Optimization of antenna configuration for MIMO systems

In this letter, we investigate the issue of selecting the number of antennas at the base station and at the mobile to optimize ergodic capacity of a multiple-input/multiple-output system, when the costs of implementing antennas at the base station and at the mobile are unequal. Total system capacity, defined as a linear combination of the uplink and downlink ergodic capacity, is used as the objective function to be maximized. The asymptotic expression for the ergodic capacity is used as an approximation. The limiting case gives some insight on how the ratio of the number of antennas at the base station to the number of antennas at the mobile may change with signal-to-noise ratio and cost ratio when the total system capacity is maximized.     

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     

Performance of maximal ratio transmission with two receive antennas

Maximal ratio transmission is a transmit beamforming technique where multiple antennas are used both for transmission and reception. It can effectively increase the diversity order without modifying the receiver. In this letter, an expression for the probability of error of maximal ratio transmission is derived for the special case of two receive antennas and multiple transmit antennas.     

基于成对用户大规模MIMO中继系统的频谱效率性能分析

该文针对成对用户大规模MIMO中继系统,在中继采用最大比合并/最大比发射（MRC/MRT）预编码方案下,利用大数定律,推导出系统频谱效率的闭合表达式,显式的描述了频谱效率与中继天线数、该文针对成对用户大规模MIMO中继系统,在中继采用最大比合并/最大比发射（MRC/MRT）预编码方案下,利用大数定律,推导出系统频谱效率的闭合表达式,显式的描述了频谱效率与中继天线数、用户对个数以及信源用户和中继发射功率的关系。基于此,分析了当天线数增大时,在用户对个数固定不变和等比例增长两种情况下,频谱效率的渐进性能和所能获得的发射功率增益。结果表明,当用户数固定时,频谱效率将随天线数呈近似对数增长规律;当用户数随天线数等比例增长时,通过调整比例值,可满足平均每个用户的频谱效率达到任意指定值,且无需额外发射功率消耗。最后,通过数值仿真验证了所推导的频谱效率闭合表达式的精确性以及所有渐进性能的分析结果。      

利用线极化天线快速测量圆极化天线轴比的方法

针对轴比测试需要连续旋转线极化天线极化轴,在高频段旋转关节难以消除高速旋转带来的电缆抖动所引起的幅度和相位不一致性,提出了一种快速、精确测量圆极化天线轴比的测试方法。基于椭圆极化波的正交分解理论,该方法利用线极化天线对待测圆极化天线进行两组正交的线极化幅度测量,通过计算得到圆极化天线的轴比等极化椭圆参数的信息。在此基础上又提出了只用三个线极化分量测量圆极化天线轴比的方法。通过在微波暗室中对圆极化天线进行多次测试,验证了该方法的有效性。该方法提高了圆极化天线的测试效率,降低了测试难度,对于工程应用有重要的应用价值。     

基于空间分集的MIMO雷达目标跟踪算法研究

针对基于空间分集的多输入多输出(MIMO)雷达多发多收的特殊结构,建立了基于逆协方差形式扩展卡尔曼滤波算法的MIMO雷达目标跟踪滤波模型,分析了影响算法滤波精度的4个因素,分别为信噪比、信号带宽、天线数以及天线与目标间的位置关系。通过使目标位置状态估计均方误差最小,在特定天线数条件下利用数值方法得到了使滤波精度达到最优的天线放置形式。仿真实验给出了不同信噪比、信号带宽、天线数以及天线与目标间不同位置关系时的MIMO雷达跟踪性能。     

Exploiting Macrodiversity with Distributed Antennas in Micro-Cellular CDMA Systems

We consider the use of distributed antennas to increase the capacity and peak data rate achievable in a microcellular CDMA system with limited bandwidth. In additon to the diversity against Rayleigh fading achievable by use of microdiversity among nearly co-located transmit or receive antennas, we exploit macrodiversity against shadow fading that more widely separated antennas permit. We report on antenna configurations for both directional and omni-directional antennas that provide the most uniform signal-to-interference ratio coverage, averaged over a large number of position vectors drawn from a spatially uniform distribution of mobiles. Call capacities and peak transmission rates are determined for an integrated system carrying traffic at different constant rates, where processing gain and the transmission rate are selected to satisfy a common chip rate. For the downlink a 5.5 dB capacity gain can be achieved for 64 kb/s calls using four antennas located on the diagonals of each square cell. A bandwidth of 5 MHz allows two or more calls to be simultaneously supported at data rates up to 512 kb/s, as opposed to only 128 kb/s for three co-located antennas. On the uplink we distinguish between the computationally simpler equal-gain combining of the antenna signals and the possibly more complex maximum-ratio combining. With equal gain combining we achieve a peak data rate of 128 kb/s and a capacity gain of 2.5 dB relative to equal gain combining of three nearly co-located antenna signals. With maximum ratio combining the peak uplink rate can be as high as 512 kb/s and the capacity is increased by 2.0 dB relative to the maximum-ratio combining of three co-located antennas.     

