Chair of Network Architectures and Services Department of Informatics Technical University of Munich Antenna Basics Markus Hamberger Friday 11 th January, 2019 Chair of Network Architectures and Services Department of Informatics Technical University of Munich
Introduction • First antenna invented in 1886 by Heinrich Hertz • Global antenna market expected to hit USD 25.46 billion by 2023 with a compound annual growth rate of 6.61% [2] • Growth driven by increased sales figures of smartphones and adoption of IoT devices Figure 2: Global antenna market 2010-2017 2 Figure 1: Heinrich Hertz 1 1 Heinrich Hertz image: https://commons.wikimedia.org/wiki/File:HEINRICH_HERTZ.JPG 2 Antenna market diagram: https://www.bccresearch.com/pressroom/ift/global-antenna-market-reach-nearly-$16.9-billion-2017 M. Hamberger — Antenna Basics 2
Physical concepts of antennas • Antennas transfer conducted electromagnetic waves into electromagnetic waves propagat- ing through space and vice versa • The structure of an antenna can be imagined as an electrical oscillator circuit • A changing magnetic field is inducing an electric field (in blue), which creates an magnetic field (in red) again [7] Figure 3: LC-Circuit Figure 4: Half-Wave Dipole Formation of a dipole from a LC-Circuit M. Hamberger — Antenna Basics 3
Physical concepts of antennas Radiation power density • The whole transmitter power P TX minus losses is converted into electromagnetic energy • Radiation power density S is described by the norm of the Poynting vector (1) • S is declining by 1 r 2 for a distance r [5] • The higher the radiation power density is at the receiving antenna, the better is the signal strength S = 1 � 2 ( � E × � H ∗ ) (1) M. Hamberger — Antenna Basics 4
Isotropic antenna • Ideal theoretical antenna that radiates equally in all directions • Used as a reference antenna for gain and radiated power • The EIRP value shows the amount of power an isotropic antenna would emit, in order to have the same power density of the compared antenna (2) [8] • The EIRP value is calculated by adding the power accepted by the antenna from the trans- mitter P t with the antenna gain in relation to an isotropic antenna G i EIRP (dBW) = P t (dBW) + G i (dBi) (2) Figure 5: Isotropic antenna radiation 1 1 isotropic antenna image: https://shopdelta.eu/dbi-power-gain-of-isotropic-antenna_l2_aid836.html M. Hamberger — Antenna Basics 5
Properties Reciprocity • The principle of reciprocity is a powerful tool of investigation a analogy in the performance of receiving and transmitting antennas • A receiving antenna can also function as a transmitting antenna and vice versa • The radiation pattern, gain, impedance, bandwidth of a receiving/transmitting antenna is the same • The better an antenna transmits in one direction, the better it receives from that direction [6] M. Hamberger — Antenna Basics 6
Properties Frequency and bandwidth • Dimensions of the antenna determen the frequency • For instance, a half-wave dipole antenna transmits and receives on frequencies which are half of the conductors length • The bandwidth is defined as the range of frequencies over which the antenna can properly receive/transmit Table 1: The Electromagnetic Spectrum Band Frequency Example Uses ELF 3 to 30 Hz SLF 30 to 300 Hz Power Lines ULF 300 to 3 kHz VLF 3 to 30 kHz Submarine communication LF 30 to 300 kHz RFID MF 300 kHz to 3 MHz AM broadcast HF 3 to 30 MHz Shortwave broadcast VHF 30 to 300 MHz FM and TV broadcast UHF 300 MHz to 3 GHz TV, WLAN,GPS,Microwave ovens SHF 3 to 30 GHz Radar, WLAN,Satellite communication EHF 30 to 300 GHz Radar, Radio astronomy, Point-to-point high rate data links,Satellite communication M. Hamberger — Antenna Basics 7
Properties Radiation patterns • Radiation patterns are used to illustrate variations in power density • Antennas which radiate non-directional (equally) in one plane are called omnidirectional • Directional antennas radiate significantly more in some directions [5] Figure 6: Half-Wave Dipole Radiation Pattern 1 Figure 7: Dish Antenna Radiation Pattern 2 1 Dipole radiation pattern image: http://www.antenna-theory.com/antennas/norm3D1lam.jpg 2 Dish antenna radiation pattern image: http://www.antenna-theory.com/basics/radpattern.php M. Hamberger — Antenna Basics 8
