Fed Corner Truncated Microstrip Patch Antenna

Fed Corner Truncated Microstrip Patch Antenna Ultra-Wide band communications attracted great interest of researchers as it has become one of the most promising technologies for short range mobile systems, Personal Area Networks (PAN) and high speed indoor data communication applications. FCC mentioned parameters for the complete functioning of UWB antennas and they have to cover the bandwidth specified by FCC to attain adequate performance. UWB has the advantage of high data rates with extremely low interference to other narrow band systems. The ultra short pulses provide extremely good spatial resolution, as the range provided by UWB is enough to seize down the major applications of daily life like in ground penetrating radars, parking radars, biomedical imaging, precision tracking and location finding. Various types of UWB antennas have been proposed and implemented with different feeding techniques, such as transmission line, probe feed, dual feed and coplanar waveguides (CPW). A compact antenna design fed by coplanar waveguide (CPW) is proposed. Overall dimensions of antenna are 28ÃÆ'-24 mm2. The design is fabricated and further analyzed to confirm its proper working in UWB range. The design of antenna is quite flexible as fiddling with the patch of microstrip antenna has been done in order to enhance the bandwidth which is the most valued obsession in the current environment. On the other hand, CPW has many advantages such as low radiation leakage, less dispersion at higher frequency, small mutual coupling between two adjacent lines which is helpful to place circuit elements close together without adding an additional layer of substrate and coplanar capability. Using CPW as feeding structure to excite a patch antenna has become very popular recently. The proposed antenna offers an excellent performance for UWB systems by providing bandwidth ranging up to 15.65GHz. Critical design parameters return loss and radiation patterns are investigated in detail. Proposed antenna provides good impedance matching, stable gain characteristics and consistent radiation patterns over its almost whole frequency band of interest. Chapter 1 Introduction Project Overview IEEE defines antenna as a device for radiating and receiving electromagnetic waves. They are used both as transmitter and receiver. This is era of wireless communication. Antennas are an important means of wireless communications now days. The need of time is compact small size antennas with enhanced bandwidth and gain. Amongst all antenna types microstrip patch antennas are most common. They are light in weight and consume low power. But patch antennas have disadvantage that they have narrow bandwidth. Many techniques are used to enhance bandwidth. Ultrawide band antennas have many applications and for many years they have been used for broadband and spread spectrum features in radar systems. The UWB performances of antennas result from excitation by non-sinusoidal signals with quickly time-varying performances [1]. UWB are low power consumption antennas and are for unlicensed applications. As name suggests, they have broad spectrum. Problem Statement Ultra wideband technology is used in low power, short range and high bandwidth communication. In UWB; through spreading information can be transmitted over a larger bandwidth and spectrum is also shared with the other users at the same time. Federal Communication Commission (FCC) allocated the license free band of 3.1GHz-10.6GHz for use in UWB applications. Since then there is a growing demand of UWB antennas for high data rate applications i.e. wireless personal area network (WPAN). UWB has had a important effect on antenna design. The major challenge in UWB antenna design is to achieve wide impedance bandwidth and stable gain while maintaining high radiation efficiency. Project Objective The purpose of this project is to design, stimulate, analyze and fabricate ultra wide band antenna using co-planer waveguide. Design and analysis of a compact antenna fed by CPW for UWB Applications is proposed Bandwidth of the proposed antenna is 15.65 GHz. Antenna offers an excellent performance for ultra-wide band systems by providing an ultra-wide bandwidth ranging from 3.1 18.75 GHz. Gain of the proposed antenna is 4.91dBi over its almost whole frequency band of interest Small size of antenna makes it suitable for applications which demand miniaturization of antenna structure and input impedance of 50 à ¢Ã¢â‚¬Å¾Ã‚ ¦. Methodology We have simulated the designed antenna using Ansoft HFSS. Then the simulated antenna is fabricated and tested on the network analyzer. The simulated and measured results are also