一种改进的可变对角加载自适应波束形成算法

由于观测方向误差的存在,使得实际获得的方向向量与其理论值产生偏差,进而对各类自适应波束形成算法性能造成较大影响。为此提出一种有效的对角加载自适应波束形成算法,首先利用目标信号的方向向量在噪声子空间中投影最小的原理,对带有误差的方向向量进行校正,然后再使用可变对角加载原理求得对角加载因子,对实际获得的自相关矩阵进行对角加载后,形成自适应波束,从而很好地消除了方向向量误差造成的影响。算法能够有效克服目标信号对消现象,并具有良好的保形能力和快速收敛的特点。计算机仿真结果验证了这些优点。     

自适应波束形成算法的现状与发展动态

近十年自适应波束形成算法在通信、雷达、声纳、生物医学工程等科技领域中得到了极为广泛的应用.在实际应用中,如果信号源、天线阵列出现误差,传统的自适应波束形成算法性能将会下降.但是对于稳健的自适应波束形成算法,环境及天线阵列的误差和不确定性是必须要考虑的关键问题.这里对稳健的自适应波束形成算法的研究现状与发展动态进行了较为详细的评述.     

自适应波束形成算法的现状与发展动态

近十年自适应波束形成算法在通信、雷达、声纳、生物医学工程等科技领域中得到了极为广泛的应用。在实际应用中,如果信号源、天线阵列出现误差,传统的自适应波束形成算法性能将会下降。但是对于稳健的自适应波束形成算法,环境及天线阵列的误差和不确定性是必须要考虑的关键问题。这里对稳健的自适应波束形成算法的研究现状与发展动态进行了较为详细的评述。     

子阵级LCMV循环优化自适应波束形成算法研究

在传统LCMV波束形成器以及子阵空间部分自适应阵的基础上,提出了一种新颖的降维方法。首先将大规模阵列按照子阵划分的某种规则划分为若干组子阵列,每一组子阵列使用相同的权值。在权值优化过程中,每一次只更新权向量的一部分,通过多次迭代更新使系统搜索得到最优权值,避免了全维相关矩阵的求逆运算。实验结果表明,与传统方法相比,该方法在大规模阵列波束形成时能够获得更高的信干噪比,并减小了求逆矩阵的维数,在一定程度上降低了计算复杂度及硬件成本。     

基于子空间逼近的特征空间波束形成算法

特征空间波束形成（ESB）算法为了得到信号子空间需要对采样协方差矩阵进行特征值分解,运算量十分巨大,这大大限制了其应用。为了减低ESB算法的运算量,利用有理子空间逼近的原理,提出一种不需要估计信号源个数的快速ESB算法。该方法利用一个介于信号和噪声特征值之间的分界值将特征空间分成两个子空间,并用矩阵幂乘和此分界值的有理式逼近这两个子空间的投影矩阵,将此投影矩阵代入到ESB算法的权值求解式中,在不降低性能的前提下,可大大提高波束形成的运算速度。计算机仿真验证了该算法的有效性,并分析了分界值取值方法的不同对子空间划分及波束形成性能的影响。     

基于子空间投影的波束形成算法性能分析

全球导航卫星系统(GNSS)接收机采用自适应天线阵进行抗干扰时,传统的自适应算法形成的旁瓣增益较大,干扰信号方向零陷较宽,会滤除部分有用信号。针对传统自适应算法的不足,分析了基于子空间投影的抗干扰波束形成算法,先采用正交子空间投影技术消除接收信号中的强干扰信号,再通过一种加权准则提高信号质量,可避免传统自适应算法的缺点。仿真结果表明,与单一的加权准则、子空间投影技术与线性约束最小方差准则相结合的算法相比,子空间投影技术与最大化信噪比准则相结合的算法能够得到近似相等的信噪比,且在干扰方向形成较窄的零陷,从而提高系统抗干扰性能。     

稳健特征子空间波束形成算法及其性能分析

基于特征子空间的稳健波束形成算法能够用于改善一般导向矢量失配的稳健性,而且相比于其它算法实现简单,然而方法在低的信噪比和较高的信号加噪声子空间维数条件下,性能急剧恶化,而且信号加噪声子空间的维数必须是已知的。为改善波束形成稳定性,提出了基于L-曲线的方法用于信号子空间及其维数的稳健估计,使得该算法的应用条件得以满足,其中还提出了广义SINR,并详细分析了理想条件下信号子空间的选取对算法性能的影响,最后进行了详细的仿真试验和性能分析,验证了所提出方法的正确性和有效性。     

