In communications systems that use microwave antennas, the energy of the side lobes and back lobe compared to the main beam is an essential consideration for antenna design and performance. These lobes are a result of the antenna's radiation pattern, which describes how the antenna radiates energy in different directions.
Main Beam: The main beam of an antenna is the primary lobe in its radiation pattern. It is the direction in which the antenna radiates the most energy and is typically the desired direction for communication with a specific target or receiver.
Side Lobes: Side lobes are additional, smaller lobes that appear in the antenna's radiation pattern along with the main beam. They are unintended radiation directions where energy is also radiated. Side lobes can cause interference with other systems or lead to signal leakage, which is undesirable as it can affect the overall performance of the communication link.
Back Lobe: The back lobe is a lobe in the radiation pattern of an antenna that appears opposite to the main beam. It is also an unintended radiation direction, and like side lobes, it can cause interference and reduce the antenna's efficiency by radiating energy away from the desired communication direction.
Ideally, in communications systems, the goal is to maximize the energy in the main beam and minimize the energy in the side lobes and back lobe. This ensures that most of the transmitted or received energy is directed toward the intended target or receiver.
Antenna engineers use various design techniques and technologies to achieve this goal, such as using carefully designed reflectors, feeds, and shielding. The performance of an antenna is often quantified using metrics like side lobe level (SLL) and back lobe level (BLL), which measure the energy in the side lobes and back lobe relative to the energy in the main beam, respectively.
In summary, in communications microwave antennas, it is crucial to minimize the energy in the side lobes and back lobe compared to the main beam to optimize the antenna's performance and reduce interference with other systems.