Systematic uncertainties of the complex antenna factor of a dipole antenna as determined by two methods

The complex antenna factor (CAF) of a dipole antenna with a balun can be determined from the effective length and the input impedance of the antenna element and the S-parameters of the balun. The effective length and the input impedance are calculated by a numerical method such as the method of moments. The S-parameters are measured using a network analyzer with its thru-, reflect-, and line-conditions (TRL) calibration. Alternatively, the CAF can be determined by a modified three-antenna method on a ground plane. In the present paper, the systematic uncertainties of the two methods are estimated in the frequency range of 30-1000 MHz in order to clarify the potential for application of the two methods and to determine areas for improvement. The CAF values determined by these two methods are compared, and the results of this comparison indicate the validity of the uncertainty estimations. In the measured balun method, the TRL measurement should be improved in the low-frequency range (30-100 MHz), and in the three-antenna method, the antenna positioning should be improved.     

Measurements of complex antenna factor by the near-field 3-antennamethod

The near-field 3-antenna method for measuring the complex antenna factor (CAF) is proposed in order to reduce the effect of the measurement site and background noise. The transmission coefficients in the far-field region are calculated from those measured in the near-field and theoretically obtained near-field correction factors (NCF). The CAF of monopole antennas are measured using the proposed method in a frequency range up to 6 GHz. From the measurement results, the dependency of CAF values on the antenna distance is small. These results indicate that our theory including the NCF is applicable for the measurements of the CAF of simple-structure antennas     

Measurement of electromagnetic fields near a monopole antennaexcited by a pulse

To observe transient radiation fields, a technique for reconstructing electromagnetic (EM) waveforms using the complex antenna factor (CAF) have been developed. However, the CAF is originally defined assuming plane wave incidence, while the waveforms are measured in a vicinity of the radiating source. In order to examine the reconstruction technique using the CAF in the near-field measurements, the EM fields radiated from a monopole antenna excited by pulsed input voltage was reconstructed and compared with calculated results. For the geometry of the experiment, the waveforms of the reconstructed and calculated EM fields have shown good agreement. Therefore, the reconstruction technique using the CAF can be used for similar dimensions or at a greater distance when sufficient sensitivity is provided     

Evaluation of antenna diversity performance for mobile handsetsusing 3-D measurement data

An evaluation of two-branch antenna diversity on mobile telephones is performed in the presence of head and hand phantoms to model the influence of the user. Two mobile telephone prototypes for the 1800-MHz band are considered. The evaluation is done by measuring the three-dimensional (3-D) complex radiation patterns from each antenna with the prototypes positioned near the phantom head and hand (i.e., in talk position) and calculating the diversity performance for three different scenarios of the incoming field. The two-branch antenna setups on both prototypes produce a calculated diversity gain of about 9 dB for selection diversity at the 99% reliability level     

基于FDTD的微带缝隙漏波天线分析

应用时域有限差分法(FDTD)对微带缝隙漏波天线进行分析,直观地得到了微带缝隙漏波天线内部的电场分布。提出了一条有效的经验公式,成功地计算了微带缝隙漏波天线的漏波传播系数,与实验数据吻合较好。比较了不同缝隙宽度和微带宽度对微带缝隙漏波天线性能的影响。证明了在微带漏波天线上开缝可以有效地减少天线尺寸及降低天线的工作频率。     

Performance of the wire-grid lens HF antenna

The wire-grid lens HF antenna is a high-frequency realization of a two-dimensional Luneburg lens. This vertically polarized high-directivity 36-beam circular antenna can operate over a 10/1 frequency band. When receiving a signal on a single beam, it exhibits a low binary-error rate equivalent to that of a nest of three high-gain rhombics required to cover the same frequency band. Improved reception is obtained by receiving a signal on a pair of adjacent beams operating in the angle-diversity mode. As a direction-finding antenna, its accuracy is limited primarily by irregularities in ionospheric propagation. Its theoretical performance, which has been calculated with precision on a high-speed digital computer, is compared with its measured performance.     

Estimation of complex permittivity using loop antenna

A method for estimating the complex permittivity of materials in the vicinity of a loop antenna is proposed. The method is based on comparing measured and numerically calculated input admittances for the loop antenna.     

Polarization diversity measurements and analysis for antenna configurations at 1800 MHz

In wireless communication systems, multipath interference has a significant impact on system design and performance. Fast fading variations are caused by the coherent summation of multiple echoes from many reflection points reaching the receive antenna. Antenna diversity is one technique that can be used to overcome multipath fading. A test system used to measure the diversity performance of an antenna pair was used to experimentally determine the complex correlation coefficient between the two antenna branches. A local mean estimation algorithm based on the channel mean square error equalization was implemented. Thus, the two parameters that determine the expected diversity gain, i.e., the complex correlation coefficient and the mean level signal difference, were estimated. The test system was used to evaluate the polarization diversity performance of different antenna pairs in Rayleigh and Rician environments, both in the absence and in the presence of a human head phantom.     

