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Lecture Wireless and mobile computing – Chapter 16: Antennas and Propagation…

The following will be discussed in this chapter: Dipole antenna, antenna gain, antenna length, radiation mechanism, radiation pattern, antenna efficiency, beam width, types of antennas, propagation modes, noise categories. | Antennas and Propagation . Lecture 16 Overview Dipole Antenna Antenna Gain Antenna Length Radiation Mechanism Radiation Pattern Antenna Efficiency Beam Width Types of Antennas Propagation Modes Noise Categories Dipole Antenna One of the most widely used antenna types is the half-wave dipole. The half-wave dipole, also called a doublet, is formally known as the Hertz antenna. A dipole antenna is two pieces of wire, rod, or tubing that are one-quarter wavelength long at the operating resonant frequency. Converting a Transmission Line into an Antenna Bending at right angles produces an efficient radiator Optimum radiation occurs when the length is 1/2 of a wavelength Magnetic fields now support each other Three-dimensional radiation pattern for a dipole. Dipole Antenna Vertically Mounted This pattern is a donut shape with the antenna passing thru the center. There is no radiation from the end of the antenna. Antenna gain (G) A dipole antenna gain is 1.64 A half-wave dipole antenna has a power gain of 1.64 (or 2.15 dB) over an isotropic source. Antenna gain relative to a dipole antenna can be expressed in decibels as dBd. Thus, an antenna with a gain of 3 dBd would have a gain of 5.15 dBi (3 dB + 2.15 dB) http://www.hedylamarr.org/ In 1936 Hedy Lamarr became the first woman to grace the silver screen in a feature film wearing nothing but her birthday suit. Five years later, at a Hollywood dinner party, she engaged in a passionate discussion with an avant-garde composer about protecting U.S. radio-guided torpedoes from enemy interference. She scrawled her phone number in lipstick on the windshield of his car so they could develop their ideas further. In 1942, unbeknownst to her adoring public, the unlikely duo secured a patent and gave it to the United States government for a "Secret Communications System" expressly constructed to assist in the defeat of Hitler. The science presented in this patent serves as the basis for the . | Antennas and Propagation . Lecture 16 Overview Dipole Antenna Antenna Gain Antenna Length Radiation Mechanism Radiation Pattern Antenna Efficiency Beam Width Types of Antennas Propagation Modes Noise Categories Dipole Antenna One of the most widely used antenna types is the half-wave dipole. The half-wave dipole, also called a doublet, is formally known as the Hertz antenna. A dipole antenna is two pieces of wire, rod, or tubing that are one-quarter wavelength long at the operating resonant frequency. Converting a Transmission Line into an Antenna Bending at right angles produces an efficient radiator Optimum radiation occurs when the length is 1/2 of a wavelength Magnetic fields now support each other Three-dimensional radiation pattern for a dipole. Dipole Antenna Vertically Mounted This pattern is a donut shape with the antenna passing thru the center. There is no radiation from the end of the antenna. Antenna gain (G) A dipole antenna gain is 1.64 A .