Spherical Vector Wave Expansion of Gaussian Electromagnetic Fields for Antenna-Channel Interaction Analysis

In this paper, we introduce an approach to analyze the interaction between antennas and the propagation channel. We study both the antennas and the propagation channel by means of the spherical vector wave mode expansion of the electromagnetic field. Then we use the expansion coefficients to study some properties of general antennas in those fields by means of the antenna scattering matrix. The focus is on the spatio-polar characterization of antennas, channels and their interactions. We provide closed form expressions for the covariance of the field multimodes as function of the power angle spectrum (PAS) and the channel cross-polarization ratio (XPR). A new interpretation of the mean effective gains (MEG) of antennas is also provided. The maximum MEG is obtained by conjugate mode matching between the antennas and the channel; we also prove the (intuitive) results that the optimum decorrelation of the antenna signals is obtained by the excitation of orthogonal spherical vector modes.      

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。     

Spatial Modulation

Spatial modulation (SM) is a recently developed transmission technique that uses multiple antennas. The basic idea is to map a block of information bits to two information carrying units: 1) a symbol that was chosen from a constellation diagram and 2) a unique transmit antenna number that was chosen from a set of transmit antennas. The use of the transmit antenna number as an information-bearing unit increases the overall spectral efficiency by the base-two logarithm of the number of transmit antennas. At the receiver, a maximum receive ratio combining algorithm is used to retrieve the transmitted block of information bits. Here, we apply SM to orthogonal frequency division multiplexing (OFDM) transmission. We develop an analytical approach for symbol error ratio (SER) analysis of the SM algorithm in independent identically distributed (i.i.d.) Rayleigh channels. The analytical and simulation results closely match. The performance and the receiver complexity of the SM-OFDM technique are compared to those of the vertical Bell Labs layered space-time (V-BLAST-OFDM) and Alamouti-OFDM algorithms. V-BLAST uses minimum mean square error (MMSE) detection with ordered successive interference cancellation. The combined effect of spatial correlation, mutual antenna coupling, and Rician fading on both coded and uncoded systems are presented. It is shown that, for the same spectral efficiency, SM results in a reduction of around 90% in receiver complexity as compared to V-BLAST and nearly the same receiver complexity as Alamouti. In addition, we show that SM achieves better performance in all studied channel conditions, as compared with other techniques. It is also shown to efficiently work for any configuration of transmit and receive antennas, even for the case of fewer receive antennas than transmit antennas.     

Slot stripline circular-polarization antennas for a few-element antenna array for a high-accuracy receiver of signals from global navigation satellite systems

New radiators for slot stripline leaky-wave circular-polarization antennas for high-accuracy GLONASS/GPS receivers have been developed. The main technical characteristics of antennas with new radiators have been theoretically and experimentally studied. It is shown that application of the new radiators improves the axial ratio, increases suppression of the cross polarization, increases the stability of the antenna phase center, and thus can increase the GLONASS/GPS positioning accuracy. The results of the analysis of the GLONASS/GPS positioning accuracy with the use of these antennas in an angle-measuring receiver and as elements of a few-element antenna array are presented.     

Effect of Pointing Errors and Range on Performance of Dual-Pencil-Beam Scatterometers

Short-range FM scatterometers with single antennas are plagued by interference set up by feedthrough and internal reflections. Dual-antenna systems have much lower internal interference, but there are problems associated with pointing the antennas at the same spot. This note quantifies these problems for Gaussian-shaped beams. The use of antennas with beamwidth ratios of up to 5: 1 is shown to improve performance significantly over that obtained with identical beamwidths. For an angle between antenna centers (as viewed from the beam intersection) that is three times the beamwidth of the narrower antenna, the usable spread of range for equal beamwidths is only about 1.85:1, while for an angular ratio of 5, the usable spread of range is > 20:1.     

Axial ratio of an antenna illuminated by an imperfectly circularly polarized source

A method for determining the axial ratio of an antenna illuminated by an imperfectly circularly polarized source is described. This method requires measurements of the right- and left-handed amplitude components and their relative phases for both the receiving and transmitting (or source) antennas. From these measured data and, of course, the theory of power transfer between the source and receiving antennas, an algorithm is derived for the actual axial ratio of the receiving antenna. Illustrative results showing the effects of the phase angle are presented.     