Properties Field regions • Depending on the distance R to an antenna, the radiation changes with the frequency λ and the antenna dimension D • Three different field regions • Reactive near-field at a distance R < 0.62 � D 3 /λ • Radiating near-field at a distance 0.62 � D 3 /λ< R < 2 D 2 /λ • Far-field at a distance R > 2 D 2 /λ • Reactive fields are dominating in the reactive near-field because the electromagnetic waves are still bound to the antenna • In the far-field the radiation pattern does not change anymore and the E and H field are in phase and have equal magnitudes • The radiating near-field is a transition zone, which is negligible for small antennas [7] M. Hamberger — Antenna Basics 9
Properties Polarization • The polarization is defined as the direction of the electric field vector • Three different types of polarization • Linear polarization • Circular polarization • Elliptical polarization • Polarization mismatch leads to a polarization loss factor (PLF) [5] PLF for linear polarization with a ψ angle difference PLF = | cos( ψ ) | 2 (3) Table 2: Expected polarization mismatch loss [3] vertical linear horizontal linear rigth-hand circular left-hand circular vertical linear 0 dB ∞ 3 dB 3 dB horizontal linear ∞ 0 dB 3 dB 3 dB rigth-hand circular 3 dB 3 dB 0 dB ∞ left-hand circular 3 dB 3 dB ∞ 0 dB M. Hamberger — Antenna Basics 10
Properties Directivity and gain • The directivity D of an antenna is defined as "the ratio of the radiation intensity in a given direction from the antenna to the radiation intensity averaged over all directions" [4] 4 π r 2 r 2 = P r P r U = 4 π U U = Sr 2 D = (6) U ave = (5) (4) U ave P r 4 π • Gain is directly related to its directivity, but besides also takes the antenna’s radiation effi- ciency e r into account [8] (7) G = e r D Figure 8: Different radiation patterns 2 2 Radiation pattern image: https://www.hamradio.me/tech-talk/antenna-gain M. Hamberger — Antenna Basics 11
Properties Impedance • An antenna’s impedance Z A is the complex resistance at its feeding point • In order to maximize the input power P in at the antenna, the impedance of the connected transmitter Z TX has to be matched • If there is a mismatch, a part of the transmitter power is reflected back, represented by the reflection coefficient Γ • The Voltage Standing Wave Ration (VSWR) is a measurement for how well the impedance is matched [8] Γ = Z A − Z TX VSWR = 1 + | Γ | (8) (9) Z A + Z TX 1 − | Γ | M. Hamberger — Antenna Basics 12
Properties Efficiency • The total antenna efficiency e 0 is defined as the product of reflection efficiency e ref , con- duction efficiency e c and dielectric efficiency e d • The product of e c and e d equals the radiation efficiency e r e ref = 1 − | Γ | 2 (10) (11) e 0 = e ref e c e d • The Friis Transmission Equation relates the power P t transmitted from one antenna to the power P r received at another antenna [5] P r λ 4 π R ) 2 D t D r PLF (12) = e 0 t e 0 r ( P t M. Hamberger — Antenna Basics 13
Legal issues • The Radio Regulations (RR) of the International Telecommunication Union (ITU) regulates and assigns the frequency bands to radiocommunication services internationally • The usage of antennas in the ISM-Band is license-free and legal for everyone, but is limited to a maximum EIRP value limited to a maximum EIRP value • For instance, indoor-only wireless lan are allowed to have a EIRP of 200mW, whereas outdoor WLAN antennas can have an EIRP value up to 1000mW [1] • National laws may differ M. Hamberger — Antenna Basics 14
Summary • Antennas turn electromagnetic waves moving in conductors into electromagnetic waves propagating through space • The main characteristics are frequency, bandwidth, radiation pattern, gain, polarization and impedance • The size of an antenna mostly specifies the frequency and the bandwidth • The Friis equation defines the overall perfomance • Laws by the ITU regulate the wireless communication M. Hamberger — Antenna Basics 15
Thanks for your attention! Email: hambergm@in.tum.de M. Hamberger — Antenna Basics 16
Bibliography [1] Itu. https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-SM.2153-2-2011-PDF-E.pdf . [2] Mordor intelligence. https://www.mordorintelligence.com/industry-reports/antenna-market . [3] Rohde & schwarz. https://rohde-schwarz.com/de/applikationen/antennengrundlagen-white-paper_230854-59777.html . [4] Ieee std 145-2013, 2014. [5] C. Balanis. Antenna theory - analysis and design, 2016. [6] M. Neiman. The principle of reciprocity in antenna theory, 1943. [7] E. Stirner. Antennen band 1: Grundlagen, 1977. [8] W. Stutzman and G. A. Thiele. Antenna theory and design, 2012. M. Hamberger — Antenna Basics 17
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