Some Noise Suppression, Signal Reception, and Polarization Measurement Properties of Crosscorrelated Antennas

Some recent results concerning the suppression of isotropic unpolarized noise fields obtained by studying the spatiotemporal crosscorrelation functions of dipoles imbedded in the spatial noise field have motivated the investigation of the signal reception properties of dipole arrangements with such noise suppression characteristics. The signal reception problem is approached by considering antenna crosscorrelation which simultaneously includes the spatial properties (i.e., the effective height function) of the antenna along with the temporal processing properties of the crosscorrelation detection process following the antenna array. The analytical techniques used include the antenna height function, crosscorrelation, and coherency matrix representation. The results obtained for a general antenna height function are applied to the specific case of dipole antennas. A technique of polarization measurement for incident radiation is derived by examining the crosscorrelation function expressed in coherency matrix notation when the dipole antenna effective height function is used.     

Direction-of-arrival estimation of broadband microwave signals in phased-array antennas using photonic techniques

A photonic technique for detecting the angle of arrival of broadband microwave signals in phased-array antennas is proposed. Using a photonic microwave filter and measuring the frequency of the notches created by the filter over the broadband signal, it is possible to derive its direction of arrival, even in the presence of several sources. The technique is intended to be used in optical-beamforming networks for phased array antennas. The architecture of the optical-beamforming network will be barely modified adding just a few additional components. Experiments showing the feasibility of the technique are provided.     

Influence of clipping during signal detection by crosscorrelation method

The crosscorrelation of a harmonic signal buried in severe noise with another of the same frequency decreases by a constant factor when clipping occurs. Calculation of this factor for a Gaussian noise shows that signal detection may be enhanced by a factor of 2.3 by overdriving the measuring channel.     

基于D-S证据理论的循环平稳频谱协作感知

为了避免干扰授权用户的正常通信,认知无线电系统需要较好的频谱检测性能。提出了基于循环平稳特征和D-S证据理论的多天线多用户频谱协作感知方法。分析了多天线接收信号的谱相关函数,在频域按照最大比合并的方法合并各天线接收信号,得到合并信号的谱相关函数。依据谱相关函数的能量,在多用户中采用D-S证据理论做协作频谱检测。仿真分析表明,基于循环平稳特征和D-S证据理论的多天线多用户频谱协作感知方法可有效改善认知无线电系统检测性能。     

智能蒙皮天线的体系构架与关键技术

区别于传统天线设计方法,提出了一种新的智能蒙皮天线设计架构,探讨了实现智能蒙皮天线的关键技术。通过在射频功能层采用可重构技术和在后端采用信号处理的方法,实现了智能蒙皮天线的波束自适应,解决了传统天线仅仅依靠信号处理方式来实现天线波束自适应的局限。分析了智能蒙皮天线的封装功能层、射频功能层以及控制与信号处理功能层的实现措施。最后针对新一代航空平台的应用需求,进一步探讨了智能蒙皮天线的关键技术和实现方法。     

A direction-finding technique for wide-band impulsive noise source

A direction-finding technique for wide-band impulsive electromagnetic interference is presented. An experimental investigation was performed using a spark generator as the impulsive noise source. The signals were captured using a two-antenna array directly sampled at 1 Gs/s. A digital signal processing based correlation technique allowed assessment of the time delay between the antennas. The results in a nonideal radio propagation environment show the bearing can be estimated to an accuracy of 20     

A calibration technique for polarimetric coherent-on-receive radarsystems

A new technique for calibrating a coherent-on-receive polarimetric radar system is proposed. A coherent-on-receive polarimetric radar is capable of measuring the Mueller matrix of point or distributed targets directly by transmitting at least four independent polarizations and measuring the vertical and horizontal components of the backscatter signal simultaneously. The technique requires the use of two calibration targets, a target with known scattering matrix (such as a metallic sphere or a trihedral corner reflector) and any depolarizing target (for which knowledge of its scattering matrix is not required) to determine the system distortion parameters. The system distortion parameters, which include the channel imbalances, the cross-talk factors of both the transmit and the receive antennas, and the phase shifts and amplitude variations of the transmitter polarizers, are determined by measuring the calibration targets for four different transmit polarizations. The validity of the new calibration technique is examined by measuring the scattering matrices of spheres and cylinders as test targets using a coherent-on-receive radar operating at 34.5 GHz. Excellent agreement between the theoretical and the measured scattering matrices for the test targets are obtained     

