3G移动通信系统中的新型宽带语音编码VMR-WB

本文介绍了一种将应用于第三代移动通信的新型语音声码器-变速率多模式宽带(VMR-WB)声码器。VMRWB 专为CDMA2000标准设计,有效语音带宽扩展为:50 Hz=7000 Hz,有四种不同速率的运行模式,每一种模式对应一定质量的平均数据速率。在相同的速率下,VMR-WB语音声码器的主观质量和性能较现有的窄带和宽带编码标准都有明显的提高。本文主要介绍其编码原理以及一些特性。     

一种小型化宽带螺旋天线的数值分析与实验

提出了一种始端为等角螺旋线、终端为阿基米德螺旋线的复合式小型化螺旋天线,改善了等角螺旋天线的低频特性,克服了阿基米德螺旋天线臂长带来的传输损耗大、效率低的缺点;并设计了一种适合单向辐射的微带线--平行双线宽频带巴伦.计算与测试结果表明:该天线的低频端阻抗特性优于相同尺寸的等角螺旋天线和阿基米德螺旋线天线,具有较好的方向图特性和圆极化特性.     

A Compact Broadband H-Slot and Horizontal H-Slot Patch Antenna for Circular Polarization

This paper presents the design of compact broadband H-slot and horizontal H-slot microstrip patch antenna with a single feed. The antenna is also used for circular polarization application with a single narrowband frequency. The performance of single feed notched and truncated corner circularly polarized microstrip antennas with the same substrate thickness for H-slot and horizontal H-slot is studied. The simulated results such as return loss S₁₁, axial ratio AR, radiation pattern (E_left and E_right), and gain are presented in this paper for different shapes of patch antenna.     

超宽带无线通信技术

本文首先介绍了超宽带(UWB)技术的定义及其频谱规划情况,分析了UWB的调制与多址技术,然后介绍了目前IEEE 802.15.3 SG3a建议使用的UWB路径损耗模型及多径信道模型,最后展望了其应用前景及目前发展状况与需进一步研究的问题.     

带有小型化Balun的C波段单片GaAs pHEMT单平衡电阻性混频器

 本文介绍了一种带有小型化无源Balun的C波段单片GaAs pHEMT单平衡电阻性混频器.Balun 采用集总—分布式结构,使其长度与常用λ/4耦合线Balun相比缩小了11倍,大大降低了将无源Balun应用于C波段单片集成电路中所需的芯片尺寸.混频器采用单平衡电阻性结构,在零功耗的情况下实现了良好的线性和口间隔离性能.测试结果显示,在固定中频160MHz,本振输入功率0dBm条件下,在3.5~5GHz RF频带内,最小变频损耗为8.3dB,1dB压缩点功率为8.0dBm,LO至IF之间的隔离度为38dB.     

Design of a Vivaldi antenna with wideband reduced radar cross section

In this paper, a low radar cross section (RCS) Vivaldi antenna is proposed. The main objective of this work is to achieve a reasonable RCS reduction without affecting the radiation performance of the antenna. With carefully inspecting the surface current distributions at different frequencies and realizing the critical role of the structural mode in reducing RCS, a simple and efficient object shaping method is employed by introducing a number of circular slots in the surface of the radiator to achieve the RCS reduction. These circular slots along the inner circular profile of the Vivaldi antenna can minimize the scattering along the surface of the radiator, which hence leads to a reduction in the monostatic RCS. Comparing the measured results between the reference antenna and the proposed antenna, a significant 11 dB RCS reduction is obtained while maintaining good radiation performance. Simulated and measured results including S-parameters, gain, RCS of the reference antenna and the proposed antenna are presented.     

