Optimum scattering from an array of half-wave dipoles

Optimization of the field scattered by an antenna has important applications in radar systems and as elements in passive communication links. A method is presented of optimizing the scattering from a linear array of half-wavelength dipoles at a prescribed bistatic angle. The array is excited by a plane wave incident at an arbitrarily specified angle. The field scattered by the array is maximized or minimized as a function of the parameters of a network connected to the accessible antenna terminals. The result is a matrix eigenvalue equation of orderN = frac{1}{2}M(M + 1)for the optimum parameters of anM-element array. It is known thatN - 1solutions of this equation exist, which yield a prescribed zero in the bistatic scattering pattern but they do not correspond to physical networks. Using linear combinations of these, we construct a family of optimum admittance matrices that satisfy necessary and sufficient conditions that they be admittance matrices of passive networks. The form of the matrices is such that the corresponding passive regions in the bistatic plane are easily determined. The corresponding network can then be realized using existing network synthesis procedures. The essential features of the theory are illustrated by synthesizing an optimum network for a two-element array. It is also shown that backscatter at any angle can be minimized independently of the receiving pattern of the array.     

Relationships between positive realness of continuous transferfunctions and their digital counterparts

The importance of positive real transfer functions derives from the fact that they describe positive linear systems. Such systems possess the property that the time-integral of their input-output product, which is a measure of the total energy, is non-negative. This property is necessary and sufficient for guaranteeing the realisability of a transfer function as the driving point impedance or admittance of a linear passive network. The interest in carrying out formulations when the positive realness of a continuous transfer function is maintained even after discretisation through a sampler and zero-order hold device is confirmed. It is proven that positive realness may always be maintained after discretisation if all the poles of the continuous transfer function are strictly stable. This is necessary for the direct input-output transmission gain of the continuous transfer function to exceed a minimum positive threshold in order for the discrete positive realness to hold     

A simple proof of the Ahlswede - Csiszár one-bit theorem (Corresp.)

It is proved that if(X,Y)are two finite alphabet correlated sources withp(x,y)>0for all(x,y) in ({cal X} times {cal Y}), and if a functionF(X,Y)isalpha-sensitive, then the rateRof transmission fromXtoYnecessary to computeF(X,Y)reliably must be greater thanH(X|Y). The same result holds if the function is highly sensitive and for everyx_{1} neq x_{2} in {cal X}, then the number of elementsy in {cal Y}withp(x_{l},y) cdot p(x_{2}, y)>0is different from one.     

Are analog neural networks better than binary neural networks?

In this paper, we study the problem of maximizing an objective function over the discrete set {–1, 1} ⁿ using a neural network. It is now known that a binary (two-state) Hopfield network can take, in the worst case, an exponential number of time steps to find even a local maximum of the objective function. In this paper, we carry this argument further by studying theradius of attraction of the global maxima of the objective function. If a binary neural network is used, in general there is no guarantee that a global maximum has a nonzero radius of attraction. In other words, even if the optimization process is started off with the neural network in an initial state that isadjacent to the global maximum, the resulting trajectory of the network may not converge to the nearby maximum, but may instead go off to another maximum. At the same time, another set of recent results shows that, if ananalog neural network is used to optimize the same objective function, thenevery local maximum of the objective function has a nontrivial domain of attraction, and conversely, the only equilibria that are attractive are the local maxima of the objective function. This raises the question as to whether analog neural networks offer some advantages over binary neural networks for optimizing the same objective function. As a motivation for this line of inquiry, we study the problem of decoding an algebraic block code using a neural network. It is shown that the binary neural network implementation has the undesirable property thatall the global maxima of the objective function have azero radius of attraction. In contrast, if an analog neural network is used to maximize exactly the same objective function, the region of attraction of each maximum contains not only the associated orthant of the state space, but also some points not in this orthant. In other words, the analog implementation exhibits the desired tolerance to transmission errors, whereas the binary neural network does not have this property. With this motivation, two open questions are posed that provide a program of research for studying the possible superiority of analog neural networks over binary neural networks.     

The Measurement of the Equivalent Admittance of 3-Port Circulators Via an Automated Measurement System (Short Papers)

A derivation of the equivalent admittance of symmetrical 3-port circulators is given which is based on the requirement that the S-matrix eigenvalues be separated by 120/spl deg/ on the unit circle for perfect circulation. This quantity has the property that if a 2-port matching network is found which matches into this admittance, then the same matching network connected in each circulator arm will match the circulator. It was used in conjunction with a computerized measurement system to determine the optimal single-step transformer matching of a stripline 3.7-4.2-GHz circulator and resulted in a device with performance better than 30 dB over this band.     

