F.-S. Zhang

Dual circularly polarized antenna of compact structure for rfid application

A compact structure is proposed to realize dual circularly polarized antenna for RFID system. In this paper, a cross-shaped aperture in the ground plane provides coupling between the patch and a single microstrip line with two ports underneath the ground plane, the means of feeding is constructed. For system requirements, some modifications are made to improve the performance. This design realizes low profile, separating the radiating patch and the feeding layer, particularly saving space by avoiding the traditional scheme based on microstrip branch line coupler. In the wireless communication system for RFID applications, circular polarization modulation (CPM) is implemented, which reduces the requirement for bandwidth effectively, and simplifies the data communication. Therefore, a dual circularly polarized antenna is an indispensable key part of this RFID system, and in some case the compact structure is necessary. In this design process, the dimensions and performance of this antenna are calculated and optimized by HFSS (High Frequency Structure Simulator). The results agree well with the measurement, and show the practicability of this scheme.

A Reconfigurable Microstrip Antenna with Switchable Polarization

A novel reconfigurable small microstrip antenna with switchable slots is proposed to achieve circular polarization diversity. Slots are cutting in the square patch and, by using the diodes to adjust the lengths of the slots, this antenna can radiate with either right hand circular polarization (RHCP) or left hand circular polarization (LHCP) using the same feeding probe. Simulation and experimental results are presented and it is demonstrated that this design is valid. The proposed antenna demonstrates useful features for wireless communication applications.

Modified Particle Swarm Optimization for Patch Antenna Design Based on IE3D

An evolutionary optimization method for patch antenna designs is presented in this paper. The modified particle swarm optimization (MPSO) based on fitness distance ratio (FDR) is combined with standard software IE3D to achieve the optimum antenna satisfying a certain design criterion. The antenna geometric parameters are extracted and optimized by a MPSO program, and simulated by IE3D. The fitness function of the optimization is calculated by the MPSO program according to the simulation results extracted from IE3D to represent the performance of each candidate design. A microstrip line fed low-profile E-shaped patch antenna is designed and optimized using the MPSO/IE3D method. The designed patch antenna is simulated, fabricated, and measured to validate the effectiveness of the MPSO/IE3D method.

Frequency Notched UWB Slot Antenna with a Fractal-Shaped Slot

A frequency notched ultra-wideband planar slot antenna is presented. By introducing a modified fractal-shaped slot to the patch, a notched band within a wide operation bandwidth is achieved. The designed antenna satisfies the voltage standing wave ratio requirement of less than 2.0 in the frequency band from 3.01 to 13 GHz above while showing the band rejection performance about 500 MHz in the frequency band of 5.59 to 6.09 GHz. Simulation and measurement results are presented for the proposed antenna.

A Microstrip-Fed Logarithmically Tapered Slot Antenna for Wideband Applications

A novel microstrip-fed logarithmically tapered slot antenna (TSA) for wideband applications is presented. The wideband impedance matching and antenna gain are improved by introducing a logarithmically tapered slot. The experimental results demonstrate that this antenna achieves an impedance bandwidth ratio of 15.5:1 for VSWR ≤2 from 0.89 to 13.80 GHz and has an antenna gain varying from 4.2 to 15.6 dBi and a cross-polarization level of more than 15 dB within the operating frequency range. The performances of the TSAs with different shapes of the tapered slot over a wide bandwidth are also compared and discussed in detail.

A novel small CPW-fed T-shaped antenna for MIMO system applications

A novel small CPW-fed T-shaped antenna for MIMO application is presented. The size of the antenna is only 35% of that of conventional CPW-fed T-shaped antenna, which has satisfied return loss bandwidth and omnidirectional radiation characteristics. A multifeed 8-element planar array is fabricated and measured. It shows that the features of small size, uniplanar structure, good radiation characteristics and small mutual coupling are promising for MIMO applications in compact portable devices.

Extreme Wideband Tapered Slot Antenna with Impedance Bandwidth in Excess of 21.6 : 1

An extreme wideband tapered slot antenna (TSA) fed by coplanar waveguide (CPW) for wideband applications is presented. A novel logarithmic flare slot and a double-Y balun are introduced into the design of the antenna. The experimental results demonstrates that this antenna achieves a ratio impedance bandwidth of 21.6 : 1 for VSWR ≤ 2 from 1.19 to 25.8 GHz, exhibits good end-fire patterns and moderate gains in the measured bandwidth from 1.2 to 13 GHz. The coplanar design, CPW feeding technique makes it easy for the integration of the antenna into circuit boards.

Conformal Array Antenna Design Using Modified Particle Swarm Optimization

A conformal array antenna composed of 8 low-profile Eshaped patches mounted on an irregular shaped surface is designed for 360° coverage in the horizontal plane. Unequal thickness substrate is used in the conformal low-profile E-shaped patch design to maintain the wide-band characteristic of the conformal E-shaped patch antenna. Fitness distance ratio (FDR) based particle swarm optimization (PSO) is used to synthesize the patterns of the conformal array. Good agreement is observed between numerical and experimental results of the conformal array antenna.

A Novel Three-Fed Microstrip Antenna for Circular Polarization Application

A novel feeding mechanism for realizing circular polarization characteristic is presented in this paper. Detailed theoretical analysis proves that a circular microstrip antenna, which is excited by three centrosymmetric feeds with equal amplitudes and relative 120° phase shifts, can obtain good circular polarization. This circular microstrip antenna is designed to work on TM11 mode. Good equal input powers with relative 120° phase shift for three feeds are provided by a Wilkinson power divider with three phase-adjusting transmission lines. Probe feeding for the radiating patch is accomplished by vertical via holes through the substrate material. The measured results show that the proposed antenna obtains a 10 dB return-loss impedance bandwidth of 22.3% and a 3 dB axial-ratio CP bandwidth of 18.9%, with the peak gain of 7.0 dBi. Additionally, the measured symmetrical radiation patterns are in good agreement with the simulated ones.

A Novel CPW-FED Monopole Antenna for Multiband Operation

In this paper, a novel CPW-fed dual folded-strip monopole antenna with a pair of inverted L-shaped stubs is proposed for multiband applications. Reasonably large impedance matching bandwidth and good omni-directional radiation patterns have been observed. The measured impedance bandwidths reach about 27% for the lower band and 32% for the higher band, which meets the required bandwidth specifications of 2.4 GHz WLAN, 2.5 GHz WiMAX, DMB and 5.2/5.8 GHz WLAN standards. The proposed antenna with relatively low profile is suitable for multiband wireless communication systems.