Modified $theta $-Scanning Technique for First/Third-Order Probes for Spherical Near-Field Antenna Measurements

This paper presents a modified $theta $-scanning technique for first/third-order probes for spherical near-field antenna measurements. Unlike the traditional $theta $-scanning technique, this new scanning technique gives a possibility, due to the cutoff property of the azimuthal spherical modes, to filter out the influence of the undesired third-order azimuthal modes of the probe near the poles of the measurement sphere. Without increasing the measurement time, the technique allows reducing the errors caused by the application of the computationally efficient first-order probe correction technique (incorrectly) to first/third-order probes. The technique is optimal for spherical near-field systems, that employ, for example, an open-ended rectangular (or square) waveguide probe, that closely approximates a first/third-order probe, and apply the well-known first-order probe correction technique. In such systems, compared to the traditional $theta $-scanning technique, the modified $theta $-scanning technique can be used to significantly reduce the errors caused by the incomplete probe correction.      

平面近场测量中取样位置误差修正方法的研究

本文提出一种修正近场天线测量中探头集团误差的方法－非线性迭代法。探头的集团误差为可知值,同激光定位系统获得。运用泰载级数展开,可将天线理想波谱表示为误差算子和近场测量数据的形式。通过计算机械模拟,得到迭代修正后精确的近场值。本文在理想值、有误差的值和修正误差后的值之间作了些比较,相应的模拟数据有助于证实此结合。     

Double $phi$-Step $theta$-Scanning Technique for Spherical Near-Field Antenna Measurements

Probe-corrected spherical near-field antenna measurements with an arbitrary probe set certain requirements on an applicable scanning technique. The computational complexity of the general high-order probe correction technique for an arbitrary probe, that is based on the Phi scanning, is O(N⁴), where N is proportional to the radius of the antenna under test (AUT) minimum sphere in wavelengths. With the present knowledge, the computational complexity of the probe correction for arbitrary probes in the case of the thetas scanning is O(N^-6), which is typically not acceptable. This paper documents a specific double Phi-step thetas scanning technique for spherical near-field antenna measurements. This technique not only constitutes an alternative spherical scanning technique, but it also enables formulating an associated probe correction technique for arbitrary probes with the computational complexity of 0(N4) while the possibility for the exploitation of the advantages of the thetas scanning are maintained.     

近场天线测量中采样原则的改进

近场天线测量中，采用大的采样间隔，有利于提高测试和数据处理的效率。本文提出一种改进的采样间隔选取原则，并通过分析采样间隔与无混叠误差方向图角域的关系，说明该采样原则比文献提出的采样原则更合理。     

Reduction of Truncation Errors in Planar Near-Field Aperture Antenna Measurements Using the Gerchberg-Papoulis Algorithm

A simple and effective procedure for the reduction of truncation errors in planar near-field measurements of aperture antennas is presented. The procedure relies on the consideration that, due to the scan plane truncation, the calculated plane wave spectrum of the field radiated by the antenna is reliable only within a certain portion of the visible region. Accordingly, the truncation error is reduced by extrapolating the remaining portion of the visible region by the Gerchberg-Papoulis iterative algorithm, exploiting a condition of spatial concentration of the fields on the antenna aperture plane. The proposed procedure is simple and computationally efficient; it does not require any modification of the measurement procedure and it allows for the usual probe correction. Far-field patterns reconstructed from both simulated and measured truncated near-field data demonstrate its effectiveness and stability against measurement inaccuracies.      

An Accurate Equivalent Behavioral Model of Antenna Radiation Using a Mode-Matching Technique Based on Spherical Near Field Measurements

A new and simple method for modeling an antenna under test (AUT) from spherical near-field (NF) measurements is presented. This method utilizes NF data to determine an equivalent behavioral model composed of magnetic and electric dipoles placed over a fictitious sphere surrounding the AUT. A spherical wave expansion (SWE) of the measured NF is developed to derive a linear relation between the transmission coefficients of the AUT and the transmission coefficients of each dipole. Dipole transmission coefficients are determined using the translational and rotational addition theorems. Finally, a least square method is employed to compute the excitation of each current source. Once the equivalent model is obtained, it can be used to study the behavior of the original AUT in different environments. Computations with electromagnetic simulation data illustrate the accuracy of the proposed method and the reliability of the derived model.     

