Antennas suitable for use in RFID devices include an insulating substrate and a first conductive micropattern disposed on or in the substrate, the first conductive micropattern defining a contiguous mesh conductor. The first conductive micropattern forms an antenna responsive to at least a frequency of 915 MHz, and includes interconnected traces having a trace width in a range from 0.5 to 20 microns. Furthermore, the first conductive micropattern is characterized by an open area fraction of at least 80% or 90%. RFID devices include such an antenna and an integrated circuit configured to transmit and receive signals using the antenna. Cards, such as financial transaction cards or identification cards, include such an antenna carried by a card layer.