explained. Organization of the thesis This report is divided into 6 chapters. Chapter 2 presents the fundamental parameters of antenna. This includes an explanation of various parameters related to antenna performance including radiation intensity ,radiation pattern, power density , gain, directivity and polarization etc. Chapter 3 discusses the Microstrip Patch Antenna and Feeding techniques. Chapter 4 includes Ultra wide band microstrip patch antenna, history of UWB antennas, their features and advantages. Chapter 5 describes antenna design, simulated results, 2D and 3D radiation patterns for different frequencies and fabricated results. Chapter 6 concludes the entire work done throughout the designing of proposed antenna. Conclusion and future work helps to explore enormity of the subject. Chapter 2 Fundamental Parameters of Antenna 2.1 Radiation Pattern The radiation pattern describes the strength of the radiated field in different directions from the antenna, at a constant distance. The radiation pattern is also reception pattern, as it describes the receiving properties of the antenna. It is defined as a mathematical function or a graphical representation of the radiation properties of antenna as a function of space coordinates. In most cases the radiation pattern is determined in far field regions and is defined as a function of the directional coordinates. Radiation properties include power flux density, radiation intensity, field strength, directivity phase or polarization [2]. The radiation pattern is three-dimensional, but measured patterns are usually two dimensional in vertical or horizontal plane view. These measured patterns are presented in either rectangular or polar format. Following figure shows radiation pattern of an antenna in polar plane and Cartesian coordinate systems. http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/images/0900aecd806a1a3e_null_null_null_08_07_07-03.jpg Figure-2.1: Radiation Pattern of an antenna in Cartesian and polar coordinates Radiation patterns are further categorized as relative and absolute radiation patterns. Absolute radiation patterns have absolute units of power or field strength. Relative radiation patterns are presented in relative units of power or field strength. The radiation measurement patterns are mostly relative to isotropic antennas, absolute gain of the antenna is established by antenna gain transfer method. The radiation pattern varies with the distance i.e. the patterns in near filed and far filed are different. The field pattern that exists close to the antenna is known as near filed, and far-field refers to the field pattern that exists at large distances. The far-field is called radiation field. Radiation field and power are what is commonly of interest, so antenna patterns are generally measured in the far-field region. For antenna pattern measurement the distance should be chose large enough not to be in near-field or in far field. The minimum allowed distance depends on the dimensions of the antenna relative to the wavelength. The formula for this distance is: rmin = 2d2/ÃŽÂ » (2.1) Where, rmin is the minimum distance from the antenna d is the largest dimension of the antenna ÃŽÂ » is the wavelength. 2.1.1 Radiation Pattern Lobes Radiation lobes are defines as portion of radiation pattern bounded by regions of relatively weak radiation intensity [3]. These lobes are categorized as follow Major Lobes Minor Lobes Side Lobes Back Lobes 2.1.2 Major Lobe A major lobe is defined as the radiation lobe containing the direction of maximum radiation [2]. Normally an antenna has one major lobe. 2.1.3 Minor Lobe Any lobe except major lobe is called minor lobe. It usually represents the radiation pattern which is not desirable. 2.1.4 Side Lobe A side lobe is a radiation lobe in any direction other than the main lobe [2]. Usually a side lobe is next to the main lobe and is in direction to the main lobe. 2.1.5 Back Lobe A back lobe is a radiation lobe whose axis makes an angle of approximately 180 ° with respect to the beam of an antenna or that is directed away from the main lobe [2]. File:Typical Antenna Pattern.jpg Figure 2.2: An illustration of major and minor lobes of radiation pattern 2.2 Field Regions The antenna fields are divided into three regions Reactive near field Radiating near field (Fresnel) Far field (Fraunhofer) http://www.nearfield.com/images/theory-ffdist.jpg Figure 2.3: Figure of Near Field and Far Field Regions 2.2.1 Reactive Near Filed It is the region immediately around the antenna. In this region the reactive filed predominates. The distance of this filed with antenna is usually R 2.2.2 Radiating Near Field (Fresnel) Radiating near filed is defines as that region of the field of an antenna between the reactive near-filed and the far-filed region wherein radiation fields predominate and wherein the angular field distribution is dependent upon the distance from the antenna [2]. The distance of inner boundary is R 2.2.3 Far Field Region (Fraunhofer) Far Field region is defined as that region of the field of an antenna where the angular filed distribution is essentially independent of the distance from the antenna [2]. 