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Chipless RFID tag decoding has some inherent degrees of uncertainty because there is no handshake protocol between chipless tags and readers. This article initially compares the outcome of different pattern recognition methods to decode some frequency-based tags in the mm-wave spectrum. It will be shown that these pattern recognition methods suffer from almost 2%–5% false decoding rate. To overcome this misdecoding problem, two novel methods of making images of the chipless tags are presented. The first method is making 2-D images based on side-looking aperture radar concepts, and the second one is making virtual 2-D images from the 1-D backscattering signals. Then, a 2-D decoding algorithm is suggested based on a convolutional neural network to decode those tag images and compare the results. It is shown that this combined decoding method has very high accuracy, and it almost eliminates any ambiguity and false decoding problems. This is the first time a deep learning method is used with image construction methods to decode chipless RFID tags. [ABSTRACT FROM AUTHOR]

This article presents a method to analyze co- and cross-polarized responses of the resonators exploited in the development of frequency-coded chipless radio frequency identification (RFID) tags. The method uses the complex radar cross Section (RCS) matrix to characterize the polarization of the scattered response of resonators. Four different symmetry states are introduced, and all resonators are classified under each category based on their structures. Then, the complex RCS matrix is obtained for each group. Then, four different resonators, each representing the respective symmetry state, are simulated and measured to validate the theory. To highlight the advantages of the presented method, two significant applications of the method are investigated. The presented theory is used in the first application to determine resonator structures for designing orientation independent cross-polarized tags. The proposed technique not only accelerates the design of frequency-coded chipless RFID tags but also helps figure out proper geometry for resonators with cross-polarized responses with minimum amplitude deviation at different azimuth plane orientation angles. In the latter application, we predict co- and cross-polarized responses of a tag at arbitrary orientation angles, using one initial measurement. This prediction provides a thorough insight into the co- and cross-polarized responses of tags at different orientation angles. [ABSTRACT FROM AUTHOR]

Chipless RFID is a potential wireless identification technology for tracking and identification applications. However, there are still some unsolved challenges in the implementation of this system in real-world applications. One of the crucial challenges in chipless RFID systems is the effect of the dynamic environment and the effect of the attached item on the tag response, which causes interference in the tag ID measurement process. One approach to solve this problem at the tag design level is to use cross-polar chipless RFID tags, which conventionally are orientation-sensitive. However, even though it is desirable to detect the tag ID in different orientations (in 2-D at least) for practical applications, having both cross-polar RCS and orientation insensitivity in a tag is a challenge. Therefore, in this article, a technique to develop cross-polar resonators and unit cells that display a consistent reflection regardless of tag orientations is proposed. The results of the simulation and measurement of a few samples of the proposed tags are depicted to demonstrate the feasibility of using the proposed tags in a system with reflective items in the background. Five cross-polar structures with low sensitivity to orientation are introduced in this article. Among all structures, the flower-shaped unit cell provides a very consistent cross-polar response at different rotational angles with a maximum of 11 dB peak RCS variation. [ABSTRACT FROM AUTHOR]

The detection of a chipless radio frequency identification (RFID) tag in stepped motion is proposed. The performance is evaluated through experiment and measured using the vector network analyzer. The postprocessing of the measured results is performed using MATLAB. A novel adaptive wavelet-based detection algorithm is used for the decoding of the tag ID. An error analysis is conducted on the experimental results to study the variation of magnitude and frequency due to the movement of a chipless RFID tag. As far as the tag signature has not been disappeared from the reading range it has the same confidence level for the detection of its tag ID. This opens a new avenue toward developing the detection algorithms and decoding techniques when the chipless RFID tag is in motion. It also opens the doors for the localization of moving chipless RFID tags and prediction of the tagged objects moving trajectory modeling in the future. [ABSTRACT FROM AUTHOR]

