Antennas are mainly two types---
- Omni directional antenna
- Directional antenna
Omni directional Antenna
The omni directional antenna radiates or receives equally well in all directions. It is also called the "non-directional" antenna because it does not favor any particular direction.
Omni antennas usually resemble vertical rods but can come in other shapes as well. Some have horizontal rods of the same length placed at their base to increase their performance/distance. These are called “ground planes”.
The key factor to note is that for receivers all four signals (or signals from any direction, for that matter) are received equally well. For transmitters, the radiated signal has the same strength in all directions. This pattern is useful for broadcasting a signal to all points of the compass (as when calling "CQ"), or when listening for signals from all points.
The omni directional antenna radiates or receives equally well in all directions. It is also called the "non-directional" antenna because it does not favor any particular direction.
Omni antennas usually resemble vertical rods but can come in other shapes as well. Some have horizontal rods of the same length placed at their base to increase their performance/distance. These are called “ground planes”.
The key factor to note is that for receivers all four signals (or signals from any direction, for that matter) are received equally well. For transmitters, the radiated signal has the same strength in all directions. This pattern is useful for broadcasting a signal to all points of the compass (as when calling "CQ"), or when listening for signals from all points.
Directional Antennas
Gain and directivity are intimately related in antennas. The directivity of an antenna is a statement of how the RF energy is focused in one or two directions. Because the amount of RF energy remains the same, but is distributed over less area, the apparent signal strength is higher. This apparent increase in signal strength is the antenna gain. The gain is measured in decibels over either a dipole (dBd) or a theoretical construct called an isotropic radiator (dBi) . The isotropic radiator is a spherical signal source that radiates equally well in all directions. One way to view the omni directional pattern is that it is a slice taken horizontally through the three dimensional sphere
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Microwave antenna
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