1. 15 Feb 2001Property of R. Struzak1 Antenna Fundamentals (3) R. Struzak ryszard.struzak@ties.itu.int 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

2. 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 These materials may not be published, copied to or issued from another Web server without the author's express permission.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 ryszard.struzak@ties.itu.int.

3. 15 Feb 2001Property of R. Struzak3 Summary Slide Transmission vs. Reception Polarization More Complex Antennas Antenna Arrays, Adaptive Antennas

4. 15 Feb 2001Property of R. Struzak4 Polarization

5. 15 Feb 2001Property of R. Struzak5 Polarization ellipse The two linear far-field components radiated by the horizontal and the vertical antenna sum up to a resultant elliptically polarized wave The polarization ellipse is defined by its axial ratio N/M (ellipticity), tilt angle  and sense of rotation EyEy ExEx M N 

6. 15 Feb 2001Property of R. Struzak6 Polarization states 45 0 LINEAR UPPER HEMISPHERE: ELLIPTIC POLARIZATION LEFT_HANDED SENSE LOWER HEMISPHERE: ELLIPTIC POLARIZATION RIGHT_HANDED SENSE EQUATOR: LINEAR POLARIZATION LATTITUDE: REPRESENTS AXIAL RATIO LONGITUDE: REPRESENTS TILT ANGLE POLES REPRESENT CIRCULAR POLARIZATIONS LHC RHC (Poincaré sphere)

7. 15 Feb 2001Property of R. Struzak7 Antenna Polarization The polarization of an antenna in a specific direction is defined to be the polarization of the wave produced by the antenna at a great distance

8. 15 Feb 2001Property of R. Struzak8 Polarization Efficiency (1) The power received by an antenna from a particular direction is maximal if the polarization of the incident wave has: –the same axial ratio –the same sense of polarization –the same spatial orientation as the polarization of the antenna in that direction.

9. 15 Feb 2001Property of R. Struzak9 Polarization Efficiency (2) When the polarization of the incident wave is different from the polarization of the receiving antenna, then a loss due to polarization mismatch occurs Polarization efficiency = = (power actually received) / (power that would be received if the polarization of the incident wave were matched to the receiving polarization of the antenna)

10. 15 Feb 2001Property of R. Struzak10 Polarization Efficiency (3) H RCH LCH 45 0 LINEAR 22 Polarization efficiency = cos 2  W A A: POLARIZATION OF RECEIVING ANTENNA W: POLARIZATION OF INCIDENT WAVE

11. 15 Feb 2001Property of R. Struzak11 Circularly-Polarized Antenna Radio wave of any polarization can be obtained by superposition of 2 linearly-polarized waves produced by 2 crossed dipoles and by controlling the amplitude- ratio and phase-difference of their excitations. y x I x cos(  t+  x ) I y cos(  t+  y )

12. 15 Feb 2001Property of R. Struzak12 More Complex Antennas

13. 15 Feb 2001Property of R. Struzak13 Antenna Over Ground: Image Theory Perfect ground = perfectly conducting plane surface Tangential electrical field component = 0 –vertical components: the same direction –horizontal components: opposite directions The field (above the ground) is the same if the ground is replaced by the antenna image + -

14. 15 Feb 2001Property of R. Struzak14 2 Antennas 2 identical antennas –Excitation: I 1 = I, I 2 =Ie j  Ant#1 field-strength: E’= C*D( ,  ) Ant#2 field-strength : E” = C*D( ,  )*e j  (  r+  ) E = E’ + E”  r = d*cos  1 2 r r r rr d 

15. 15 Feb 2001Property of R. Struzak15 Antenna Array Factor (AAF) Resultant field-strength E = E’ + E” E = C*D( ,  )*[1+e j  (  r+  ) ] = C*D( ,  )*AAF( ,  )  Pattern multiplication |AAF( ,  )| 2 = Antenna array factor = Gain of array of isotropic antennas

16. 15 Feb 2001Property of R. Struzak16 2 Antenna Array Factor (1) AAF(  ) = 1+e j  (  r+  ) ;  (  r+  ) = x AAF(  ) = 1+e jx = 2[(1/2)(e -jx/2 +e jx/2 )]e jx/2 = 2cos(x/2)e jx/2 |AAF(  )| = 2cos(x/2) = 2cos[  (d/2)cos  +  /2) = 2cos[(  d/ )cos  +  /2] |AAF(  )| 2  Antenna Array Factor

