Radiation characteristics of a spherical array of circularly polarized elements

The radiation properties of a spherical phased-array antenna with circularly polarized elements are studied. Each antenna element is assumed to have a cosine type of field pattern. It is found that such an array is capable of providing complete hemispherical coverage without appreciable loss of gain. The radiation produced by the array stays circularly polarized in all directions, and the state of polarization is independent of beam steering. A special distribution of elements on a spherical surface is developed. This considerably suppresses the grating lobes in the pattern and thereby makes the antenna array broadband. Numerical calculations are made to determine the directivity and half-power beamwidth for the radiation patterns produced under various situations.     

Hemispherical coverage using a double-folded monopole

A traveling-wave current distribution can be produced on a monopole over a ground plane by inserting a resistance of suitable magnitude one-quarter wave length from its end. It has been shown that the resistor can be replaced with a modified folded dipole which has a radiation resistance approximately equal to that of the resistor. Furthermore, it was found that when the folded element was about 0.1λ above the ground plane, near hemispherical coverage was obtained in the plane of the element. In this paper, the resistor is replaced with orthogonal folded elements. The main objective is to obtain an antenna which is circularly polarized and which has near hemispherical coverage. The input impedance, current distribution, and radiation patterns of this antenna were computed using the numerical electromagnetics code (NEC); the radiation patterns and input impedance were also measured. To produce a circularly polarized wave it is necessary to tilt the folded elements. After experimenting with a number of different configurations an antenna design having directional and polarization properties approaching those that were desired was obtained. All computations and measurements were conducted near 1.6 GHz, a frequency close to that of the proposed IRIDIUM communications system and the L1 band of the Global Positioning System (GPS). The double-folded monopole may prove to be a very low cost option as a ground antenna for these systems     

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     

Realizable feed-element patterns and optimum aperture efficiency inmultibeam antenna systems

The results of an earlier paper by Y. Rahmat-Samii et al. (ibid., vol.AP-29, pp.961-3, 1981), regarding realizable patterns from feed elements that are part of an array that feeds a reflector antenna, are extended. The earlier paper used a cos^q &thetas; model for the element radiation pattern, whereas here a parametric study is performed, using a model that assumes a central beam of cos^q &thetas; shape, with a constant sidelobe level outside the central beam. Realizable q-values are constrained by the maximum directivity based on feed element area. The optimum aperture efficiency (excluding array feed network losses) in an array-reflector system is evaluated as a function of element spacing using this model as well as the model of the earlier paper. Experimental data for tapered slot antenna arrays are in agreement with the conclusions based on the model     

倾斜波束圆极化天线的CSRR-FS结构设计研究

为了拓展倾斜波束圆极化天线(Circularly Polarized Antenna with Tilted Beam,CPA-TB)的带宽,在分析了该天线结构及其特征的基础上,提出了一种花纹式螺旋臂(Flower-Spiral,FS)协同互补开口谐振环(complementary split ring resontor,CSRR)的CSRR-FS结构.该结构通过FS增加了天线表面电流路径,实现了天线驻波比(voltage standing wave ratio,VSWR)的拓展;利用CSRR改变了低频点反射板的电流分布,实现反射板小型化的同时,减小了天线的交叉极化分量,增强了天线的辐射性能,拓展了天线的轴比带宽.仿真和实测结果表明:与普通的平面反射板相比,在保证圆极化、波束倾角30°的条件下,基于CSRR-FS结构的CPA-TB相对带宽为24%(5.5-7GHz),天线工作带宽拓展了1.8倍.CSRR-FS结构的提出为CPA-TB带宽的拓展提供了新的途径.     

双频圆极化天线设计方法综述

根据圆极化和双频天线的设计原理,总结了双频圆极化天线的设计方法,通过不同馈电方式和谐振方式分为四类进行阐述。归纳了近几年拓展双频圆极化天线带宽的方法,从结构上分别按照微带缝隙天线、平面单极子天线和阵列天线进行介绍。列表分析了各种设计方法的实现难度和典型天线各项性能参数,最后简述了适用于双频圆极化天线小型化的优化方案,并对未来发展趋势进行了展望。     

24 GHz active retrodirective antenna array

A 24 GHz active Van Atta planar antenna array proposed for increasing the vehicle radar echo in a vehicle collision avoidance system is designed and demonstrated. The antenna array contains two parallel linear sub-arrays. Each sub-array is composed of four receiving microstrip antennas, four transmitting microstrip antennas and four transistor amplifiers. At the angles of -40°<&thetas;<40°, except those very close to the specular direction (&thetas;=0°), the measured backscattering field levels of the fabricated array have variations <3 dB and are at least 10 dB higher than those of a metal plate of the same size     

