NASA’s quarter-wavelength crossed-slot antenna offers a form factor that is much smaller than other half-wavelength RFID antennas that provide similar functionality. (Image: NASA)

Innovators at NASA Johnson Space Center have developed a quarter-wavelength RFID slot antenna that provides polarization diversity and employs dual resonances, but in a form factor that is much smaller than other RFID antennas that provide similar functionality.

Typically, antennas designed to provide this performance are on the order of half-wavelength structure, which means a larger form factor. Development of this antenna was motivated by the Hyper-Distributed RFID Antenna (HYDRA) system. The HYDRA design seeks a barely visible implementation, with a coaxial cable connecting a number of RFID antennas that are not much bigger than the coaxial cable itself.

The HYDRA system enables a new approach in routing the RFID signal, greatly increasing extensibility and the number of antennas that can be served by a single reader. However, increasing the number of antennas in any environment is often undesirable unless the antenna size is inconspicuous. Basing this RFID slot antenna on a quarter-wavelength structure allows it to be smaller than an antenna designed for half-wavelength structure, reducing overall mass. NASA’s RFID Slot Antenna is enabled by utilizing two different types of resonance modes a slot mode and a microstrip patch mode.

An innovative feed architecture allows for coupling from the RFID reader into both modes, with the impedance of each mode approximately equal at respective resonant frequencies. The antenna is designed such that each mode resonates at a different portion of the operating bandwidth, and further with each mode radiating an orthogonal polarization to the other. Frequency-hopping RFID protocols, used in conjunction with this RFID antenna, result in the polarization diversity required for readers to reliably communicate with arbitrarily oriented RFID tags.

Although the RFID Slot Antenna was originally developed for the HYDRA system, this antenna has other applications. For example, small antennas with polarization diversity in handheld RFID readers have long been a challenge. The industry standard is a ceramic half-wavelength puck that is somewhat heavy and leads to ergonomic problems with handheld RFID readers. This innovation could provide a substantial improvement in handheld readers, and similarly with drone-based readers, for applications in which mass is almost always a primary factor.

NASA is actively seeking licensees to commercialize this technology. Please contact NASA’s Licensing Concierge at This email address is being protected from spambots. You need JavaScript enabled to view it. or call at 202-358-7432 to initiate licensing discussions. For more information, visit here .



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This article first appeared in the September, 2023 issue of Tech Briefs Magazine.

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