the phase constant while the denominator does not. So,(2.15)Using the by-line integrating equation,Applying this equation gives on (2.15)Since and the above equation b ecomes,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 preliminary equations has been substituted assuming free space as the medium of propagation. The last equation can be pen 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 former 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 elementary types of antennas. Now we will discuss the important characteristics of antennas as radiators of elec tromagnetic energy. These characteristics are normally considered in the far field and are as follows. And have been treated 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 level pattern. The normalization of is with respect to the maximum value of the so that the maximum 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 thi s equation we can obtain the E-plane pattern as the polar pattern of by 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 devotion of an antenna is defined as(3.3)Using the above equation, the total average power radiated can be expressed as(3.4)(3.5)Where d= is the differential solid angle in steradian (sr). The radiation intensity level 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 oversightIt can also be regarded as the ability of the antenna to direct radiated power in a given direction. It is usually 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 broadside 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,Wher e, =120 and(3.11)3.4 Bandwidth (Impedance Bandwidth)By definition 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 talent 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 any 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 speci fied using the total efficiency instead of the radiation efficiency only. This total efficiency is a combination of the radiation efficiency and efficiency connectored to the impedance duplicate 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 bound 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 pointer representing the instantaneous electric field. The field must be observed along the direction of propagation.3.7 Return redThe 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 waves 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 creation 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 stumpering 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 wide 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 corporeal objects and the environment.The first such software brought into use is XFDTD. It is a three-dimensional full wave electromagnetic solver establish on the finite difference time domain method. It is fully three-dimensional. Complex CAD objects can be imported into XFDTD and combining and editing can be through with(p) within XFDTD using the midland 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 plain 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 biz 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 depth knowledge of XFDTD before 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 studied 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(a) carrier wave frequency. Thus the dipole modeled in XFDTD has the following specificationsLength of 30cmFrequency used 1 GHzThin wire was used to create the dipoleSource was devoted 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 Figure 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 extension 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 similar to the theoretical description, whereas the outdo 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 lotion of Three-Dimensional Finite-Difference Time Domain 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 check the validity. The result of our manage 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 e xpertise 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 giv es us the comparison between the two.Figure 4.6 obtained from the XFDTDFigure 4.7 Results of S11 parameters from published IEEE coverChapter 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 rigid 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 human body 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.A rrays of micro strip elements with single or multiple feeds are used to achieve greater directivities.5.1.2 nutriment MethodsThere are numerous methods that can be used to feed micro strip antennas. The quaternion most common and popular are the micro strip line, coaxial probe, aperture coupling 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 squeeze bandwidth and it is more difficult to model.5.2 Rectangular PatchThe rectangular patch is one of the most widely used configurations of Micro strip antennas. It is very easy to analyze using either the transmissi on line model or the cavity model, which have higher accuracy for thin substrates as explained by Balanis 4. In our desig