Passive Antenna Research Articles

Recent Advances in Passive UHF-RFID Tag Antenna Design for Improved Read Range in Product Packaging Applications: A Comprehensive Review

Radio frequency identification (RFID) is a rapidly developing technology, and RFID sensors have become important components in many common technology applications. The passive ultra-high frequency (UHF) tags used in RFID sensors have a higher data transfer rate and longer read range and usually come in unique small and portable application designs. However, these tags suffer from significant frequency interference when mounted on metallic materials or placed near liquid surfaces. This paper presents the recent advancements made in passive UHF-RFID tag designs proposed to resolve the interference problems. We focus on those designs that are intended to improve antenna read range as well as scalability designs for miniaturized applications.

Ultra-Wideband Systems with Energy Harvesting Units for Sensors, 5G, IoT and Medical Systems

The high tech industrial revolution in the last fifty years depleted and ruined the planet natural resources. Energy harvesting is the main challenge in the research in green technologies. Compact wideband efficient antennas are crucial for energy harvesting portable sensors and systems. Small antennas have low efficiency. The efficiency of 5G, IoT communication and energy harvesting systems may be improved by using wideband efficient passive and active antennas. The system dynamic range may be improved by connecting amplifiers to the small antenna feed line. Ultra-wideband portable harvesting systems are presented in this paper. This paper presents new Ultra-Wideband energy harvesting system and antennas in frequencies ranging from 0.15 GHz to 18 GHz. Three wideband antennas cover the frequency range from 0.15 GHz to 18 GHz. A wideband metamaterial antenna with metallic strips covers the frequency range from 0.15 GHz to 0.42 GHz. The antenna bandwidth is around 75% for VSWR better than 2.3:1. A wideband slot antenna covers the frequency range from 0.4 GHz to 6.4 GHz. A wideband fractal notch antenna covers the frequency range from 6 GHz to 18 GHz. Printed passive and active notch and slot antennas are compact, low cost and have low volume. The active antennas may be employed in energy harvesting portable systems. The antennas and the harvesting system components may be assembled on the same, printed board. The printed notch and slot antennas bandwidth are from 75% to 100% for VSWR better than 3:1. The slot and notch antenna gain is around 3 dBi with efficiency higher than 90%. The antennas electrical parameters were computed in free space and near the human body. There is a good agreement between computed and measured results.

A Novel Mode-Stirred Reverberation Chamber Design for 5G Millimeter Wave Bands

A novel mode-stirred reverberation chamber (RC) is designed and analyzed for millimeter wave bands. The size of the proposed RC with dimensions of 0.9 m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times0.9$ </tex-math></inline-formula> m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times1.1$ </tex-math></inline-formula> m is suitable for user equipment (UE) tests. Two Z-shaped mode-stirrers are applied to generate a uniform field. To fulfill the communication and test requirements for user equipment, reference, measurement and link antennas with a large bandwidth are utilized, which can support both the frequency range (FR) 1 and FR2 bands of the 5G spectrum. The lowest usable frequency (LUF) and mode density were first calculated and examined. Then, the power transfer function (PTF) from 2 GHz to 40 GHz was obtained to verify the path loss. Three measurement campaigns were carried out to verify the accuracy of the RC. Firstly, the transmission power of the passive antenna for a conductive test was compared with the RC over the air (OTA) total radiated power (TRP) for single-tone signals. Then, signals with bandwidths of 100 MHz and 400 MHz were applied. A maximum power difference of only 0.8 dB was found in the above two experiments. Furthermore, the TRP for the same commercial 5G UE in both RC and compact antenna test range (CATR) systems was measured and compared. To the best of the authors’ knowledge, this is the first work to provide TRP results for 5G millimeter wave bands in a RC. The test results show that the TRP values for the two systems are almost the same with a maximum deviation of 0.5 dB, while the time required to carry out tests using the RC is lower than that for the CATR system.