Indirect coupling method for RFID tag antenna design

Proposed is an indirect coupling method for designing an RFID tag antenna, which can not only achieve broadband operation, but can also conveniently implement a complex conjugate impedance match between an antenna and an RFID chip. An equivalent circuit model of the proposed coupling method is presented to characterise the performance of the antenna. An example is included to demonstrate the coupling method for an antenna with half-power bandwidth of approximately 16% (840-985 MHz), and which covers the entire UHF RFID frequency band. Estimated and simulated results are shown to be in good agreement with measured ones.     

Comparison of different antenna arrays for the BER reduction in indoor wireless communication

In this paper, we use the ultra wideband antenna array combined with particle swarm optimization (PSO) to minimize the BER for indoor communication systems. Three types of antenna arrays, namely the circular shape, L shape, and Y shape arrays, are used in the transmitter and their corresponding BER on several paths in the indoor environment are calculated. On the basis of the topography of the antenna array and the BER formula, the array pattern synthesis problem can be reformulated into an optimization problem and solved by the PSO. The novelties of our approach is not only choosing BER as the object function instead of the sidelobe level of the antenna pattern, but also considering the antenna feed length effect of each array element. The particle swarm optimization algorithm is employed to optimize the excitation voltages and feed lengths for these antenna arrays to reduce the BER. The strong point of the PSO is that it can find the solution even if the performance index cannot be formulated by simple equations. By the obtained antenna patterns, we can know the route with the lowest BER; meanwhile, transmission power using this route can be reduced. Numerical results show that the synthesized antenna array pattern is effective in focusing maximum gain to the line‐of‐sight path for these antenna arrays. The synthesized array pattern also can mitigate severe multipath fading in complex propagation environments. As a result, the BER can be reduced substantially in indoor ultra wideband communication systems. The investigated results can help communication engineers improve their planning and design of indoor wireless communication.Copyright © 2011 John Wiley & Sons, Ltd.     

An offset bifocal reflector antenna design for wide-angle beam scanning

A synthesis procedure and performance results for an offset dual reflector with perfect focusing atpm 8degof beam scan are presented. This bifocal antenna extends the theory of the previously reported symmetric system to an offset design. Approximations, such as the smearing of focal points into a "focal ring," are eliminated, as is blockage. The offset design affords greater design flexibility, although the synthesis is more complex. Computed and experimental results demonstrate the improved beam-scanning performance of this antenna.     

Axial-radiation plasma antenna

The possibility of applying a cylindrical isotropic collisionless plasma column with a thin dielectric shell as an antenna of strictly axial radiation is investigated. It is assumed that the phase velocity of radiated waves approaches the velocity of light and the radiated wavelength substantially exceeds the radius of the antenna. Radiation patterns of azimuthally symmetric and azimuthally nonsymmetric current waves are calculated. It is shown that, in contrast to the symmetric wave used in traditional traveling-wave antennas, the first harmonic of a nonsymmetric current wave in plasma is a source of radiation reaching its maximum at the zero angle to the antenna’s axis.     

On the empirical optimization of antenna arrays

Empirical optimization is an algorithm for the optimization of antenna array performance under realistic conditions, accounting for the effects of mutual coupling and scattering between the elements of the array and the nearby environment. The algorithm can synthesize optimum element spacings and optimum element excitations. It is applicable to arrays of various element types having arbitrary configurations, including phased arrays, conformal arrays and nonuniformly spaced arrays. The method is based on measured or calculated element-pattern data, and proceeds in an iterative fashion to the optimum design. A novel method is presented in which the admittance matrix representing an antenna array, consisting of both active and passive elements, is extracted from the array's element-pattern data. The admittance-matrix formulation incorporated into the empirical optimization algorithm enables optimization of the location of both passive and active elements. The methods also provide data for a linear approximation of coupling as a function of (nonuniform) element locations, and for calculation of element scan impedances. Computational and experimental results are presented that demonstrate the rapid convergence and effectiveness of empirical optimization in achieving realistic antenna array performance optimization.     

