Scattering Characteristics of VHF Television Broadcasting Waves by Steel Towers of Overhead Power Transmission Lines

To determine the scattering characteristics of VHF television waves by steel towers for power lines, waves having a frequency 40 times that of television waves were radiated on a 1/40 scale model tower. The reflection characteristics were measured by rotating the model tower and changing the receiving point. A 50-cm by 50-cm metallic reflector was positioned at the model tower when measuring the reflection field and comparison was made of the receiving power from the model tower and that from the metallic reflector. The results showed that the maximum value of the reflection field attenuated in approximate proportion to the distance between the tower and the receiving point. This fact led to an experimental formula for determining the maximum value of the reflection field when the wave is incident upon the tower at a uniform strength in the vertical direction.     

VHF/UHF波段树干电磁散射特性分析

运用FDTD方法计算树干的宽带电磁散射特性.即将地面的散射场与入射场视为两个激励场作用于树干,从而得到地面背景下树干的散射场.给出了树干时域、频域、极化域和空域的电磁散射特性,并对这些特性进行了分析.     

VHF／UHF宽带功率放大器设计

设计了一种30-520MHz功率放大器。采用传输线和集中常数相结合的阻抗匹配方式。实现了功率放大管的宽带匹配;对滤波器电子开关进行了分析并采用ADS进行仿真,插损及隔离度在全频段达到了设计要求;最后给出了测试结果,满足了指标的设计要求。该功率放大器已应用于某宽带通信设备且工作良好。     

VHF/UHF波段树干超宽带散射特性研究

本文用时域方法研究了树干的超宽带散射特性.由于树干及地面均为色散有耗媒质,因此树干散射特性是复杂的频率函数.时域有限差分算法(FDTD)尤其适合于此类具有色散特性的超宽带散射特性研究.运用FDTD算法建立起树干散射模型后,经过计算,可以得到整个时域过程的散射,对时域散射场进行快速傅立叶变换(FFT),则可获取全部感兴趣的超宽带频域特性.相对于矩量法(MOM)而言,FDTD能更方便快捷地为叶簇穿透(FOPEN)检测目标提供全面的时频信息.     

VHF/UHF radar. 1. Characteristics

Low-frequency radars have the potential to counter stealth efforts and detect low-flying targets beyond the horizon. This paper gives an overview of the fundamental properties of radars at metric wavelengths, based on research over the past few years conducted at the German Research Institute for High-Frequency Physics and Radar Techniques (FGAN-FHR). It provides an analysis of radar cross-section to underline the anti-stealth properties of the low-frequency range and presents simulations as well as measurement results to demonstrate the beyond-the-horizon detection and foliage penetration capability of metric waves. Specific clutter properties are highlighted     

超短波数传设备的关键技术指标分析

超短波数据链的发展使得高速超短波数传设备的研制倍受关注,超短波数传设备能实现的最快速率、系统灵敏度等指标成为设备研制者关注的问题。根据香农的信息容限理论和超短波设备的噪声系数在理论上对超短波数传的灵敏度、系统信息容限进行了分析。分析结果表明,白噪声干扰条件下的系统灵敏度受噪声系数、温度、信号带宽的影响;系统带宽较窄时,系统信息容限和带宽成正比,频带利用率高;带宽增加到一定程度后容量不再随带宽变化,频带利用率降低到接近0。     

基于对流层散射的VHF/UHF不对称分集传输技术研究

针对VHF/UHF频段单信道电台仅能视距通信的应用局限,通过理论分析和信道特性试验探讨了将对流层散射传输体制用于VHF/UHF频段超视距通信的可行性,并在此基础上提出了一种基于对流层散射的不对称分集传输技术方案,即在保留单信道电台硬件结构不变的前提下,通过增加超视距传输波形并且建立地面赋能站的方式实现其超视距通信能力。最后通过对设备原理样机的信道模拟测试和野外试验证实了该技术的可行性和有效性。     

VHF/UHF无线高速数据传输中的级联编码

介绍了在VHF/UHF无线通信系统中进行高速数据传输时 ,采用RS码与卷积码的级联码对传输的数据纠错编码以及对提高数据传输可靠性的影响 ,并在加性高斯白噪声信道环境下对能够达到的误码性能进行了仿真分析。     