Intelligent Surface-Aided Transmitter Architectures for Millimeter-Wave Ultra Massive MIMO Systems

In this paper, we study two novel massive multiple-input multiple-output (MIMO) transmitter architectures for millimeter wave (mmWave) communications which comprise few active antennas, each equipped with a dedicated radio frequency (RF) chain, that illuminate a nearby large intelligent reflecting/transmitting surface (IRS/ITS). The IRS (ITS) consists of a large number of low-cost and energy-efficient passive antenna elements which are able to reflect (transmit) a phase-shifted version of the incident electromagnetic field. Similar to lens array (LA) antennas, IRS/ITS-aided antenna architectures are energy efficient due to the almost lossless over-the-air connection between the active antennas and the intelligent surface. However, unlike for LA antennas, for which the number of active antennas has to linearly grow with the number of passive elements (i.e., the lens aperture) due to the non-reconfigurablility (i.e., non-intelligence) of the lens, for IRS/ITS-aided antennas, the reconfigurablility of the IRS/ITS facilitates scaling up the number of radiating passive elements without increasing the number of costly and bulky active antennas. We show that the constraints that the precoders for IRS/ITS-aided antennas have to meet differ from those of conventional MIMO architectures. Taking these constraints into account and exploiting the sparsity of mmWave channels, we design two efficient precoders; one based on maximizing the mutual information and one based on approximating the optimal unconstrained fully digital (FD) precoder via the orthogonal matching pursuit algorithm. Furthermore, we develop a power consumption model for IRS/ITS-aided antennas that takes into account the impacts of the IRS/ITS imperfections, namely the spillover loss, taper loss, aperture loss, and phase shifter loss.

Passive UHF RFID Voice Prosthesis Mounted Sensor for Microbial Growth Detection

Capacitive loading due to human tissue can lead to low efficiency for implantable Passive Radio Frequency Identification (RFID) antennas. The presented passive UHF antenna sensor provides read distances above 0.5 meters (within a body phantom) by utilizing a convoluted half-wave dipole design. It is able to detect simulated early to mature Candida albicans biofilm growth when mounted upon a voice prosthesis (up to a $30~\mu \text{m}$ biofilm thickness). Depending on the propagation frequency of interest, as early 4-hour growth (5 to $10~\mu \text{m}$ biofilm thickness) equivalent could be detected and before any device failure could occur due to the colonization. This was accomplished by utilising thin layers of polyurethane to decouple the saliva from the presented UHF sensor (biofilm growth is known to increase layer hydrophobicity). This presented sensor has better functionality within the U.S. UHF frequency band as it detects changes above $5~\mu \text{m}$ . If there is a need for implantation within additional tissues with variable dielectric properties, a shunt capacitance of 2.6 pF could allow the system functionality within the permittivity range of 21 to 58. Allowing for immediate medical intervention before medical prosthesis failure.

Ultra slim and small UHF RFID tag design for mounting on curved surfaces

This paper proposes a UHF flexible passive tag antenna for Radio Frequency Identification (RFID) which operates at 902–928 MHz frequency band. As main contribution, we design an electrically small and slim tag antenna by using a flexible commercial substrate. The small antenna has dimensions of 13 mm × 28 mm × 0.35 mm. The geometry of the tag antenna was optimized, using a Genetic Algorithm, to maximize its read range. The antenna performance was evaluated on flat and curve surfaces, by means of simulations of input impedance, reflection coefficient, gain and read range. Measurements of reflection coefficient were also developed. Results prove that the tag antenna can be wrapped on cylindrical surfaces with read ranges above one meter, suitable for applications related to industrial asset management, access control and identification of small objects such as hardware tools, tin cans, spray bottles and tin PET cylindrical containers.

Optically Transparent Flexible Robust Circularly Polarized Antenna for UHF RFID Tags

Optically transparent flexible tag antennas are highly desired for some applications, where unobtrusiveness and capability of mounting on curved surfaces are required. On the other hand, circular polarization minimizes signal degradation due to polarization mismatch between the reader and tag antennas, thus ensuring good communication quality and accuracy. In this letter, we present an optically transparent and flexible radio frequency identification passive tag antenna operating in the ultrahigh frequency band and exhibits circular polarization. It is thin, lightweight, and completely encapsulated inside transparent polymer, which protects it against dust, water, heat, and mechanical stress. The tag antenna is made by utilizing highly flexible and transparent conductive-mesh-polymer composite through a simple and low-cost manufacturing process. The antenna design is based on a planar square ring. It achieves a measured maximum read range of about 8.3 m and approximately 47 MHz (885-932 MHz) 3 dB axial-ratio bandwidth (ARBW).

