Fundamental Limits for Radio Signals with Large Bandwidth

Radio services have traditionally used narrow frequency bands individually assigned. More recently, the concept of sharing very wide frequency bands by several users has been advanced, and this opens the door for the use of much larger bandwidths than in the past. This paper investigates the limits imposed by nature on the bandwidth of line-of-sight radio services operating in the earth's atmosphere. Furthermore, it investigates the limits for time resolution of radio signals, as well as the related limit of the angular resolution of a line array of sensors that receive signals with large bandwidth, and compares it with the classical resolution angle that holds for sinusoidal signals with vanishing bandwidth. Finally, an example is given where the concept of a practically finite bandwidth of a signal reaches its limit, and a more rigorous specification of the signal is required.     

Measurement Bandwidth Extension Using Multisine Signals: Propagation of Error

We describe a post-processing technique that extends the effective measurement bandwidth of narrowband vector receivers by phase aligning overlapping measurements. We study the repeatability of the method and the propagation of errors as increasing numbers of bands are stitched together. The method can be used to find phase errors both in the excitation band of frequencies, as well as in distortion products, for periodic multisine signals.      

Radio Signals with Large Relative Bandwidth for Over-the-Horizon Radar and Spread-Spectrum Communications

It is known that radio signals must have a small relative frequency bandwidth if structures and circuits resonating with sinusoidal functions are to be used for radiation and reception. This paper develops concepts showing that a small relative frequency bandwidth is also required for the use of amplitude or frequency modulation of sinusoidal radio carriers in the usual form. However, it is easy to modify the usual methods of amplitude and frequency modulation for signals with large relative frequency bandwidth. The primary application of such methods is for over-the-horizon radar and spread-spectrum communications in the short-wave region where the desired relative frequency bandwidths are neither small (in the order of 0.01 or less) nor close to 1.     

Multitrack Recording of Reduced Bandwidth TV Signals

The system described here was developed in order to record the pseudorandom scan television signal developed by Deutsch. The objective was to investigate the possibility of recording a 200 kHz video signal on a 1/4 in tape running at 15 in/s. The difficulties which arise in such a task are two-fold: 1) bandwidth limitations of the recorder; and 2) flutter and skew of the recorder. Since a tape recorder at this speed has a bandwidth of about 45 kHz, time-division multiplexing was used to reduce the signal into low-frequency signals. The problem is to reassemble the signals at playback. This is a difficult task since these signals are shifted in time randomly by flutter and skew. Experiments disclose that the skew is linearly distributed across the tape; therefore, by knowing this time shift between two tracks at any instant, the position of the appropriate sample at any other track can be predicted. For skew and flutter compensation purposes two reference signals are recorded on the two outer tracks of the tape. The phaseshift of the reference signals at playback is used as a measure for the skew prediction system for each track. Thus the video signals are sampled at the correct value. In order to reassemble the samples in the correct time sequence, they are stored in analog memory cells. The memory cells are read out with the aid of an oscillator which is in turn synchronized with flutter. The deflection waveforms are also generated synchronous with this oscillator.     

Ranging With Ultrawide Bandwidth Signals in Multipath Environments

Over the coming decades, high-definition situationally-aware networks have the potential to create revolutionary applications in the social, scientific, commercial, and military sectors. Ultrawide bandwidth (UWB) technology is a viable candidate for enabling accurate localization capabilities through time-of-arrival (TOA)-based ranging techniques. These techniques exploit the fine delay resolution property of UWB signals by estimating the TOA of the first signal path. Exploiting the full capabilities of UWB TOA estimation can be challenging, especially when operating in harsh propagation environments, since the direct path may not exist or it may not be the strongest. In this paper, we first give an overview of ranging techniques together with the primary sources of TOA error (including propagation effects, clock drift, and interference). We then describe fundamental TOA bounds (such as the CramÉr–Rao bound and the tighter Ziv–Zakai bound) in both ideal and multipath environments. These bounds serve as useful benchmarks in assessing the performance of TOA estimation techniques. We also explore practical low-complexity TOA estimation techniques and analyze their performance in the presence of multipath and interference using IEEE 802.15.4a channel models as well as experimental data measured in indoor residential environments.      

Comparing Bandwidth Requirements for Binary Baseband Signals

The percentage of total power passed through ideal bandlimited channels with bandwidths equal to various multiples of the bit rate is examined for 14 unique binary baseband signaling schemes. The channel bandwidth required to pass 5 percent of the total power is determined as a measure of the need for near-dc channel response. Conclusions are reached as to which signals would be most suitable for high-rate magnetic tape recording.     

Propagation Velocity of Electromagnetic Signals

The propagation velocity of electromagnetic signals has been a vexing problem for about a century. The often-mentioned group velocity fails on two accounts, one being that it is generally larger than the velocity of light for waves in the atmosphere; the other that its derivation implies a transmission rate of information equal to zero. The reason why this problem has resisted a solution for so long is that Maxwell's equations fail for signals propagating in a lossy medium. The propagation velocity is of interest only in a lossy medium, since its value in a loss-free medium has been known since d'Alembert's solution of the wave equation. For infinite signal-to-noise ratios and ideal receivers, the propagation velocity of signals in media with ohmic losses equals the velocity of light; it decreases with decreasing signal-to-noise ratio and eventually approaches zero.     

光子学技术生成微波信号

文章对现有通过光子学技术生成微波信号的方法作了简要的综述,并介绍了我们提出的一种利用激光拍频产生可调谐微波信号的新方法.这种方法基于光纤光栅法珀滤波器与光纤环形腔激光器技术,产生波长间隔可调谐的双波长单纵模激光,使用高速光电探测器对双波长激光进行拍频,生成频率可调的微波信号.实验上获得了频率为9.4885～10.0712GHz的微波信号.文中所提出的方法在无线接入网,无线传感网,射频信号光纤传输,软件无线电等方面有应用前景.     