对角反相探针馈电贴片天线研究

在传统L形探针耦合馈电贴片天线的基础上进行了改进,采用了探针对角反相馈电技术构成了宽带、双极化贴片天线。采用基于有限元法的数值仿真方法对对角反相探针耦合馈电天线进行了研究,给出了实测结果。该天线适合作为通信基站阵列天线、智能天线及机载＼舰载相控阵天线阵列阵元。     

同轴探头法测量片状介质材料的微波介电常数

提出了一种可用于测量片状介质材料微波复介电常数的同轴探头技术,该技术将同轴探头紧贴有导电衬底的片状介质,通过测量探头终端的矢量反射系数来确定介质的微波复介电常数。详细介绍了所采用的理论模型和测量系统。测量了一些常见介质材料的介电常数,测量值与理论值基本吻合。文章的同轴探头技术不仅可用于测量厚度较小的片状介质,而且可用测量样品量有限的液体。     

A New Linearization Technique for CMOS RF Mixer Using Third-Order Transconductance Cancellation

A new third-order transconductance (g_m3) cancellation technique is proposed and applied to a conventional radio frequency (RF) mixer for improving circuit linearity. The bulk-to- source voltage is applied to adjust the peak value position of gms. The cancellation of g_m3 is utilized by a negative peak g_m3 transistor combined in parallel with a positive peak g_m3 transistor. For a single device, the measured adjacent channel power ratio (ACPR) and third-order intermodulation (IMD3) distortion are both improved over 15 dB. A Gilbert-cell mixer in commercial 0.18-mum CMOS process was designed using the proposed method to further evaluate the linearity. The compensated g_m3 device is placed in the input RF gm-stage and then reducing the principle nonlinearity source of the mixer. From the experiment results, the ACPR and IMD3 of the mixer are improved about 10 and 15 dB, respectively.     

无相位近场测量和全息诊断中基于泛函极值的相位恢复方法

相位恢复是无相位近场测量和全息诊断的关键技术.本文考虑探头修正,构造加权目标泛函,给出避免局部极值的无相位测量条件.为提高计算效率和工程实用性,对Fletcher-Reeves共轭梯度法采取再开始技术、FFT算法和构造迭代初值等改进措施.数值模拟表明,应利用有关天线和近场测量的先验信息,选取尽量少的搜索变量.实验结果验证了本文方法的正确性和有效性.     

Investigation of Surface-Wave Reduction in UC-PBG Patch Antenna by Using a Transient Electrooptic Near-Field Mapping Technique

A transient electrooptic near-field mapping system based on a gain-switched distributed feedback (DFB) pulsed laser and a CdTe electrooptic crystal was used for characterizing transient near-field patterns of conventional and uniplanar compact photonic bandgap (UC-PBG) patch antennas fabricated on a low-cost FR4 substrate. Effect of the UC-PBG structure on reduction in surface waves in the UC-PBG patch antenna was investigated experimentally by comparing transient near-field patterns of the conventional and UC-PBG patch antennas     

基于随机扰动技术的共形阵列失效单元非凸压缩感知近场诊断方法

在基于压缩感知的阵列失效单元近场诊断方法中,使用结构化随机采样策略构造的观测矩阵约束等距特性未知,采用1范数极小化凸优化算法将无法确保阵列失效单元的高概率精确诊断.针对这一不足,本文在深入研究非凸优化算法的基础上提出了一种基于随机扰动技术的非凸压缩感知近场诊断算法.首先在失效单元个数满足稀疏性的前提下构造差异性阵列,其次按照随机欠采样方式获取近场幅相信息,最后利用所提基于随机扰动技术的非凸优化算法对差异性阵列激励进行重构,从而实现对阵列失效单元的高概率精确诊断.数值仿真实验表明,所提算法避免了由于观测矩阵的约束等距特性未知对诊断性能造成的不利影响,并且克服了非凸范数易于陷入局部最优解的弊端,有效提高了阵列失效单元的诊断成功概率.     

