Xiao-Qun Chen

An Overview on Defected Ground Structure

This paper focuses on a tutorial overview of defected ground structure (DGS). The basic conceptions and transmission characteristics of DGS are introduced and the equivalent circuit models of varieties of DGS units are also presented. Finally, the main applications of DGS in microwave technology field are summarized and the evolution trend of DGS is given.

A NOVEL DUAL BAND TRANSMITTER USING MICROSTRIP DEFECTED GROUND STRUCTURE

This paper presented a novel dual band transmitter which operates as power amplifier or frequency doubler with the stop band characteristic of defected ground structure (DGS). It works as a power amplifier at 2.4 GHz which satisfies the 802.11b/g wireless LAN standard or performs as an active frequency doubler at 6.8 GHz which depends on the input frequency and. The equivalent circuit and the stop band characteristic of the proposed microstrip DGS are analyzed and simulated. For the proposed transmitter, second harmonic suppression is below −52.6 dBc in the amplifier mode, and fundamental suppression is below −41 dBc in the frequency doubler mode with the stop band characteristic of DGS. The designed transmitter used GaAs InGaP Heterojunction broadband MMIC. It achieves 13.7 dBm of P1 dB and its gain is 16.5 dB in amplifier mode, and its maximum output power is 7.8 dBm at 6.8 GHz in frequency double mode.

A NOVEL LOW PASS FILTER USING ELLIPTIC SHAPE DEFECTED GROUND SSTRUCTURE

This paper presents a novel elliptic shape defected ground structure (DGS) for low pass filter (LPF) applications. An equivalent RLC circuit model is presented and its corresponding parameters are also extracted from the measured S-parameters. The filter presents the advantages of compact size, high selectivity; low insertion loss and high out-band suppression from 5.15 GHz to 10 GHz below −31 dB. Good agreement with response of equivalent circuit, electromagnetic simulation, and measurement is demonstrated

Design of a Novel EBG Structure and its Application in Fractal Microstrip Antenna

In this paper, a novel electromagnetic bandgap structure (EBGs) is proposed, which is similar to the mushroom-like EBG. By introducing double reverse split rings (RSR) into the square patch, the size of EBG cell is reduced by 30%, and the bandgap achieves bandwidth about 65%. A fractal microstrip antenna is implemented using the EBGs as a ground plane, and the measured results show that the reduction in the surface wave level is remarkable. Compared with the reference antenna at 5GHz, an approximately 8dB improvement of the return loss is achieved, and the back lobe is reduced by 10dB in E plane and 8.73dB in H plane at the resonant frequency, respectively. The front-back ratios of the antenna have signiflcantly increased from 4.9GHz to 5.2GHz.

A Novel Unequal Wilkinson Power Divider for Dual-Band Operation

This paper presents the design of a novel dual-band unequal Wilkinson power divider. The proposed power divider can operate at arbitrary two frequencies without reactive components. To achieve the dual-band operation, four groups of transmission lines called network 1, 2, 3 and 4 are introduced. The design and analysis of power divider are presented. Closed-form design equations are derived based on network theory. The validity of this analysis is confirmed through the design, simulation, and experimental results with a power divider for 1 and 2 GHz.

A Novel Microstrip Array Antenna with Coplanar Parasitic Elements for UHF RFID Reader

A novel RFID reader antenna for 910–915 MHz is proposed. The antenna is microstrip array configuration, which mainly consists of three elements rectangular radiation patches and several coplanar parasitic elements. The parasitic elements could broaden impedance bandwidth in the limited substrate thickness and rectify the resonant frequency well. In the paper, the antenna configuration, design methodology, simulated and measured results are carefully discussed. The experimental results indicate, in the operating band, that VSWR is less than 1.25. And because of arranging array, the antenna radiation pattern has a good coverage in H-plane. It makes the tag be identified in large range and high speed. The antenna is well suitable for the application in railway RFID circumstance.

DESIGN OF A FRACTAL DUAL-POLARIZED APERTURE COUPLED MICROSTRIP ANTENNA

In this paper, a fractal dual-polarized aperture-coupled microstrip antenna is presented. The proposed antenna adopts 1st Minkowski fractal patch and is fed by the aperture-coupled structure with H-shaped and H-shaped loaded capacitance. The size of Minkowski fractal patch is reduced by 20% compared with a square patch. Results show that the T/R isolation is better than 35dB, improved by 2dB compared with the double H-shaped slots. The gain is more than 8dB, and the front-back ratio is greater than 20dB in the operating frequency range. Both simulated and experimental results are in good agreement.

A Novel Double-Layer Microstrip Antenna Array for UHF RFID

A novel RFID reader antenna is designed for UHF band. The proposed antenna consists of double-layer two elements rectangular patches and impedance tuning stub. The lower-layer patches are the chief radiation elements. The upper-layer patches could perfectly improve impedance matching and broaden impedance bandwidth. Meanwhile, the antenna adopts series-fed at one edge to simplify the feeding-net. The simulated and measured results demonstrate that the proposed antenna has a lower VSWR (≤ 1.2) in a wide bandwidth (882–945 MHz, 6.88%), which greatly covers the operated band (902–928 MHz). In H-plane, the gain gets 11.45 dBi and 7.15 dBi at 0° and ±50° respectively, that could make the reader have a farther identification distance in the horizontal direction in the case of vehicle identification.

A wide stopband CPW low pass filter using quarter wavelength stepped impedance resonators

A novel wide stopband coplanar waveguide (CPW) low pass filter (LPF) using quarter wavelength stepped impedance resonators (SIR) is presented. The bandstop characteristics of the quarter wavelength short circuited stubs SIR are demonstrated. By cascading three tapered quarter wavelength short circuited stubs SIR and a CPW spurline resonator, the fabricated low pass filter has sharp rejection with cutoff frequency of 3.5 GHz, and deep attenuation from 3.7 GHz to 11 GHz lower than −24 dB. Good agreement between simulated and measured results is demonstrated.

Wideband Yagi-Uda Antenna Design Using Adaptive Differential Evolution Algorithm

A series of control parameter researches of differential evolution algorithm (DE) and adaptive DE (ADE) for a wideband six-element Yagi-Uda antenna optimization is presented. A method of moments code (NEC) was used to evaluate each of the antenna designs generated by ADE and DE. The optimized Yagi-Uda antenna is fabricated and measured to validate the efficiency and the flexibility of the parameter analysis. The simulated and measured impedance bandwidth of VSWR < 1.5 achieves 14.0%, which trebles the bandwidth of the Yagi-Uda antenna with a driven dipole element. The measured maximum antenna gain across the operating frequency band reaches 12.75 dB. Measured results of the fabricated antenna prototype is in good agreement with simulated results. Numerical and measured results confirm that the proposed ADE method is superior to or at least competitive with the conventional DE in terms of convergence speed and solution quality.