Qi-Zhong Liu

MINIATURIZED CIRCULARLY-POLARIZED ANTENNA USING TAPERED MEANDER-LINE STRUCTURE

A novel miniaturized circularly-polarized antenna is presented. By using tapered meander-line structure, the designed antenna has a size reduction rate of 96% compared with a traditional turnstile dipole antenna. The unequal lengths of the two meander- line dipoles are properly adjusted to achieve a circularly polarized radiation. Furthermore, the impedance matching is effectively realized by a lumped matching network. A prototype of the antenna with a size of 64 × 64 mm 2 has been implemented and tested. Good agreement is achieved between the simulated results and the measured results, which shows that the axial ratio is less than 3.0 dB and the VSWR less than 2.0:1 in the frequency range of 450 ± 1.5 MHz.

Modified Two-Element Yagi-Uda Antenna with Tunable Beams

A modifled two-element Yagi-Uda antenna with tunable beams in the H-plane (including four signiflcant beams: forward, backward, omni-directional, and bi-directional beams) is presented. These tunable beams are achieved by simply adjusting the short-circuit position of the transmission line connected to the parasitic element. The principle of operation is investigated by examining the current relations between the driven and parasitic elements. Measured results of a fabricated prototype are presented and discussed.

COMPACT CIRCULARLY POLARIZED MICROSTRIP ANTENNA WITH WIDE BEAMWIDTH FOR COMPASS SATELLITE SERVICE

A compact circularly polarized (CP) microstrip antenna with inserted nine cross slots is proposed to reduce the size and widen the beamwidth. The antenna is operated at 1.268GHz, and built by using a substrate with a coaxial probe feed. The impedance bandwidth (VSWR < 2) is 1.5% and the 3dB axial ratio bandwidth is 0.52%. The measure gain is 4.5dBi and beamwidth is about 110 - . The measured results for the compact CP antenna with embedded cross slots size shows that the resonate frequency is signiflcantly lowered from 1.951GHz to 1.268GHz, corresponding to a 35% antenna size reduction compared with the one without any slot.

EFFICIENT OPTIMIZATION AND REALIZATION OF A SHAPED-BEAM PLANAR ARRAY FOR VERY LARGE ARRAY APPLICATION

The optimization and simulated realization of planar 2-D antenna array with a flat-top shaped-beam pattern are proposed in this paper. The shaped-beam planar array can be used as an element of Very Large Array for the Deep Space Detection. A conventional genetic algorithm is chosen for the optimization. However, the synthesis of flat-top shaped-beam using a planar 2-D array is difficult because of the inherently large number of degrees of freedom involved in the algorithm (in generally, the amplitude and phase of each element must be determined). Therefore, a sub-array rotation method, which lies on the flat-top pattern synthesis itself, is proposed in this study to resolve the design problem. Besides, the proposed synthesis has taken the actual element patterns but identical and isotropic ones into account, which can reduce the error between computation and realization. A 8 × 8 (64)-element rectangular array is exampled, and the results of the optimized flat-top patterns are shown to illustrate the validity and high efficiency of the technique.

Study on a Dual-Band Notched Aperture UWB Antenna Using Resonant Strip and CSRR

An ultra-wideband (UWB) aperture antenna with dual band-notched characteristic is presented. The antenna consists of a circular monopole on the front side and a U-shaped aperture on the back ground plane. By attaching a rainbow-shaped resonant strip on the aperture plane and etching a complementary split ring resonator (CSRR) on the circular monopole, two notched band, 3.3–3.6 GHz for WiMAX and 5.15–5.825 GHz for WLAN, are achieved respectively. The antenna is successfully simulated and measured, showing that dual-band notched characteristic can be obtained by using two different structure. Moreover, the band notched structure is also studied based on the input impedance of the proposed antenna.

Study on a CPW-Fed UWB Antenna with Dual Band-Notched Characteristic

A compact ultra-wide band (UWB) CPW-fed antenna with dual band-notched characteristic is proposed. By using only one H-shaped slot etched on the radiation patch, two notched band, 3.3–3.6 GHz for WiMAX and 5.15–5.825 GHz for WLAN, are achieved. The antenna yields an impedance bandwidth of 3.1–10.6 GHz with VSWR < 2, except the notched bands. The antenna is successfully simulated and measured, showing dual band rejected characteristic can be obtained by using the only one H-shaped slot. Moreover, conceptual circuit model, which is based on the input impedance of the proposed antenna, is also shown to discuss the dual band notched characteristic.

Compact Broadband Printed Antenna for Multi-functional Mobile Terminals

A printed antenna having a low profile and a broad bandwidth is presented. The antenna consists of a loop structure constructed with two-layered meander strips. The loop structure and meander strips are used to enhance the impedance bandwidth and reduce the antenna size, respectively. A prototype of the proposed antenna with a small antenna height of 5 mm is constructed and tested. The measured results show that the antenna has a bandwidth of 30.2% (643 MHz) according to −10 dB return loss in 2.1 GHz band. In addition, effects of the main geometrical parameters on the performance of the antenna are also investigated.

Modified Mode Decomposition for Analyzing Antennas with Body of Revolution Radome

Two improvements are made on mode decomposition for analyzing the antennas with body of revolution (BOR) radome by the method of moments (MoM). First, the integral calculations in mode decomposition of the incident fields are replaced by Fast Fourier Transform (FFT). Then a method is introduced to automatically select the calculated modes. Simulation results are also presented, which indicate the effectiveness and efficiency of the proposed approach.

A LOW-PROFILE AND BROADBAND CONICAL ANTENNA

A novel electric small conical antenna working on a very broad band, 0.47-6 GHz, with the height of only 60 mm, is presented. A capacitive ring on the top of the cone and three oblique shorted lines are used to expand the work band. By changing the width of the ring and the slope of the oblique line, the impedance of the antenna matches 50-ohm feed line commendably. Simulation and experiment results demonstrate that this antenna provides very broad band and low-profile characters, which exhibits a 12.8 : 1 impedance bandwidth with voltage standing wave ratio (VSWR) below 2 : 1 (the impedance bandwidth is 11.9 : 1 with the VSWR below 1.5 : 1) and with the height only 0.094 wavelength associated to the lowest frequency.

A Hybrid Fe-Bi Method for Electromagnetic Scattering from Dielectric Bodies Partially Covered by Conductors

A hybrid technique combines the finite element (FEM) and boundary integral (BI) methods is used to analyze electromagnetic scattering problems from structures consisting of an inhomogeneous dielectric body attached to perfectly conducting bodies. The hybrid approach takes advantage of the strengths of each numerical technique in order to solve problems that neither technique alone could model efficiently. Numerical results are presented to validate the accuracy and demonstrate the application of this method.