15 Feb 2001Property of R. Struzak1 Antenna Fundamentals (1) Prof. R. Struzak School on Digital and Multimedia Communications Using Terrestrial and Satellite Radio Links The Abdus Salam International Centre for Theoretical Physics ICTP Trieste (Italy) 12 February – 2 March 2001

15 Feb 2001Property of R. Struzak2 Note: These materials may be used for study, research, and education in not-for-profit applications. If you link to or cite these materials, please credit the author, Ryszard Struzak. These materials may not be published, copied to or issued from another Web server without the author's express permission. Copyright © 2001 Ryszard Struzak. All commercial rights are reserved. If you have comments or suggestions, please contact the author at

15 Feb 2001Property of R. Struzak3 Summary Slide Introduction PFD Directivity and Gain EIRP

15 Feb 2001Property of R. Struzak4 Introduction

15 Feb 2001Property of R. Struzak5 Radio Link Antenna Transmitter Antenna Receiver Antennas: important elements of any radio link Radio wave

15 Feb 2001Property of R. Struzak6 Photographs of Various Antenna Types

15 Feb 2001Property of R. Struzak7 T-Antenna Transmitting antenna transforms power in the form of time-dependent electrical current into time-and-space-dependent electro-magnetic (EM) wave.

15 Feb 2001Property of R. Struzak8 R-Antenna Receiving antenna t ransforms time-and-space-dependent EM wave into time-dependent electrical current (power)

15 Feb 2001Property of R. Struzak9 Intended Antennas Radiocommunication antennas –Transmitting –Receiving EM applicators –Industrial –Medical Measuring antennas

15 Feb 2001Property of R. Struzak10 Unintended Antennas Any conductor/ installation carrying electrical current –(e.g. electrical installation of vehicles) Any conducting structure/ installation irradiated by EM waves –Permanent (e.g. Antenna masts, or power network) –Time-varying (e.g. Windmills, or helicopter propellers) –Transient (e.g. Re-radiating aeroplane)

15 Feb 2001Property of R. Struzak11 PFD

15 Feb 2001Property of R. Struzak12 PFD: Isotropic Radiator Notes Loss-less propagation medium assumed Isotropic radiator cannot be physically realized PFD does not depend on frequency/ wavelength r Power Flux Density (PFD)

15 Feb 2001Property of R. Struzak13 PFD: Distance Dependence

15 Feb 2001Property of R. Struzak14 PFD: Example 1 What is the PFD from TV broadcast GEO satellite at Trieste? EIRP = 180 kW (52.5 dB(W)) Distance: ~38'000 km Free space

15 Feb 2001Property of R. Struzak15 PFD: Example 2 What is the PFD from a hand-held phone at the head? EIRP = 180 mW Distance = ~3.8 cm Free space

15 Feb 2001Property of R. Struzak16 PFD: Example 3 What is the ratio of the powers required to produce the same power flux density at a GEO- satellite and at a LEO-satellite.? Distances: –GEO: km –LEO: km

15 Feb 2001Property of R. Struzak17 PFD concept Used often in the management/ regulating the use of the radio frequency spectrum To define the restrictions imposed on radiocommunication systems To assure electromagnetic compatibility Relates to the field-strength of plane wave

15 Feb 2001Property of R. Struzak18 PFD Limits The WRC 2000 decided that the PFD at the Earth’s surface produced by emission from a space station in Fixed-satellite service shall not exceed the limit shown in the figure. The figure is valid for stations at the geostationary orbit in frequency band GHz and reference band 4 kHz. For other cases see RR Table S21-4.

15 Feb 2001Property of R. Struzak19 PFD: Real Antenna PFD produced by physically realizable antennas depends on –power and distance (as isotropic source) –horizontal direction angle (  ) –vertical direction angle (  )

15 Feb 2001Property of R. Struzak20 Directivity and Gain

15 Feb 2001Property of R. Struzak21 Radiation Intensity Radiation intensity = Power per steradian = =  ( ,  ) [watts/steradian] x y z   OP Transmitting antenna r Distance (r) is very large measure of the ability of an antenna to concentrate radiated power in a particular direction