On the relationship between fractal dimension and the performance of multi-resonant dipole antennas using Koch curves

This paper relates for the first time, multiple resonant frequencies of fractal element antennas using Koch curves to their fractal dimension. Dipole and monopole antennas based fractal Koch curves studied so far have generally been limited to certain standard configurations of the geometry. It is possible to generalize the geometry by changing its indentation angle, to vary its fractal similarity dimension. This variation results in self-similar geometry which can be generated by a recursive algorithm. Such a variation is found to have a direct influence on the input characteristics of dipole antennas. The primary resonant frequency, the input resistance at this resonance, and the ratio of first two resonant frequencies, have all been directly related to the fractal dimension. Curve-fit expressions can also be obtained for the performance of antennas at their primary resonance, in terms of fractal iteration and fractal dimension. The antenna characteristics have been studied using extensive numerical simulations and are experimentally verified. These findings underscore the significance of fractal dimension as an important mathematical property of fractals that can be used as a design parameter for antennas. The use of these ideas would not only reduce the computational intensity of optimization approaches for design of fractal shaped antennas, but also help antenna designers approach the problem systematically. Design formulation for antennas based on other fractal geometries can be similarly obtained after identifying suitable parameters of variation. This would therefore help analytical design of multiband and multifunctional antennas using fractal geometries.     

RF energy harvesting with multiple antennas in the same space

It is highly desirable to increase the amount of energy derived from a given space by an energy-harvesting device. In this paper, multiple energy-harvesting antennas in essentially one space or area are proposed and experimentally studied as a means to increase the energy or power/area ratio. Four cooperating antennas are proposed in a square area that is less than twice the area required for a single antenna. The results obtained suggest that this can be a very promising method for energy harvesting.     

V-BLAST系统中选择性最大比合并算法

通过选择性最大比合并(SC/MRC)算法,在并行干扰抵消(PIC)技术的基础上,对V-BLAST系统各接收天线的干扰抵消结果按照SC/MRC合并,实现了分集接收.该算法最多可以实现与接收天线数等同的分集增益,而通过选择信道条件较好的几个接收天线进行合并,可以在性能与复杂度之间取得折衷.MRC合并只需与选择合并的天线数线...     

Analyzing the FCC's DTV spectral emission mask and potentialdegradation to adjacent channels due to antenna pattern differences

The FCC DTV spectral emission mask is analyzed with an NTSC subjective noise weighting function to determine the desired NTSC to undesired adjacent channel DTV signal ratio at the threshold of visibility of interference. Factors which alter the NTSC/DTV adjacent channel signal ratio at various receiving locations within the NTSC service are examined: (1) the azimuth patterns of the NTSC and DTV broadcast antennas; (2) the elevation patterns of the NTSC and DTV broadcast antennas; and (3) the centers of radiation of the NTSC and DTV broadcast antennas. These factors together with the NTSC/DTV authorized power ratio may make the DTV spillover spectrum exceed acceptable picture (and sound) interference levels even though compliance with the FCC DTV spectral emission mask is met. Spectral shaping solutions are examined by use of the NTSC subjective noise weighting     

Axial ratio improvement in aperture antennas using high-impedance ground plane

High-impedance surfaces are studied as a means of improving the radiation pattern symmetry in aperture antennas. Compared to a solid metal ground plane, the results suggest that high-impedance surfaces can significantly improve the axial ratio of circularly polarised antennas. This can be used to reduce interference between left and right polarisation components.     

A practical method for measuring the complex polarization ratio of arbitrary antennas

A technique for measuring the complex polarization ratio of an arbitrary antenna is presented. The technique requires the use of two antennas which are not circularly polarized but are otherwise arbitrary. Only reciprocity and linearity are assumed. Six amplitude and phase measurements are performed, two measurements for each pair of antennas. The complex polarization ratio of each antenna is then calculated from the six measurements. The specific details of the measurement technique are described and some measurement results presented.     

Experimental investigation on a method of lowering the silhouette of conical log-spiral antenna

The experimental investigation was made on a low silhouette conical (LSC) log-spiral antenna, which has an advantage of shorter height compared with a conical log-spiral antenna of similar performance. The LSC antennas were constructed, and such antenna properties as radiation pattern, front-to-back ratio, voltage standing wave ratio (VSWR), and axial ratio were experimentally investigated.