Bao-Hua Sun

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 Tri-Band Claw-Shaped Monopole Antenna for Wlan/wimax Applications

A compact microstrip-fed tri-band printed monopole antenna is presented for wireless applications in wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) applications simultaneously. The antenna is composed of a novel claw-shaped monopole and a modified rectangular ground plane. The three arms of the antenna generate three desired resonate frequencies and exhibit a relatively independence while being tuned separately. The antenna is simple in configuration outlining an overall size of 38 × 30 × 1.6 mm3. The measured 10 dB bandwidth for return loss is from 2.35 to 2.72, 3.34 to 3.7, and 4.81 to 6.74 GHz for WiMAX and WLAN applications. Good radiation characteristics and antenna gains for the operating bands have been obtained. Effects of varying the monopole dimensions on the antenna performance have also been studied.

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.

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.

RECONFIGURABLE DUAL CIRCULARLY POLARIZED MICROSTRIP ANTENNA WITHOUT ORTHOGONAL FEEDING NETWORK

A polarization reconfigurable microstrip antenna is proposed without orthogonal feeding network. The antenna is composed of a suspended patch, two printed probes and a simple switch circuit. Reconfigurable circularly polarization, i.e., right-hand circular polarization (RHCP) or left-hand circular polarization (LHCP), is produced by controlling the states of the switch circuit. A prototype is designed and tested. The simulation and measurement results show that the proposed antenna demonstrates wide impedance bandwidth and a good axial ratio in the circularly polarized states.

DESIGN AND INVESTIGATION OF BROADBAND MONOPOLE ANTENNA LOADED WITH NON-FOSTER CIRCUIT

The possibility of using non-Foster circuit to expand the bandwidth of a monopole antenna is investigated theoretically. Beginning with an inductor-loaded monopole antenna resonating at difierent frequencies by changing the value of the loaded inductor, we show that a frequency-dependent inductor is needed to enhance the bandwidth of the monopole antenna. The curve for the reactance of the frequency-dependent inductor versus frequency is fltted, which enlightens us to use a non-Foster reactive circuit to realize the frequency-dependent inductor. Based on the above studies, a monopole antenna loaded with a non-Foster circuit is presented. Simulated results demonstrate that the input reactance of the loaded antenna becomes stable and approaches zero, which favors the impedance matching and extends the bandwidth to a certain extent. Finally, a passive (Foster) matching circuit is designed to improve the bandwidth further. A 0.69-m monopole antenna with 2.0:1 VSWR in the frequency range 30{150MHz is designed and investigated.

A Differential Rectangular Patch Antenna with Marchand Balun for UWB Applications

A two-element array antenna using rectangle patch elements for UWB application is proposed. A novel Marchand balun is chosen as the feeding structure. This balun excites signals of Equi-amplitude and 180 degree phase difference. The radiation pattern of the antenna is omnidirectional at H-plane and bidirectional at E-plane. The measured VSWR is less than 2 over the frequency bandwidth (3–11 GHz). The simulated gain is 2.8–8.49 dB, especially increased at higher frequencies because of the array factor effect. The measured results are in good agreement with the simulated results.

PSO-Based Fast Optimization Algorithm for Broadband Ayyray Antenna by Using the Cubic Spline Interpolation

This paper describes a fast pattern synthesis method for a broadband array antenna using the particle swarm optimization (PSO) and cubic spline interpolation (CSI). Being an indispensable part of a high speed space-division communication system, the array antenna operates in a wide frequency band (200–400 MHz) and has stable patterns with 60-degree half power beam width (HPBW) in the whole frequency band. Firstly, by establishing a versatile objective function, the complex excitations of the circular array at the selected seven frequency points are determined via the PSO algorithm. Then, the complex excitations of the circular array at arbitrary frequency points in the whole working frequency band are calculated effectively using the CSI method. A uniform circular array with six broadband dipole elements is examined. The broadband patterns with 60-degree HPBW and the accuracy of the interpolation method are demonstrated.

Dual-Band Yagi-Uda Antenna for Wireless Communications

A dual-band (915–935MHz and 1760–1805MHz) Yagi-Uda antenna with branch structures is proposed. The parameters of the branch structure are optimized to obtain the antenna that operates perfectly in the two bands. Prototype is fabricated and measured, and the results are in good agreement with the simulated ones. The presented antenna achieves directional radiation in the two operating bands, and gets the performances that VSWR<2, gain 5–6.6 dBi and front-to-back ratio 6–9.1dB, making it suitable for the non-fixed base station backhaul in wireless communications.