Discrete time-scale characterization of wideband time-varying systems

Wideband time-varying systems can be found in many applications, including underwater acoustics and ultra-wideband technologies. The time variation due to Doppler scaling effects, coupled with dispersive scattering due to multipath propagation, can severely limit the performance of wideband systems. Just as the discrete time-frequency model can efficiently improve narrowband processing, a discrete time-scale system characterization is important in processing wideband time-varying systems. In this paper, a time-scale model is proposed as a discrete characterization of wideband time-varying systems. This representation decomposes a wideband system output into discrete time shifts and Doppler scalings on the input signal, weighted by a smoothed and sampled version of the wideband spreading function. The proposed transform-based approach uses the Mellin transform that is inherently matched to scalings to geometrically sample the scale parameter and the Fourier transform to arithmetically sample the time-delay parameter. Using this proposed model, and by properly designing the signaling and reception schemes using wavelet techniques, a joint multipath-scale diversity can be achieved over a dyadic time-scale framework in wideband wireless systems. The simulation results demonstrate that, based on the proposed model, performance can be increased by exploiting the diversity intrinsically afforded by the wideband system.     

Uniplanar EBG structure with improved compact and wideband characteristics

In recent years, there has been growing interest in investigating electromagnetic bandgap (EBG) structures, and diverse kinds of EBG structures have been suggested for applications of microwave circuits and antennas [1?7]. To make EBG more suitable for actual applications, much effort has been devoted to realise compact size for the EBG structure. Uniplanar compact EBG (UC-EBG), as a successful compact EBG structure introduced by F. Yang et al., has been exclusively investigated because of the easy fabrication, low cost and compatibility with standard planar circuit technology [5?7].     

A modified ground apollonian ultra wideband fractal antenna and its backscattering

This paper presents the design of a modified ground apollonian ultra wideband (UWB) fractal antenna. The printed fractal antenna has been designed on a substrate with dielectric constant ?_r = 4.3 and thickness h = 1.53 mm. The antenna has been fabricated with optimized dimension and tested. The experimental result of this antenna exhibits UWB characteristics from frequency range 3 GHz to 18 GHz. This corresponds to 142.86% impedance bandwidth with center frequency of 10.5 GHz. The experimental radiation patterns of this antenna are nearly omni-directional in H-plane and bidirectional in E-plane. The effect of various design parameters on UWB characteristics have also been analyzed using a 3D electromagnetic simulator based on FEM method. The simulated and experimental results are in good agreement. The backscattering RCS of this UWB fractal antenna is better than ?31 dB throughout the FCC band (3.1 GHz to 10.6 GHz). The proposed coplanar waveguide feed appollian fractal antenna can be easily integrated with radio-frequency/microwave circuitry with low-manufacturing cost and useful for UWB applications.     

New compact ultra wideband bandpass filter using modified multi-mode resonator

A new compact ultra wideband (UWB) bandpass filter (BPF) using modified multi-mode resonator (MMR) is presented. The filter consists of a multi-mode resonator with dual spur-lines for providing the dual notch bands at 5.2 and 5.8 GHz and connected with a stepped impedance structure for controlling the transmission zeros at lower and higher passband edge. The interdigital coupling input/output (I/O) lines are used for coupling enhancement. The |S₂₁|-magnitude and the frequencies of notch bands can be well determined by tuning the dimensions of the dual spur-lines. The designed procedures are discussed and good agreement between the measurement and EM simulation are compared.     

The adaptive multirate wideband speech codec: system characteristics, quality advances, and deployment strategies

Wideband speech is the major differentiation and attraction of third-generation network services in both the circuit and packet switched domain. Increased audio bandwidth introduces a significant leap in perceived quality of service compared to currently utilized narrowband telephony in second-generation mobile communications and the PSTN. The adaptive multirate wideband (AMR-WB) speech codec is the service enabler for improved user experience. It is an established 3GPP and ITU-T wideband speech codec standard and represents the state-of-the-art in speech quality as well as robustness in error prone radio channels. It is also the first codec algorithm standardized for wideband speech for mobile communications.     