稳健自适应波束形成器设计与仿真

针对自适应波束形成器在进行对角加载时存在选取对角加载值的不可靠问题,设计了一种稳健的自适应波束形成器。通过采用收缩方法(Shrinkage Method)获得了对协方差矩阵更精确的估计,以代替标准Capon波束形成器(SCB)中的采样协方差矩阵。与传统自适应波束形成器相比,能够根据给定数据完全自主的计算出对角加载值而不需要指定任何用户参数,有效的抑制干扰信号,改善输出信噪比,且具有良好的波束保形能力和较快的收敛速度,特别是在快拍数较少的情况下具有很好的性能。计算机仿真验证了设计方法的正确性和有效性。     

波束形成算法研究与改进

近年来,智能天线在抗干扰方面应用广泛,多种不同的自适应波束成形算法被相继提出。首先讨论了LMS、GSC、MMSE三种波束形成算法的性能,对于均匀线性阵列天线,在相同条件的情况下,通过计算机仿真比较了三种算法的特点。最后提出了对MMSE算法的改进,通过对单个天线逐个权值的调整,使阵列输出信号与参考信号差异最小,减少计算复杂度,自适应地产生最优权值,实现了很好的抗干扰效果。     

基于FFT的矩形阵波束形成算法

为提高矩形阵的波束形成算法的效率,在波束形成中引入了快速傅立叶变化.基于快速傅立叶变换,将阵所接收的数据从时域变换到频域,通过对相位进行均分,使数据在空间域上进行排序重组,再次利用快速傅立叶变换从空间域转化到波数域上,经过相位修正形成波束图.仿真实验表明,随着阵元数增大,采用快速傅立叶变换能有效降低运算量,提高运算速度,降低对硬件的要求,易于工程实现.     

Broadband T‐bar fed slot antenna array with stable horizontally polarized omnidirectional radiation

A broadband horizontally polarized omnidirectional antenna array is proposed, which consists of a circular array of four identical broadband T‐bar fed cavity‐backed slot antenna elements and a 1‐to‐4 power divider. The proposed omnidirectional antenna array has a compact diameter of only 0.44λ₀, a broad bandwidth of 75.9% (450‐1000 MHz) and a favorable omnidirectional radiation pattern in the azimuth plane with a gain variation below 3 dB in the operating band. Moreover, the cavity‐backed structure makes the proposed antenna array hardly affected by metal environment and the all metal construction allows for high‐power applications, and the reserved cable channel behind the cavities of the antenna elements ensures the extensionality and stability of the proposed array when longitudinal array expansion is needed. Design procedures of the proposed antenna array have been described in detail, simulations and measurements of the proposed antenna array have also been carried out to validate its performance in this article.     

宽带圆极化阵列天线设计

提出了一种应用于S波段小型宽带圆极化微带贴片天线阵列。单点背馈式方形贴片印刷于Duroid5880介质板上,在贴片上加载两个相邻矩形缝隙,一方面实现圆极化辐射,另一方面拓展天线单元的阻抗带宽。利用该单元组阵,通过采用连续相位旋转法馈电天线单元拓展天线阵列的轴比带宽,仿真结果表明,线阵和面阵的阻抗和轴比带宽均达到10%以上。     

稳健的全阵波束形成方法

由于相干干扰和角度估计误差影响波束形成性能,对此提出一种稳健的波束形成方法。采用加权空间平滑算法去除相干性;对期望信号施加约束,保证一定角度估计误差范围内算法的稳健性;进行全阵波束形成变换,避免阵列孔径损失。仿真结果表明,在相干干扰环境中,该算法的方向图在期望信号方向有明显主瓣,有利于接收期望信号;在一定的角度估计误差范围内,该算法可保持比较高的且比较平坦的输出信干噪比;随着输入信噪比的增加,输出信干噪比几乎线性增大。     

一种改进的智能天线盲波束形成算法

将空分多址技术引入无线通信系统中,针对无线电信号普遍具有的循环平稳特性,提出了非线性条件下的改进盲波束形成算法。通过对算法的权向量进行再次优化,改善了方向图零陷的位置和深度,提高了输出SINR。优化算法的输出SINR对导引向量随机误差具有稳健性,对期望信号的功率变化表现出不敏感的特性,算法具有很好的理论价值以及应用前景。理论分析与计算机仿真实验都证明了算法的有效性。     

一种水平极化平面印刷全向天线的设计

介绍了一种水平极化全向天线,先仿真设计再加工制作,最后实际测试。结果表明:在2.4GHz频段上,获得了120MHz的带宽(VSWR<3)和良好的全向方向图。该天线被印刷在一块面积只有24.3×24.3mm2的FR-4介质板上,结构简单紧凑,可用于无线局域网终端通信。     

