A monofilar spiral antenna and its array above a groundplane-formation of a circularly polarized tilted fan beam

A monofilar spiral antenna is analyzed in the presence of a conducting plane reflector, using the method of moments. The circumference of the spiral antenna is chosen to be 2.3 wavelengths. A tilted beam of circular polarization is realized by superposing the fields from two active regions. The gain of the tilted beam is approximately 8 dB. The frequency bandwidths for 1-dB gain drop and 3-dB axial ratio criterions are 12% and 23%, respectively. An array consisting of the four monofilar spiral antennas is also analyzed, where the array element spacing is chosen to be 0.8 wavelength at a design frequency f₀. The input impedances of the four spirals are almost the same as the impedance of the single monofilar spiral antenna at f₀. The array radiates a tilted fan beam with a gain increase of approximately 6 dB from the gain of the single spiral antenna at f₀. The frequency bandwidth for a 3-dB axial ratio criterion is almost the same as that of the single spiral antenna     

Accordion shape monofilar axial mode helix for RFID reader

An accordion shape monofilar axial mode helical antenna designed by curving the helix along the axis is proposed. This antenna achieves a low-profile characteristic as the 10-turn helix's axial length is 0.354/spl lambda/. The impedance bandwidth (SWR<1.5) is 9% from the frequency of 880 to 963 MHz and the axial ratio bandwidth (AR<3 dB) is 6.5%. The measured gain is 10.2 dBi. This antenna operated at the centre frequency of 915 MHz and has a tilted radiation of 17/spl deg/ to the curving side.     

用于无线局域网的轴向模螺旋天线设计

根据无线局域网通信天线的要求,设计了三种工作在5GHz频段性能良好的轴向模螺旋天线,其中一种为普通螺旋天线,第二种为加绕寄生螺旋天线,第三种为锥形加绕寄生螺旋天线。通过电磁仿真软件HFSS计算及对结果分析表明,加绕寄生螺旋将改善天线的轴向辐射特性,而锥形结构将扩展天线带宽。     

带异形反射腔和寄生螺旋的均匀升角轴向模螺旋天线

为了改善轴向模螺旋天线的辐射特性,在带有寄生螺旋的均匀升角轴向模螺旋天线基础上,设计了一种带有曲反射面背腔的螺旋天线,并用HFSS软件对天线的辐射特性进行了仿真分析。通过对比几种不同形式的螺旋天线的仿真结果,证明了该种螺旋天线可以有效地提高轴向模螺旋天线增益系数,圆极化一致性良好,是一种提高轴向模螺旋天线性能的有效方法。     

一种应用于卫星通信地面站的新型单臂螺旋天线及其阵列的研究

研究了一种应用于卫星通信地面站的新型单臂平面螺旋天线,该天线采用圆柱螺旋激励同轴线馈电,可以形成倾斜的波束,通过改变圆柱螺旋的参数可以调整其输入阻抗以达到阻抗匹配的目的.用矩量法求解了天线的电流分布和三维辐射方向图以及增益轴比等参数,计算结果与参考文献很吻合.为了增强天线的方向性系数和增益,以四元天线阵为例,研究了这种天线组成的天线阵的辐射特性,给出了天线阵的三维辐射方向图.计算结果表明,该天线组成的天线阵同样具有倾斜的波束指向,各天线单元的输入阻抗为接近50 Ω的纯电阻,增益比单个天线单元提高6.3 dB.     

应用于智能交通系统的小型化圆极化微带天线

提出了一种应用于智能交通系统的小型化圆极化微带天线。该天线由一个开缝的方形贴片及围绕方形贴片的两级寄生贴片组成,通过模式解调实现圆极化,并利用寄生贴片增加带宽和提高天线增益。测试结果表明,天线的-10 dB 阻抗带宽为10. 9%,3 dB 轴比带宽为2. 7%,在中心频率5. 8 GHz 处的增益为5. 4 dBi,交叉极化不低于21 dB。天线尺寸为25 mm×25 mm×1. 6 mm,与其它应用于智能交通系统的天线相比,该天线具有更小的平面尺寸。     

Broadband quasi-taper helical antennas

A unique approach is described for widening the bandwidth of a helical antenna with improved gain, pattern, and axial ratio characteristics. The antenna may be described as a nonuniform or quasi-taper helix, which consists of a combination of uniform and tapered helix sections. Measured patterns, gain, axial ratio, and VSWR for various helical antenna configurations are presented and compared. It is shown that a nonuniform quasi-taper helix can provide an operating bandwidth twice that of a conventional uniform-diameter helix.     