New simulated corrugated scattering surface giving wideband characteristics

Simultaneous elimination of specular reflection and backscattered power from a plane metallic surface by simulated corrugated surfaces of constant period and variable strip width for TM polarisation is reported. This new configuration offers almost a ten-fold frequency bandwidth compared with a regularly spaced strip grating of the same size.<>     

Propagation characteristics for wideband outdoor mobilecommunications at 5.3 GHz

In this paper, empirical channel models and parameters are derived from the wideband measured data at 5.3 GHz in outdoor mobile communications. The path loss exponents and intercepts are obtained by using the least square method. The mean excess delay and mean root-mean-square (rms) delay spread are within 29-102 ns and 22-88 ns, respectively. The correlation distances and bandwidths are within 1-11 λ and 1.2-11.5 MHz, respectively, when the envelope correlation coefficients equal 0.7 in line-of-sight cases. These correlation values depend strongly on the base station antenna heights. The window length for averaging out the fast fading components is about 1-2 m for microcells and picocells. The multipath number distributions follow both Poisson's and Gao's distributions, but Gao's distribution is better in the high probability region. Large excess delays up to 1.2 μs and rms delay spread about 0.42 μs are found in the urban rotation measurements, where the receiver is close to a large open square     

Empirical millimeter-wave wideband propagation characteristics of high-speed train environments

Owing to the difficulties associated with conducting millimeter-wave (mmWave) field measurements, especially in high-speed train (HST) environments, most propagation channels for mmWave HST have been studied using methods based on simulation rather than measurement. In this study, considering a linear cell layout in which base stations are installed along a railway, measurements were performed at 28 GHz with a speed up to 170 km/h in two prevalent HST scenarios: viaduct and tunnel scenarios. By observing the channel impulse responses, we could identify single- and double-bounced multipath components (MPCs) caused by railway static structures such as overhead line equipment. These MPCs affect the delay spread and Doppler characteristics significantly. Moreover, we observed distinct path loss behaviors for the two scenarios, although both are considered line-of-sight (LoS) scenarios. In the tunnel scenario, the path loss exponent (PLE) is 1.3 owing to the waveguide effect, which indicates that the path loss is almost constant with respect to distance. However, the LoS PLE in the viaduct scenario is 2.46, which is slightly higher than the free-space loss.     

调频天线驻波比过大故障分析与维护

天津调频天线采用6层4面双偶极板天线,承载功率120kW.本文针对机房开关板上反应的驻波变大现象进行逐级排查、分析,并对判断步骤、维修方法进行阐述,给出天线振子由于进水导致驻波变大的解决方法.     

Ultrathin wideband slot and patch FSS elements with sharp band edge characteristics

ABSTRACT

Two diverse applications of FSS as bandpass and bandstop filters with wideband and sharp band edge characteristics are investigated in this paper. The proposed design comprised of a tapered tripole element in aperture and patch type printed on either side of a dielectric material to act as bandpass and bandstop filters respectively. The structures are ultrathin in design; structures comprise two metallic layers, isolated by single thin substrates with a thickness of 0.027λ. In the case of bandpass, the structure shows a relative bandwidth (?1 dB) of 8.87% with insertion loss better than 0.2 dB at normal incidence. Whereas, in the case of bandstop, it shows 24.36% (?10 dB). Further, the parametric analysis is performed for obtaining optimal performance. Both structures in the proposed form have spectacular application in bandpass filtering (slot FSS) and electromagnetic shielding (patch FSS). Further, two design techniques are presented namely dielectric encapsulation and substrate integrated waveguide (SIW) based FSS structures to develop a periodic structure to cater the high power handling in microwave sources. Finally, a fabricated prototype along with experimental verification proves the validity of simulated results.     

Improving TV Transmitter System VSWR and Related Frequency Response

This paper establishes the quantitative relation between a TV transmitter load VSWR and the system frequency response. The need for a low value of VSWR is stressed, particularly for multimode transmitting systems.     