一种新的矢量传感器线列阵波束形成算法

为了提高基于矢量线列阵的目标方位估计能力,将基于时域解析信号实现最小方差无畸变响应（ MVDR）的方法——TAMVDR算法引入到了矢量线列阵信号处理中,提出了实现矢量线列阵波束形成的VTAMVDR算法。理论分析了矢量线列阵VTAMVDR算法的原理,该算法通过Hilbert变换对时域宽带信号引入复权向量,不需要进行子带分割,且不需要对数据进行分块处理,获得稳定优化权向量估计所需要的数据长度远小于频域MVDR方法,数据长度合适时,单次快拍即可实现波束形成,大大降低了运算量。仿真和海上试验数据分析结果表明：VTMVDR算法相比于频域MVDR算法具有较好的性能,具有更高的分辨率和更窄的波束角,有更好的探测性能。     

A wideband circularly polarized antenna array with sequential rotation feed

A novel wideband circularly polarized (CP) antenna array is designed, which consists of a horizontally placed wideband phase shifting feed network and four vertically placed linearly polarized dipole antenna elements, and the circular polarization is realized based on sequential rotation feeding technology. By placing two parasitic strips and two grounding strips on the top and side of each T‐shaped dipole antenna element, the impedance bandwidth and circular polarization performance of the antenna can be further improved. The simulation results show that the 10‐dB impedance bandwidth of the antenna is 93% (1.56‐4.27 GHz) and the 3‐dB AR bandwidth is 80.7% (1.7‐4.0 GHz). The measured results are in good agreement with the simulation results. Due to the use of orthogonally placed wideband feed network and wideband array elements, the proposed antenna array has a wider circular polarization bandwidth than the similar antenna arrays reported.     

Wideband and compact horizontally polarized omnidirectional antenna using composite dipole elements

A wideband horizontally polarized (HP) omnidirectional antenna is constructed and experimented in this article. The antenna consists of four composite dipoles forming a circular array in the azimuth plane and four pairs of parallel strip lines as impedance transformer networks. Two kinds of dipoles compose the composite dipole to achieve a wideband operation. By utilizing the composite dipole, four resonances can be simultaneously excited and manipulated to increase the bandwidth. A prototype is manufactured to validate the method. The dimensions of the antenna are just 0.62λ₀ × 0.62λ₀ × 0.03λ₀ (λ₀ is the free‐space wavelength at center frequency). The measured results show that the presented antenna has a impedance bandwidth of 58.6% (1.63–2.98 GHz) for VSWR ≤2. The gain variations are less than 0.6 dB at the azimuth plane in the operating band. Meanwhile, the cross‐polarization is less than 20 dB and the peak gain reaches 1.7 dBi among in the band. These advantages of the antenna make it suitable for 4G mobile communication applications.     

A quantized water cycle optimization algorithm for antenna array synthesis by using digital phase shifters

In this article, a quantized water cycle algorithm (QWCA) is used for the antenna array pattern synthesis with low side‐lobe levels (SLLs) and nulls at desired directions by using four‐bit digital phase shifters. In addition to the standard features as a metaheuristic algorithm, QWCA has an internal quantization mechanism and a precalculated array factor method. The latter provides an accelerated procedure to QWCA under favour of the digitized values that can be stored in a three‐dimensional array. This acceleration is based on the reality that the accessing data in the memory need less time than the usage of the mathematical functions throughout the optimization process. The internal quantization mechanism of QWCA is utilized to achieve digital values matching to the discrete values of the phase shifter instead of the simple rounding up/down routines after optimization. The numerical results showed that QWCA can obtain very good SLLs and null depth levels (NDLs) on the synthesized pattern. Moreover, the results are achieved in remarkably short optimization times. SLL and NDL values obtained by QWCA are also compared with the available literature values. The comparisons reveal that QWCA is able to produce better results than the other compared alternatives. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:21–29, 2015.     

A wideband compact horizontally polarized omnidirectional antenna for 2G/3G/LTE

A compact horizontally polarized omnidirectional slot antenna with a wide working band is presented in this article. The proposed antenna consists of 4 shorter driven cross‐shaped slots, 4 longer parasitic cross‐shaped slots, and a feeding network. Four shorter slots, placed on the same side of a circular substrate, are fed by a feeding network printed on the other side with uniform phase and magnitude. To enhance the bandwidth of the antenna, 4 longer cross‐shaped slots are inserted between adjacent longer slots to produce an additional resonant frequency. All 8 slot radiators placed symmetrically along the circumference results in an omnidirectional horizontal polarized radiation pattern. By utilizing cross‐shaped slots, a compact size of 0.53λ_L × 0.53λ_L × 0.005λ_L (λ_L is the free space wavelength at the lowest operational frequency) is achieved. The prototype of the proposed antenna is fabricated and measured. The measured results reasonably agree with the simulated results. The measured working band for |S₁₁|<–10dB is from 1.62 to 2.81 GHz which successfully covers the 1.7 to 2.7 GHz 2G/3G/LTE bands. The measured gain variation in azimuthal angle is <1.7 dB within 1.7 to 2.7 GHz, and the cross polarization level is <–27 dB in the horizontal plane.