Reflector Antennas

Prof. Girish Kumar Electrical Engineering Department, IIT Bombay

[email protected] (022) 2576 7436 Flat Reflector Antennas

Plane Corner 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

Top View of Corner Wave incident at 900 Corner Reflector Antenna Reflector reflects back in the same direction Corner Reflector Antenna

Prospective View Wire Grid Arrangement Images for Corner Reflector Antennas

3 Images for 900 Corner 5 Images for 600 Corner Reflector Antenna Reflector Antenna Images for Corner Reflector Antennas

7 Images for 450 Corner 11 Images for 300 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,,,,,,,,,,   E1 r 1    E 2 r 2    E 3 r 3    E 4 r 4    Array Factor for 90° Corner Reflector Antenna

Array factor of the 90° Corner Reflector Antenna:

E AFksks,2  cossin coscossin sin   E0

In the Azimuthal Plane, ( = /2)

E AFksks  / 2,  2 cos cos cos sin  E0 Radiation Pattern of 900 Corner Reflector Antenna

For s > 0.7λ, main beam splits.

For s = λ, null in the broadside direction. Array Factor of Corner Reflector Antenna for other α

For  = 60 o XXY AF ,4sincoscos3  222 For  = 45o XY    AFXY,2 cos( ) cos( ) 2coscos     22    For  = 30o 33 YX    AFXXYY,  2 cos( )  2cos   cos   cos(  ) 2cos cos 2  22    2 where X kssin cos Y kssin sin S-Limit for Corner Reflector Antennas

There is Limit on S-value for single lobe in the radiation pattern. S < 0.7λ α = 900 Parabolic Reflector Antenna

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

d 1 f  112 2 d 0 tantan 22 d f 1 f   16 f d 16

f/d 0.4 0.5 0.6 0.7 0.8 1.0

θ0 64.0 53.1 45.2 39.3 34.7 28.1 Gain and Aperture Efficiency of Parabolic Reflector Antenna

 퐒퐩퐢퐥퐥퐨퐯퐞퐫 퐞퐟퐟퐢퐜퐢퐞퐧퐜퐲 (∈풔): fraction of the total power that is radiated by the feed, intercepted, and collimated by the reflecting surface.

 퐓퐚퐩퐞퐫 퐞퐟퐟퐢퐜퐢퐞퐧퐜퐲 (∈풕) :uniformity of the amplitude distribution of the feed pattern over the surface of the reflector.

 퐏퐡퐚퐬퐞 퐞퐟퐟퐢퐜퐢퐞퐧퐜퐲 (∈풑): phase uniformity of the field over the aperture plane.

 퐏퐨퐥퐚퐫퐢퐬퐚퐭퐢퐨퐧 퐞퐟퐟퐢퐜퐢퐞퐧퐜퐲 (∈풙): polarization uniformity of the field over the aperture plane

 퐁퐥퐨퐜퐤퐚퐠퐞 퐞퐟퐟퐢퐜퐢퐞퐧퐜퐲 (∈풃)  푹풂풏풅풐풎 푬풓풓풐풓 푬풇풇풊풄풊풆풏풄풚 (∈풓) Effect of Feed Pattern on Efficiency Spillover and Taper Efficiencies of Parabolic Reflector Antenna

Spillover Efficiency

Reflector Aperture Angle, θ0 Taper Efficiency

Reflector Aperture Angle, θ0 (in degrees) Aperture Efficiency of Parabolic Reflector Antenna

Reflector Aperture Angle, θ0 (in degrees) Cassegrain Reflector Antenna Gain of Large Reflector Antennas