Propagation model for the HVAC duct as a communication channel

Heating, ventilation, and air conditioning (HVAC) ducts in buildings are typically hollow metal pipes which can be used as waveguides to carry signals and provide network access to offices. Knowledge of channel properties is crucial to designing such a communication system. The paper presents a propagation model for a straight HVAC duct terminated at both ends. At high frequencies, this duct behaves as a multimode waveguide with a transmitting antenna coupling in and a receiving antenna coupling out. We derive a simple analytical expression for the frequency response of this channel using conventional techniques. Experimental data taken on real circular ducts excited by monopole probe antennas confirm the theoretical results. This model represents an initial step toward the development of a tool for planning a wireless distribution system using building HVAC ducts.