2.3 Radiation Intensity Radiation Intensity is the power radiated from an antenna per unit solid angle. It is the parameter of far field radiation. 2.4 Directivity Directivity is figure of merit for antennas. It is the power density an antenna radiates in direction of maximum radiation to the average power density radiated by an isotropic antenna. Directivity for an isotropic antenna is always unity. It is expressed as D= (2.2a) (2.2b) Where, D is directivity and U is radiation intensity, Uo is Intensity if an isotropic source and Prad is total radiation power. 2.5 Gain The gain and directivity of an antenna are closely related to each other. However for gain in denominator it is total power accepted by an antenna rather than total power radiated by an antenna. G= (2.3) Gain is dimensionless. According to IEEE standards, gain doesnt include losses arising from impedance mismatching or polarization mismatches. 2.6 Bandwidth The bandwidth is basically the difference or range between highest and lowest frequencies on which an antenna is operated. It is advantageous to have an antenna with high bandwidth. The bandwidth is expressed in term of ratio of upper cut off to the lower cutoff for broadband antennas. 2.7 Beamwidth Beamwidth is the angle usually measured in degrees; between the -3dB power radiated in the main lobe of radiation pattern. img383 Figure 2.4: Illustration of Beamwidth 2.8 Return Loss It is the amount of power that is reflected back in to the transmission line due to mismatching or any other error. It is the efficiency of power delivered to the load from the transmission line. Mathematical representation of Return loss is RL = 10log (2.4) Return loss is measured in dB. http://www.mwrf.com/Files/30/11240/Figure_05.gif Figure 2.5: Return Loss 2.9 Polarization Polarization is defined as point of reference of the electric field of the wave radiated by the antenna. It is categorized in three types: Linear Circular Elliptical 2.9.1 Linear Polarization When there is zero phase difference between x and y component of a wave then polarization is called linear polarization. Linear polarization is further divided into Horizontal polarization Vertical polarization http://www.ccrs.nrcan.gc.ca/glossary/images/3104.gif Figure 2.6: Linear Polarization 2.9.1.1 Horizontal Polarization Horizontal polarization is the one in which wave propagates in x-direction and there is no propagation along y direction. A horizontally polarized wave is explained as a function of time T and E-field position Ex = E1 sin ( É ·t à ¡Ã‚ µÃ‚ z) (2.5) http://www.cfht.hawaii.edu/~manset/PolHoriz.gif Figure 2.7: Horizontal Polarization 2.9.1.2 Vertical Polarization Vertical polarization is the one in which wave propagates in y-direction and there is no propagation along x direction. It can be written in mathematical form as Ey = E2 sin ( É ·t à ¡Ã‚ µÃ‚ z) (2.6) http://www.cfht.hawaii.edu/~manset/PolVert.gif Figure 2.8: Vertical Polarization 2.9.2 Circular Polarization If there is equal phase difference between two waves then there is circular polarization, either clockwise or anticlockwise. Wave moving in clockwise rotation is said to be left circularly polarized and the one propagating in counterclockwise rotation is right circularly polarized. Mathematically it is defined as Ex = E1 sin (É ·t à ¡Ã‚ µÃ‚ z) (2.7) Ey = E2 sin (É ·t à ¡Ã‚ µÃ‚ z + ÃŽÂ ´) (2.8) E1 is the amplitude of wave linearly polarized in x direction. E2 is the amplitude of wave linearly polarized in y direction. ÃŽÂ ´ is the phase difference. http://www.cfht.hawaii.edu/~manset/PolCirc.gif Figure 2.9: Circular Polarization 2.9.3 Elliptical Polarization If two waves have unequal amplitude or phase then there is elliptical polarization. graphic 1 Figure 2.10 (a): Graphical Representation of Elliptical Polarization http://www.nsm.buffalo.edu/~jochena/images/elliptic2.gif Figure 2.10 (b): 3-D view of Elliptical Polarization 2.10 Voltage Standing Ratio VSWR is the ratio between maximum voltage and the minimum voltage. If there is a difference between load impedance and input impedance then there occurs reflection which causes instructive interference and destructive interference. Instructive and destructive interference produces maximum and minimum amplitudes