VAE/MPM/GA Technique for DoA Estimation Using Optimized Antenna Arrays

Many algorithms have been proposed to estimate the direction of arrival for the targets, but through using a large number of snapshots. In real time applications such as automotive radar, this is unacceptable as it causes delay and heavy processing. Instead, if only a small number of snapshots or, optimally, a single snapshot is available for DoA estimation, it will be fast and efficient. Single snapshot algorithms have a drawback as they require a large number of antenna elements, which considered a limiting factor. In this paper, a single snapshot DoA estimation technique is introduced by using optimized antenna arrays. The proposed algorithm is based on utilization of virtual array extension, matrix pencil method, and the genetic algorithm. The use of virtual array extension greatly improves the MPM performance. Furthermore, it exhibits a high DoA estimation accuracy by using a reduced number of antenna elements. The genetic algorithm is employed to determine the minimum number of antenna elements, which are required to estimate the DoAs with minimal root mean square error.

     

A 2–40 GHz Probe Station Based Setup for On-Wafer Antenna Measurements

A probe station based setup for on-wafer antenna measurements is presented. The setup allows for measurement of return loss and radiation patterns of an on-wafer antenna-hence-forth referred to as the antenna under test (AUT), radiating at broadside and fed through a coplanar waveguide (CPW). It eliminates the need for wafer dicing and custom-built test fixtures with coaxial connectors or waveguide flanges by contacting the AUT with a coplanar microwave probe. In addition, the AUT is probed exactly where it will be connected to a transceiver IC later on, obviating de-embedding of the measured data. Sources of measurement errors are related to calibration, insufficient dynamic range, misalignment, forward scattering from nearby objects, and vibrations. The performance of the setup is demonstrated from 2 to 40 GHz through measurement of an on-wafer electrically small slot antenna (lambda₀/35 times lambda₀/35,3.5 times 3.5 mm²) radiating at 2.45 GHz and an aperture coupled microstrip antenna (2.4 times 1.7 mm²) radiating at 38 GHz.     

A New Time Domain Technique for Velocity Measurements Using Doppler Ultrasound

A new technique for determining the Doppler frequency shift in a phase-coherent pulsed Doppler system is presented. In the new approach, the Doppler frequency shift is given directly in the time domain in terms of the measured I and Q components of the measured Doppler signal. The algorithm is based on an expression for the instantaneous rate of change of phase which separates rapidly varying from slowly varying terms. It permits noise smoothing in each term separately. Since the technique relies solely on signal processing in the time domain, it is significantly simpler to implement than the classic Fourier transform approach. In addition, the algorithm can be shown to give rigorously accurate values for instantaneous frequency and outperform the Fourier transform approach in poor signal-to-noise environments. Experimental results are presented which confirm the superiority of the new domain technique.     

A Shunt Technique for Microwave Measurements

A new method of measuring low-loss quantities at microwave frequencies, which employs a Iossy shunt structure, is described. The additional loss introduced thereby reduces the excessively high VSWR's to values lying in the measurable range. The relevant information is abstracted from the data in a precision manner independent of the parameters of the shunt structure itself. Applications are made to the measurement of low-loss dielectric constants, structures with shunt representations such as certain bolometer elements, attenuation constants, and VSWR's of slightly Iossy variable short circuits. Physical realizations of such shunt structures are discussed.     

用于瞬态电磁场测量的宽带脉冲天线

脉冲天线是脉冲雷达、瞬态电磁场测量等应用的关键设备之一。本文描述了用于瞬态电磁场测量的一种宽带脉冲天线的设计，给出了测量结果，测量结果表明，该天线具有高保真和宽频带特性，有有效地发射或接收毫微秒脉冲信号。实际制作的天线已成功地应用于外场瞬态电磁测试系统。     

A Dynamic Measurement Technique for Third-Order Distortion in Optical Phase Modulators

A novel two-tone measurement technique for characterizing distortion in optical phase modulators is proposed and demonstrated. The technique is used to characterize an InGaAsP-InP modulator in a monolithically integrated receiver. Results for forward and reverse bias conditions in the modulator show a phase IP3 of 7.2pi and 0.97pi rad, respectively