Near Field Coupling in Wireless Systems for Identification, Sensing and Communication

Antennas for radio communication systems (e.g. radio links, cellular networks, WLAN, remote sensing) are designed giving a lot of attention to antenna gain, polarization, radiation pattern characteristics (e.g. half power beam width, front to back ratio, etc.). All above parameters are defined in the antenna far-field (FF) region, so they are suitable to characterize a communication system in which the transmitter and the receiver antennas are far enough. On the other hand, some applications exist that exploit antenna features in its near-field (NF) region. In this context, NF coupling between antennas has been studied since a long time and most researches have been focused on coupling effects in antenna arrays, field sensing for near-field antenna scanning systems, magnetic coupling between loops operating at LF-HF frequency bands. During his PhD course, the author designed and tested several antennas for Near-Field applications such as UHF RFID Desktop Reader. Moreover, he developed numerical codes to analyze a novel method to estimate the deep human tissues status with a near-field sensor, determining its prediction capability and determining critical parameters that affect its accuracy. Finally, he studied the mutual coupling effect between antennas integrated in commercial PV panels for wireless communication systems

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

Dual-sense slot-based CP MIMO antenna with polarization bandwidth reconfigurability

In this letter, a compact, planar circularly polarized (CP) sub-GHz slot-based multiple-input-multiple-output (MIMO) antenna with dual sense CP along with polarization bandwidth reconfigurability is presented. The pentagonal reactively loaded slot is fed by two folded tapered feedlines to achieve CP. The antenna offers left-hand-circular polarization (RHCP) with the as well as right hand circular polarization (LHCP). The antenna exhibit linearly polarization (LP) by exciting two ports simultaneously. Moreover, the antenna CP resonance can be reconfigured by varying the capacitance of the varactor diode. The antenna has a wide −10 dB operating frequency band from 578–929 MHz. while the axial ratio (AR) bandwidth ranges from 490–810 MHz. Moreover, the two elements MIMO are optimized and placed on compact dimensions 100 × 100 × 0.76 mm3 to realize pattern diversity. The antenna’s key characteristics are compact size, wide-band sub-GHz operation, dual sense CP, polarization bandwidth reconfigurability and good MIMO performance. Thus, it is a suitable candidate to be utilized in CubeSats applications in sub-GHz bands

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

Dual-Band Circularly Polarized Stack-Ring Antenna

A stack-ring configuration is proposed for designing a dual-band circularly polarized (CP) antenna. Each ring generates different resonant frequencies. A good CP performance at both resonant frequencies is achieved by adjusting the relative distance between the two rings. The two operating bands are separated with a small frequency ratio of 1.07. Measured results show that radiation patterns with good CP characteristics are obtained at the two resonant frequencies

Design And Practical Implementation Of Harmonic-Transponder Sensors

Harmonic radar is a nonlinear detection technology that transmits and receives radio-frequency (RF) signals at orthogonal frequencies, so as to suppress the undesired clutters, echoes and electromagnetic interreferences due to multipath scattering. Its implementation generally comprises a nonlinear tag (i.e, a harmonic transponder), which picks the interrogation signal at specific fundamental frequency (f0) and converts it into a high/sub-harmonic signal (nf0). Such a technology has been successfully applied to tracking small insects and detection of electrically-small objects in the rich-scattering environment. Similarly, a harmonic sensor is used to interrogate electrically-small and passive sensors, of which the magnitude and peak frequency of output harmonics (e.g., second harmonic) are functions of the parameter to be sensed. A harmonic tag or sensor comprises one or multiple antennas, a frequency modulator, a sensor, a microchip and matching networks. Here, we propose and experimentally validate compact, low-cost, low-profile, and conformal hybrid-fed microstrip antennas for the harmonics-based radar and sensor systems. The proposed 98 microstrip antennas are based on a simple single-layered and hybrid-feed structure. By optimizing the feed position and the geometry of microstrip patch, the fundamental mode and particular higher-order modes can be excited at the fundamental frequency and the second harmonic. We have derived the analytical expressions for calculating the antennas’ resonant frequencies, which have been verified with numerical simulations and measurements. Our results show that the proposed hybrid-feed, single-layered microstrip antennas, although having a compact size and a low profile, can achieve descent realized gain (1.2 – 3.5 dB), good impedance matching (return loss \u3c -15 dB), high isolation (\u3c-20 dB), and favorable co/cross-polarization properties. The proposed microstrip antennas may benefit various size-restricted harmonic transponders used for harmonic radars, harmonic sensors, medical implants, passive radio-frequency identification (RFID), and internet-of-things (IoT) applications