Kama Huang

A Miniaturized Dual-band Power Divider with Harmonic Suppression for Gsm Applications

In this paper, a miniaturized dual-band power divider based on artificial transmission lines is proposed for GSM applications. The design consists of four sections of recently developed planar artificial transmission lines, an LC tank circuit in shunt, and an isolation resistor. The experimental results show that the proposed configuration has good performance at both 0.9 GHz and 1.8 GHz. Meanwhile, it achieves a significant size reduction compared to traditional dual-band planar power dividers. At the center frequency 1.35 GHz, the dimension of the proposed dual-band power divider is only 43 mm × 21 mm, or equivalently 0.29λg × 0.14λg. With the harmonic suppression nature of artificial transmission lines and the shunt LC tank, the wideband response of the proposed dual-band power divider reveals good harmonics suppression.

A Miniature Planar Antenna for Bluetooth and UWB Applications

The paper puts forward a miniature microstrip antenna at the operating frequency of 2.4–2.5 GHz (Bluetooth) and 3.1–10.6 GHz (UWB). The omnidirectional radiation patterns can be obtained at the whole operating frequency band by cutting the ground conductor and adding a branch at the top of the antenna. Simulated results show that the antenna has attractive characteristics such as stable phase center, constant group delay, linear phase and good time-domain impulse response. Both the reflection coefficient and radiation patterns of the antenna are in good agreement with measured results. Experiment also shows that the cross polarization level is very low with flat gain. Consequently, the proposed antenna can well meet the requirements of wireless communication in both the Bluetooth and UWB bands.

Application of Micro-Genetic Algorithm to the Design of Matched High Gain Patch Antenna with Zero-Refractive-Index Metamaterial Lens

This paper presents a method for the computer aided design of high gain patch antenna with Zero-Refractive-Index (ZRI) metamaterials using Micro-Genetic Algorithm (MGA) and finite-difference time-domain (FDTD). The ZRI metamaterials, which is composed of metallic grids with periodic square lattice and slices of medium, is placed in front of the conventional patch antenna as a lens. The design progress and results are presented and discussed. A prototype of such a designed antenna has been fabricated and tested. The measured radiation patterns and return loss of the antenna are compared with the computed results, and a good agreement is observed. The ZRI lens can maintain 10 dBi maximum gain enhancement compared to the conventional patch antenna from 11.5 GHz to 12.5 GHz. The measured results show that the patch antenna with the ZRI lens has an impedance bandwidth in the range from 11.70 GHz to 12.56 GHz for S 11 < −10 dB.

Transient Power Loss Density of Electromagnetic Pulse in Debye Media

This paper is to point out the mistakes of previous expression of power loss density of the electromagnetic pulse (EMP) in Debye media. We derive the precise expression of transient power loss density both from the electrodynamic (ED) approach and equivalent circuit (EC) approach. In the ED approach, the expression is derived from the energy conservative law and Debye equation. For the harmonic field, the expression reduces to the well-known formula. The physical meaning can be clearly explained in the EC approach. The expression derived from the EC approach is consistent with that from the ED approach. A 1-D example is used to show the negative power loss of the EMP in Debye media and the error of temperature rise calculated from the previous expression.

Transformation Optics for Computing Heating Process in Microwave Applicators With Moving Elements

Moving elements have been widely used to improve heating uniformity in microwave applicators, such as rotating turntables and mode stirrers. However, it remains a challenge to compute the heating process due to the difficulty of meshing the element’s dynamic locations. In this paper, we propose a novel algorithm to solve this problem accurately and efficiently. Being surrounded by moving elements with a time-varying anisotropic layer on the basis of transformation optics, the electromagnetic field inside applicators can be computed with consideration of continuous motion of moving elements. A 2-D applicator model with a rotating turntable is used to illustrate the proposed algorithm in detail. Furthermore, we also compute the heating process of a practical 3-D applicator model with a rotating turntable. Compared with the conventional method, the proposed algorithm is more efficient and accurate. The computational results are in good agreement with experiments.

