52 IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, VOL. 23, NO. 1, JANUARY 2013 A Novel Chipless Identification Tag Based on a Substrate Integrated Cavity Resonator Hatem El Matbouly, Naimi Boubekeur, and Frédéric Domingue Abstract—This letter presents a novel tag structure for mi- crowave identification. The new tag is based on a high quality factor substrate integrated cavity resonator in which data are encoded by introducing a variation in the effective per- mittivity which gives a unique and identifiable frequency spectral signature. The proposed tag design operates in the frequency range of 10.5–11 GHz. The substrate integrated tag presented has the advantages of being low cost, zero power consumption, com- pact and can be also transferred to different types of substrates, making it suitable for many mass production applications. Index Terms—Cavity resonators, RFID, substrate integrated waveguide (SIW), tag. I. INTRODUCTION A S the wireless applications are rapidly increasing in recent years, radio frequency identification (RFID) is becoming more and more needed. Passive chipless RFID tags offer the advantage of identification at a distance with zero power con- sumption and unlimited lifetime [1]. Coplanar waveguide had been used to implement such tags [2] and had been demonstrated in the range of 7–10.7 GHz range. Another chipless tag based on a microstrip line and spiral resonators that can code up to 6-bits and operates at 30 GHz had been also demonstrated [3]. These solutions are based on stan- dard planar transmission lines. On the other hand, Substrate integrated waveguide (SIW) structures are attracting more and more attention in recent years [4]. SIW structures have many advantages such as high factor, low insertion loss, and high power capability; fur- thermore, SIW microwave components can be integrated with other planar circuit to form a compact microwave system [5]. SIW structures have been fabricated on paper based substrate using ink-jet printer [6] as well as on flexible plastic (PET) substrates [7]. This letter demonstrates the concept and the prototyping of a novel SIW structure for microwave identification. The pro- posed chipless tag structure is based on a single substrate in- tegrated cavity resonator which encodes data into the magni- tude of the spectrum of the interrogation signal by means of air holes introduced inside the resonator structure. Since the dielec- tric constant changes, the proposed structure has the advantage Manuscript received August 07, 2012; accepted December 09, 2012. Date of publication January 01, 2013; date of current version January 16, 2013. This work was supported by the National Science and Engineering Research Council of Canada (NSERC), the university support through a research Chair, and the CMC Microsystems for access to test equipment. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LMWC.2012.2236081 Fig. 1. 3-D structure of the substrate integrated tag. of encoding without increasing the resonator size. Each tag is designed to operate in the frequency band of 10.5–11 GHz and have a different frequency spectral signature in this band for tag identification. II. TAG OPERATION PRINCIPLE Fig. 1 represents the basic structure of the substrate integrated cavity resonator with the interrogation antenna used to imple- ment the tag. The resonance frequency of the substrate integrated cavity resonator operating in the -like mode is given by (1) where is the speed of the electromagnetic wave in vacuum, is the relative permittivity of the substrate, and and are the effective width and length of the resonator cavity [8], [9]. Given that the dimensions of the resonator do not change, a variation in the dielectric constant introduces a change in the resonance frequency given by (2) where the proportionality constant depends on the dimensions of the substrate integrated resonator. It is important to note that the change in resonance frequency is negative which indicates that the frequency shift will be always lower than the initial resonance frequency. To introduce a signature, a change in the effective dielectric constant of the substrate is introduced by a variable number of air via. The basic principle of the proposed tag operation is presented in Fig. 2. The interrogator sends a broadband signal to the tag 1531-1309/$31.00 © 2012 IEEE