Investigation of Loop and Whip Antennas in Tire Pressure Monitoring Systems

Tire Pressure Monitoring System (TPMS) modules that are mounted in tires are usually powered by batteries that cannot be replaced or recharged. Since most of the power consumed by these modules is due to the wireless communication, antenna efficiency is a primary concern. TPMS modules typically employ antennas that are much smaller than a wavelength at the frequency of operation. Peak efficiencies are obtained by antennas with a high quality factor, but high-Q antennas are susceptible to detuning caused by environmental factors beyond the control of the TPMS designer. This paper investigates the performance of loop- and whip-antenna designs commonly used in TPMS applications, and explores the environmental factors that affect the radiation efficiency and quality factor of these antennas.