New Compact Wearable Metamaterials Circular Patch Antennas for IoT, Medical and 5G Applications

The development of compact passive and active wearable circular patch metamaterials antennas for communication, Internet of Things (IoT) and biomedical systems is presented in this paper. Development of compact efficient low-cost wearable antennas are one of the most significant challenges in development of wearable communication, IoT and medical systems. Moreover, the advantage of an integrated compact low-cost feed network is attained by integrating the antenna feed network with the antennas on the same printed board. The efficiency of communication systems may be increased by using efficient passive and active antennas. The system dynamic range may be improved by connecting amplifiers to the printed antenna feed line. Design, design considerations, computed and measured results of wearable circular patch meta-materials antennas with high efficiency for 5G, IoT and biomedical applications are presented in this paper. The circular patch antennas electrical parameters on the human body were analyzed by using commercial full-wave software. The circular patch metamaterial wearable antennas are compact and flexible. The directivity and gain of the antennas with Circular Split-Ring Resonators (CSRR) is higher by 2.5dB to 3dB than the antennas without CSRR. The resonant frequency of the antennas without CSRR is higher by 6% to 9% than the antennas with CSRR. The computed and measured bandwidth of the stacked circular patch wearable antenna with CSRR for IoT and medical applications is around 12%, for S11 lover than −6dB. The gain of the circular patch wearable antenna with CSRR is around 8dBi.

Corrigendum to “Experimental Study on Strain Reliability of Embroidered Passive UHF RFID Textile Tag Antennas and Interconnections”

<p />

Human Muscle Mass Measurement through passive Flexible UWB-Myogram Antenna sensor to diagnose Sarcopenia

Sarcopenia disease is due to low muscle mass in humans. Sarcopenia leads to osteoporosis, metabolic syndrome and difficulty in performing day-to-day activities. At present, Dual-energy X-ray Absorptiometry (DXA) measures muscle mass with few limitations. They are variations in measurements according to region under investigation, irregularities in hydration status, and low precision in tall and obese persons. These limitations are due to low dosage level of X-ray radiations in certain muscle regions of human body such as heart, head, lower and upper extremities. This paper presents a non-invasive passive flexible Ultra Wide Band (UWB) Myogram antenna sensor for the prediction of Sarcopenia through human muscle mass measurement. This antenna is adhesively fixed on ventral surface of forearm and biceps for the measurement of skeletal and lean mass respectively. The proposed antenna sensor performs electromagnetic energy absorption from muscle tissues under radiating near-field condition. The muscle tissue signal from antenna is applied to blind source filtering-Non-negative Matrix Factorization (NMF), then subjected to Multi-Synchro Squeezing Transform (MSST), and finally correlated using linear regression machine learning algorithm to diagnose Sarcopenia. Furthermore, the proposed methodology is developed as a product through the MATLAB Mobile App compatible with Android devices. The proposed method of diagnosing Sarcopenia achieves an accuracy of 85% in fifty samples.

Insights into Fabrication and Measurements of PCB-Based Passive Millimeter Wave Antennas

Future cellular communication systems might be based on millimeter wave frequencies. So, there is a need to design and deploy antennas which operate in the millimeter wave spectrum integrated in mobile terminals, portable wireless devices, base stations and access points. Even though a lot of articles exist on the design of such antennas, fabrication and measurement nuances of such antennas are addressed rarely in the open literature. Initially, the fabrication process of printed circuit board (PCB) antennas is discussed in detail with sources of error and possible precautions. A case study of microstrip-based tapered slot antenna operating at 28 GHz is presented. The variations in the antenna characteristics with slight variations due to fabrication errors are presented. A detailed discussion on S-parameters, pattern and gain measurements is also presented along with possible sources of errors associated with them.

Hybrid Active and Passive Antenna Selection for Backscatter-Assisted MISO Systems

In this article, we propose and investigate hybrid active and passive antenna selection for backscatter-assisted multiple input and single output (MISO) systems. Specifically, each transmit antenna is allowed to work on either the active radio (AR) mode or the passive radio (PR) mode, which are respectively powered by the battery as in traditional communication and the external power source as in the backscatter communication (BackCom). The advantage is that the link reliability can be enhanced, and the power consumption can be opportunistically reduced by switching between the AR and the PR modes. Adaptive antenna selection is investigated and analyzed, where the antenna is selected over all combinations of antennas and their working modes. However, the antenna with the best channel quality will always be chosen. In order to circumvent this problem, two alternative schemes, referred to as reactive antenna selection and proactive antenna selection, are considered, where all antennas take turns to transmit/backscatter the signal. Specifically, in the reactive antenna selection scheme, the working mode for each antenna is determined by choosing the maximum value of the transmit power in the AR mode and the backscatter power in the PR mode. The working mode for the proactive antenna selection scheme is, however, chosen beforehand. Since the exact closed-form expression for the average symbol error rate (SER) is not attainable, approximations and their asymptotic performance are derived for proposed schemes. The power consumption is also analyzed. Simulation results demonstrate the correctness and the tightness of our analysis, and the effectiveness of proposed schemes.

