School on Digital and Multimedia Communications Using Terrestrial

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 Antenna Fundamentals (2) R. Struzak ryszard. struzak@ties. itu. int 15 Feb 2001 Property of R. Struzak 1

• 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 These materials may not be published, copied to or issued from another Web server without the author's express permission.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 ryszard. struzak@ties. itu. int. 15 Feb 2001 Property of R. Struzak 2

Summary Slide • • • Power Transfer EM Field Linear Antenna Radiation Resistance Radiation Pattern 15 Feb 2001 Property of R. Struzak 3

Power Transfer 15 Feb 2001 Property of R. Struzak 4

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 = Ae / A A: physical area of antenna’s aperture, square meters 15 Feb 2001 Property of R. Struzak 5

Power Transfer in Free Space • : wavelength [m] • PR: power available at the receiving antenna • PT: power delivered to the transmitting antenna • GR: gain of the transmitting antenna in the direction of the receiving antenna • GT: gain of the receiving antenna in the direction of the transmitting antenna • Matched polarizations 15 Feb 2001 Property of R. Struzak 6

Power Transfer: Example 1 • What is the power received from GEO satellite ( =0. 1 m, PT =440 W, GT=1000) at Trieste (distance ~38'000 km, GR=1)? • Free space 15 Feb 2001 Property of R. Struzak 7

Power Transfer: Example 2 • What is the power from a transmitter ( =0. 1 m, PT=440 m. W, GT=1) received at distance of 3. 8 cm (GR=1)? • Free space 15 Feb 2001 Property of R. Struzak 8

EM Field 15 Feb 2001 Property of R. Struzak 9

EM Field of Linear Current Element Er z E OP dz r E y x dz: electric current element (short electrical dipole) 15 Feb 2001 Property of R. Struzak 10

EM Field of Current Element Idz: “moment of linear current element” Johnson & Jasik: Antenna Engineering Handbook; T. Dvorak: Basics of Radiation Measurements, EMC Zurich 1991; J. Dunlop, D. Smith Telecommunications Engineering 1995, p. 216 15 Feb 2001 Property of R. Struzak 11

Field Components 15 Feb 2001 Property of R. Struzak 12

Field Impedance Field impedance Z = E/H depends on the antenna type and on distance 15 Feb 2001 Property of R. Struzak 13

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 2001 Property of R. Struzak 14

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

Linear Antenna 15 Feb 2001 Property of R. Struzak 16

Arbitrary Linear Antenna • I(z): antenna current • r: distance 15 Feb 2001 Property of R. Struzak 17

EM Field of Linear Antennas O 15 Feb 2001 • 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 Property of R. Struzak 18

Very Short Antenna • r: distance • Le: effective length of antenna 15 Feb 2001 Property of R. Struzak 19

Radiation Resistance 15 Feb 2001 Property of R. Struzak 20

Self- Impedance • Transmitting antenna • Receiving antenna E j. X: energy stored in near-field components (E C, H L) Z Rrad: energy radiated Z E = Electromotive force (open-circuit voltage) induced by radio wave Rlos: energy loss 15 Feb 2001 Property of R. Struzak 21

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(Le/ )2 – For other antennas it is much easier to measure the antenna impedance. 15 Feb 2001 Property of R. Struzak 22

Integration Surface rd rsin d. S = 2 r 2 sin( )d r d 15 Feb 2001 Property of R. Struzak 23

Radiation Pattern 15 Feb 2001 Property of R. Struzak 24

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 2001 Property of R. Struzak 25

Short Dipole in Free Space FF 1 -1 Horizontal plane: GVi /GVimax = 1 Vertical plane: GHi /GHimax = |sin | 15 Feb 2001 Property of R. Struzak 26

Elements of Radiation Pattern Main lobe Emax Sidelobes Emax / 2 Nulls -180 15 Feb 2001 0 Beamwidth 180 • • Gain Beam width Nulls (positions) Side-lobe levels (envelope) • Front-to-back ratio Property of R. Struzak 27

Long Antenna with Sinusoidal Current Distribution r(z) z r z cos r: distance 15 Feb 2001 Property of R. Struzak 28

Demonstration (Simulation) Lin. Ant. Long This program simulates radiation pattern of linear antenna of arbitrary length. It produces 2 D radiation diagrams that show the positions and magnitudes of radiation lobes, and positions of zeros depend on the antenna length 15 Feb 2001 Property of R. Struzak 29

Half-wave Dipole (l = /2) • Radiation resistance = 73. 1 ohm 15 Feb 2001 Property of R. Struzak 30

Half-wave Dipole at Harmonics Odd harmonics 15 Feb 2001 Property of R. Struzak 31

Antenna Mask (Example 1) • Typical relative directivitymask of receiving antenna (Yagi ant. , TV dcm waves) [CCIR doc. 11/645, 17 -Oct 1989) 15 Feb 2001 Property of R. Struzak 32

Antenna Mask (Example 2) 0 d. B Phi 0/2 -3 d. B Phi Reference pattern for co-polar and cross-polar components for satellite transmitting antennas in Regions 1 and 3 (Broadcasting ~12 GHz) 15 Feb 2001 Property of R. Struzak 33