Improved Large Signal Analysis of the Dual-Wavelength Linearization Technique of Optically Phase-Modulated Analog Microwave Signals

This paper presents simple closed-form expressions, in terms of the ordinary Bessel functions, for the amplitudes of the third- and fifth-order intermodulation products of the dual-wavelength linearized phase modulated link for any scenario of the microwave driving voltage. The results obtained for a microwave driving voltage comprising equal-amplitude two- and three-tones show that the third-order intermodulation can be minimized for values of phase modulation depth less than 0.2 over a relatively wide range of the ratio between the powers in the TM and TE waves of the link. Using these results it is possible to adjust the phase modulation depth and/or the ratio between the powers of the TM and TE waves to achieve a dual-wavelength linearized phase modulated link with a predetermined intermodulation performance.     

Interaction of Signals in Ferromagnetic Microwave Limiters

A weak secondary signal is partially absorbed in a ferromagnetic microwave limiter that is saturated by a strong primary signal; the absorption is greatest when the two signals are close in frequency. The width of this absorption is determined here, and is found to be proportional to the spin wave linewidth and to the square root of the excess power in the primary signal. The theory of this effect is presented and is found to agree well with experiment.     

Compact Frequency and Bandwidth Reconfigurable Microwave Filter

This paper details the construction and working of a compound reconfigurable filter capable of frequency and bandwidth reconfiguration in the frequency range from 2 to 3 GHz. The switching between frequency and bandwidth reconfiguration is inherited by two PIN diodes. Bandwidth tuning is facilitated by tuning two transmission zeros individually using varactor diodes, giving flexibility in reconfiguring the upper and lower pass edges. The two transmission zeros are obtained using simple concentric square loop resonators. The maximum bandwidth obtained is 1.5 times the minimum bandwidth offered by the filter. Hence the filter can be used for dynamic bandwidth allocation. This prototype is fabricated and validated in real-time. The simulated and measured results are analogous to each other.

     

Bandwidth Reduction of Video Signals via Shift Vector Transmission

An experimental shifting technique applied to real television images in order to reduce their redundancy is described. The technique consists of dividing the images into zones and then transmitting vectors that connect correlated zones in successive frames. A threshold which is a function of frame-to-frame zone velocity and inherent points luminance is introduced to determine the shift vector. Image reconstructions are obtained with an information rate equal to 0.7 bit/pel.     

罗兰-C脉冲水下传播特性高精度预测理论算法研究

对罗兰-C脉冲水下传播特性预测模型算法进行推导研究,综合考虑了信号先沿陆海表面、再由空气入水传播时的路径损耗、相位延迟、色散效应及空气海水界面两侧场量的约束条件.分析了0~10m不同海水深度罗兰-C电场幅度与相位的变化,并与无畸变的标准场信号进行比较.结果显示:随着入水深度增加,色散效应导致脉冲前沿展宽,跟踪点相位超前.该结果去除了由参比场量近似引入的误差,精度更高.     

窄带线性相位微波滤波器的设计

给出了利用ADS线性仿真器和EM全波仿真器(HFSS)设计线性相位滤波器的方法．利用该方法设计了6级线性相位滤波器。实验结果和理论结果具有较好的一致性,证明了这种设计的有效性。     

有损介质中脉冲信号的传播

本文讨论了有损介质中麦克斯韦方程组的暂态解。并采用高斯积分法给出了计算结果，最后分析了单位阶跃函数，单个脉冲函数，Ｎ个脉冲函数在有损介质中传播时电场强度的波形变化。     

Microwave Propagation in Saline Dust Storms

Dielectric constant of sand-powder sampled from saline dust area have been measured at W band by means of wave-guide method. Based on the analysis of the characteristics of saline dust storms, the microwave and millimeter wave attenuation and phase shift in saline dust storms are investigated.     

On Stored Energy and Bandwidth in TEM-Mode Microwave Networks

From time domain considerations, a method is presented to calculate the energy stored in certain resonant TEM-mode microwave networks. The time average of the stored energy is then used to define an instantaneous signal bandwidth parameter through the definition of a Q or quality factor. It is demonstrated by experiment that the Q factor is inversely proportional to the rise time of the envelope of the step-modulated response of the network at resonance.     

Optoelectronic Pulse Compression of Microwave Signals

Optically switched transmission line resonators are shown to generate short microwave pulses of higher output peak power than the CW input signal. This kind of pulse compression is achieved by using the resonator as a storage element and an optoelectronic switch as the output mirror. A theoretical analysis of the efficiency of this device is presented. Experimentally, a peak power enhancement of 14 has been observed at a frequency of 1 GHz. A comparison with numerical results is finally carried out.     

On Optimal Detection of Band-Limited PAM Signals with Excess Bandwidth

PAM data transmission receivers accomplishing maximum likelihood sequence detection (MLSD) usually require a matched filter prefilter, a sampler at the symbol rate, and a Viterbi algorithm detector. When the channel is unknown or slowly changing, one must use an adaptive matched filter prefilter. We examine an alternative optimum receiver whose optimality is independent of the matched filter prefilter and which is applicable when the channel is effectively band-limited. The sampler in the proposed receiver operates at a rate faster than the data symbol rate, enabling one to replace the matched filter by a fixed low-pass filter and still ensure that the maximum likelihood detector is supplied with a set of sufficient statistics. It is shown that the matched filter is incorporated within a modified Viterbi detector without increasing the number of states in the algorithm, although the Viterbi detector must perform computations at approximately twice the usual rate. Simulations support the optimality of the new receiver and quantitatively indicate the degradation in performance experienced by some adaptive receivers previously proposed.