Ka-Band Passive Phased-Array Antenna With Substrate Integrated Waveguide Tunable Phase Shifter

A low-cost and low-profile Ka-band passive phased-array antenna (PAA) using continuously tunable substrate-integrated waveguide (SIW) phase shifter is presented in this article. The phase shifting mechanism is based on perturbing the electric field of the slotted SIW (SSIW) line by putting a high dielectric constant slab over the slot of SIW. A systematic approach based on a simple transmission line (TL) circuit model which can support different modes is developed as a fast method for design optimization. It provides insightful physical understanding of the operating mechanism of the proposed phase shifter. In addition, a fully verified TL model of the 1 x 4 SIW PAA is presented and used to predict and optimize the overall reflection coefficients and radiation patterns at different scanning angles. The TL circuit model is verified by full-wave simulations. As a design example, a 1 x 4 SIW-based phased-array is designed, fabricated, and measured to validate phase shifter performance and capabilities. The prototype exhibits a continuous beam scanning range from -20° to +20° covering the whole operating band of 29-31 GHz.

A Miniature Actively Matched Antenna for Power-Efficient and Bandwidth-Enhanced Operation at Low VHF

Active matching techniques with non-Foster reactive elements have been introduced to overcome fundamental performance limits on electrically small passive antennas. While several experimental studies have demonstrated successful bandwidth enhancement with active matching applied to small unmatched passive antennas, their radiation performance against similar-sized, efficient, resonant antennas alone (and/or applied to active matching) has not yet been confirmed to assess their effectiveness for practical wireless communications applications. Beginning with a highly miniaturized efficient resonant antenna (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /50 in height), we design an active matching network derived from an antenna impedance model. We conduct an extensive simulation analysis to address challenging issues associated with the design arising from a tradeoff between degree of bandwidth enhancement and stability of the matching network. Based on experimental performance assessment, the effective 3 dB bandwidth of the proposed actively matched antenna is improved by more than three times compared with the passive version and improved in efficiency by more than 10 dB relative to cases that apply active matching techniques to similar-sized, unmatched passive antennas.

Thermally Stable Wireless Patch Antenna Sensor for Strain and Crack Sensing.

Strain and crack are critical indicators of structural safety. As a novel sensing device, a patch antenna sensor can be utilized to wirelessly estimate structural strain and surface crack growth through resonance frequency shift. The main challenges for the sensor are other effects such as temperature fluctuation that can generate unwanted resonance frequency shift and result in large noise in the measurement. Another challenge for existing designs of patch antenna sensor is the limited interrogation distance. In this research, thermally stable patch antenna sensors are investigated for more reliable measurement. Fabricated on a substrate material with a steady dielectric constant, a new passive (battery-free) patch antenna sensor is designed to improve reliability under temperature fluctuations. In addition, another newly designed dual-mode patch antenna sensor is proposed to achieve a longer interrogation distance. Extensive experiments are conducted to characterize the patch antenna sensor performance, including thermal stability, tensile strain sensing, and emulated crack sensing. The two new patch antenna sensors are demonstrated to be effective in wireless strain and crack measurements and have potential applications in structural health monitoring (SHM).

Decoupling of folded-end dipole antenna elements of a 9.4 T human head array using an RF shield.

Dipole antennas have recently been introduced to the field of MRI and successfully used, mostly as elements of ultra-high field (UHF, ≥ 7 T) human body arrays. Usage of dipole antennas for UHF human head transmit (Tx) arrays is still under development. Due to the substantially smaller size of the sample, dipoles must be made significantly shorter than in the body array. Additionally, head Tx arrays are commonly placed on the surface of rigid helmets made sufficiently large to accommodate tight-fit receive arrays. As a result, dipoles are not well loaded and are often poorly decoupled, which compromises Tx efficiency. Commonly, adjacent array elements are decoupled by circuits electrically connected to them. Placement of such circuits between distantly located dipoles is difficult. Alternatively, decoupling is provided by placing passive antennas between adjacent dipole elements. This method only works when these additional components are sufficiently small (compared with the size of active dipoles). Otherwise, RF fields produced by passive elements interfere destructively with the RF field of the array itself, and previously reported designs have used passive dipoles of about the size of array dipoles. In this work, we developed a novel method of decoupling for adjacent dipole antennas, and used this technique while constructing a 9.4 T human head eight-element transceiver array. Decoupling is provided without any additional circuits by simply folding the dipoles and using an RF shield located close to the folded portion of the dipoles. The array reported in this work demonstrates good decoupling and whole-brain coverage.

