Antennas are used to send out the electric wave energy launched by transmitters directionally or send the electric wave energy received into receivers. There are two common types of microwave antennas.
- Parabolic Antennas
- Cassegrainian Antennas
The two types of antennas have the same reflection plane but different feeder sources
Parabolic antenna has the feeder source in front of it. Generally small and can only transmit a short distance.
Cassegrainian antenna has the feeder source behind it. Generally big and can transmit a long distance
The microwave antenna diameter generally varies according to the local climate condition, frequency and distance between stations. Sometimes according to the operator.
Generally following diameter antennas are used for Microwave Link
0.3 m for , 0.6 m, 1.2 m, 1.8 m, 2.0 m, 2.4 m, 3.0m, 3.2 m, etc
Radiated Power Distribution of an Antenna
The radiated power of an antenna is basically distributed to the main lobe, the side lobe and the tail lobe. The main lobe has the highest power, which extends to the two sides. The position where the power decreases to half of the maximum power is called the “half-power point” and the angle between the two half-power points is called the “half-power angle”.
Antenna Adjustment
The objective of antenna adjustment is to align the main lobe of the near end antenna to the main lobe of the far end antenna. Generally the ODU has an interface called RSSI. Using this interface, can be determined the receiving level of antenna.
During antenna adjustment, change the direction vertically or horizontally. Meanwhile, use a multimeter to test RSSI at the receiving end. The peak point of the voltage wave indicates the main lobe position in the vertical or horizontal direction. When antennas are poorly aligned, only a small voltage may be detected in one direction.
The wrong alignment cause Low receiving level. Cannot meet the required RF level.The correct alignment cause good. Receiving level without interference
