Antenna Fundamentals Lecture 1,2,3 PDF

Lecture - 1- Antenna Fundamentals What is an Antenna? 19 o An Antenna is a tr...

Lecture - 1- Antenna Fundamentals What is an Antenna? 19 o An Antenna is a transducer, which converts electrical power into electromagnetic waves and vice versa. An Antenna can be used either as a transmitting antenna or a receiving antenna. (J, 9) (954 8519) where is the of P) (Antenna name S coms fros  Their name is borrowed from zoology, in which the Latin word antennae is used to describe the ( long, thin( feelers possessed by r many insects. A metallic conductor's structure is called an win= 15 24 "antenna" while the wire form is called an “aerial”. 2 S14 , i w= Es ->  Just as in humans the ears are the transducers that convert acoustic waves into electrochemical impulses. -Did -> Ed jo  The antenna is the transition between a guiding device (transmission line, waveguide) and free space (or another usually 19305 unbounded medium). Its main purpose is to convert the energy of a guided wave into the energy of a free space wave (or vice versa) as efficiently as possible, while at the same time the radiated power has a certain desired pattern of distribution in I - 199 Bois space. - 8  An antenna intercepts some of the power of an electromagnetic wave to produce a tiny voltage at its terminals, which is applied to -Ding 39 is invis · a receiver to be amplified.-> -gja". & 3 i -/ pot % jii s - Q) where the antine so - S consist of ? -  Typically an antenna consists of an arrangement of metallic conductors ("elements"), electrically connected (often through a transmission line) to the receiver or transmitter. Radiation Mechanism  - &  To create radiation, /5there must be a time-varying current or an Q acceleration (or deceleration) of charge. A  For a transmission line, to become a waveguide or to radiate power, Sol has to be processed as such: - - 1. If a charge is not moving, current is not created and there is no radiation. -sig 2. If charge is moving with a uniform velocity: ② & -There is no radiation if the wire is straight, and infinite in extent. Fi - There is radiation if the wire is curved,( bent,S 10 & &= 350 discontinuous, terminated, or truncated, as shown in Figure 1.1 25 3 - -S a 3. If charge is oscillating in a time-motion, it radiates even if the wire is straight X  The radiation from an antenna can be explained with the help of Figure 1.2 which shows a voltage source connected to a two conductor transmission line. When a sinusoidal voltage is applied across the transmission line, an electric field is created and these results in the creation of electric lines of force which are tangential to the electric field. · hi ; St ~ g  The free electrons on the conductors are forcibly displaced by the ( , %51j] electric lines of force and the movement of these charges causes the flow of current which in turn leads to the creation of a magnetic field.  Due to the time varying electric and magnetic fields, electromagnetic waves are created and these travel between the conductors. g 01 & ja I Isis 1  As these waves approach open space, free space waves are formed by connecting the open ends of the electric lines.  Inside the transmission line and the antenna, the electromagnetic i ! & waves are sustained due to the charges, but as soon as they enter the free space, they form closed loops and are radiated. Figure 1.1   Maxwell's equations describe how electric charges and electric currents create electric and magnetic fields. Further, they describe how an electric field can generate a magnetic field, and vice versa E: electric field [volt/m] H: magnetic field intensities [ampere/m] D: electric flux densities also called the electric displacement [coulomb/m2] B: magnetic flux densities or magnetic induction [weber/m2] or [tesla]. ρ: free electric charge density [coulomb/m3] J: electric current density (charge flux) of any external charges (that is, not including any induced polarization charges or magnetization currents in a material [ampere/m2] ∇× is the curl operator ∇· is the divergence operator The charge and current densities ρ, J may be thought of as the sources of the electromagnetic fields. For wave propagation problems, these densities are localized in space; for example, they are restricted to flow on an antenna. The generated electric and magnetic fields are radiated away from these sources and can propagate to large distances to the receiving antennas. , Basic Types of Antennas Antennas may be divided into various types depending upon:  The physical structure of the antenna.  The frequency ranges of operation.  The mode of applications. Physical structure: Following are the types of antennas according to the physical structure.  Wire antennas  Aperture antennas  Reflector antennas  Lens antennas  Micro strip antennas  Array antennas Frequency of operation: Following are the types of antennas according to the frequency of operation.  Very Low Frequency (VLF) ,Low Frequency (LF)  Medium Frequency (MF)  High Frequency (HF) , Very High Frequency (VHF)  Ultra High Frequency (UHF), Super High Frequency (SHF)  Micro wave  Radio wave Mode of Applications: Following are the types of antennas according to the modes of applications-  Point-to-point communications  Broadcasting applications  Radar communications  Satellite communications The physical structure of the antenna. 