An active RFID tag has an antenna inside RF-blocking enclosure having a port with a selected shortest dimension. An RFID reader located outside the enclosure at a reader position transmits a downlink RF signal through the port as a directional RF signal on a downlink carrier frequency corresponding to a downlink wavelength smaller than the selected shortest dimension. The port is selectively configured so that the directional downlink RF signal can pass through the port in an access mode during a selected access time interval and are attenuated by at least 60 dB in a restricted mode during a selected restricted time interval that does not overlap with the access time interval.