Technical paper on DAS design process examines use of radiating cable

Bird Technologies says that what DAS design essentially boils down to "is a combination of node placement and simple mathematics."

Mar 27th, 2014

A 4-page technical brief with detailed schematic examples from RF engineering specialist Bird Technologies notes that "the first step of distributed antenna system (DAS) design is to obtain an accurate and up-to-date blueprint of the building. An architectural drawing is best, but even a fire exit map will suffice, as long as it’s drawn to scale."

Bird Technologies adds that what DAS design essentially boils down to "is a combination of node placement and simple mathematics." The brief continues, "With a scaled building blueprint in hand and a good understanding of the particular limitations of the project, the designer can now sit down and map out all the DAS nodes, i.e. [the] locations of the antennas."

While the article mainly focuses on design guidelines for coax and antenna types of DAS, the RF engineering specialist notes that the layout of a radiating cable DAS can use these same guidelines. As explained by Bird Technologies: " [A radiating cable] is essentially a coax cable with lots of tiny slits cut along the length of the cable. Each slit functions as a tiny antenna with RF energy leaking out of it, hence the nickname 'leaky cable.'"

The brief goes on to explain that, when used in DAS applications, "the signal levels coming out of the radiating cable are pretty low, so the coverage area is typically no more than 20 or 30 ft. on either side of the cable. Therefore, it’s better suited for areas that are long and narrow such as tunnels or long hallways. Because [RF] signals are coming out of the cables throughout, the insertion loss of the cable is typically higher than comparable coax, and it’s something to keep in mind during the DAS design."

The technical brief is the second in a 2-part series of articles from Bird Technologies describing "How to Properly Design an In-Building DAS."

View/Download the technical brief.

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