A $4 \times 4$ dual polarized (DP) aperture-coupled microstrip patch antenna (ACMPA) array for a universal millimeter (mm)-wave chipless RFID tag reader is presented. The mm-wave DP ACMPA array is capable of reading all types of frequency domain-based chipless RFID tags (linearly polarized, orientation insensitive, cross-polarized (CP), and DP) within its operating frequency bandwidth. The developed antenna is operating over the 22–26.5-GHz frequency band with 16-dBi realized gain and over 35-dB isolation. A systematic approach is followed up for designing the mm-wave antenna array where, first, a single antenna element is designed. Then, a 1–32-way corporate feed network for the dual offset feeding of cross slots is designed using multistage power dividers. After that, the $4 \times 4$ mm-wave DP ACMPA array is designed, optimized, fabricated, assembled, and tested. Simulation and measurement results for different development stages of the array are described in detail. Finally, the assembled antenna is used for measuring 10 orientation insensitive (OI) thermal printed mm-wave chipless RFID tags on a paper substrate to validate its functional accuracy. The developed mm-wave DP ACMPA array with high port-to-port isolation can be used in a universal commercial mm-wave chipless RFID tag reader due to its low cost, high gain, and low-profile structure. [ABSTRACT FROM PUBLISHER]

A slotted waveguide antenna, as part of a wireless battery system for a bone fixation implant called the Echidna Pin is proposed. The antenna has 3-dB beamwidth of 65^\circ in both E- and H-planes and its gain is 7.7 dBi at 21 GHz. The proposed antenna is conformal to the body of the pin and uses the pin as a waveguide. It is shown that placing a small Perspex plate after the waveguide launcher allows satisfactory return loss performance at all resonant frequencies as the length of the waveguide changes. The pin is used in distraction osteogenesis and allows the distance between the two surgically broken pieces of bone to be changed, thus expanding both soft tissue and bone volume simultaneously. The wireless battery system allows reception of RF power and eliminates the need for daily manipulations on an externally fitted device, or an operation on the body to change the length of the pin. It also makes the treatment significantly less painful for the patient and reduces the risk of infection. [ABSTRACT FROM AUTHOR]

A low-power consumption, small-size smart antenna, named electronically steerable parasitic array radiator (ESPAR), has been designed. Beamforming is achieved by tuning the load reactances at parasitic elements surrounding the active central element. A fast beamforming algorithm based on simultaneous perturbation stochastic approximation with a maximum cross correlation coefficient criterion is proposed. The simulation and experimental results validate the algorithm. In an environment where the signal-to-interference-ratio is 0 dB, the algorithm converges within 50 iterations and achieves an output signal-to- interference-plus-noise-ratio of 10 dB. With the fast beamforming ability and its low-power consumption attribute, the ESPAR antenna makes the mass deployment of smart antenna technologies practical. [ABSTRACT FROM AUTHOR]

An empirical formula for resonant frequency of a circular cavity-enclosed circular-patch antenna is tested with measured results. The patch miniaturization in the presence of the cavity is proved. Different design curves in terms of resonant frequencies and bandwidth are derived to facilitate antenna design without a priori knowledge of complex numerical techniques. A simple gain formula for circular-patch antenna is derived and tested against the measured gain data. Results agree very well. The beamwidth, axial ratio, and mutual coupling in the presence of the cavity are investigated. [ABSTRACT FROM AUTHOR]

Analyzes the design and development of a microstrip circular phased array using microwave antenna computer-aided design tools. Incorporation of the scattering parameters of the radio frequency switches and phase shifters; Performance of radiating and beam-forming layers of a phased array.

Investigates circulatory polarized aperture-couple circular microstrip patch antennas with the goal of obtaining an impedance and ellipticity bandwidth in L-band. Configurations of the antenna and design procedures; Description of a single-feed aperture-couple circular patch (SF-ACCP) with perturbation segments; Overview of the SF aperture-couple stacked circular patch with perturbation segments.