A wideband patch antenna with a pair of antisymmetric balun as differentially fed network

A novel singly differentially‐fed microstrip patch antenna (DFMA) is proposed, which is composed of a radiating patch, a differentially‐fed network with a twin antisymmetric miniaturized baluns and a ground plane for unidirectional radiation. In the differentially‐fed network, the signal is coupled to the two feedlines on both sides by the two miniaturized baluns. The radiating patch is excited by the coupling feed sheet located below the radiating patch, and the coupling feed sheet is connected to the upper end of the feedline. The lower end of the feedlines is connected to the ground plane, and there is a slot on the ground of the feeding network. Due to the existence of coupling feed sheet and slot, a second nonradiating resonant is achieved, and a wideband property is obtained. Finally, the prototype of the antenna is fabricated and studied experimentally. Simulated and measured results show that the impedance bandwidth of the antenna is 30.3% (1.71‐2.32 GHz) for S₁₁ < ?10 dB. Besides, a stable symmetric radiation pattern is obtained with gain around 9.6 dB and cross‐polarization less than ?21 dB, which demonstrates the designed antenna has the property of wideband, high gain and low cross polarization.     

Compact dual‐polarized dipole antenna with high isolation using hybrid balun circuit

In this article, a crossed dipole antenna with compact size (43 × 43 mm²) and high isolation (42 dB) is proposed using a hybrid balun circuit. The hybrid balun consists of a tapered balun and a Marchand balun. The tapered balun transforms the microstrip line into the parallel feeding lines for one pair of dipoles, and the Marchand balun transforms the stripline transmission line into a couple of out‐of‐phase feeding lines for the crossed pair of dipoles. Due to the low coupling between two different baluns, a high isolation of the antenna can be achieved when the crossed dipole antenna is cascaded with the hybrid balun. Moreover, these two baluns can improve impedance matching and therefore further miniaturize the size of the crossed dipole antenna. The impedance matching of two baluns can be controlled and adjusted independently. As a result, the proposed dual‐polarized antenna has the bandwidth of 1.7 to 2.8 GHz for S11 < ?15 dB with compact size and high isolation. The proposed antenna with the hybrid balun circuit are fabricated, and the simulated and measured results meet well.     

High two-signal dynamic range and accurate frequency measurement for close frequency separation wideband digital receiver using adaptive gain control and adaptive thresholding

In electronic-warfare (EW) receiver applications, real-time measurement of the radar signals' carrier frequencies is mandatory and considered to be one of the most important radar parameters. Accurate frequency detection can be used to sort and deinterleave signals in a dense signal environment where multiple signals arrive simultaneously presenting severe problems unless they can be differentiated appropriately. Researchers and engineers are actively looking for new algorithms for high resolution wideband receivers with easier implementation. This paper presents an adaptive gain control and dynamic thresholding wideband digital receiver to accurately detect two simultaneous high dynamic range signals, even when their signal frequencies are very close. The proposed fast Fourier transform (FFT) based receiver examines incoming signal characteristics and provides real-time accomplishment of these tasks, by way of using an adaptive gain-control amplifier, a squarer, two analog-to-digital converters, and two FFT's. The wideband receiver offers high probability of intercept over wide instantaneous RF bandwidths, high dynamic ranges and sensitivity. Two simultaneous signal accommodations and their characteristics are provided to demonstrate the improvements over presently used receivers in this field.     

基于调制宽带转换器的低频射电天文信号采集电路设计及实现

针对射电天文信号观测中传统的信号采集电路存储数据需较大的存储空间的问题,提出一种基于调制宽带转换器（MWC）的低频射电天文信号采集的硬件电路设计方法。首先,将观测信号与4路伪随机周期信号相乘后分为4路,并将这4路信号分别进行二阶巴特沃兹低通滤波器滤波;然后,对4路滤波后的信号进行采样,数据传输至现场可编程门阵列（FPGA）中进行存储;最后,用正交匹配追踪（OMP）算法进行信号重构。理论分析和实验测试结果表明,重构信号与观测信号的均方误差为1.27×10^-2,数据存储空间压缩率为20%,该硬件电路设计方法降低了电路设计成本,也释放了存储空间。