A printed hemispherical helical antenna for GPS receivers

A self-matched printed hemispherical helical antenna for potential use in global positioning system receivers is introduced. Unlike wired hemispherical helical antennas, its printed form renders it a much more stable and endurable structure and also easier for fabrication. The optimized antenna shows an impedance bandwidth of 6%, a 3-dB axial ratio bandwidth of 6%-7%, a return loss greater than 20 dB, and a gain of about 9 dB at the center frequency. The patterns of the antenna show a larger mainlobe in the upper half space with relatively small backlobes. Both theoretical and experimental results was presented.     

Human proximity effects on circular polarized handset antennas inpersonal satellite communications

Satellite-based systems are the next step in mobile communications. Several low and medium Earth orbit mobile communication satellite systems have been proposed and are currently being deployed. For all these systems, high-performance circularly polarized antennas for the mobile terminals are of importance. Although considerable material is available on circularly polarized antennas, there is an absence of information on how the human's close proximity to the antenna affects the circular polarization purity of the radiated field. This paper presents an analysis of representative circularly polarized helical handset antennas. The helix is used because of its wide bandwidth properties and capability to provide both circular and linear polarization. Thus, this element could be used for handsets that are planned to work with both the terrestrial-based communications systems of today and the satellite-based communication systems of tomorrow. The intent is to characterize the effects the close proximity of a human head model has on the computed performance of the circular polarized antenna. The method of moments (MoM) and finite-difference time-domain (FDTD) numerical techniques are used to study various helix structures on top of a small box representing a handset. In order to be able to effectively apply the FDTD, a novel square helix structure is introduced. Results computed with these two techniques are compared to illustrate the accuracy of each implementation. The results indicate significant polarization purity degradation caused by the presence of a human head. For the particular geometry simulated, the presence of a head model degraded the average axial ratio within a 50° vertical cone from 2.9 to 9.1 dB. This significant increase in axial ratio can have profound effects on link budgets     

Coaxial-feed axial mode hemispherical helical antenna

A coaxial-feed axial mode hemispherical helical antenna is studied experimentally and theoretically. Results for a 3-turn hemispherical helix indicate that circular polarisation can be obtained over a broad beamwidth. The gain bandwidth is ~33% and the peak gain is 7.6 dB. The input impedance shows that it is a standing wave antenna     

基于矩量法的螺旋天线设计

螺旋天线具有宽波束、圆极化等特性。以往的轴向螺旋天线多为端射式,辐射方向单一。为弥补这一不足,提出了一种新型的中馈轴向螺旋天线。基于RWG(Rao-Wihon-Glisson)边元的矩量法,采用MATLAB仿真计算出中馈螺旋天线的方向图、反射系数、增益等重要参数。又利用高频结构仿真软件(HFSS)对所设计的中馈螺旋天线进行了仿真。通过两种方法仿真得到的结果吻合较好,仿真结果的正确性得到了验证。实验结果表明:中馈轴向螺旋天线不仅具有以往轴向螺旋天线所具备的定向性好和高增益等优点,还具有两个反向且强度相同的辐射方向,同时天线增益可以达到8dB以上,半功率波束宽度可达33°。这种天线可以应用到多边通信及中继通信等领域。     

宽带高增益圆极化微带天线与阵列

设计了一副宽带高增益圆极化微带天线,并进行组阵分析。天线中心频率2.6 GHz,通过增加寄生贴片和空气层来提高天线单元的增益和带宽。上下两层介质板上边长不同的切角方形贴片分别激励一个低频与高频的圆极化模,有效地拓宽了轴比带宽。仿真结果表明,反射系数|S11|<-10 dB带宽21.8%,3 dB轴比带宽12.0%,中心频率点增益9.0 dBi。对天线单元进行加工测试,与仿真结果较为吻合。设计了2×4元阵列,并进行了仿真,增益提升至17.5 dBi,3 dB轴比带宽10.4%。     

Circularly polarised rhombic hula hoop antennas

Radiation elements, designated as rhombic hula hoop antennas, are proposed for circularly polarised antennas. The current distribution, radiation pattern and axial ratio are analysed. By selecting the loop configuration, an axial ratio bandwidth (⩽2 dB) of ~10% and gain of ~10 dBi are obtained     

Radiation characteristics of helix antenna with parasitic elements

An antenna system consisting of a driven balanced helix and two parasitic helices is compared with a continuously wound balanced helix with the same total turns. The similarity in the radiation pattern, axial ratio and directive gain are found by theoretical investigation.     