On the anti-sidetone telephone circuit

The anti-sidetone telephone circuit is a frequency-independent passive reciprocal 3-port whose scattering matrix between three prescribed resistive terminations (transmitter, receiver, line) meets a certain specification. In their 1920 paper, Campbell and Foster (CF) showed that the prescribed 3-port can be realized as a lossless 4-port consisting in two 3-winding transformers closed on one resistance (the balancing network). If one (two) relations are imposed between the terminating resistances of the 4-port, realizations involving a single 3-winding (2-winding) transformer are available, and the resulting 136 (38) distinct realizations have been listed by CF. In this paper, we reestablish the CF-results (which were stated almost without proof in their paper and have never been rediscussed in the literature) and present a genetic classification of their 136 + 38 circuits. Recently, a realization of the anti-sidetone 3-port containing more than one internal resistance (in addition to the balancing network, a light-emitting diode serves to illuminate the dial) has been described by D. R. Means; in this paper, we present a complete characterization of that wider class of circuits.     

Mesh-star transformation

An equivalent star network exists for a given mesh network if the latter satisfies the Wheatstone relaflonship. Using this fact, it is shown that all the offdiagonal cofactors of the datum-node admittance matrix of such a mesh network are equal. From this property, a simple relationship between the elements of the two networks is derived.     

A passive network termination for BISDN optical subscriber lines

Considerable cost saving and overall simplification can be achieved if the protocol for the access digital section is made identical to the one at the T interface. The network termination (NT1) may then be realized as a passive device, such as a simple connector. All active functions associated with the NT1 can then be performed on a time-shared basis from the premises of the network provider. This scheme obviates the need for remote power feeding and activation mechanisms of the NT1. The time sharing of active functions, such as optical time domain reflectometry (OTDR) for supervision of the physical conditions of the lines, allows a substantial cost reduction of the subscriber access. It is shown that this technique yields a more efficient maintenance scheme than that afforded by an active NT1, resulting in a cost saving also in the long term. Ways of implementing the passive NT1 are discussed, and also its position in the evolution of passive optical networks (PON) towards BISDN.     

On the filtering problem for stationary random /spl Zopf//sup 2/-fields

It is shown that whenever a stationary random field (Z/sub n,m/)/sub n,m/spl isin/z/ is given by a Borel function f:/spl Ropf//sup z/ /spl times/ /spl Ropf//sup z/ /spl rarr/ /spl Ropf/ of two stationary processes (X/sub n/)/sub n/spl isin/z/ and (Y/sub m/)/sub m/spl isin/z/ i.e., then (Z/sub n, m/) = (f((X/sub n+k/)/sub k/spl epsi/z/, (Y/sub m + /spl lscr// )/sub /spl lscr/ /spl epsi/z/)) under a mild first coordinate univalence assumption on f, the process (X/sub n/)/sub n/spl isin/z/ is measurable with respect to (Z/sub n,m/)/sub n,m/spl epsi/z/ whenever the process (Y/sub m/)/sub m/spl isin/z/ is ergodic. The notion of universal filtering property of an ergodic stationary process is introduced, and then using ergodic theory methods it is shown that an ergodic stationary process has this property if and only if the centralizer of the dynamical system canonically associated with the process does not contain a nontrivial compact subgroup.     

An ideal integrator as a reciprocal two-port network using two time-varying passive elements

It is shown that a voltage gatio transfer function (1/s), representing an ideal integrator, can be exactly realized by a reciprocal netwogk consisting of two time-varying passive elements. A design parameter in this network can be arbitrarily chosen to make the time variation of these two elements as small as desired from practical considerations.     

邻居发现协议在基于FPGA的IPv6 over AOS网关上的实现

针对IPv6协议接入空间通信网络的需求,重点讨论了邻居发现协议(NDP)在基于现场可编程门阵列(FPGA)的IPv6 over CCSDS-AOS网关上的实现。在IPv6 over CCSDS-AOS网关系统上搭建NDP协议模块,实现网关地址解析;通过状态机控制实现NDP协议模块功能。实验表明,该设计解决了IPv6 over CCSDS-AOS网关主动和被动地址解析以及邻居缓存表查找和管理问题,不需要网关对NDP进行协议转换和转发。目前已在IPv6 over CCSDS-AOS网关中应用。     

Calculating transfer function and its first- and second-order sensitivities using one network analysis

The method calculates the transfer function and its sensitivities at a single frequency for both passive and active networks including constant delays. As the method requires only a single network analysis it is particularly useful for large networks. Although it uses nodal admittance representation it can be extended to other methods of network analysis.     

