RF tagging system (10) has a plurality of resonant circuits (13) on a tag (12). When the tag (12) enters a detection zone (14), the system determines the resonant frequency of each of the resonant circuits (13) and produces a corresponding code. Preferably, resonant frequency detection is implemented by simultaneously radiating signals at each possible resonant frequencies for the tag circuits (13). The system is useful for coding any articles such as baggage or production inventory. Preferably, the radiated signals are phase shifted during the detection process, and signals received by receiver antennas, besides transmitter signals, may be monitored to improve the reliability of detecting the resonant circuits (13). Also, a preferred step adjustment configuration for capacitive metalizations (106, 110) of the resonant circuits is described. For radiating signals into the detection zone (14), focused beam antennas (201) may be used such that each resonant circuit location on the tag can be separately monitored. Also, an apparatus (300) for producing customized resonant circuit tags in accordance with a specified input code is described.