The contribution of motor unit pairs to the correlation functions computed from surface myoelectric signals

The contribution of motor unit action potential trains (MUAPT) of distinct motor units (MU) to the crosscorrelation function between myoelectric signals (MES) recorded at the skin surface is studied. In specific, the significance of the correlation between the firing activity of concurrently active MUs (which results in cross-terms in the overall correlation function) is compared to the representation obtained using the contributions of single MUs at each recording site (auto-terms). A model for the generation of surface MUAPs is combined with the generation of MU firing statistics in order to obtain surface MUAPTs. MU firing statistics are simulated to incorporate MU synchronization levels reported in the literature. Alternatively, experimental firing statistics are fed to the model generating the MUAPTs. The contribution of individual MU pairs to the global myoelectric signal correlation function is assessed. Results indicate that the cross-terms from different MUs decrease steadily contributing very little to the overall correlation for record lengths as short as 30 s. Thus, the error expected when computing the crosscorrelation function between two channels of MES as the superposition of the auto-terms contributed by single MUs (i.e., ignoring the cross-terms from different MUs) is shown to be very small.     

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.     

Crosscorrelation properties of pseudorandom and related sequences

Binary maximal-length linear feedback shift register sequences (m-sequences) have been successfully employed in communications, navigation, and related systems over the past several years. For the early applications, m-sequences were used primarily because of their excellent periodic autocorrelation properties. For many of the recent systems applications, however, the crosscorrelation properties of such sequences are at least as important as the autocorrelation properties, and the system performance depends upon the aperiodic correlation in addition to the periodic correlation. This paper presents a survey of recent results and provides several new results on the periodic and aperiodic crosscorrelation functions for pairs of m-sequences and for pairs of related (but not maximal-length) binary shift register sequences. Also included are several recent results on correlation for complex-valued sequences as well as identities relating the crosscorrelation functions to autocorrelation functions. Examples of problems in spread-spectrum communications are employed to motivate the choice of correlation parameters that are considered in the paper.     

Simultaneous Electromagnetic Measurement Using a Parallel Modulated Probe Array

A simultaneous measurement method using a parallel modulated probe array is proposed to measure the electromagnetic field radiated by antennas at different locations simultaneously. Each modulated probe is excited by a local signal with different frequency, so that the received intermediate frequency (IF) signal contains different frequency components which indicate the relative magnitude of the radio-frequency signal at positions of the probes, and all the IF components are measured simultaneously by a broadband microwave receiver. The effect of the local signal on the received IF signal and interaction effect between the probe array and the measured antenna are investigated. The accuracy of the method is shown by measuring the antenna radiation pattern. A 3D antenna radiation measurement system based on the present method is also developed. The performance of the system is demonstrated by measuring the radiation efficiency of antennas.     

Novel method of UWB antenna optimization for specified input signal forms by means of genetic algorithm

A novel optimization procedure for the design of antennas for ultrawideband (UWB) wireless communication systems is presented. The optimization is based on the time-domain characteristics of the antenna. The optimization procedure was applied to a simplified version of the volcano smoke antenna proposed by Kraus. However, any other type of UWB antenna can be treated with the same technique. Our optimization procedure aims at finding an antenna not only with low VSWR but also a low-dispersion one which will ensure high correlation between the time-domain transmitting antenna input signal and the receiving antenna output signal. In pulse communications systems, usually an input signal form suited to a particular purpose is used. Hence, we strive to design the best antenna for a given input signal form. The optimization technique adopted here makes use of genetic algorithm (GA) search concepts. The electromagnetic analysis of the antenna is done by means of a finite-difference time-domain method using the commercially available CST Microwave Studio software.     

Early history of the OSU ElectroScience Laboratory

The early history of the Antenna Laboratory (the name was later changed to the ElectroScience Laboratory) of The Ohio State University is sketched. The development of scale model antenna techniques is described, as applied to measuring the patterns of aircraft and missile antennas. Other projects included one for measuring full-scale antenna patterns of vehicular antennas for the U.S. Army and another on the development of a CW technique for studying the reflections from radar targets. Emphasized is the importance of including in historical accounts of the works of engineering the human involvement of the engineers who create them.     