High-power VCSEL arrays for emission in the watt regime at roomtemperature

Selectively oxidized InGaAs vertical-cavity surface emitting lasers (VCSELs) at an emission wavelength of λ=980 mm are investigated for high-power applications. Densely packed arrays consisting of 19 single devices with an active diameter of 50 μm emit 1.08 W of continuous-wave (CW) optical output power at room temperature. At 10°C, heat sink temperature the output power increases to 1.4 W, which corresponds to a chip size averaged power density of 1 kW·cm². Low divergence angle of less than 16° full-width at half-maximum (FWHM) and the circularly symmetric far-field pattern allow for simple focusing of the beam with power densities above 10 kW·cm²     

Design and characterization of single- and multiple-beam mm-wavecircularly polarized substrate lens antennas for wireless communications

Single- and multiple-beam circularly polarized ellipsoidal substrate lenses suitable for millimeter-wave wireless communications have been designed, implemented, and experimentally characterized at 30 GHz. The lenses are made out of low-cost low-permittivity Rexolite material. The single-beam lens achieves a directivity of 25.9 dB, a front-to-back ratio of 30 dB, and an axial ratio of 0.5 dB is maintained within the main lobe. The measured impedance bandwidth is 12.5% within a SWR⩽1.8:1. The single-beam antenna is well suited for broad-band wireless point-to-point links. On the other hand, the multiple-beam lens launches 31 beams with a minimum 3-dB overlapping level among adjacent beams. The coverage of the lens antenna system has been optimized through the utilization of a hexagonal patch arrangement leading to a scan coverage of 45.4° with a maximum loss in directivity of 1.8 dB due to multiple reflections. The multiple-beam lens antenna is suitable for indoor point-to-multipoint wireless communications such as a broad-band local area network or as a switched beam smart antenna. During the proposed design process, some fundamental issues pertaining to substrate lens antennas are discussed and clarified. This includes the depolarization properties of the lenses, the effect of multiple internal reflections on the far-field patterns and the directivity, the nature of the far-field patterns, the estimation of the lens system F/B ratio, and the off-axis characteristics of ellipsoidal lenses     

一种新颖的宽带圆极化单极天线

该文设计了一种新颖的宽带圆极化单极子天线,该天线采用微带馈电模式。天线由C型贴片和改进的地板组成,整个天线尺寸仅为25×25×1 mm3。通过在C型贴片上切角和在地板上增加三角形微扰结构,可以有效增加天线的阻抗带宽和轴比带宽。该文给出了天线的设计流程,从表面电流分布分析了圆极化天线的工作机理。加工了天线实物,并对其进行了测量。仿真和实测结果表明天线具有超宽的阻抗带宽和轴比带宽。天线的工作频带为4.35～12 GHz(相对带宽为93.6%),3 dB轴比带宽为4.15～11.8 GHz(相对带宽为95.9%)。测量了天线的辐射性能和增益特性,实测结果与仿真结果吻合较好,证明了该天线的有效性。该天线可以应用于超宽带无线通信系统和卫星通信系统中。     

A compact circularly polarized subdivided microstrip patch antenna

A compact circularly polarized subdivided microstrip patch antenna is proposed. The antenna is composed of the interconnection of four corner patches alternating with four strips and a fifth central patch. It presents the very small size of 0.28λ_g by 0.28λ_g at resonance (5.85 GHz), which represents a surface reduction of 60% compared with a conventional microstrip square patch antenna. The proposed antenna exhibits a gain of 4.3 dBi to 5 dBi and an axial ratio lower than 1.8 dB in the range of its bandwidth, which is of 30 MHz     

Narrow and wide band monopole antenna design using heterogeneous bidirectional recurrent neural network for LTE and UWB applications

The proposed antenna is a small wideband monopole with wideband circular polarization using heterogeneous bidirectional recurrent neural network for both narrow and wide band applications (NWB-MAD-HBRNN). The electromagnetic structure is designed, fabricated, and simulated with 1 mm thickness on FR4 substrate material along dielectric constant 4.3. The proposed antenna includes 4.3–8.85 GHz for ultrawideband applications; it contains reconfigurable narrow band for L-band 1.27 GHz, LTE, and ultrawideband applications. To enhance the antenna impedance bandwidth (BW) along axial ratio bandwidth (ARBW), a slit is etched at the antenna patch, a rectangular stub is inserted into the ground plane, and semicircular stub is added to the top of antenna feed line. The better agreement is observed in the measured and simulated gain performance of 4.8 dB for LTE band applications. The proposed NWB-MAD-HBRNN design provides 13.50%, 18.91%, and 22.58% higher bandwidth and 18.36%, 20.38%, and 27.58% lower return loss than the existing designs, such as bio-inspired wideband antenna for wireless applications based on perturbation technique (BWA-WA-PA), a compact circularly polarized modified printed monopole antenna for wireless applications (CCP-MPMA-WA), and new multiband monopole antenna for certain broadband wireless applications along wireless personal communications (PA-MMA-BWA), respectively.     