Design and Implement of a CPW-Fed Meander Monopole Antenna with V-Shape Notched Ground for Wlan

A dual-band CPW-fed meander monopole antenna with V-shape notched ground for WLAN communications covering the 2.4 GHz and 5.2 GHz band is reported. V-shape notched coplanar ground is applied to enhance the impedance bandwidth at the 5.2 GHz band. A prototype is fabricated and tested. The measured −10 dB impedance bandwidth are 310 MHz and 850 MHz respectively, which successfully meets the bandwidth requirement of IEEE 802.11b/a/g and HIPERLAN2 standards. Good omnidirectional radiation characteristics in the desired band are achieved.

A Novel Microstrip Grid Array Antenna with Both High-Gain and Wideband Properties

A novel microstrip grid array antenna that is simultane- ously high in gain and wide in bandwidth is proposed. To enhance its bandwidth, the antenna adopts elliptically shaped and variably dimensioned radiation elements as well as a linearly tapered ground plane, and is optimized by a parallel genetic algorithm (GA) on a clus- ter system. A prototype antenna was fabricated and tested. Results of simulation and measurement agree well and show the antenna ex- hibits encouraging properties, e.g., a maximum gain of approximately 15.1dBi at 5.8GHz; the jS11j < i10dB bandwidth and the 3dB gain- drop bandwidth are 25.6% (from 5.03GHz to 6.51GHz) and 27.6% (from 5.0GHz to 6.6GHz), respectively, of the center frequency, both of which are much wider than that of conventional microstrip grid ar- ray antennas. Moreover, the overlap between the antennas impedance bandwidth and the gain bandwidth results in a wide efiective operating frequency bandwidth of 25.6%, which is the largest so far achieved for microstrip grid-array antennas.

The analysis of “power window” induced by thermal effect during the microwave heating

The “windows” are often considered as the evidence of microwave non-thermal effect. Here, enzyme catalysis acrylonitrile reaction was carried out and the coupled multiphysics field equations were solved by finite difference time domain (FDTD) method. The temperature curves can be obtained under the different power. Then, the results calculated by chemical reaction kinetic show that the power window of product concentration can be induced by thermal effect. The power window cannot be a criterion of microwave non-thermal effects.

A Novel Electrically Small Meandered Line Antenna with a Trident-Shaped Feeding Strip for Wireless Applications

A novel electrically small antenna (ESA) which based on the meandered line structure is designed, fabricated, and measured. The proposed antenna whose total size is 13.50mm×13.51mm×0.8mm is designed to cater for the ISM (industrial, scientific, and medical) band of 2.45u2009GHz with a 𝑆11<−10dB bandwidth of 3.9%. By introducing a trident-shaped feeding strip and inserting 4 pairs of triangular slot stubs at the central feed line, the resonant frequency of the antenna drops to 2.45u2009GHz from 2.50u2009GHz and the impedance matching is improved significantly. The dimension parameters of this antenna are optimized to achieve wide impedance bandwidth, reasonably high gain, as well as omnidirectional radiation pattern.

A New Noninvasive Method for Determining the Conductivity of Tissue Embedded in Multilayer Biological Structure

A significant conductivity difference between normal and tumorous biological tissue has been reported in the literature. Such a conductivity difference makes it possible to diagnose the pathological tissue by measuring the change of tissue conductivity. A new noninvasive method is proposed to determine the conductivity of tissue embedded in a stratified biological structure. An open-ended coaxial line is used to measure the reflection coefficient of the structure, and then the conductivity of the tissue of interest can be obtained making use of an inverse calculation based on Genetic Algorithm (GA). To explore the feasibility of the proposed method, a numerical simulation is presented in this paper. In the simulation, the field distribution near the end of the coaxial line is computed making use of finite-difference time-domain (FDTD) method. Also, FDTD is employed to calculate the reflection coefficient from preset tissue conductivity, and then the forward-calculated reflection coefficient plus random noise is used to simulate the measured reflection coefficient. From the measured reflection coefficient, the tissue conductivity is obtained by a GA inverse calculation. Such calculated tissue conductivity is compared with its preset value to validate the accuracy of the proposed method. Also, the sensitivity of the reflection coefficient corresponding to the tissue conductivity change is investigated at different operating frequencies, and an optimal frequency is explored for maximum measurement sensitivity. The results of the numerical simulation verify the feasibility of the proposed new method, which has a potential application for cancer detection.