Dau-Chyrh Chang

Multiple-polarization microstrip reflectarray antenna with high efficiency and low cross-polarization

This paper presents the study and prototype demonstration of the concepts of antenna focusing, cross-polarization reduction, and multiple-polarization capability of a planar microstrip reflectarray antenna. A square patch with two equal microstrip delay lines connected to its two orthogonal feeding points is used as the antenna element of the planar reflectarray. The length of the delay lines, which varies from patch to patch, is schematically designed to focus the plane wave to the feed point. The measured overall efficiency of the prototype antenna is above 50% in the normal operating band, and in some frequency ranges the efficiency has reached 70%. The experimental patterns show that the measured cross polarization due to special arrangement of the delay lines is quite low at the direction of the main beam. X-polarization and Y-polarization measured data show that the antenna is suitable for multiple-polarization applications (dual linear and dual circular). Surprisingly, the antenna has achieved approximately greater than 7% of gain bandwidth (-3 dB gain drop). These results demonstrate the feasibility of such an antenna for radar and communication system applications. >

CPW-Fed Dual-Mode Double-Square-Ring Resonators for Quad-Band Filters

We propose the improved CPW-fed configurations with dual-mode double-square-ring resonators (DMDSRR) for quad-band applications. The resonant frequency equations of DMDSRR are introduced for simply designing quad-band bandpass filter (BPF). Resonant frequencies can be controlled by tuning the perimeter ratio of the square rings. To obtain lower insertion loss, higher out-of-band rejection level and wider bandwidth of quad-band, the improved CPW-fed and dual-mode perturbations are designed. The proposed filter is successfully simulated and measured. It can be applied to 0.95, 1.26, 1.89 and 2.29 GHz systems.

CPW-Fed Circular Fractal Slot Antenna Design for Dual-Band Applications

Using configuration synthesis and design map, the CPW-fed circular fractal slot antennas are proposed for dual-band applications. In practice, the experimental results with broadband and dual-band responses (47.4% and 13.5% bandwidth) and available radiation gains (peak gain 3.58 and 7.28 dBi) at 0.98 and 1.84 GHz respectively for half-wavelength design are achieved firstly. Then, the other broadband and dual-band responses (75.9% and 16.1% bandwidth) and available radiation gains (peak gain 3.16 and 6.62 dBi) at 2.38 and 5.35 GHz for quarter-wavelength design are described herein. Contour distribution patterns are applied to figure out the omni-directional patterns. The demonstration among the design map and the EM characteristics of the antenna is presented by current distributions.

Smart Antennas for Advanced Communication Systems

Blooming in data-communication applications is beyond all expectations. Smart antennas as now regarded as one of enabling technologies for next-generation wireless communication systems with its promised performance on enhancing network capacity. This paper presents a detailed analysis of the classes of smart antenna systems (SASs), including adaptive arrays, multibeam multiple-input-multiple-output (MB-MIMO) antennas, and diversity-antenna systems. This study also demonstrates practical examples of communication system with developed smart antennas, and shows that using smart antennas instead of traditional antennas highly improves the system performance.

Energy Patterns of UWB Antenna Arrays With Scan Capability

A beam scanning technique is developed with a time delay for ultrawideband (UWB) arrays. In addition, we give a formulation for the time domain array factor for UWB antenna arrays. An UWB comb taper slot antenna array with large element spacing and impulse excitation is studied and four-element UWB linear array systems with element spacings of 2.5, 8.5, and 18 cm in the broadside direction and 20 degree scanning are implemented. The voltage response, spectrum response, energy pattern and energy gain for from simulation and measurement are in good agreement. The periodic grating lobes of the UWB antenna array do not occur in the energy pattern, even if the element spacing and scan angle are large. Simulation and measurement results for the energy pattern and voltage response in various directions are studied to validate the theory of an UWB antenna array with scan capability. The measured peak energy gain of arrays in the broadside direction and 20 degree beam scanning with element spacings of 8.5 and 18 cm are 10.79/10.78 dBi and 9.53/9.06 dBi, respectively.

