Passive tags use two antennas with only limited mutual coupling, one of which receives a power/clock field and the other of which receives a data signal. An area-reading antenna, or two or more antennas, are deployed to generate the power/clock field, from a base station. The base station, or active tags, or both, generate the data signals from time to time. This topology together with the use of low frequencies permits area reads, and permits small and economical passive tags, and further permits localization of a particular passive tag as being nearby to a particular active tag.