Estimating population abundance with a mixture of physical capture and PIT tag antenna detection data

The inclusion of passive interrogation antenna (PIA) detection data has promise to increase precision of population abundance estimates ([Formula: see text]). However, encounter probabilities are often higher for PIAs than for physical capture. If the difference is not accounted for, [Formula: see text] may be biased. Using simulations, we estimated the magnitude of bias resulting from mixed capture and detection probabilities and evaluated potential solutions for removing the bias for closed capture models. Mixing physical capture and PIA detections (pdet) resulted in negative biases in [Formula: see text]. However, using an individual covariate to model differences removed bias and improved precision. From a case study of fish making spawning migrations across a stream-wide PIA (pdet ≤ 0.9), the coefficient of variation (CV) of [Formula: see text] declined 39%–82% when PIA data were included, and there was a dramatic reduction in time to detect a significant change in [Formula: see text]. For a second case study, with modest pdet (≤0.2) using smaller PIAs, CV ([Formula: see text]) declined 4%–18%. Our method is applicable for estimating abundance for any situation where data are collected with methods having different capture–detection probabilities.

Principal Component Analysis-Based Broadband Hybrid Precoding for Millimeter-Wave Massive MIMO Systems

Hybrid analog-digital precoding is challenging for broadband millimeter-wave (mmWave) massive MIMO systems, since the analog precoder is frequency-flat but the mmWave channels are frequency-selective. In this paper, we propose a principal component analysis (PCA)-based broadband hybrid precoder/combiner design, where both the fully-connected array and partially-connected subarray (including the fixed and adaptive subarrays) are investigated. Specifically, we first design the hybrid precoder/combiner for fully-connected array and fixed subarray based on PCA, whereby a low-dimensional frequency-flat precoder/combiner is acquired based on the optimal high-dimensional frequency-selective precoder/combiner. Meanwhile, the near-optimality of our proposed PCA approach is theoretically proven. Moreover, for the adaptive subarray, a low-complexity shared agglomerative hierarchical clustering algorithm is proposed to group the antennas for the further improvement of spectral efficiency (SE) performance. Besides, we theoretically prove that the proposed antenna grouping algorithm is only determined by the slow time-varying channel parameters in the large antenna limit. Simulation results demonstrate the superiority of the proposed solution over state-of-the-art schemes in SE, energy efficiency (EE), bit-error-rate performance, and the robustness to time-varying channels. Our work reveals that the EE advantage of adaptive subarray over fully-connected array is obvious for both active and passive antennas, but the EE advantage of fixed subarray only holds for passive antennas.

Effect of electron kinetics on plasma density in inductively coupled plasmas using a passive resonant antenna

We investigated the profiles of electron and ion densities dependence on the gas pressure in the inductively coupled plasma with a passive resonant antenna. The inner powered antenna and the passive resonant antenna are independently installed on the top of the chamber, and a power of 13.56 MHz is applied to the powered antenna. A significant change in the plasma density profile is observed when the capacitance of the passive resonant antenna is adjusted from non-resonance to resonance. At a high pressure of 50 mTorr, the point of maximum electron density and temperature shift from near the powered antenna to near the passive resonant antenna. However, at a low pressure of 1 mTorr, the profile of the electron density and temperature hardly change, and the maximum electron density at resonance increases about 1.4 times (at 150 W) to 4 times (at 50 W) higher than at non-resonance. The controllability of the electron density profile, which depends on the gas pressure, can be understood by the electron kinetics effect, and the increase in the electron density can be explained by the increase in power transfer efficiency calculated from the circuit model. The electron density profile at bulk is compared to the ion density distribution at the wafer-level, and the results are discussed with the relevant physical mechanisms.

Near-Field Scan of Multiple Noncorrelated Sources Using Blind Source Separation

A method for separation of the field contributions generated by multiple noncorrelated sources is proposed. The measurements are implemented using one scanning probe and one (or more) stationary reference probe, avoiding the requirement to measure the spatial correlations of the random fields. The contribution of each source can be determined with the assistance of the blind source separation technique. Averaging over realizations allows to cancel the uncorrelated part in the mixed signal measured by the scanning probe. The separated results can be used to localize the emission sources and their contribution to the field pattern. The method was tested on different signals with amplitude and frequency modulation with passive (antenna) and active (IC) sources.