Antenna Fundamentals (1).ppt

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1、15 Feb 2001,Property of R. Struzak,1,Antenna Fundamentals (1),Prof. R. Struzak ryszard.struzakties.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

2、 2001,15 Feb 2001,Property of R. Struzak,2,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 These materials may not be published, copied to or issued from another We

3、b server without the authors express permission. Copyright 2001 Ryszard Struzak. All commercial rights are reserved. If you have comments or suggestions, please contact the author at ryszard.struzakties.itu.int.,15 Feb 2001,Property of R. Struzak,3,Summary Slide,Introduction PFD Directivity and Gain

4、 EIRP,15 Feb 2001,Property of R. Struzak,4,Introduction,15 Feb 2001,Property of R. Struzak,5,Radio Link,Antenna,Transmitter,Antenna,Receiver,Antennas: important elements of any radio link,Radio wave,15 Feb 2001,Property of R. Struzak,6,Photographs of Various Antenna Types,15 Feb 2001,Property of R.

5、Struzak,7,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 2001,Property of R. Struzak,8,R-Antenna,Receiving antenna transforms time-and-space-dependent EM wave into time-dependent electr

6、ical current (power),15 Feb 2001,Property of R. Struzak,9,Intended Antennas,Radiocommunication antennas Transmitting Receiving EM applicators Industrial Medical Measuring antennas,15 Feb 2001,Property of R. Struzak,10,Unintended Antennas,Any conductor/ installation carrying electrical current (e.g.

7、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 2001,Property of R. Struzak,11,PFD,15 Feb 2001,Pr

8、operty of R. Struzak,12,PFD: Isotropic Radiator,Notes Loss-less propagation medium assumed Isotropic radiator cannot be physically realized PFD does not depend on frequency/ wavelength,Power Flux Density (PFD),15 Feb 2001,Property of R. Struzak,13,PFD: Distance Dependence,15 Feb 2001,Property of R.

9、Struzak,14,PFD: Example 1,What is the PFD from TV broadcast GEO satellite at Trieste? EIRP = 180 kW (52.5 dB(W) Distance: 38000 kmFree space,15 Feb 2001,Property of R. Struzak,15,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 2001

10、,Property of R. Struzak,16,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: 38 000 km LEO: 1 000 km,15 Feb 2001,Property of R. Struzak,17,PFD concept,Used often in the management/ regulating th

11、e 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 2001,Property of R. Struzak,18,PFD Limits,The WRC 2000 decided that the PFD at the Earths surface produced

12、 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 10.7-11.7 GHz and reference band 4 kHz. For other cases see RR Table S21-4.,15 Feb 2001,Property of R. Struzak,19

13、,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 2001,Property of R. Struzak,20,Directivity and Gain,15 Feb 2001,Property of R. Struzak,21,Radiation Intensity,Radiati

14、on 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 2001,Property of R. Struzak,22,Antenna Directivity,D Has no units Note: P0 = power

15、 radiated,15 Feb 2001,Property of R. Struzak,23,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 (P0 ) Gain power delivered to antenna (PT),: radiation efficiency (50% - 75%) G has no

16、 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 2001,Property of R. Struzak,24,PFD vs. Antenna Gain,S0 = PFD produced by a loss-less isotropic radiator,15 Feb 2001,Property of R. Struzak,25,Other Defi

17、nitions 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 fl

18、ux-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 2001,Property of R. Struzak,26,Antenna Gain,Actual antenna,P = Power Delivered to the antenna,S = Power receive

19、d at a great distance,Measuring equipment,Reference antenna,Po = Power Delivered to the antenna,S = Power received at a great distance,Measuring equipment,Antenna Gain (in the specific direction) = P / Po,15 Feb 2001,Property of R. Struzak,27,Reference Antennas,Isotropic radiator isolated in space (

20、Gi, absolute gain, or isotropic gain) Half-wave dipole isolated in space, whose equatorial plane of symmetry contains the given direction (Gd) Short vertical antenna (much shorter than /4), close to, and normal to a perfectly conducting plane which contains the given direction (Gv),15 Feb 2001,Prope

21、rty of R. Struzak,28,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 /(4r2) Theoretical concept, cannot be physically realized,Radiation pattern in vertical plane,Rad

22、iation pattern In horizontal plane,15 Feb 2001,Property of R. Struzak,29,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 ortho

23、gonal plan,Radiation pattern in vertical plane,Radiation pattern In horizontal plane,15 Feb 2001,Property of R. Struzak,30,Typical radiation pattern,Omnidirectional Broadcasting Mobile telephony Pencil-beam Microwave links Fan-beam (narrow in one plane, wide in the other) Shaped-beam Satellite anten

24、nas,15 Feb 2001,Property of R. Struzak,31,Typical Gain and Beam-width,15 Feb 2001,Property of R. Struzak,32,Gain and Beam-width,Gain and beam-width of directive antennas are inter-relatedG 30000 / (1*2)1 and 2 are the 3-dB beam-widths (in degrees) in the two orthogonal principal planes of antenna ra

25、diation pattern.,15 Feb 2001,Property of R. Struzak,33,EIRP,15 Feb 2001,Property of R. Struzak,34,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 Fe

26、b 2001,Property of R. Struzak,35,e.i.r.p.: Example 1,PFD = e.i.r.p./(4d2) e.i.r.p. = PFD*(4d2) -160 dB 10-16 W/(m2*4kHz) d2 1.29*1015m2 4d2 4*1015m2 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/(m2*4kHz) at the earth surface in Equator (distance 35900 km) ?,15 Feb 2001,Property of R. Struzak,36,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,