Path Loss For Short Range Telemetry

The popular Friis transmission formula is used to evaluate the amount of path loss in free space between the transmit and receive antennas for the design of wireless transceivers. It is could be also used to estimate the path loss for the link of the on-body network when there is no barrier and no body surface in between. Paying special attention to short-range communication, this paper develops composite expressions for path loss between two dipoles. Theoretical analysis is used to prepare an impedance-based model and an Sparameter-based model to extract the path loss. These expressions support the validity of Friis formula up to a certain separation distance, below which an error is induced, possibly resulting in miscalculation of required transmission power, sensitivity and margins, during the design of transceivers. Simulations and experiments were carried out to verify the proposed model, and their results match up well. The difference in values of path loss obtained by the proposed analytical model and Friis path loss formula in free space is highlighted. This is important to be aware of while choosing design parameters for transceivers that will be used in applications operating at short ranges as compared to wavelength at the frequency of operation.