15 Feb 2001Property of R. Struzak1 Antenna Fundamentals (2) 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 These materials may not be published, copied to or issued from another Web server without the author's express permission.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 Power Transfer EM Field Linear Antenna Radiation Resistance Radiation Pattern

15 Feb 2001Property of R. Struzak4 Power Transfer

15 Feb 2001Property of R. Struzak5 Antenna Effective Area Measure of the effective absorption area presented by an antenna to an incident plane wave. Depends on the antenna gain and wavelength Aperture efficiency:  a = A e / A A: physical area of antenna’s aperture, square meters

15 Feb 2001Property of R. Struzak6 Power Transfer in Free Space :wavelength [m] P R :power available at the receiving antenna P T :power delivered to the transmitting antenna G R :gain of the transmitting antenna in the direction of the receiving antenna G T : gain of the receiving antenna in the direction of the transmitting antenna Matched polarizations

15 Feb 2001Property of R. Struzak7 Power Transfer: Example 1 What is the power received from GEO satellite ( =0.1m, P T =440 W, G T =1000) at Trieste (distance ~38'000 km, G R =1)? Free space

15 Feb 2001Property of R. Struzak8 Power Transfer: Example 2 What is the power from a transmitter ( =0.1m, P T =440 mW, G T =1) received at distance of 3.8 cm (G R =1)? Free space

15 Feb 2001Property of R. Struzak9 EM Field

15 Feb 2001Property of R. Struzak10 EM Field of Linear Current Element x y z   OP r ErEr EE EE dz: electric current element (short electrical dipole) dz

15 Feb 2001Property of R. Struzak11 EM Field of Current Element Johnson & Jasik: Antenna Engineering Handbook; T. Dvorak: Basics of Radiation Measurements, EMC Zurich 1991; J. Dunlop, D. Smith Telecommunications Engineering1995, p. 216 Idz: “moment of linear current element”

15 Feb 2001Property of R. Struzak12 Field Components

15 Feb 2001Property of R. Struzak13 Field Impedance Field impedance Z = E/H depends on the antenna type and on distance

15 Feb 2001Property of R. Struzak14 Far-Field, Near-Field Near-field region: –Angular distribution of energy depends on distance from the antenna; –Reactive field components dominate (L, C) Far-field region: –Angular distribution of energy is independent on distance; –Radiating field component dominates (R)

15 Feb 2001Property of R. Struzak15 EM Field: Elementary Current Loop dm: “magnetic dipole moment”

15 Feb 2001Property of R. Struzak16 Linear Antenna

15 Feb 2001Property of R. Struzak17 Arbitrary Linear Antenna I(z): antenna current r: distance

15 Feb 2001Property of R. Struzak18 EM Field of Linear Antennas Summation of vector components E (or H) produced by every antenna element In the far-field region, the vector components are parallel to each other O

15 Feb 2001Property of R. Struzak19 Very Short Antenna r: distance L e : effective length of antenna

15 Feb 2001Property of R. Struzak20 Radiation Resistance

15 Feb 2001Property of R. Struzak21 Self- Impedance Transmitting antennaReceiving antenna jX: energy stored in near-field components (E  C, H  L) Rrad: energy radiated Rlos: energy loss Z Z E E = Electromotive force (open-circuit voltage) induced by radio wave

15 Feb 2001Property of R. Struzak22 Short Antenna Radiation Resistance The PFD in the far field is given by the Poynting’s vector = |= E  | 2 /(120  ) Antenna radiation resistance = = 80  2 (L e / ) 2 –For other antennas it is much easier to measure the antenna impedance.

15 Feb 2001Property of R. Struzak23 Integration Surface dS = 2  r 2 sin(  )d  r rd  dd rsin  

15 Feb 2001Property of R. Struzak24 Radiation Pattern

15 Feb 2001Property of R. Struzak25 Radiation Pattern Radiation Intensity = Power per steradian radiated in a given direction Radiation Pattern = Radiation Intensity as function of the azimuth/ elevation angles Generally 3 dimensional

15 Feb 2001Property of R. Struzak26 Short Dipole in Free Space FF Horizontal plane: G Vi /G Vimax = 1 Vertical plane: G Hi /G Himax = |sin  | 1

15 Feb 2001Property of R. Struzak27 Elements of Radiation Pattern E max E max /  2 Beamwidth Sidelobes Nulls Main lobe Gain Beam width Nulls (positions) Side-lobe levels (envelope) Front-to-back ratio

15 Feb 2001Property of R. Struzak28 Long Antenna with Sinusoidal Current Distribution r: distance z  z cos  r(z) r

15 Feb 2001Property of R. Struzak29 Demonstration (Simulation) LinAntLong This program simulates radiation pattern of linear antenna of arbitrary length. It produces 2D radiation diagrams that show how the positions and magnitudes of radiation lobes, and positions of zeros depend on the antenna length

15 Feb 2001Property of R. Struzak30 Half-wave Dipole (l = /2) Radiation resistance = 73.1 ohm

15 Feb 2001Property of R. Struzak31 Half-wave Dipole at Harmonics Odd harmonics

15 Feb 2001Property of R. Struzak32 Antenna Mask (Example 1) Typical relative directivity- mask of receiving antenna (Yagi ant., TV dcm waves) [CCIR doc. 11/645, 17-Oct 1989)

15 Feb 2001Property of R. Struzak33 Antenna Mask (Example 2) Reference pattern for co-polar and cross-polar components for satellite transmitting antennas in Regions 1 and 3 (Broadcasting ~12 GHz) 0dB -3dB Phi 0 /2 Phi