Real time frequency domain fiberoptic temperature sensor

The excited state phosphorescence lifetime of alexandrite crystals is used to monitor temperature in the physiological range from 15-45°C with precision and accuracy of 0.2°C. A 500-μm cubic alexandrite crystal bounded to the distal end of an optical fiber of similar core dimensions is excited with pulsed Ne-He laser light. This apparatus uses a sampler for data acquisition and frequency domain methods for data fitting. The instrument amplifies the AC components of the detector output and band limits the signal to 12.5 kHz. The fundamental frequency of the excitation is set to 195.13 Hz to obtain 64 harmonics. This band limited signal is sampled and averaged over few hundred cycles in the time domain. The frequency domain representation of the data is obtained by employing fast Fourier transform algorithms. The phase delay and the modulation ratio of each sampled harmonic are then computed. Five to 50 values of the phase and modulations are averaged before computing the sensor lifetime. The instrument is capable of measuring precise and accurate excited state lifetimes from subpicowatt luminescent signals in plastic optical fibers. A least squares fit yields the lifetimes of single exponentials. A component of zero lifetime is introduced to account for the backscatter excitation seen by the photodetector leaking through optical interference filters. The phosphorescence lifetimes measured reproducibly to about three parts in a thousand are used to monitor physiological temperature. Temperatures are computed employing empirical polynomials. The system drift is negligible over 15 h of continuous operation. The instrumentation and methods allow 1.3-s update times and 30-s full response times     

FDTD法计算高频单极天线特性

用时域有限差分法（Ｆｉｎｉｔｅ Ｄｉｆｆｅｒｅｎｃｅ Ｔｉｍｅ Ｄｏｍａｉｎ Ｍｅｔｈｏｄ）计算天线阻抗特性,可以使用不同的激励方式,文章比较了采用不同激励方式时,天线的输入阻抗。文中的主要内容是将表面阻抗法用于ＦＤＴＤ中,计算架设在介质平面上单极天线的辐射特性,并用ＦＤＴＤ法计算了介质平面上铺设不同尺寸的导体平面时,单极天线的输入阻抗随导体平面尺寸变化的特性。     

Cross-shaped dielectric resonator antenna analysis using conformalfinite difference time domain method

A cross-shaped dielectric resonator antenna, designed for circular polarisation, is analysed via the conformal finite difference time domain technique. The conformal technique, which can handle canted surfaces that do not conform to the Cartesian system of co-ordinates, is used to generate accurate results with a relatively coarse mesh, e.g. it is shown that the conformal FDTD offers a 2:1 advantage over staircasing, without compromising accuracy     

Modelling of coaxial-fed microstrip patch antenna by finite difference time domain method

A direct three-dimensional finite-difference time-domain (FDTD) method is applied to coaxial-fed microstrip antennas. The model is shown to be an efficient and accurate tool for modelling coaxial-fed structures. The reflection coefficient can be determined from the simulated time-domain wave that is reflected down the coaxial line. Excellent agreement over a wide frequency range is shown in two cases between the measured and FDTD derived results.<>     

Comparison of MC-CDMA with DS-CDMA using frequency domain and time domain RAKE receivers

In this paper a multicarrier CDMA (MC-CDMA) system with a soft decision differential phase shift keying (DPSK) frequency domain RAKE receiver is described. We compare a MC-CDMA system with a direct sequence CDMA system using RAKE receivers. In contrast with previous MC-CDMA systems, guard intervals are not used and the carriers are spaced at the reciprocal of the bit rate, optimising the usage of the bandwidth. In this way a comparison can be made between the multicarrier CDMA system described and a direct sequence (DS-CDMA) system with the same bandwidth. The results presented are received bit error rates from Monte Carlo simulations. The simulations are conducted in a multipath channel with Rayleigh fading and 300 Hz Doppler spectrum with additive white Gaussian noise. It is shown that the multicarrier CDMA matched filter receiver performs favourably compared to the direct sequence CDMA matched filter receiver for 1 -path fading. For a single user at a receive bit error rate of 1×10^–3 in the 4-path fading channel the multicarrier RAKE receiver requires no knowledge of the channel delay spread and performs 3 dB worse than the DS-CDMA RAKE receiver simulated. The performance of the MC-CDMA RAKE receiver for a single user increases with increasing channel dispersion. The performance of the DS-CDMA RAKE receiver for multiple user is superior to that of the MC-CDMA RAKE receiver.     

Mixed time/frequency domain approach to model reduction

The letter considers the problem of reducing the transfer function of a given system to a lower order. The approach proposed appears to be suitable in cases where both the frequency-domain and the time-domain characteristics of the given system are to be preserved in the reduced order model.     