Single-Feed Circularly Polarized Aperture-Coupled Stack Antenna With Dual-Mode Square Loop Radiator

The authors propose a compact single-feed stack antenna consisting of a square loop radiator with perturbation, an aperture-coupled structure, and a straight-strip feed line for circular polarization (CP) and unidirectional radiation applications. This perturbation applies both dual-mode and orthogonal-mode effects simultaneously in the square loop resonator to present bandwidth and CP characteristics. The stack antenna presents the desired axial ratio (AR) bands of 2.42 GHz with 3-dB bandwidth (BW) = 62 MHz (2.5%). The circular polarization is demonstrated with AR spectrum and orthogonal modes distributions. The proposed antenna is successfully simulated and measured with frequency responses, radiation patterns, and current distributions.

New Development of Parallel Conformal FDTD Method in Computational Electromagnetics Engineering

In this paper, we summarize the new development of hardware-acceleration techniques and a parallel conformal Finite-Difference Time-Domain (FDTD) method in computational electromagnetics engineering. We investigate the performance of a parallel conformal FDTD method on different hardware platforms, such as Intel and AMD processors, with vector-arithmetic logic unit (VALU) acceleration, a regular PC cluster, a high-performance server cluster, the use of a graphics-processing unit (GPU), and an IBM CELL processor. The FDTD method, which is parallel in nature, is one of the best candidate numerical methods for using multiple-core processors and computer clusters to efficiently simulate various electromagnetic problems. Several representative examples, such as a UWB (ultra-wideband) antenna array and reflector antennas, are employed to demonstrate the engineering applications of the parallel conformal FDTD method.

A CPW-fed U type monopole antenna for UWB applications

A CPW-fed U type monopole antenna for UWB applications is proposed and experimentally studied. The proposed antenna is a simple structure and compact size. The maximum size is 22mm by 29.5mm. It provides a wide impedance bandwidth adjustable by variation of its parameters, such as the relative permittivity and thickness of the substrate, width, and feed and ground plane dimensions. Experimental results show that the return loss is from 3.8GHz to 18.2GHz. The azimuthal radiation patterns of the proposed antenna are omnidirectional and the peak gain is 2.9dBi.

Analysis of edge slots in rectangular waveguide with finite waveguide wall thickness

A novel analysis for computing the admittance characteristics of edge slots with a salient feature in successfully considering the finite waveguide wall thickness is presented. The variational equation for the electric field in the slot region between the inner and outer waveguide walls is derived by applying the variational reaction theory and solved by the finite-element method. The division of the slot region into small elements of triangular cylinders and the basis function for each element are described in detail. In the limiting case of zero wall thickness, this finite-element analysis is reduced to a moment-method analysis using Galerkins approach with triangular basis functions. The effects of waveguide wall thickness on the characteristics of the slot are investigated by comparing the numerical results with and without considering the wall thickness. Negligence of the wall thickness may result in a severe underestimation of the resonant length by as large as 14% for edge slots cut in typical X-band waveguides. The computed results with the finite wall thickness taken into account have been checked with the measured data published in previous literature and those obtained by a carefully devised experimental setup. Good agreement between theoretical and experimental results is obtained to demonstrate the validity of the analysis.

The study of Butler matrix BFN for four beams antenna system

In this paper, four beam patterns with frequency range from 1.7 GHz/spl sim/2.2 GHz is generated by a 4/spl times/2 antenna array. The directions of these beam patterns are /spl plusmn/12/spl deg/ /spl plusmn/40/spl deg/. The antenna directivity changes from 18 dBi to 18.7 dBi for these beam patterns. And the antenna gain changes from 10 dBi to 12.3 dBi. The H-plane 3 dB beamwidth changes from 21 degrees to 24.4 degrees. The test results are quite in agreement with that of simulation.