CORNER REFLECTOR (cont) - A point-radiation source is placed at the focal point F. The field leaves this antenna with a spherical wavefront. As each part of the wavefront moving toward the reflector reaches the reflecting surface, it is shifted 180 degrees in phase and sent outward at angles that cause all parts of the field to travel in parallel paths. Because of the shape of a parabolic surface, all paths from F to the reflector and back to line XY are the same length. Therefore, all parts of the field arrive at line XY at the same time after reflection.
- A parasitic array to direct the radiated field back to the reflector, or a feed horn pointed at the paraboloid is used to make the beam sharper and to concentrates the majority of the power in the beam.
- The radiation pattern of the paraboloid contains a major lobe, which is directed along the axis of the paraboloid and several minor lobes. Very narrow beams are possible with this type of reflector.
Figure 5.7 : Parabolic radiation pattern
- The wave at the focus point will be directed to the main reflector and will be reflected parallel to the parabola axis. Thus the wave will travel at the same the and phase at A`E` (XY) line and the plane wave produce will be transmitted to the free space.
- Waves are emitted from the focal point of the wall and bounced back in line with the axis of the parabola and will arrive on time and with the same phase of the line and will form the next plane waves emitted into free space
- The plane wave received which is parallel to the parabola axis will be reflected by the main reflector to the focus point.
- All received waves parallel to the axis of the parabola will be reflected by the wall to the point of convergence.
- This characteristic makes the parabola antenna to possess high gain and a confined beam width.
- These features causes a parabola has a high gain and width of the focused beam.
Do'stlaringiz bilan baham: |
