Over the past few years,Radio Frequency IDentification (RFID) has stridden significantly due to its adoption in many business and daily life activities.RFID empowers end-to-end and item-by-item visibility,letting the customers or decision-makers effectively trail the personnel and resources for improved management.Significant research and development in this area have transformed the inexpensive,miniaturized technology of RFIDs without chip inside.Chipless Radio Frequency IDentification (CRFID) is a unique wireless technology based on radar principle to sense,identify,and track the objects.CRFIDs are simplified and miniaturized tags of traditional RFID,which can widely be used in small and cheap objects/applications in our daily life.This paper reviews the definition,principle,and most recent development in CRFIDs.Based on the reported researches,the ElectroMagnetic Spectrum (EMS) method is typical,which has been concerned by many RFID researchers.Therefore,this paper reviews different types of EMS CRFID tag and classifies these tags based on structure design emphasizing their significant geometries in comparison with performance parameters.Antenna and coding methods of the EMS CRFID are also elaborated,contrasting the tag capacity and coding performance.Finally,we briefly summarize the challenges and limitations in this emerging field and look forward to the prospects of future CRFID.