Design of Circularly Polarized Modified Minkowski Fractal Based Antenna for UHF RFID Reader Applications

A compact, square shaped microstrip fractal antenna with asymmetrical pairs of T-slits for circularly polarized (CP) radiation and radio frequency identification (RFID) reader applications is proposed and experimentally investigated. Design is based on narrow slit modified Minkowski island fractal geometry. Circular polarization along with size reduction is achieved by inserting four symmetrical pairs of T-slits at the square patch boundary of the single-probe-feed radiator. Proposed geometry is tuned at resonant frequency of 914 MHz by optimization of dimensions of the two T-slits. Compactness of the antenna is achieved by increasing the overall sizes of the slits. Antenna is fabricated on FR4 substrate with a size of 47.2×47.2×1.6 mm3 (0.143λ0 X 0.143λ0 X 0.005λ0) and tested to validate the simulated results. The 3-dB axial-ratio (AR) bandwidth and impedance bandwidth of the proposed antenna design are found to be 7 MHz (911-918 MHz) and 24 MHz (909-933 MHz) respectively. A design equation is develped based on the parametric study that can be used to design a compact antenna with CP for UHF RFID applications covering the frequency range from 887 to 1023 MHz

Circular Microstrip Patch Antenna for UHF RFID Reader

This paper presents an analysis of Circular shape patch antenna for Ultra High-Frequency Identification (UHF) Radio Frequency Identification (RFID) Reader Applications. The fabricated antenna has lightweight, simple structure, low profile and easy for fabrication due to the used of FR-4 materials with loss tangent 0.019, the dielectric constant of 4.7 and thickness of 1.6 mm. It can be operated for UHF RFID system in Malaysia with the frequency assigned from 919 MHz to 923 MHz. The antenna simulation was analysed by using CST Studio Suite 2016. From the results, the antenna has the reflection coefficient (S11) less than -10dB together with the bandwidth of 90 MHz. Other results of antenna parameter such as voltage standing wave ratio (VSWR), circular polarized radiation pattern, return loss and gain were also discussed. The complete size of the proposed antenna is 120 mm x 120 mm x 1.6 mm. Thus, it is suitable for RFID portable reader applications

A Miniature RFID Antenna at UHF Band using Meander-Line Technique

This paper displays a new design of a small antenna proposed for radio-frequency identification (RFID) applications in the UHF band (ultra-high frequency). Our antenna is constituted of two rectangular patches linked together with a meander line. Using this technique reduction in antenna size of equal to 62% with respect to the conventional antenna was achieved. The antenna has a simple structure and small antenna size of 60 x 74mm2 or 0.184 λ0 x 0.226 λ0. It has been fabricated on a low-cost FR4 substrate and measured to validate the simulation performances.The measured bandwidth is around 54.4 MHz (889.3 - 943.7 MHz) with reflection coefficient less than 10 dB, which covers all of the American RFID band (902 - 928 MHz), Chinese RFID band (920.5 - 924.5 MHz), Korea Republic and Japan RFID band ( 917 - 923.5 MHz).The design and simulations have been effected by electromagnetic simulators HFSS and CST microwave studio. A good accord is getting between the simulated and measured results. This antenna is intended for the reader of RFID applications

The Circularly Polarized Corner-Truncated Rectangular Patch Antenna with Double Slits for UHF RFID System

This paper presents a circularly polarised rectangular patch antenna for ultra-high-frequency (UHF) radio frequency identification (RFID) applications using for Thailand standard. The antenna consists of a corner-truncated patch with double slits and a ground plane. The rectangular patch is fed by a single probe. The circular polarisation can be achieved by using three techniques such as adding double slits, using square shape and using a slanted cutting corner. The antenna has a compact size and appropriate for RFID system of Thailand standard. The measurement results show that |S11| (dB) is less than -10 dB. The antenna gain is 8.83 dBic with the unidirectional radiation pattern. The 3-dB axial ratio beamwidth is 65º over the frequency band of 914.4 - 929.9 MHz covering the UHF RFID applications for Thailand standard

Advances in Antennas and High-Frequency Material Characterization for Wireless Body-Area Networks