respectively. Mathematical Expression for VSWR is VSWR= (2.9) http://www.microwaves101.com/encyclopedia/images/VSWR/waves5.jpg Figure 2.11: Different Voltage amplitudes at different distances 2.11 Types of antennas There are six different types of antennas [2]. Microstrip Patch Antenna Lens Antenna Wire Antenna Array Antenna Reflector Antenna Aperture Antenna 2.11.1 Microstrip Patch Antenna Microstrip patch antennas fall into the category of printed antennas [4]. A radiating patch is printed on a grounded substrate which is usually feed via a transmission line or coaxial cable. Patch can be of any shape and size i.e. circular, square, triangular or rectangular. Amongst all printed antennas i.e. Dipole, Slots, Tapered Slots antennas; Microstrip Patch Antennas are most famous. They are small in size, light in weight and low power consuming. But their bandwidths are smaller and have low gain. They are easy to integrate, good radiation control and cost of production is low. To increase bandwidth many techniques are used that is introducing slots and slits etc. They are used commercially in radars, wireless communications, satellites and mobiles etc. Figure 2.12: Microstrip patch Antenna http://images.books24x7.com/bookimages/id_22121/fig188_01.jpg Figure 2.13 (a): Rectangular Patch Antenna (b): Circular Patch Antenna Microstrip Patch antennas are used in Microwave frequency range. They are used in arrays to increase the bandwidth and gain and for other purposes. http://www.antennamagus.com/database/antennas/99/Stacked_microstrip_patch_array-antenna_design.png Figure 2.14: Array of rectangular patch antennas 2.11.2 Lens Antenna Lens antennas are used to convert spherical radiated waves into plane waves in specific direction by using a source with microwave lens. It actually stops the divergent radiated energy to spread in undesired directions. These are mostly used for the high frequencies. A lens antenna may be of concave or convex shape. They are directional antennas and can scan wider angles. In comparison to reflectors; their gain is 1 or 2 dB less. Lens antennas may be constructed of non-metallic dielectrics or of metallic (artificial) dielectrics [5]. http://www.xibao-electronictech.com/images/product/2/210Lens-Antenna.gifhttp://telecom.esa.int/telecom/media/img/largeimage/WaveguideLensAntennaPrjObj_404.jpg Figure 2.15 (a): Lens Antenna Figure 2.15 (b): Wave guide Lens Antenna 2.11.3 Wire Antenna Wire antennas consist of a simple wire that is used to radiate electromagnetic energy. These wire antennas can be of different shapes. Most commonly used are straight wire antennas i.e. dipoles, loops and helix. Beside half-wave dipoles and quarter wave monopoles, wires of arbitrary lengths are often used to form antennas. Wire antennas can be vertical, horizontal or sloppy with respect to the ground. They may be fed from centre, at end or anywhere in between. The wires can be thick or thin, the radiation of antenna depends upon the thickness of the wire. Antennas with length larger than ÃŽÂ »/2 are called Long-wire antennas. Figure 2.16 (a): Wire Antennas (a) Figure 2.16 (b): Dipole Circular loop 2.11.4 Array Antenna Array antennas are made up of more than one element basic of which is a dipole. Array antennas are the combination of radiating elements in such way that the radiation from these add up giving maximum or minimum radiation in a specific direction. They are used for higher directivity. They are made up of helices, dishes and other antennas. These elements are arranged to form broadside, end fire, collinear, driven and patristic arrays [5]. They are used in applications in which radiation cannot be achieved from single radiating element. They are low weight and low cost antennas. Examples of array antennas are Yagi-Uda, http://www.tennadyne.com/images/tennlpdanavy.JPG Figure 2.17: Log Periodic Dipole Array Antenna 2.11.5 Reflector Antenna They are widely used to modify the radiation pattern of radiating elements. They are classified as active and passive reflectors. The active reflectors have corners made up of plane surfaces and they include periscopic antennas, flat-sheet reflectors and corner-reflector antennas. An active reflector may have corner elliptical, parabolic or spherical shape. Active reflectors include parabolic dish, truncated parabola, pill box etc. Reflectors are simple in design, involve only one surface and obey simple laws of optics. The applications of reflector antennas are radars and other point to point communication systems [5]. http://www.sameercal.org/images/reflector_antenna.jpg Figure 2.18: A co-secant Reflector Antenna 2.11.6 Aperture Antenna Aperture antenna is an important antenna for space communication. As the name suggests