Investigation of a short conical helix antenna

The input impedance, radiation pattern, axial ratio, and power gain of a conical helix antenna with a short arm are calculated as a function of frequency, using theoretically determined current distributions. It is shown that the antenna radiates a circularly polarized wave over a frequency range ratio of about 1:1.2, having a power gain of about 7.7 dB. The experimental results are also presented.     

谐振式四臂螺旋天线的矩量法分析

本文对Nakano简化的曲线天线积分方程核做了更便于数值计算的处理;运用矩量法分析,计算了谐振式四臂螺旋天线的圆极化方向图、增益、轴比、前后比及赋形特性等,并研究了馈电方法和导电板对天线性能的影响。     

Investigation of circularly polarized loop antennas with a parasitic element for bandwidth enhancement

It is demonstrated that the bandwidth of circular polarization (CP) can be significantly increased when one more parasitic loop is added inside the original loop. A single-loop antenna has only one minimum axial ratio (AR) point while the two-loop antenna can create two minimum AR points. An appropriate combination of the two minimum AR points results in a significant enhancement for the CP bandwidth. A comprehensive study of the new type of broad-band circularly polarized antennas is presented. Several loop configurations, including a circular loop, a rhombic loop, and a dual rhombic loop with a series feed and a parallel feed, are investigated. The AR (/spl les/2 dB) bandwidth of the circular-loop antenna with a parasitic circular loop is found to be 20%, more than three times the AR bandwidth of a single loop. For the rhombic-loop antenna with a parasitic rhombic loop, an AR bandwidth (AR/spl les/2dB) of more than 40% can be achieved by changing the rhombus vertex angle. The AR (/spl les/2 dB) bandwidths of the series-fed and parallel-fed dual rhombic-loop antennas with a parasitic element are 30% and 50%, respectively. A broad-band balun is incorporated into the series-fed dual rhombic-loop antenna for impedance matching. The broad-band CP performance of the loop antennas is verified by experimental results.     

Quadrifilar loop antenna

A new quadrifilar antenna has been developed for generating circularly polarized backfire radiation. The antenna consists of two orthogonal rectangular conducting loops, each incorporating capacitive coupling and fed using either a single or two coaxial cables. Though the geometry is much simpler than a conventional quadrifilar helix antenna, the radiation pattern performance is very similar. Measured and simulated patterns are compared for two antennas with different feed arrangements. It is shown that the resonant structure can produce a cardioid pattern with a directivity of 4.5 dB (120/spl deg/ 3 dB beamwidth) and a front-to-back ratio of more than 20 dB at the center operating frequency. A 10% impedance bandwidth (VSWR<2) over which the axial ratio is less than 3 dB is demonstrated.     

Analysis and measurements for improved crank-line antennas

This paper describes the radiation characteristics of crank-line antennas radiating a circularly polarized wave. First, the radiation efficiency versus substrate permittivity is evaluated. Second, a 12-cell crank-line antenna of substrate permittivity ε_r=1 and antenna height B=λ_11.85 is investigated as a reference antenna, where λ_11.85 is the wavelength at a frequency of 11.85 GHz. It is found that the main beam direction of the reference antenna varies 7° over a frequency range of approximately 6%, with an axial ratio of less than 3 dB and a gain of approximately 21 dB. Third, attention is paid to the gain behavior versus the antenna height. A way to increase the gain by modifying the antenna height is proposed. An increase of 1.5 dB from the gain of the reference antenna is demonstrated. Finally, the axial ratio, gain, and decoupling factor for crank-line antenna arrays are presented and discussed     

一种新式背射天线

本文提出一种新式背射天线，它把单线背射螺旋作为短背射天线的馈源。这种天线具有结构简单，馈电方便，频带宽，增益中等，易于产生圆极化波等特点，较相同直径接地板的螺旋天线有更优的性能。