17. 15 Feb 2001Property of R. Struzak17 2 Antenna Array Factor (2) |AAF(  )| 2 = {2cos[(  d/ )cos  +  /2]} 2 Gain: Max{|AAF(  )| 2 } = 4 (6 dBi) when (  d/ )cos  +  /2 = 0, , …, k  Nulls: when (  d/ )cos  +  /2 =  /2, …, (k + 1)  /2 Relative gain = |AAF(  )| 2 / Max{|AAF(  )| 2 }

18. 15 Feb 2001Property of R. Struzak18 Demonstration (Simulation) Array2ant This program simulates radiation pattern of 2 antenna-array factor. It produces 2D diagrams showing how the radiation lobes maximums and minimums depends on the antennas distance and excitation phases and magnitudes

19. 15 Feb 2001Property of R. Struzak19 Antenna Arrays

20. 15 Feb 2001Property of R. Struzak20 Yagi-Uda Arrays Only one antenna- element fed Other elements unexcited (parasitic) Non-identical elements Non-identical distances Directors Reflector Driver

21. 15 Feb 2001Property of R. Struzak21 Linear Array of n Antennas equally spaced antennas in line currents of equal magnitude constant phase difference between adjacent antennas numbered from 0 to (n-1) F = 1+e jx +e j2x +e j3x +…+e j(N-1)x = (1-e jNx ) / (1-e jx ) |F| = |(1-e jNx ) / (1-e jx )| = [sin(Nx/2) / sin(x/2)] = F(  )  array factor x/2 = (  d/ )cos  +  /2

22. 15 Feb 2001Property of R. Struzak22 Demonstration (Simulation) Array_Nan This program simulates radiation pattern of N - antenna-array factor. It produces 2D diagrams showing how the radiation lobes maximums and minimums depends on the antenna distance increment and on excitation phase and magnitude functions

23. 15 Feb 2001Property of R. Struzak23 Mutual Impedance Array of antennas V 1 = I 1 Z 11 +I 2 Z 12 +…+I n Z 1n V 2 = I 1 Z 12 +I 2 Z 22 +…+I n Z 2n. -…… V n = I 1 Z 1n +I 2 Z 2n +…I n Z nn Z 1input = V 1 /I 1 = Z 11 +(I 2 /I 1 )Z 12 +…+(I n /I 1 )Z 1n The input impedance depends on mutual impedance (coupling) with other antennas and on relative currents

24. 15 Feb 2001Property of R. Struzak24 Example: Impedance of Dipole ~73  ~300  /2 < /4

25. 15 Feb 2001Property of R. Struzak25 Phased Arrays Array of N antennas in a linear or spatial configuration The amplitude and phase excitation of each individual antenna controlled electronically (“software-defined”) –Diode phase shifters –Ferrite phase shifters Inertia-less beam-forming and scanning (  sec) with fixed physical structure

26. 15 Feb 2001Property of R. Struzak26 Antenna Arrays: Benefits Possibilities to control –Direction of maximum radiation –Directions (positions) of nulls –Beam-width –Directivity –Levels of sidelobes using standard antennas (or antenna collections) independently of their radiation patterns Antenna elements can be distributed along straight lines, arcs, squares, circles, etc.

27. 15 Feb 2001Property of R. Struzak27 Beam Steering Beam- steering using phase shifters at each radiating element Radiating elements Power distribution Phase shifters Equi-phase wave front  = [(2  / )d sin  ] 33 22 0  d Beam direction

28. 15 Feb 2001Property of R. Struzak28 4-Bit Phase-Shifter (Example) 0 0 or 22.5 0 0 0 or 45 0 0 0 or 90 0 0 0 or 180 0 InputOutput Bit #4 Bit #3 Bit #2 Bit #1 Steering/ Beam-forming Circuitry

29. 15 Feb 2001Property of R. Struzak29 Switched-Line Phase Bit 2 delay lines and 4 diodes per bit Input Output Diode switch Delay line

30. 15 Feb 2001Property of R. Struzak30 Switching Diode Circuit a:RF short-circuited in forward bias b: RF short-circuited in reverse bias PIN diode Tuning element PIN diode Tuning element a b

31. 15 Feb 2001Property of R. Struzak31 Adaptive “Intelligent” Antennas

32. 15 Feb 2001Property of R. Struzak32 Adaptive (“Intelligent”)Antennas Array of N antennas in a linear or spatial configuration Used for receiving signals from desired sources and suppress incident signals from undesired sources The amplitude and phase excitation of each individual antenna controlled electronically (“software- defined”) The weight-determining algorithm uses a-priori and/ or measured information The weight and summing circuits can operate at the RF or at an intermediate frequency w1 wN  Weight-determining algorithm 1 N