频率步进激励信号的时域特性研究

将频率步进扫频信号用于电声测量系统工作过程中的激励信号,测量精度相对较高,但测量速度慢。并且,在频率不同的两段正弦激励信号衔接播放时,时域信号存在冲击量,如不加以改善,既延长了激励信号的过渡过程时间,又降低了测量精度。使用希尔伯特变换计算激励信号的时域包络曲线,可以分析冲击量的强度,且通过在激励信号频率步进衔接段采用时域加窗及平滑方法,可以降低这一冲击量的强度。理论分析和实验试听表明,该方法可以提高正弦激励信号频率步进时信号播放时的平滑度,降低冲击量,缩短过渡过程时间,且为改善测量精度提供一定的支持。     

A template for shaped-beam satellite antenna patterns

A modified template is proposed for shaped-beam satellite antenna patterns for use in orbit-planning studies of a fixed satellite service. Based on a previously discussed simple model, the template now includes the effects of beam scanning, aperture blockage, and surface errors. It is found to agree well with the measured data on current satellites and is a reasonable upper bound specification for future satellite antennas     

Time domain antenna holography

Time domain holography from direct time domain far field measurements is presented as a novel, fast approach to antenna diagnostics, which offers a greater insight into the electrical properties of antennas than that possible using standard frequency domain holography. Experimental results from one array antenna measured in a compact range are presented which illustrate the effectiveness of the new approach     

Dual frequency microstrip antenna

A single-feed dual-frequency microstrip antenna is reported. It can be impedance-matched independently at the two frequencies of operation. The tested antenna has a VSWR of 1.33 at 2.32 GHz and 1.12 at 9.425 GHz. The configuration reported here can be impedance matched over a wider frequency range using standard impedance-matching techniques.     

Block time and frequency domain modified covariance algorithms forspectral analysis

Block modified covariance algorithms are proposed for autoregressive parametric spectral estimation. First, the authors develop the block modified covariance algorithm (BMCA) which can be implemented either in the time or in the frequency domain-with the latter being more efficient in high-order cases. A block algorithm is also developed for the energy weighted combined forward and backward prediction. This algorithm is called energy weighted BMCA (EWBMCA) and its performance is analogous to that of the weighted covariance method proposed by Nikias and Scott (1983). Time-varying convergence factors, designed to minimize the error energy from one iteration to the next, are given for both algorithms. In addition, three updating schemes are presented, namely block-by-block, sample-by-sample, and sample-by-sample with time-scale separation. The performance of the proposed algorithms is examined with stationary and nonstationary narrowband and broadband processes, and also with sinusoids in noise. Lastly, the authors discuss the computational complexity of the proposed algorithms and give performance comparisons to existing modified covariance algorithms     

基于时域/频域OCDMA系统的一种新型二维变码重光正交码构造

构造了一种适用于光码分多址(OCDMA)系统的新型二维变码重光正交码(2D-VWOOC),用于满足不同用户及业务对服务质量(QoS)的不同要求,以两两正交拉丁方阵序列(MOLS)为波长跳频序列,以一维严格变码重光正交码(1D-SVWOOC)为扩时序列。分析了该码字在不同参数(码长、码重及波长数)下的码字性能;在相同条件下与其他二维变码重光正交码进行对比,该码字码容量较大,误码率相对其他码字低9～17个数量级。在Optisystem仿真中,当系统传输速率为16 Gbits/s时,码重为4比码重为2的用户误码率低2个数量级,能获得清晰端正的眼图。     

Skin effect losses of interconnect lines in frequency and time domain

The influence of the frequency-dependent resistive losses of interconnect lines on the propagation of very-high-speed digital pulses is investigated using different loss models. It is shown that, depending on the range of the frequency spectrum of digital pulses and/or the cross-sectional dimensions of an interconnect structure, the DC losses and losses caused by Wheeler's incremental inductance rule are to be extended by broadband skin effect losses, to obtain a better prediction of the pulse deformation.<>     

Sidelobe control of antenna patterns

Using the iterative sampling method, sidelobe peaks can be made to conform to a specified shape within a given tolerance. The iterative sampling method allows the specifications for a given problem to be just satisfied, thereby avoiding an overdesigned pattern which may have a complicated current distribution or wide main beam. The type of calculations involved are typically only summations of series of elementary functions and, consequently, the method is easy to apply to both large and small antennas. Several computer examples are presented, all of which have low ratios of maximum to minimum current amplitudes and low super directive ratios.     

频域差分和时域差分检测OFDM的误码率性能对比

在多径衰落信道条件下,分析了正交频分复用系统的频域差分检测和时域差分检测的误码率性能,得到了两种系统的误码率解析表达式,并进行了仿真验证.分析和仿真的结果表明:在保护时隙长度不小于最大多径时延长度的条件下,时域差分检测的误码率性能不受信道相干带宽变化的影响,时域差分检测的误码率性能主要受到信道相干时间变化的影响;频域差分检测的误码率性能同时受到信道相干时间和相干带宽变化的影响,并且相干带宽对频域差分检测的影响更大.     

A new dielectric grating antenna at millimeter wave frequency

The development of a dielectric grating antenna at K/sub a/ band is presented. The antenna performance is analyzed using perturbation analysis and a numerically based commercial software. The effect of the grating profile and various dimensions on the performance is presented. Based on the analytical results a rectangular profile grating antenna is designed. The antenna is optimized, fabricated and measured. Close agreement between the simulated and measured results is obtained.     

Adjustable frequency dielectric resonator antenna

An easy method of tuning the resonant frequency of cylindrical and ring dielectric resonator (DR) antennas using different diameters of conducting plates is presented. This technique can tune a DR antenna to operate at the design frequency without changing antenna performance. The maximum frequency tuning range can reach up to 300-500 MHz