Initial weight computation method with rapid convergence for adaptive array antennas

This paper presents a rapid initial weight computation method for adaptive array antennas. The proposed method estimates a correlation matrix and a correlation vector, where the correlation matrix is estimated using not only received samples with the desired signal, but also those before starting the transmission of the desired signal. The proposed method reduces the number of known symbols required for weight convergence. Furthermore, the combined use of the proposed method and the decision-feedback minimum mean square error combining method significantly improves weight convergence. Numerical results show that the combined method converges an array with sixteen antennas by using less than ten known symbols.     

FMCW系统在工业中的应用

本文首先讨论了提高测量精度的方案,然后列举测量吹氧炼钢炉料位、高压输电线振动和冰层厚度的应用实例,最后介绍利用直达信号的单、双天线的固态系统以及用多波束测量多目标、多参数的FMCW系统.     

Iterative Frequency Domain Joint-over-Antenna Detection in Multiuser MIMO

Multiuser multiple-input-multiple-output (MIMO) wireless systems have great potential in improving information rate, diversity and resistance to against interference. The primary objective of this paper is to derive for broadband signaling a new iterative frequency domain (FD) multiuser MIMO signal detection technique for joint-over-antenna (JA) detection. The proposed detector is based on soft-cancellation and minimum mean square error (MMSE) filtering, followed by maximum a posteriori probability (MAP) detector to detect several of each users transmit antennas. The purpose of jointly detecting several transmit antennas is to preserve the degrees of freedom (DoF) for MMSE. Computational complexities with FD and its time domain (TD) counterpart are evaluated in this paper, and it is shown that FD requires significantly lower complexity than TD. Numerical results show that JA significantly outperforms the receiver that detects transmit antenna signals antenna-by- antenna (AA). The proposed iterative FD JA technique achieves larger performance gains compared to AA when the total number of transmit antennas is larger than the number of receiver antennas, as well as in the presence of spatial correlation.     

Signal correlation between two normal-mode helical antennas for diversity reception in a multipath environment

The spatial correlation coefficient of signals received by two normal-mode helical antennas in a multipath environment characterized by Clarke's model is rigorously obtained. A new formula relating the signal correlation coefficient to the mutual impedance is derived. The mutual impedance is defined and calculated in a new manner. Our findings show that: 1) the envelope correlation coefficient of two helical antennas is greater than that of two monopole antennas; 2) the envelope correlation coefficient is dependent on the antenna terminal load and the mutual impedance and an optimal antenna load can be determined to produce the smallest correlation coefficient; and 3) the frequency response of the envelope correlation coefficient resembles that of the voltage standing-wave ratio.     

序列偶循环相关函数及其界的研究

根据提出的序列偶的周期互相关及其自相关函数的概念,进一步讨论了序列偶间的互相关函数的变换关系。在此基础之上定义了相应的偶相关函数量值,并推导形成了有关序列偶的界的理论估计。     

Impedance matching of tapered slot antenna using a dielectrictransformer

A new impedance matching technique for tapered slot antennas using a dielectric transformer is presented. The technique is demonstrated by measuring the input impedance, VSWR and the gain of a Vivaldi antenna (VA). Measured results at Ka-band frequencies are presented and discussed     

A novel mode content analysis technique for antennas in multimode waveguides

This paper presents a novel technique for analyzing the mode content excited by antennas placed in multimode waveguides. The technique is based on measuring the frequency response between the two antennas coupled into a waveguide and using that information to extract the mode content generated by the transmitting antenna. The technique is applicable to cases in which the mode amplitudes are approximately constant over the frequency range of interest. This method is valuable for determining the mode mix generated by arbitrary transmitting antennas in a multimode waveguide propagation environment. An example of such an environment is heating, ventilation, and air-conditioning (HVAC) ducts used for indoor communications, where an important antenna characteristic is the mode sensitivity (analogous to the antenna directive gain in free space). We validate our technique with the example of a monopole probe antenna coupled into a multimode cylindrical HVAC duct.