When to use: Use to estimate the coverage radius of a single antenna for DAS design, antenna placement planning, and in-building coverage checks. Uses the log-distance path loss model with a propagation exponent (n) suited to the environment. Enter EIRP from the EIRP calculator and the minimum required RSSI (−95 dBm for NFPA 1221). Coverage area = π × radius². Divide total floor area by single-antenna coverage area to estimate antenna count.
The Antenna Coverage Radius Calculator estimates the usable coverage radius of a single antenna for in-building DAS design, BDA system layout, and public safety radio coverage planning. Engineers use it to determine how many antennas are needed to cover a given floor area at the required minimum received signal strength.
Coverage radius is derived from the log-distance path loss model: RSSI = EIRP − FSPL(1m) − 10·n·log10(d), rearranged to solve for distance d given a minimum acceptable RSSI threshold. The free-space path loss at a 1-meter reference distance is FSPL(1m) = 20·log10(f_MHz) − 27.56 dB. The propagation exponent n characterizes how rapidly signal attenuates with distance in a given environment — n = 2 for free space, n = 3 to 3.5 for typical indoor environments, and n = 4 to 5 for dense masonry or concrete construction.
Coverage area per antenna is then calculated as π × r², and the number of antennas required to cover a total floor area is obtained by dividing total area by per-antenna coverage area. This approach is consistent with ITU-R and IEEE 802.11 path loss models used for in-building wireless system planning.
NFPA 1221 Section 9.6 establishes a minimum inbound and outbound RSSI of −95 dBm (DAQ 3.0) at any location within the covered area for public safety radio systems. IFC Section 510 (2018/2021 editions) requires 95% area coverage at −95 dBm for buildings over 10,000 sq ft or as required by the AHJ. The log-distance model used in this calculator aligns with the propagation assumptions documented in TIA-TSB-88 for land mobile radio systems. Okumura-Hata and COST-231 models are also referenced for outdoor and macro-cell planning at 150–2000 MHz.
Always use the worst-case propagation environment for the target space — concrete and masonry construction yields n = 4 or higher, significantly reducing coverage radius. The EIRP input should come from the EIRP Calculator, accounting for transmitter power, cable losses, and antenna gain. Stairwells, elevator shafts, and basements may require dedicated antennas because penetration losses through floor slabs (15–25 dB for concrete) reduce coverage from adjacent antennas dramatically. Add a 3–6 dB safety margin to the minimum RSSI threshold (e.g., use −89 dBm instead of −95 dBm) to account for shadowing and measurement uncertainty during walk testing.
Enter the antenna EIRP in dBm (use the EIRP Calculator if you have TX power, cable loss, and antenna gain separately). Enter the operating frequency in MHz — 800 MHz is standard for P25 public safety systems. Set the minimum required RSSI to −95 dBm for NFPA 1221 compliance, or lower for more conservative designs. Select the propagation environment that best matches the building construction. The calculator returns the coverage radius in feet and meters, coverage area, and maximum allowable path loss. Divide the total floor area by the per-antenna coverage area to determine the minimum antenna count.
NFPA 1221 Section 9.6.3 requires −95 dBm minimum for both inbound and outbound paths. Some AHJs (Los Angeles, New York City) enforce −90 dBm. Always confirm the requirement with the local Authority Having Jurisdiction before finalizing the design.
Use n = 4 (Indoor – hard partition) for spaces with concrete block or poured concrete walls and floors. Dense urban high-rise cores may warrant n = 4.5 to 5. Light drywall construction can use n = 3 to 3.5.
Higher frequencies suffer greater free-space path loss at a given distance. At 100 m, FSPL is approximately 72 dB at 155 MHz but 84 dB at 851 MHz — a 12 dB difference. This means 800 MHz systems require more antennas than equivalent 150 MHz systems for the same coverage area.
Floor penetration loss for concrete slabs ranges from 15 to 25 dB, effectively eliminating antenna coverage from an adjacent floor. Each floor should be treated as an independent coverage zone. Riser cable with vertical distribution antennas per floor is the standard DAS approach for multi-story buildings.
Yes — select the Free Space (n = 2) or Suburban (n = 3) model for outdoor coverage estimation. For macro-cell planning above 150 MHz, the Okumura-Hata model provides better accuracy over distances greater than 1 km by incorporating Height Above Average Terrain (HAAT) and urban clutter corrections.
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