1. Wire antennas (single-element) Simple to make but their dimensions are commensurable with the wavelength. This limits the frequency range of their applicability (at most 1-2 GHz). At low frequencies, these antennas become increasingly large. -Usually used in personal applications, automobiles, buildings, ships, aircrafts and spacecraft 2. Aperture antennas (single element) - Horn antennas, waveguide opening - Waveguide transmission lines were primarily developed to transfer high power microwave EM signals (centimeter wavelengths). These types of antennas are preferable in the frequency range from 1 to 20 GHz.  = idl it g/: · , & categ 3. Microstrip antennas :patch antennales , go dis -The patch antennas consist of a metallic patch etched on a dielectric j substrate, which has a grounded metallic plane at the opposite side. ] - & - Used in aircraft, spacecraft, satellites, missiles, cars, mobile phones etc. - ( N Es'9S I Et , Ej , # As lo &" 4. Reflector antennas 30 5215s ? - A reflector is used to concentrate the EM energy in a focal point where op the receiver/feed is located, Reflector antennas have very high gain and -> os9 · directivity. and - Typical applications: radio telescopes, satellite communications, microwave communication. 5. Lens antennas -Lenses play a similar role to that of reflectors in reflector antennas, usually used for very high frequency applications (f > 100 GHz). -They are classified according to their shape and the material they are made of. 6. Antenna arrays Antenna arrays consist of multiple (usually identical) radiating elements. Arranging to achieve very high gain applications with added advantage, such as, controllable radiation pattern, which cannot be obtained through a single element. (Yagi-Uda antenna, microstrip patch array, aperture array, slotted waveguide array)  Antenna – Basic Parameters The equivalent circuit of an antenna: - a) transmission-line Thevenin equivalent circuit of a radiating (transmitting) antenna Vg - voltage-source generator (transmitter); Zg - impedance of the generator (transmitter); Zc - impedance of the transmission lines; Rrad - radiation resistance (related to the radiated power as 𝑟𝑎𝑑=𝐼𝐴2×𝑅𝑟𝑎𝑑 ) RL - loss resistance (related to conduction and dielectric losses); jX A - antenna reactance. The antenna impedance is (𝑍𝐴= (𝑅𝑟𝑎𝑑+𝑅𝐿) +𝑗𝑋𝐴) One of the most important issues in the design of high-power transmission systems are the matching of the antenna to the transmission line (TL) and the generator. Matching is specified most often in terms of voltage standing wave ratio (VSWR). Standing waves are to be avoided because they may cause arching or discharge in the TL. The resistive/dielectric losses are undesirable, too. They decrease the efficiency of the antenna. b) transmission-line Thevenin equivalent circuit of a receiving antenna The antenna is a critical component in a wireless communication system. A good design of the antenna can relax system requirements and improve its overall performance. Radiation Pattern  An antenna radiation pattern (RP) or antenna pattern is defined as “a mathematical function or a graphical representation of the radiation properties of the antenna as a function of space coordinates.  In most cases, the radiation pattern is determined in the far field region and is represented as a function of the directional coordinates.  Radiation properties include power flux density ‫ﻛﺜﺎﻓﺔ‬, radiation intensity‫ﺷﺪة‬, field strength, directivity, phase or polarization.  A trace of the received electric (magnetic) field at a constant radius is called the amplitude field pattern (typically represents a plot of the magnitude of the electric or magnetic field as a function of the angular space Figure (a))  A graph of the spatial variation of the power density along a constant radius is called an amplitude power pattern (typically represents a plot of the square of the magnitude of the electric or magnetic field as a function of the angular space Figure (b)).  Note: The power pattern and the amplitude field pattern are the same when computed and plotted in dB as Figure (c).  Radiation Pattern Lobes 4 21 D  Pattern lob is a portion of the RP whose local radiation intensity si maximum is relatively weak radiation intensity. -=S g) · Sl jdi  A major lobe (also called main beam) is defined as “the radiation lobe containing the direction of maximum radiation.” 1 Y'255 8.41 &  A minor lobe is any lobe except a major lobe. & A side lobe is “a radiation lobe in any direction other than the - -6/1 &I  I & I intended lobe.” (Usually a side lobe is adjacent to the main lobe 55 - sigg ? and occupies the hemisphere in the direction of the main beam.)  Side lobes are normally the largest of the minor lobes. Ojwi midi is gigs !"I A back lobe is “a radiation lobe whose axis makes an angle of &I &d  200819/ 951 & approximately 180◦ with respect to the beam of an antenna.” Usually it refers to a minor lobe that occupies the hemisphere in a · direction opposite to that of the major (main) lobe. s