一款用于翻盖手机中的四单元天线系统

提出了一款用于翻盖手机中的四单元天线。该天线的阻抗带宽可以覆盖无线通信中的两个常用频段。在整个工作频段内的天线单元之间的互耦均小于-10分贝。参数分析给出了关键的结构参数对天线性能的影响。计算得到的相关系数和平均有效增益显示该天线系统能够提供很好的分集性能。     

Ku波段新型双辐射体天线的电气特性分析

为满足水下航行器在复杂海况中接收来自海面高速数据对天线的需求,文中提出了一种Ku波段双辐射体天线的设计方案. 首先在半波振子天线的正交方向添加寄生辐射体,在限定天线线径比的情况下利用寄生辐射体改善天线在复杂海况中的全向性,通过计算天线的寄生辐射体之间的间距衔接天线不同辐射体之间的电流分布;然后对天线振子上的电流分布进行近似推导,得到新型双辐射体天线的具体结构参数;最后通过电磁仿真计算,得出天线的电气特性,并进行实物测量和对比. 仿真和测量结果表明,新型双辐射体天线在复杂海况造成的全部运动姿态中,水下反射系数小于0.45,水下增益高于?40 dBi,在所处水平面之上呈现全向性,实测结果与仿真结果具有较好的一致性. 该天线具有线径比大、全向、水下增益较高的特点,性能受不同运动姿态的影响较小,为水下航行器的高频拖曳天线提供了一种新颖的天线结构.     

共面波导馈电超宽带天线研究

设计了一种刻蚀在单层覆铜介质基板上的共面波导馈电超宽带天线。所用介质基板由相对介电常数为2.65的聚四氟乙烯制成,尺寸为35.0 mm×35.0 mm×1.6 mm。利用仿真软件HFSS对该天线的参数进行了仿真和优化,并根据优化参数进行了实物天线的制作和性能测试。结果表明,通过在共面波导地面上刻蚀非对称结构的多边形槽,可使天线的频带宽度达到2.2~8.0 GHz(S11<–10 dB),相对带宽达到114%。该天线具有良好的方向图和增益性能,满足超宽带天线的性能要求。     

PBG结构在微带有源天线中的应用

微带有源天线的应用具有降低通信系统的复杂度、减小系统尺寸的优点,但由于天线与有源器件集成在一起,有源器件产生的谐波可以引起天线的伪辐射。该文研究了PBG(Photonic Band-Gap)结构在有源天线中的应用。计算和实验结果都表明PBG结构的应用可以大大降低谐波引起的辐射,从而改善了系统的性能。     

Mirror antenna dual-band lightweight mirror design

The mirror antenna, sometimes called an inverse Cassegrain antenna, is used in modern radar systems where efficient wide angle scan is required in combination with light weight and small size. Although previous applications have been single band, an additional advantage of the mirror antenna is that it is practical to implement dual-band configurations which can greatly enhance the capability of radar or other radiating systems. The most difficult part of a dual-band mirror antenna design is the90degpolarization rotating mirror (half-wave plate). The challenge is to achieve effective performance at two bands and maintain that performance over a wide range of aspect angle. Basic mirror antenna operation and design and fabrication techniques for a dual-band half-wave plate mirror are described. The solution for design parameters is derived for perfect90degpolarization rotation at a given aspect angle for each of the two bands. The design approach includes a process for optimizing the design for the full desired range of aspect angles. Practical fabrication considerations are discussed along with inclusion of the effects of capacitive susceptance of a protective mirror coating in the design theory. Theoretical performance is compared with measurements of mirror samples.     

Plane wave spectrum scattering analysis of near-field obstacle effects on directive antenna patterns

A plane wave spectrum scattering analysis of the effects of a near-zone obstacle on the pattern performance of a directive antenna is discussed. The free-space azimuth monopulse antenna is characterized by its sum and difference mode plane wave spectra, and a computed plane wave scattering dyad is used to characterize the scattering by a metallic right circular cylinder when it is excited by the incident antenna spectra. An efficient computer algorithm has been developed to compute the far-zone scattered and total fields for the antenna/cylinder system. Extensive experimental data have been obtained, and the patterns calculated using the present analysis are in agreement with the measured data.     

鱼骨天线集合线建模对计算结果的影响研究

为确保电磁建模的准确性,以有效设计短波全频段性能优越的鱼骨天线,研究了鱼骨天线集合线的建模方式对计算结果的影响。对集合线按等效网络和导线结构两种方式建模,基于Pocklington方程和正弦插值基函数,采用矩量法对实际地面上的短波鱼骨天线进行计算。对两种建模方式计算得到的天线方向图、增益、最大辐射仰角、效率以及阻抗特性进行了比较研究,并分析了集合线对鱼骨天线辐射特性的影响。研究结果表明:在某些情况下集合线的建模方式对计算结果的影响较大,为得到更接近实际情况的计算结果,确保短波全频段鱼骨天线设计的有效性,采用按导线建模的方式更为合适。