超短波跳频信号源的实现

简单介绍了跳频信号源的组成框图和工作原理。重点对该信号源为实现快速跳频所采用的控制方式、高速综合器、快速变频、软件控制技术,以及为实现宽频带、高隔离度、高平坦度和低杂散等指标所采取的措施进行了详解,对如何利用Gold码产生不同的跳频图案以及跳频图案在信号源中的作用进行了必要的说明。最后对所测得的技术指标进行了较为详细的列述,对设备所具备的诸多特点进行了介绍。     

Propagation of Wide-Band Signals at VHF/UHF

The experimental jam-resistant secure voice communications (JRSVC) system developed by M.I.T. Lincoln Laboratory was used to conduct a series of VHF/UHF (225-400 MHz) propagation measurements, representative of a veriety of tactical communications situations, both ground to ground and ground to low-flying aircraft. Results are unusual in two regards: they were made with the receiver in motion, covering many contiguous propagation paths, and the JRSVC system, by frequency-hopping over almost an octave and averaging the results, largely eliminated the effects of frequency-selective (multipath) fading that generally dominate VHF/UHF propagation measurements.     

浅谈VHF/UHF固定监测系统的建设

随着无线通信事业的迅速发展,无线电频谱资源日趋紧张,空中电波环境日益复杂,无线电干扰逐渐增多,为加强对无线电频谱的监测,为频谱管理、频率指配及规划提供监测数据,加强无线电监测系统建设,尤其是VHF/UHF固定监测系统建设,是各级无线电管理部门所面临的重要而紧迫的工作。VHF/UHF固定监测系统投资多,工程大,在实际建设中,应结合各地无线电发展情况,资金来源,需要完成的任务等,对监测系统的建设方案有一个周密的分析,尽量做到功能完善、布置合理、性能可靠、经济实用。系统功能VHF/UHF固定监测系统一般由一个主站和三个以上分站组…     

Scattering of Electromagnetic Waves on a Subwave Lattice of Square Strip Conductors

Journal of Communications Technology and Electronics - Simple formulas are obtained for calculating the scattering matrix of a plane electromagnetic wave incident normally on an infinite 2D lattice...     

浅述基于TDS-OFDM技术的数字电视传输系统

本文简单介绍了DMB-T传输系统的调制模式,以及DMB-T所采用的主要技术和系统特点。     

VHF/UHF宽带低噪声放大器设计

介绍了VHF/UHF宽带低噪声放大器的设计与实现。利用软件对放大器的电性能及有源芯片的沟道温度进行了仿真、优化。电路制作完成后,与实际测试结果进行了对比分析,并且结合不同电路形式,开发了系列化放大器。该系列放大器采用GaAs PHEMT管芯,微波薄膜工艺,封装在密封的金属或陶瓷管壳中,性能优异,体积小、噪声低、动态范围大,可适应目前微波整机向小型化、高可靠方向发展的需求,有着广泛的应用前景。     

ALTAIR VHF/UHF observations of multipath and backscatterenhancement

During the Defense Nuclear Agency (DNA) PEAK (propagation effects assessment-Kwajalein) experiment in August 1988, the ALTAIR VHF/UHF wide bandwidth radar was used to track spherical satellites in low-earth orbit. The purpose of the experiment was to obtain radar data during the most severe natural propagation disturbances. The PEAK experiment was successful, giving many measurements of strong scintillation as well as the first measurements of frequency-selective fading on propagating radar pulses. Experimental results are used to demonstrate an enhancement, due to scattering, in the average received power that is observed during severe scintillation. The observed statistics of the enhancement are compared to analytic calculations using the Nakagami-m distribution with very good agreement     

数字电视数字广播技术与传输标准探析

当前数字电视数字广播技术为我国电子技术领域带来了新的影响,为模拟信号向数字信号转换提供技术支持。使用数字电视技术对信号进行处理与分析,有效保证了数字信号传输的安全性。根据数字电视数字广播传输的标准需求,并结合国家标准的系统框架处理流程,对关键技术的细节进行研究,并对数字电视数字广播传输的相关问题进行探析。     

评中国地面数字电视广播传输标准

依据昊奕彦等采用的"系统载噪比性能的公正比较"方法和样机测试结果说明:中国地面数字电视广播传输标准(C-std)优于ATSC或DVB-T.并建议对该标准增加一些可选项,以改进其性能.     

数字微波传输网在广播电视信号传输中的作用分析

数字微波技术凭借自身诸多的优势,在广播电视信号的传输中发挥着至关重要的作用,能够在很大程度上促进广播电视向着数字化的进程发展.本文根据数字微波传输技术的发展现状,就数字微波传输网在广播电视信传输号中的作用进行了深入的研究分析.