15 Feb 2001Property of R. Struzak22 Antenna Directivity D Has no units Note: P 0 = power radiated

15 Feb 2001Property of R. Struzak23 Antenna Gain The directivity and gain are measures of the ability of an antenna to concentrate power in a particular direction. Directivity – power radiated by antenna (P 0 ) Gain – power delivered to antenna (P T )  : radiation efficiency (50% - 75%) G has no units –Usually relates to the peak directivity of the main radiation lobe –Often expressed in dB –Known as “Absolute Gain” or “Isotropic Gain”

15 Feb 2001Property of R. Struzak24 PFD vs. Antenna Gain S 0 = PFD produced by a loss-less isotropic radiator

15 Feb 2001Property of R. Struzak25 Other Definitions of Gain For practical purposes, the antenna gain is defined as the ratio (usually in dB), of the power required at the input of a loss-free reference antenna to the power supplied to the input of the given antenna to produce, in a given direction, the same field strength or the same power flux-density at the same distance. When not specified otherwise, the gain refers to the direction of maximum radiation. The gain may be considered for a specified polarization. [RR 154]

15 Feb 2001Property of R. Struzak26 Antenna Gain Actual antenna P = Power Delivered to the antenna S = Power received at a great distance Measuring equipment Reference antenna P o = Power Delivered to the antenna S = Power received at a great distance Measuring equipment Antenna Gain (in the specific direction) = P / P o

15 Feb 2001Property of R. Struzak27 Reference Antennas Isotropic radiator –isolated in space (G i, absolute gain, or isotropic gain) Half-wave dipole –isolated in space, whose equatorial plane of symmetry contains the given direction (G d ) Short vertical antenna –(much shorter than /4), close to, and normal to a perfectly conducting plane which contains the given direction (G v )

15 Feb 2001Property of R. Struzak28 Reference Antennas (1) Isotropic antenna Sends (receives) energy equally in (from) all directions Gain = 1 (= 0 dB) When supplied by P, produces at distance r power flux density = P /(4  r 2 ) Theoretical concept, cannot be physically realized Radiation pattern in vertical plane Radiation pattern In horizontal plane

15 Feb 2001Property of R. Struzak29 Reference Antennas (2) Half-Wave Dipole Linear antenna, realizable Gain = 1.64 (= 2,15 dB) in the direction of maximum radiation Figure-eight-shaped radiation pattern in the dipole plane, omnidirectional (circular) in the orthogonal plan Radiation pattern in vertical plane Radiation pattern In horizontal plane

15 Feb 2001Property of R. Struzak30 Typical radiation pattern Omnidirectional –Broadcasting –Mobile telephony Pencil-beam –Microwave links Fan-beam (narrow in one plane, wide in the other) Shaped-beam –Satellite antennas

15 Feb 2001Property of R. Struzak31 Typical Gain and Beam-width Type of antennaG i [dB] HPBW [ 0 ] Isotropic0360x360 Dipole2360x120 Helix (10 turn)1435x35 Small dish1630x30 Large dish451x1

15 Feb 2001Property of R. Struzak32 Gain and Beam-width Gain and beam-width of directive antennas are inter-related G ~ / (  1 *  2 )  1 and  2 are the 3-dB beam-widths (in degrees) in the two orthogonal principal planes of antenna radiation pattern.

15 Feb 2001Property of R. Struzak33 EIRP

15 Feb 2001Property of R. Struzak34 e.i.r.p. Equivalent Isotropically Radiated Power (in a given direction): The product of the power supplied to the antenna and the antenna gain relative to an isotropic antenna in a given direction

15 Feb 2001Property of R. Struzak35 e.i.r.p.: Example 1 PFD = e.i.r.p./(4  d 2 ) e.i.r.p. = PFD*(4  d 2 ) -160 dB  W/(m 2 *4kHz) d 2 ~ 1.29*10 15 m 2 4  d 2 ~ 4*10 15 m 2 e.i.r.p. ~ 0.4 W/4kHz What is the maximum e.i.r.p. of a GEO satellite station if RR impose PFD limits of (-160) dB (W/(m 2 *4kHz)) at the earth surface in Equator (distance km) ?

15 Feb 2001Property of R. Struzak36 e.r.p. Effective Radiated Power (in a given direction): The product of the power supplied to the antenna and its gain relative to a half-wave dipole in a given direction