Foldable all-textile cavity-backed slot antennas for personal UWB localization

An all-textile multimoded cavity-backed slot antenna has been designed and fabricated for body-worn impulse radio ultra-wideband (IR-UWB) operation in the 3,744-4,742.4 MHz frequency band, thereby covering Channels 2 and 3 of the IEEE 802.15.4a standard. Its light weight, mechanical flexibility, and small footprint of 35 mm x 56 mm facilitate integration into textile for radio communication equipment for first aid responders, personal locator beacons, and equipment for localization and medical monitoring of children or the elderly. The antenna features a stable radiation pattern and reflection coefficient in diverse operating conditions such as in free space, when subject to diverse bending radii and when deployed on the torso or upper right arm of a test person. The high isolation toward the wearer's body originates from the antenna's hemispherical radiation pattern with a -3 dB beamwidth of 120 degrees and a front-to-back ratio higher than 11 dB over the entire band. Moreover, the antenna exhibits a measured maximum gain higher than 6.3 dBi and a radiation efficiency over 75%. In addition, orientation-specific pulse distortion introduced by the antenna element is analyzed by means of the System Fidelity Factor (SFF). The SFF of the communication link between two instances of this antenna is higher than 94% for all directions within the antenna's -3 dB beamwidth. This easily wearable and deployable antenna is suitable to support IR-UWB localization with an accuracy in the order of 5 cm

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Antennas and Propagation

This Special Issue gathers topics of utmost interest in the field of antennas and propagation, such as: new directions and challenges in antenna design and propagation; innovative antenna technologies for space applications; metamaterial, metasurface and other periodic structures; antennas for 5G; electromagnetic field measurements and remote sensing applications

Microwave antennas for biomedical application

Medical diagnosis is one of the key steps to determine the problem of the human body. The current diagnostic tools are expensive, bulky and long exposure to some of these diagnostic tools can be injurious to the human body. Hence, researchers are now exploring through different possibilities to replace current diagnostic tools. Microwave regime is one of the potential candidate to replace current diagnostic system providing with a chip, portable system suitable for the human body. One of the fundamental tool for a microwave diagnostic system is microwave antenna. The current findings on designing microwave antennas for biomedical diagnosis lacks due to low microwave power penetration inside the human body, high specific absorption rate (SAR), low directivity and compactness. This thesis aims on improving the microwave penetration inside the human body and develop antennas that can perform efficiently for biomedical diagnosis application. A multi-layer reflection model is investigated for evaluation of the combined material characteristics of different lossy human tissues, along with the enhanced antenna designs, suitable for biomedical application, operating on-body and as an implant, have been presented within this thesis. The rationale behind this work relates to the early detection of cancerous tissues, internal injuries and other characteristic changes inside the human body with the primary goals being to improve microwave power penetration inside the human body and to provide low SAR and compact microwave antenna system for biomedical diagnosis. The penetration of microwave power inside a human head model is improved by employing calculated permittivity inside a rectangular waveguide used as the microwave transmission source. Firstly, a multi-layer reflection model is created from various human tissue material. The wave impedance of the multi-layer is then extracted from the overall reflection coefficient found at the edge of the multi-layer tissue model. Furthermore, a rectangular waveguide is constructed and an L-probe rectangular waveguide feeding technique is presented. The measured results validate the approach with an increment in power penetration inside the human head 1.33 dB at 2.45 GHz.  Antennas are characterized in-front of homogeneous and a frequency-dependent inhomogeneous human head and shown that inhomogeneous phantom provides with real-life scenario for the measuring antenna whereas the homogeneous phantom only resembles the scenario. The effect of superstrate at the boresight of an on-head matched antenna for biomedical applications is analysed and shown that superstrate layer at the boresight direction of the antenna provides with ~8 dB increased directivity towards the human head with 0.0731 W/kg reduction of SAR compared to the antenna without the superstrate. The design of a 3-D on-body antenna and a coplanar waveguide (CPW) fade antenna matched with an inhomogeneous human head provides the second investigation area. Specific focus has been given to make the designs compact, increase the front to back ratio (FBR) of the radiation pattern and decrease the SAR of the antenna. The 3-D antenna is realized combining a folded inverted F-like structure and a slot-loaded ground plane and backed by a rectangular cavity to minimize side and back lobe radiation. An FBR of 17 dB with SAR less than 0.0147 W/kg is achieved throughout the operating frequency ranging from 1 - 1.7 GHz by the designed antenna while acquiring a compact dimension of 0.23 × 0.23 × 0.04 λ in size with respect to the lowest operating frequency.  An inhomogeneous human head phantom is constructed and used to analyze the antennas performance in real-life scenario. Moreover, the choice of operating frequency for on-head antennas and effect of a superstrate on on-head matched antennas is investigated. An FBR of 20 dB with SAR less than 0.037 W/kg is achieved throughout the operating frequency ranging from 0.788 - 2.5 GHz by the designed antenna while acquiring a compact dimension of 0.1 × 0.1 × 0.008 λ in size with respect to the lowest operating frequency. Finally, the design of an implantable coil antenna is investigated for wireless power transmission inside the human body. The biocompatibility of the building material is analyzed. Polydimethylsiloxane (PDMS) and gold (Au) is utilized as the biocompatible building material to realize the designed implantable antenna. Furthermore, the antenna is characterized in a "complete medium" composed of fetal bovine serum (FBS), penicillin-streptomycin and dulbecco's modified eagle's medium (DMEM) which is used as the cell culture media to resemble designed antennas operation environment. The antenna is impedance matched at 5 MHz frequency with a maximum received voltage of 35 mV is recorded by utilizing the designed implantable antenna