一种新型布局的圆极化微带天线阵优化设计

提出了一款高增益低副瓣新型圆极化微带天线阵。单元天线采用叠层切角圆极化微带结构,通过八边形边界布局和顺序旋转交叠组阵技术,实现了天线阵方向性图的对称性和圆极化辐射性能的最优化;馈电网络采用威尔金森功分器和最大平坦式阻抗变换器实现不等功分宽带阻抗匹配,通过改进馈电方向寻求对称结构,简化了馈电网络的设计。制作了天线阵实物并进行了测量。测试结果表明:天线在3.2~4.6 GHz频段内S₁₁<-10 dB,阻抗相对带宽36%;在3.8~4.5 GHz频段内顶点轴比小于3 dB,圆极化相对带宽17%;在4~4.4 GHz频段内天线增益均在15 dB以上,最高增益达17 dB。     

A switchable multi-sector antenna for indoor wireless LAN systemsin the 60-GHz band

A switchable multi-sector antenna for indoor wireless local-area network (LAN) systems in the 60-GHz band has been proposed. The antenna has a pyramidal configuration. Each isosceles-triangular surface of the pyramid has been inclined 30° from the vertical axis in order to cover an appropriate elevation angle range. This antenna excites a right-handed circularly polarized wave to suppress unwanted multipath delayed waves. The low-loss curved microstrip-line feeding has been introduced at the junction between antenna feed lines and monolithic microwave integrated circuit (MMIC) amplifiers at the bottoms of the pyramid. Using this antenna, a terminal receiver for indoor wireless LAN systems in the 60-GHz band has been developed     

Electronically steerable Yagi-Uda microstrip patch antenna array

This paper describes a dual-frequency circularly polarized electronically steerable microstrip patch antenna array suitable for land-mobile communications. Based on a four-element Yagi-Uda (1928) patch antenna, the four antennas forming the array are located radially from a single square reflector patch on a double-sided printed circuit board. The main lobe of the array covers the elevation angles from 20 to 70° with a peak gain of 8.4 dBi at 1.54 GHz and 11.7 dBi at 1.62 GHz. Full azimuthal coverage is possible by electronically switching between the four elements     

Helical antenna for satellite transmission†

The use of helical antennas for satellite transmission is proposed. The polar diagram, directivity and polarization characteristics are outlined. The advantages of circularly and elliptically polarized waves transmitted from the helical antenna for Faraday rotation experiments are discussed. The use of helical array is comparatively more compact, radiation characteristics are frequency independent and the polarization of the radiated wave is more stable. These features enable an accurate measurement of the Faraday rotation which is likely to yield a better estimate of total electron content.     

Time Division Circular Polarization: A Simple Technique for Increasing Propagation Experiment Productivity

A simple technique, time division circular polarization (TDCP), is described which permits the simultaneous measurement of attenuation and depolarization for two orthogonal linearly polarized waves and two orthogonal circularly polarized waves in a slowly varying linear propagation medium using only a single frequency beacon switched between two linearly polarized antenna ports.     

Realization of dual-frequency and wide-band VSWR performances usingnormal-model helical and inverted-F antennas

The effects of parasitic elements on the voltage standing wave ratios (VSWR's) of two antennas are investigated. First, a parasitic monopole is used for a normal-mode helical antenna. The VSWR investigation shows that dual-frequency operation is obtained by the parasitic element effects. The dual-frequency operation is revealed as a function of monopole position above a ground plane (monopole height). As the monopole height decreases, the separation of a higher resonance frequency f_H from a lower resonance frequency f_L increases. For a monopole length of L_MP≈0.4λ_HX , where λ_HX is the resonance wavelength of the helix, the frequency bandwidth for a VSWR=2 criterion is 12.5% in the lower frequency f_L region and 5.2% in the higher frequency f _H region, with a frequency separation ratio of f_H/f_L=2.14. Secondly, L-figured parasitic elements are used for an inverted-F antenna (IFA). The parasitic elements improve the VSWR performance. The frequency bandwidth for a VSWR=2 criterion is approximately two times as wide as that of the single IFA. It is also found that bending the horizontal sections of the IFA and parasitic elements contributes to reducing the antenna size while not significantly deteriorating the VSWR bandwidth. The radiation patterns are also presented and discussed     

Electrically steerable passive array radiator (ESPAR) antennas

A novel ground-plane shape to improve the horizontal gain for electrically steerable passive array radiator (ESPAR) antennas is investigated. The peak directivity of a monopole antenna with a finite ground plane, such as a circular or rectangular ground plane is at a higher angle from the horizon. Thus, the horizontal gain is lower than that of a dipole antenna. Using a circular ground plane of a half-wavelength radius with a skirt of a quarter wavelength wound around it, the angle of the peak directivity and the horizontal gain for the ground-based communication system were improved. For an ESPAR antenna - one of the monopole arrays - the horizontal gain was also improved. It was confirmed that it was possible to form the main-beam radiation and a beam in the horizontal plane, each in an arbitrary direction, by changing the control voltage to the passive element. This was shown by an experiment with an ESPAR antenna with a finite reflector, a feed element, and seven passive elements.