Most chipless RFID systems use the electromagnetic properties of materials and/or
design various conductor layouts/shapes to achieve particular electromagnetic
properties/behaviour. The main focus of this thesis will be on chipless RFID systems.
There have been some reported chipless RFID tag developments in recent years. However,
most are still reported as prototypes and only a handful are considered to be commercially
viable or available. The challenge for researchers when designing chipless RFID tags is how
to perform data encoding without the presence of a chip. In response to this problem two
general types of RFID tags can be identified: time domain reflectometry (TDR)-based and
spectral (frequency) signature-based chipless RFID tags. Fig. 3 shows the classification of
reported chipless RFID tags.