Fu-Chiarng Chen

Reduction of the Peak SAR in the Human Head With Metamaterials

The electromagnetic interaction between the antenna and the human head is reduced with metamaterials. Preliminary study of SAR reduction with metamaterials is performed by the finite-difference time-domain method with lossy Drude model. It is found that the specific absorption rate (SAR) in the head can be reduced by placing the metamaterials between the antenna and the head. The antenna performances and radiation pattern with metamaterials are analyzed. A comparative study with other SAR reduction techniques is also provided. The metamaterials can be obtained by arranging split ring resonators (SRRs) periodically. In this research, we design the SRRs operated at 900 and 1800 MHz bands. The design procedure will be described. Numerical results of the SAR values in a muscle cube with the presence of SRRs are shown to validate the effect of SAR reduction. These results can provide helpful information in designing the mobile communication equipments for safety compliance

A Reconfigurable Quadri-Polarization Diversity Aperture-Coupled Patch Antenna

We present a novel reconfigurable quadri-polarization diversity aperture-coupled patch antenna which can provide four polarization states. By controlling the dc bias voltage of the pin-diodes on the feeding network, we can reconfigure the proposed antenna to provide a pair of orthogonal linear polarizations and a pair of orthogonal circular polarizations. Numerical and experimental results validate our design. This novel antenna provides potential polarization diversity features for wireless local area networks and multiple-input multiple-output systems

Experimental verification of super resolution in nonlinear inverse scattering

This letter presents an experimental verification of the super-resolution phenomenon in a nonlinear inverse scattering algorithm, namely the distorted Born iterative method, by using an experimental setup based on a recently developed time-domain ultra-wide-band radar imaging system at the University of Illinois at Urbana-Champaign. The experimental result also demonstrates that the distorted Born iterative method can recover information on the backside of a penetrable scatterer even though scattering data are collected only from limited viewing angles on the front side of the scatterer.

A new calibration algorithm of wide-band polarimetric measurement system

The principle and experimental results of a new self-consistent calibration algorithm for a wideband polarimetric scattering measurement system are presented. The calibration targets include a flat plate, a dihedral corner reflector, and a rotated dihedral corner reflector. The rotation angle of the third calibrator can be derived in the calibration process and used to verify the calibration performance. Experimental results show that the calculated rotation angle of the third calibrator over the operation bandwidth is in good agreement with its actual angle, hence it provides a self-consistent parameter of the calibration algorithm. Based on the signal-to-noise consideration, an optimal rotation angle for a dihedral corner reflector is found to be 22.5 degrees . This calibration technique is also useful in characterizing the frequency and polarization responses of dual-polarization antennas. >

TIME-DOMAIN ULTRA-WIDEBAND MICROWAVE IMAGING RADAR SYSTEM

This paper describes the time-domain (TD) ultrawideband (UWB) microwave imaging radar system developed at the University of Illinois at Urbana-Champaign recently. The TD-UWB imaging radar system successfully combines the UWB impulse radar system and inverse scattering imaging algorithms for nondestructive evaluation (NDE) and remote sensing purposes in the near-field region. Both the system hardware and inverse scattering algorithms of the system will be discussed in this paper. The TD-UWB imaging radar system can detect dielectric or metallic targets located in air or shallow subsurface with a high resolution image reconstruction capability. Reconstructed images of different types of targets are shown to be in good agreement with the target geometry. The experimental results demonstrate the potential of the system as an useful tool for NDE and remote sensing applications.

Asymmetric Coplanar Waveguide (ACPW) Zeroth-Order Resonant (ZOR) Antenna With High Efficiency and Bandwidth Enhancement

A novel low-profile zeroth-order (ZOR) antenna is presented. The feature of ZOR based on periodic structures is employed to reduce the antenna size, while these antennas generally suffer from narrow bandwidth. A single-layer asymmetric coplanar waveguide (ACPW) structure is proposed to realize a bandwidth-extended ZOR antenna, where the antenna bandwidth is characterized by an equivalent circuit model. The ACPW structure not only provides the design freedom, but also overcomes the design constraint of the traditional CPW. The ACPW ZOR antenna is verified by both full-wave simulations and experiments. As an advantage of the proposed method, the size of antenna is reduced, and the resonant frequency of zeroth-order mode is 1.94 GHz with radiation efficiency of 85%, measured 10-dB fractional bandwidth up to 10.3%, and omnidirectional peak gain of 2.3 dBi.

On-Body Adhesive-Bandage-Like Antenna for Wireless Medical Telemetry Service

This paper presents a novel planar, via-free, printed antenna for wireless medical telemetry service (WMTS). The antenna structure is simple and looks like an adhesive bandage, and can be placed on human tissue. Depending on the application, the antenna can be used as a standalone antenna when it is fed by a coaxial cable, or it can be integrated with a single-chip sensor, with the chip placed in the center. Antenna parameters, such as reflection coefficients, radiation patterns, radiation efficiency, and the specific absorption rate, were evaluated in various scenarios to validate the proposed design. The measured radiation efficiency of the proposed adhesive-bandage-like antenna was 89.5% in free space and 44.7% when mounted on tissue-equivalent phantom. The antenna also retained its broad side radiation characteristics when it was bent at 90 °. The proposed antenna is a favorable candidate for use in wireless body area networks (WBANs). This paper presents the detailed design considerations of the proposed antenna.

CRLH Leaky Wave Antenna Based on ACPS Technology With 180

This study presents a novel composite right/left-handed (CRLH) leaky wave antenna (LWA) with horizontal plane scanning capability. This LWA consists of 10 CRLH unit cells and coplanar waveguide to coplanar stripline transitions. The proposed balanced CRLH unit cell is based on an asymmetric coplanar stripline structure (ACPS). The parameters of the CRLH unit cell can be determined analytically, enabling easy modification for any other frequency band. Because of its planar and horizontal plane scanning property, the proposed design can also be extended to a sector-shaped multisection LWA, achieving a scanning range of more than 180° in the horizontal plane. By varying the operating frequency, the CRLH leaky wave antenna shows the continuously beam-scanning property from backward to forward in the horizontal plane. A 10-cell prototype exhibits the beam-scanning capability in the horizontal plane, and a 20-cell multisection sector-shaped LWA confirms the approach of designing the wide-range beam-scanning LWA. Experimental results show that the proposed design is in good agreement with the simulation. The planar and low-profile characteristics of the novel CRLH LWA make it suitable for integration with other microwave circuits, and can be applied to applications that require a wider beam-scanning range.

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In this letter, we present a low-profile switchable quadri-polarization diversity aperture-coupled patch antenna. The proposed antenna can provide four polarization states by controlling the DC bias voltage of four pin diodes in the feeding network. The experimental results validate the novel antenna provides polarization diversity features for wireless local area networks (WLANs) and multiple-input multiple-output (MIMO) systems.

Horizontal Plane Scanning Capability

This paper describes the ongoing pursuit of developing a time-domain (TD) ultra-wideband (UWB) microwave imaging radar for nondestructive evaluation (NDE) purposes at the University of Illinois at Urbana-Champaign. The TD-UWB microwave imaging radar system successfully combines the time-domain UWB radar system hardware and inverse scattering imaging algorithms for nondestructive evaluation (NDE) and remote sensing purposes in the near-field region. Both the system hardware and inverse scattering algorithms of the system are discussed.