Reflector Antennas Prof. Girish Kumar Electrical Engineering - PowerPoint PPT Presentation

Reflector Antennas Prof. Girish Kumar Electrical Engineering Department, IIT Bombay gkumar@ee.iitb.ac.in (022) 2576 7436

Flat Reflector Antennas Corner Plane

Curved Reflector Antennas Prime Focus Reflector Cassegrain Reflector

Vertical Dipole Antenna over Infinite Perfect Ground Plane (Reflector)

Directivity and Radiation Resistance of Vertical Dipole Antenna over Infinite Reflector Directivity and radiation resistance of a vertical infinitesimal dipole as a function of its height above an infinite perfect electric conductor

Radiation Pattern of Vertical Dipole Antenna over Infinite Ground Plane (Reflector) Elevation patterns of a vertical infinitesimal dipole for different heights above an infinite perfect electric conductor

Horizontal Dipole Antenna over Infinite Ground Plane (Reflector)

Directivity and Radiation Resistance of Horizontal Dipole Antenna over Infinite Reflector Directivity Radiation Resistance Radiation resistance and directivity of a horizontal infinitesimal electric dipole as a function of its height above an infinite perfect electric conductor

Radiation Pattern of Horizontal Dipole Antenna over Infinite Ground Plane (Reflector) Elevation patterns of a horizontal infinitesimal dipole for different heights above an infinite perfect electric conductor

Corner Reflector Antenna Wave incident at 90 0 Corner Top View of Corner Reflector Antenna Reflector reflects back in the same direction

Corner Reflector Antenna Wire Grid Arrangement Prospective View

Images for Corner Reflector Antennas 3 Images for 90 0 Corner 5 Images for 60 0 Corner Reflector Antenna Reflector Antenna

Images for Corner Reflector Antennas 7 Images for 45 0 Corner 11 Images for 30 0 Corner Reflector Antenna Reflector Antenna No. of Images = 360/ α - 1

90 ° Corner Reflector Antenna Total field will be sum of contributions from the feed and its images.                         E r , , E r , , E r , , E r , , E r , , 1 1 2 2 3 3 4 4

Array Factor for 90 ° Corner Reflector Antenna Array factor of the 90 ° Corner Reflector Antenna: E                  AF , 2 cos  ks sin cos cos ks sin sin  E 0 In the Azimuthal Plane, (  =  /2) E                  AF / 2, 2 cos ks cos cos ks sin   E 0

Radiation Pattern of 90 0 Corner Reflector Antenna For s > 0.7 λ , main beam splits. For s = λ , null in the broadside direction.

Array Factor of Corner Reflector Antenna for other α  o = 60 For         X X Y             AF , 4sin  cos cos 3          2 2 2  o For = 45       X Y          AF , 2 cos( X ) cos( ) Y 2cos   cos         2 2  o For = 30           3 Y X 3                   AF , 2 cos( X ) 2cos X cos cos( ) Y 2cos cos Y            2  2 2  2          X ks sin cos Y ks sin sin where

S-Limit for Corner Reflector Antennas There is Limit on S-value for single lobe in the radiation pattern. S < 0.7 λ α = 90 0

Parabolic Reflector Antenna For Parabola: OP + PQ = constant = 2f OP = r’ and PQ = r’cos  ’ So, r ’ (1+ cos  ’) =2f

Parabolic Reflector Antenna Equations   1 f d     2 d  2     1 1 tan tan 0 2 2   d f 1   f     16 f d 16 f/d 0.4 0.5 0.6 0.7 0.8 1.0 θ 0 64.0 53.1 45.2 39.3 34.7 28.1

Gain and Aperture Efficiency of Parabolic Reflector Antenna  𝐓𝐪𝐣𝐦𝐦𝐩𝐰𝐟𝐬 𝐟𝐠𝐠𝐣𝐝𝐣𝐟𝐨𝐝𝐳 (∈ 𝒕 ) : fraction of the total power that is radiated by the feed, intercepted, and collimated by the reflecting surface.  𝐔𝐛𝐪𝐟𝐬 𝐟𝐠𝐠𝐣𝐝𝐣𝐟𝐨𝐝𝐳 (∈ 𝒖 ) : uniformity of the amplitude distribution of the feed pattern over the surface of the reflector.  𝐐𝐢𝐛𝐭𝐟 𝐟𝐠𝐠𝐣𝐝𝐣𝐟𝐨𝐝𝐳 (∈ 𝒒 ) : phase uniformity of the field over the aperture plane.  𝐐𝐩𝐦𝐛𝐬𝐣𝐭𝐛𝐮𝐣𝐩𝐨 𝐟𝐠𝐠𝐣𝐝𝐣𝐟𝐨𝐝𝐳 (∈ 𝒚 ) : polarization uniformity of the field over the aperture plane  𝐂𝐦𝐩𝐝𝐥𝐛𝐡𝐟 𝐟𝐠𝐠𝐣𝐝𝐣𝐟𝐨𝐝𝐳 (∈ 𝒄 )  𝑺𝒃𝒐𝒆𝒑𝒏 𝑭𝒔𝒔𝒑𝒔 𝑭𝒈𝒈𝒋𝒅𝒋𝒇𝒐𝒅𝒛 (∈ 𝒔 )

Effect of Feed Pattern on Efficiency

Spillover and Taper Efficiencies of Parabolic Reflector Antenna Spillover Efficiency Reflector Aperture Angle, θ 0 Taper Efficiency Reflector Aperture Angle, θ 0 (in degrees)

Aperture Efficiency of Parabolic Reflector Antenna Reflector Aperture Angle, θ 0 (in degrees)

Cassegrain Reflector Antenna

Gain of Large Reflector Antennas