ReflectorAntennas.ppt

7/28/2019 ReflectorAntennas.ppt

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Reflector Antenna

Jason Miksovsky

Abhishek KhannaMohammed ArifPeter Krammer


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Two main purposes of Antenna

Impedance matching: matches impedanceof transmission line to the intrinsic

impedance of free space to preventwanted reflection back to source.

Antenna must be designed to direct theradiation in the desired direction.


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Reflector Antenna

Reflector antenna such as parabolicantenna are composed of primary

radiator and a reflective mirror.

Source: http://ksrs.or.kr


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Characteristics

Effective area of reflector antenna:

Projected physical aperture:

Gain:

Loss in efficiency due to due to radiation in undesireddirection

Spillover loss

Focal point errors

Feedhorn sidelobesImperfections in parabolic surface

Feedline line

pIAAe

4

2DAp

2/ DIGain


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Loss


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Characteristics

Aperture:r= radius of the diameter

Larger dish has more gain than smallerClear line of sight is important

2^rA

Source: Lecture (12/05/02)


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Calculations

Physical area:

D= Diameter

Effective area: = illumination efficiency

Wavelength:

Gain:

3db beamwidth:

4

2^DAp

ApiAe *

f

c

2^4AeGi

DegreesD

dB

703


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Half power beamwidth

The half power graph showing the angle betweenthe half power point on either side of maximum


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Radiation pattern for parabolic antenna


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DIRECTV Specs

D of reflector = 18 = 0.457 m

Operating frequency = 12.4 GHz

Illumination Efficiency

(http://www.mitre.org/pubs/showcase/fcc_may01/mitrereport_4_01.pdf)

%8.77778.0 I


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Projected Physical aperture ofparabolic reflector

2

22

164.04

)457.0(4

mmDAp


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Effective Area

22 127.)164.0(778.0)( mmAA pIe


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Gain

27360242.

)457(.778.0

)(22

m

mDG ii

mGHzf

c0242.

4.12

103 8


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Gain in dB

dBiGG idBi 38.342736log10log10


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3-dB Beamwidth

71.3

457.0

0242.70703

m

m

D

dB


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3dB beamwidth for DirecTV


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Documents

ReflectorAntennas.ppt