they consist of some cavity through which electromagnetic waves are transmitted or received. Apertures may be of any shape i.e. rectangular, circular or spherical. Larger the size of antenna larger will be the gain. Aperture antennas have to be placed carefully because they have narrow beam widths. Examples of aperture antennas include waveguides, reflectors horns, slots and lenses. Aperture antennas are commonly used in aircraft and spacecraft applications. http://www.analyzemath.com/antenna_tutorials/introduction_3.gif Figure 2.18: Horn Aperture Antenna Chapter 3 Microstrip Patch Antenna and Feeding techniques 3.1 Introduction Spaceships, aircrafts and other military applications such as missiles where important constraints to consider are performance, manufacturing expenditures, smooth profile and ease of installation and now a days other systems such as wireless communication requires similar type of specifications to consider . And the basic component which is required by these listed applications for transmission of instructions or data and to receive these instructions on the receiver end is antenna. Hence to meet the requirements listed above e.g. smooth profile, cost and performance etc Microstrip antennas are used. Microstrip antennas are diminutive profile, conformable to planar and non-planar surfaces, easy and cheap to construct using the up to date printed circuit technology. Microstrip antennas have very flexible behavior to polarization, resonant-frequency, and impedance and radiation pattern. They are also used to increase the bandwidth. They consist of a ground plane over which a substrate is mounted and the radiating patch is mounted on the substrate. Generally the ground plane and the dielectric substrate have equal length and width. The Microstrip antennas are illustrated by the width, length and the height of the dielectric substrate which is sandwiched in between the ground plane and the radiating patch 3.2 Structural Configuration The structural configuration of micro strip patch antenna is shown in figure Figure 3.1: Structural Configuration of Patch Antenna It consist of a thin (t Figure 3.2: Side View of Patch Antenna The length of the patch is usually ÃŽÂ »/3 3.3 Formula for Rectangular Patch Antenna To draw the width of the patch we use the formula (3.1) And the length of the patch can be drawn as: (3.2) To reduce the fringing effects we use the following formula à ¢Ã‹â€ Ã¢â‚¬  L= 0.412h (3.3) Here à ¢Ã‹â€ Ã¢â‚¬  L is the trimmed length from antenna. (3.4) 3.4 Feeding Methods Following feeding methods are most popular and are used with microstrip antennas 1. Microstrip line feed 2. Coaxial probe feed 3. Aperture coupled feed 4. Proximity coupled feed 5. Coplanar waveguide feed These methods are either contacting or non-contacting. Contacting methods are those in which there is a direct contact between the transmission line and the radiating surface whereas in non-contacting methods, electromagnetic field coupling method is used to transfer the power. 3.4.1 Microstrip Line Feed In this feeding method, the line feed is conducting strip of small width as compared to the patch. It is the easiest feeding method; easy to fabricate and simple to model. The radiating strip is placed at radiating patchs edge and it is of the same material that is used for patch. If length of the strip is greater than the wavelength, losses will be generated. It can be reduced if the strip line has a substrate with high dielectric constant and low weight, so that the fields are confined to the strip line. A line feed of dimensions 17x3mm is used to obtain 50ÃŽÂ © input resistance. Figure 3.1: Patch with Microstrip Line Feed 3.4.2 Coaxial probe feed In coaxial probe feeds, coax inner conductor is attached to the radiating patch while the other conductor is connected to the ground plane. It is used widely. Its fabrication is easy and has low spurious radiation that is radiation outside the band frequency. It is has narrow bandwidth and it is hard to model for thick substrate. Matching also becomes difficult for thicker substrate because of increase length of probe make it more inductive, its inductance effect can be reduced by using a series of capacitors. Figure 3.2: Patch with coaxial probe feed 3.4.3 Aperture coupling feed It is the non-contacting feed. The two substrates are separated by ground plane in it. The microstrip feed line is on the bottom side of the lower substrate there is a; whose energy is coupled to the patch through a slot on the ground plane which separates the two substrates. A material with higher dielectricity is used for bottom substrate therefore, by this arrangement independent optimization of the feed mechanism and the radiating element can be carried out. For top substrate a thick, low dielectric constant material is used. The ground plane between the two substrates isolates the feed from the radiating element and minimizes the interference. The configuration is shown in the figure Figure 3.3: Patch with aperture coupling feed Matching is performed by controlling the width of the feed line and the length of the slot. Amongst all four techniques this is the hardest to fabricate and has narrow bandwidth. It is somehow easy to model and has moderate spurious radiation. 