4.3 The Passive DAS
Now that we know the function of all the passive components, we are able to make a design of a passive distributed antenna system. Passive DAS systems are the most used approach when providing indoor solutions, especially to small buildings.
4.3.1 Planning the Passive DAS
The passive DAS is relatively easy to plan; the main thing you need to do is to calculate the maximum loss to each antenna in the system, and do the link budget accordingly for the particular areas that each antenna covers. You will need to adapt the design of the passive DAS to the limitations of the building with regards to restrictions to where and how the heavy coax can be installed. Often the RF planner will make a draft design based on floor plans before the initial site survey, and afterwards adapt this design to meet the installation requirements of the building. In fact, the role of the RF planner is often limited to installation planning, not RF planning, when designing passive DAS.
It is very important that you know all the cable distances and types so that you can calculate the loss from the base station to each individual antenna. Therefore you must do a detailed site survey of the building, making sure that there are cable routes to all of the planned antennas. When doing passive DAS design, you will often be limited and restricted as to where you can install the rigid passive cables. Frequently, the limitations of installation possibilities will dictate the actual passive DAS ...