RF in-building coverage has become a fast growing market in recent years. Commercial wireless users increasingly demand reliable communications inside office and residential buildings for their business and personal needs. At the same time, various local municipalities have issued ordinances to ensure that construction of new buildings include adequate radio coverage of public safety signals. Efforts are also underway to develop and implement national level model codes for public safety in-building communications, as seen by recent initiatives at National Fire Protection Association (NFPA) and the International Code Council (ICC).
A typical in-building coverage system consists of two major components, a bi-directional amplifier (BDA, or signal booster) relaying and amplifying the RF signal traffic between the remote base station and the portable or mobile radios, and a network to distribute the signal to every corner of the desired coverage area. The most common type of the distribution network is a system of coax cables and indoor antennas called a Distributed Antenna System or DAS.
Most of the reference materials and application notes on in-building coverage solutions have focused on the booster technologies or system design architecture. One often overlooked aspect in the system design is the DAS implementation. This includes connecting all the cables and antennas throughout the building and balancing the signal levels at each DAS node. If ignored, an improperly designed DAS results in degraded performance and unnecessary cost increases. This 2-part series of articles is an effort to outline a simple process of designing a DAS in order to achieve the most efficient RF coverage distribution. Part I talks about the Use of Directional Couplers in DAS and Part II covers the DAS Design Process.