The development of the personal body-centric communication system is an essential part of the novel generation of wireless communication systems and one of the communication technology challenges. The versatility of body-centric communication revolutionizes healthcare by allowing continuous and in-all- conditions human health monitoring and human-centered authentication. Recently, with the extra-low power consumption and low-complexity backscatter communications, the passive ultra-high-frequency (UHF) radio-frequency identification (RFID) technology has been considered a promising approach for the wireless body area network. An inevitable part of this system is the wearable antenna, which plays a critical role in ensuring the efficient wireless link of the signal in the presence of the wearer. The wearable antenna should be fabricated with textile materials and equipped with various radiation configurations to enhance robustness and the operation’s versatility for long-term use. The difficulty of the wearable antenna development is to obtain the property information of the unknown textile substrate and conductor. To address the above-mentioned challenges, this thesis starts with the novel textile material characterization method to single out the relative permittivity and loss tangent of the substrate and bulk conductivity of the conductor. Unlike conventional approaches, our method simply applied the testing structure of the microstrip line composed of the textile material and simple data processing with the least square estimation. Then, a variation of the textile wearable antenna development with a low-profile planar in geometry is proposed in the next part of the thesis. The headgear RFID tag and forearm RFID reader antennas were developed based on quasi-Yagi configurations and periodic surface to obtain a directive pattern along the body surface. Another type of antenna configuration developed in this thesis is the circular polarization patch antenna for the wearable RFID tag. This type of antenna significantly reduced the polarization mismatch between the reader and the tag; hence, the detection capability and radiation efficiency are remarkably upgraded. The promising performance of the antennas was rigorously analyzed in simulation and verified with on-body measurement

A Wearable Textile RFID Tag Based on an Eighth-Mode Substrate Integrated Waveguide Cavity

A novel wearable textile Radio Frequency Identification (RFID) tag based on an eighth-mode substrate integrated waveguide cavity is presented. Antenna size reduction for effective operation in the [865-870]-MHz RFID UHF band is obtained by exploiting the H-field symmetry planes of a cylindrical Substrate Integrated Waveguide (SIW) cavity. High isolation from the human body and excellent robustness with respect to variations in antenna-body distance are achieved using an energy-based design strategy, aiming to reduce ground plane size. The resulting tag exhibits very low manufacturing complexity and may be produced at low-cost. Design and simulations were performed using CST Microwave Studio, and a prototype of the tag has been manufactured and tested in a real environment

2-Dipoles Circularly-Polarized Antenna Integrated in Lamp Holder for Fixed RFID Reader

The paper presents a solution to integrate a circularly polarized antenna in a tracklight housing that contains both a lamp and a UHF-RFID reader. The antenna is located outside the tracklight housing since the cylindrical lamp holder is metallic and small in terms of wavelength, and there is no space enough inside it. Furthermore, the antenna does not interact with the lamp, so no specific lamp is required. The solution makes use of a standard print-circuit-board fabrication technique combined with a low-cost metal sheet cavity, that can be also drilled for aesthetical reasons. An antenna prototype has been designed for the North America market. The measurements showed a reflection coefficient less than -15dB and a gain greater than 6dBi in the band of interest (902-928 MHz)

Doctor of Philosophy

dissertationAntenna design and reduction of losses in antenna systems are critical for modern communications systems. Two categories of antennas suffer from limited power supply and difficult operating environments: implantable antennas and antennas for spacecraft applications. Minimizing and controlling losses in these two antenna types is critical for developing next-generation implantable devices, spacecraft, and satellites. Research suggests that future tattoo antennas will be made from low-conductivity ink utilizing the natural insulating property of the body's fat and lossy ground plane of muscle. This paper supports tattoo antenna work by: (1) demonstrating the insulating properties of fat and conductivity of muscle with various antenna systems, (2) showing the effect of biological materials on the current distribution of subdermal antennas, and (3) validating the use of lower-conductivity materials in subdermal antenna design including a novel gold nanoparticle material. Simulations and measurements are used to evaluate current distributions shared between solid, segmented, and meshed strip dipole antennas and surrounding body tissues. Fat insulates the antenna similar to a thin layer of plastic wrap. Muscle acts as a conductive ground plane. Dipole antennas with mesh or gap structures are more strongly coupled to body tissues than solid antennas. A minimum acceptable conductivity benchmark of 105 S/m is established for dipole antennas and Radio-Frequency Identification (RFID) antennas. This work also provides novel information on the design of low-cost, circularly polarized (CP), Ka-band (26 GHz), millimeter-wave, 50 Ω edge-fed, corners truncated patch antennas on RT/duroid 5880 (εr = 2.2, ½ oz. copper cladding). Microstrip feed width, axial ratio (AR) bandwidth, and best AR at 26 GHz are optimized by the use of 10 mil substrate. The effects of corner truncation are further investigated, showing that increasing corner truncation increases AR bandwidth, increases percent offset between best S11 and AR frequencies, and worsens the best AR. A truncation of 0.57 mm is a good compromise between these effects with AR bandwidth of 6.17 % (measured) and 1.37 % (simulated). Increasing ratio of substrate thickness to design frequency, t / λd, improves AR bandwidth. For t / λd below a certain threshold a corners truncated patch antenna will not produce CP. A new nearly-square, corners truncated patch antenna is measured and simulated as a method of increasing circular polarization bandwidth (CPBW)