3.4.4 Proximity coupling feed In this feeding method, microstrip line is placed between two substrates and the radiating patch is placed on the upper substrate. This coupling is capacitive in nature. This coupling has the largest bandwidth as high as 13%. It is easy to model and has low spurious radiation. Its fabrication is somehow difficult. However, length of the stub help in improving the bandwidth, and width-to-line ratio of the patch can be used to control the match. The coupling feed is shown Figure 3.4: Patch with Proximity Coupling Feed 3.4.5 Coplanar Waveguide Feed This feeding technique is used when patch antenna is used in microwave monolithic integrated circuits (MMIC). The coplanar feed is fabricated on a ground plane and coupling is achieved through a slot. This feeding method reduces the radiation from feed structure because of its unusual method of coupled slot. Since CPW (coplanar waveguide) has many advantages such as low radiation leakage, less dispersion and small mutual coupling between two adjacent lines, which is helpful to place circuit elements close together without adding an additional layer of substrate, using CPW as the feeding structure to excite the patch antenna through a slot has become very popular recently. In addition, CPW structure can maintain constant characteristic impedance while varying its geometry, which provides a better impedance matching possibility Figure 3.5: Patch with Coplanar Waveguide Feed 3.3 Categorization on the basis of bandwidth:- On the basis of range of frequency bands, microstrip patch antennas can be categorized into three main classes which are: antenna for narrow band applications antenna for wide band applications antenna for ultra wideband applications Chapter 4 ULTRA WIDEBAND 4.1 Introduction A series of very short baseband pulses with time duration in nano-seconds that exist on ALL frequencies simultaneously. Pulse repetition frequency (PRF) can range from hundreds of thousands to billions of pulses/second. Very low power: 41dbm/MHz (FCC) and wide bandwidth: 3.110.6 GHz Modulation techniques include pulse-position modulation binary phase-shift keying And others Radio technology that modulates impulse based waveforms instead of continuous carrier waves 4.1.1 Narrow band vs. Wide band signals UWB could be used to Indoor, short-range communications for high data rates, OR Outdoor, long-range, but for very low data rates 4.1.2 Large Relative Bandwidth UWB is a form of extremely wide spread spectrum where RF energy is spread over gigahertz of spectrum. Wider than any narrowband system by orders of magnitude. Power seen by a narrowband system is a fraction of the total.UWB signals can be designed to look like imperceptible random noise to conventional radios 4.1.3 Large Fractional Bandwidth Large fractional bandwidth leads to High processing gain and Multipath resolution and low signal fading. Fractional Bandwidth is the ratio of signal bandwidth (10 dB) to center frequency: Bf = B / FC = 2(Fh-Fl) / (Fh+Fl) 4.1.4 Scalable Technology with Low Power UWB benefits from basic information theory results when: Signal Bandwidth >> Data Rate .Power efficient low-order modulation can be used even for relatively high data rates.Data rates can scale independent of PRF by integrating bit intervals over multiple pulse intervals 4.1.5 Multipath Performance Ultra-wide bandwidth provides robust performance in multipath environments . 4.1.6 UWB Data Rates 4.2 UWB channels Indoor Within a room (LOS NLOS) Investigates the impact of Distance Rx/Tx antenna heights Antenna polarization C:mat_dirsuwblimitsindoor5.tif UWB Emission Limit for Indoor Systems Outdoor Campus environment Low altitude Mobility C:mat_dirsuwblimitsoutdoor5.tif UWB Emission Limit for Outdoor Hand-held Systems 4.3 Emission limits for UWB UWB Emission Limits for GPRs, Wall Imaging, Medical Imaging Systems. Operation is limited to law enforcement, fire and rescue organizations, scientific research institutions, commercial mining companies, and construction companies. UWB Emission Limits for Thru-wall Imaging Surveillance Systems 4.4 Features of UWB :- Ultra-short pulses Baseband transmission Low duty