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Reflector antenna
Reflector antennas use a primary feed antenna and a reflecting surface to direct the radio waves in a desired direction. The most common types of reflector antennas are flat sheet, corner, and parabolic reflectors. A corner reflector uses two flat surfaces joined at an angle, typically 90 degrees, to concentrate the radiation in the forward direction. The analysis of a corner reflector models the feed antenna and its multiple images formed by the reflector surfaces as an array of current elements on a circular path, which reinforces the radiation in the desired direction. Properly designing the dimensions and spacing of the feed from the reflector vertex results in a corner reflector with a gain of around 9 dB or more compared to a half-
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Reflector antenna
- 1. Unit-V VHF,UHF and MICROWAVEANTENNA PREPARED BY B.SIVA NAGESWARARAO DEPT OF ECE ASST PROF ESWAR COLLEGE OF ENGINEERING NARASARAOPET ANDHRA PRADESH
- 2. Reflector antennas mostimportant in microwave radiation applications At microwave frequency size of anteena small Frequency and size are inversely proportional Any shape of reflector produce desire directivity
- 3. In Reflectorantenna, another antenna need to exite it. Dipole Horn Slot used for exite so called primary antenna Reflector called as secondary antenna
- 4. Reflector represent anyshape Most common geometrics are Plane Corner Curved or parabolic reflectors
- 5. flat sheet reflectoror plane reflector Simplest form of reflector antenna Is kept infront of the feed Energy is radiated in the desired direction To increase the directivity, large flat sheet placed infront of the half dipole Main advantage is Reduce backward radiation and increase gain in forward direction
- 7. Corner reflector Dis-advantageof flat reflector is back and side radiation Modified, join two flat reflector with some angle concentrate radiation in forward direction Called corner reflector Angle called include angle Angle is 90 degrees, some times angle other than 90 degrees used
- 9. Two types ofcorner reflectors 1)active (with source) 2)passive( without source)
- 12. System Effiencydepend on the spacing between the vertex of the reflector and feed element S THAT IS ‘d’ Distance is adjusted by include angle Include angle decreases ,spacing between feed and reflector increased
- 13. Most ofthe time feed element is dipole or array of collinear dipoles placed parallel to the vertex placed at distance ‘d’ Dimensions are Aperture of coner reflector is Da Length of reflector is L Height h
- 14. Da islamda < Da< 2 lamda Lamda/3 <d< 2lamda/3 L=2d
- 15. Analysis ofradiation field of source with corner reflector Alpha=pi/N, N IS Integer Apply image principle Field produced between two corner reflectors is same as an array of 2N CURRENT ELEMENTS SPACED EQUIDISTANCE ON CIRCULAR PATH WITH RADIUS ‘d’ with adjacent elements opposite polarities
- 16. Number of images,polarities and position depend on include angle and polarization feed element Multiple images on circular path for different angles
- 25. Same methodcan be extended to analyze corner reflector with corner angles
- 26. For 60 degreecorner reflector one driven and five images For 45 degree corner reflector one driven and 7 images Field strength of corner reflector along axis due to a driven element and three image elements is 4 times the field strength of the half wave dipole In the free space All image elements add to driven element
- 27. Power radiated bythe driven antenna of corner reflector is 1.7 times than the half wave dipole in free space Gain of the corner reflector antenna along the axis is almost 9db or more
- 29.