Understanding Antenna Aperture and BDA Systems
Utilizing a directional antenna for a BDA donor antenna isn’t just about the gain it provides, but also how the antenna narrows the aperture of the antenna. Using a directional donor antenna focuses the energy to-and from the supported repeater site resulting in 3 important advantages:
- Gain: There’s typically between 70 and 120 dB of free-space path loss between the repeater antenna(s) and the BDA donor antenna. So, having an additional 5 to 15 dB of gain is almost always an advantage and often, necessary.
- Interference to other nearby in-band users: Tightening the donor antenna aperture can reduce the impact, if not eliminate, any potential interference to those other systems. A tight donor antenna aperture, correct placement of the donor antenna on the roof, and suitable alignment of the BDA’s donor antenna are all critical elements to proper design and installation of a BDA and the DAS it supports.
- Insufficient coverage within the building: Nearby in-band users can impact the gain of a BDA resulting in the amplifiers going into Power Control to protect itself from damage. Power Control functions to reduce the gain of the BDA and the signal level output of the BDA as a result of that reduction in gain. This loss of gain and signal strength of the desired frequencies because of the other nearby high power users can result in areas where coverage “should” be but is nonexistent because the BDA is in Power Control.