A wideband stepped-impedance open-slot antenna with end-fire directional radiation characteristics

In this paper, new techniques are proposed to increase the front-to-back ratio of the stepped-impedance (SI) open-slot antenna for operation from 1.67 GHz to 4.25 GHz, covering the required frequency bands of the wireless communications systems, such as DCS, PCS, IM-2000, and WLAN. By designing a stub-protruded feedline and adding two symmetrical stubs at the edge of a quarter-wavelength slot, additional capacitance is introduced to the resonator. Hence, the impedance-matching condition of the SI open-slot antenna is not only effectively improved, but also the resonance frequency of the slot antenna is significantly shifted down and then an improvement in impedance bandwidth is achieved. In order to decrease the back radiation, two pairs of symmetrical open slots with uniform width are etched at the back of the blocking open slot such that the currents along the longitudinal edges of the ground plane cannot flow to the back direction. In addition, by embedding an array of seven slits beside the radiating slot, the back lobe at the upper frequency bands can be reduced. Two pairs of three-element metal strips are utilized as a power director to increase the forward power and enhance the front-to-back ratio of the SI open-slot antenna. Compared to conventional unidirectional radiation antennas, the proposed antenna demonstrates improved wideband unidirectional radiation characteristics and relatively smaller size.     

毫米波宽带高增益介质超透镜天线设计

基于相位补偿原理设计了一款全介质超透镜,同时使用喇叭天线作为馈源对透镜进行馈电.通过改变介质单元的高度和介质孔的深度实现了足够的相位补偿范围.该透镜共有506个单元,口径尺寸为44.6 mm×46.6 mm,该传输阵天线的焦径比为1.天线使用全介质结构,因此使用3D打印技术加工该全介质透镜,可以降低加工成本.仿真与实测...     

Indoor channel characteristics based on wideband MIMO measurements at 5.25 GHz

Extensive indoor channel measurements were conducted in Beijing with wideband multiple-input multiple-output （MIMO） sounder at 5.25 GHz. Both line-of-sight （LOS） and non-line-of-sight （NLOS） propagation were measured in the indoor office and hotspot scenarios. On the basis of measured data, statistical channel characteristics are presented in this article, including the empirical path loss （PL） models, three excess delay parameters, circular azimuth spread （CAS）, and circular elevation spread （CES）. Comparative analysis of different propagation mechanisms in two scenarios is conducted. These values are significant for indoor coverage and technical research of MIMO and orthogonal frequency division multiplexing （OFDM） for the international mobile telecommunications-advanced （IMT-Advanced） system.     

Magnified and Squared VSWR Responses for Microwave Reflection Coefficient Measurements

In conventional microwave impedance measuring the measured ratio of maximum to minimum detector signal level is ideally equal to the voltage standing-wave ratio (VSWR) of the termination. In this paper, it is shown how radically types of response are obtainable in which the observed ratio may approximately equal the square of the VSWR or may be magnified any desired amount. Theory k given enabling accurate ments by interesting techniques. Accuracies of 0.1 per cent in VSWR to 2.0 have been achieved using magnitied response techniques.     

CDMA-800MHz频段低温低驻波比放大电路设计

为用HEMT晶体管设计L波段低驻波比放大电路,本文用输入无源复反射系数在输出反射平面上的共轭匹配区表达式,将驻波比约束转化为无源匹配区域的映射.同时为了计算放大电路低温下噪声,通过有损输入模型导出了噪声的温度关系式.实测CDMA-830MHz高温超导前端放大器噪声温度小于30K,输入驻波比小于1.3,输出驻波比小于1.8,增益大于17dB.     

小驻波、低损耗慢波线设计

介绍了频扫雷达天线中小驻波、低损耗慢波线设计的关键技术,着重描述了经过改型的小驻波、低损耗慢波线耦合单元、180°波导E面弯头的设计和性能,最后给出了研制出的两型慢波线与国内国外同型慢波线的性能比较。     

A Low VSWR Matching Technique (Correspondence and Authors' Reply)

I would like to call your attention to a certain error in the above correspondence. The admittance function plotted by the author on the Smith chart winds counter-clockwise. This is contrary to the laws of nature for passive linear networks. These laws prescribed that the plot of the admittance function wind clockwise from the low to the high frequency.     

Probe-fed wideband AMC-integrated hexagonal antenna with uniform gain characteristics for WLAN applications

Wireless Networks - Demand of antennas those possess wide radiation bandwidth while operating in S-band for wireless communication systems is increasing day by day. Thick substrates are popular...