Selection of zeros of reflection coefficient in design of filters by insertion loss

It is shown that a characteristic function that can be expressed as the square of an odd rational function in ?, with poles on the j? axis and at infinity, is always realisable without using transformers by the selection of the zeros of p(s), and this is the key for a filter design based on 2-port synthesis theory.     

Symmetrical and Asymmetrical Edge-Coupled-Line Impedance Transformers with a Prescribed Insertion Loss Design

Distributed element synthesis is used for obtaining edge-coupled-line impedance transformers. A gain factor is introduced in a characteristic transfer function representing a line and stub network. A redundant form of this network is identified with the equivalent circuit of the edge-coupled line pair. The transfer function is then used to synthesize Butterworth and Chebyshev coupled-line transformers. Design tables are presented for the symmetrical transformer. Transformation ratios different from unity are obtained only if the symmetrical structure is reflective. Asymmetrical transformers may exhibit nonunitary transformation ratios while being perfectly matched. Finally, applicability range is discussed.     

High power and high sensitivity planar lightwave circuit moduleincorporating a novel passive alignment method

A high-power, high-sensitivity planar lightwave circuit (PLC) module, comprising a laser diode (LD) and a photodiode (PD) surface mounted on a PLC platform, has been realized by a novel passive alignment technique. We used a spot-size transformed LD and a corner-illuminated PD to form a highly efficient optical coupling between the devices and a PLC waveguide. We used the unique marker alignment method to ensure accurate positioning of them. The positioning precision achieved in the lateral direction was within 1 μm for the LD's and within 10 μm for the PD's. The rotational precision was within 0.4° for both chips. We realized high power operation (>8 mW) with a high receiver sensitivity (0.3 A/W). In this paper, we describe a high power, high sensitivity PLC incorporating a novel passive optical alignment technique for LD's and PD's     

Computer-Aided Large-Signal Measurement of IMPATT-Diode Electronic Admittance

A technique for the measurement of the Iarge-signal electronic admittance of IMPATT diodes as a function of frequency and RF voltage level using the network analyzer is described. The method de-embeds the admittance of the active region of the device from the mounting and measurement circuitry without physical disturbance of the diode. The small series resistance of the diode at breakdown is included in the embedding network together with the mount and diode package parameters. The determination of transformation networks between the measurement port and the active chip through a simple calibration procedure, a knowledge of the diode admittance below breakdown, and computer-aided optimization constitute the de-embedding procedure. Experimental electronic admittance curves are given for a low-power (100-mW) silicon IMPATT diode in the frequency range 5.7-6.5 GHz and with RF voltage levels applied across the active chip in the range 0-24 V, with an estimated error of less than 20 percent (typically 5 percent) in admittance values.     

Linear Phase Networks With Hyperbolic Tangent Function and Their Applications

This paper describes several methods to realize passive and active networks. with linear phase frequency response applicable to the video signal processing circuit especially for the FM transmission system. The methods are based on employing the hyperbolic tangent function realized by using passive LC ladder networks. They are also based on a time base conversion technique which provides the zero phase network. Using these methods, video signal processing circuits with linear phase property such as pre-emphasis and de-emphasis networks for the FM transmission TV system are introduced.     

A Method of Transformation from Symbolic Transfer Function to Active-RC Circuit by Admittance Matrix Expansion

Active-RC circuits containing 2-terminal linear passive elements and ideal transistors or operational amplifiers are derived from symbolic voltage or current transfer functions by admittance matrix transformations without any prior assumption concerning circuit architecture or topology. Since the method is a reversal of symbolic circuit analysis by Gaussian elimination applied to a circuit nodal admittance matrix, it can generate all circuits using the specified elements that possess a given symbolic transfer function. The method is useful for synthesis of low-order circuits, such as those used for cascade implementation, for deriving alternative circuits with the same transfer function as an existing circuit or for realizing unusual transfer functions, as may arise, for example, where a transfer function is required that contains specific tuning parameters     

A method of avoiding loss of accuracy in nodal analysis

Conventional steady-state nodal analysis may lead to inaccurate answers if some admittances in the network are very much greater than others. It is shown that this inaccuracy can be avoided by pivotal condensation of the indefinite (instead of the usual definite) admittance matrix.     

Comments, with reply, on `Passive equalization of semiconductordiode laser frequency modulation' by S.B. Alexander et al

Some flaws in a recent article by S.B. Alexander et al. (ibid., vol.7, no.1, p.11-23, Jan. 1989) on the theory of equalization of FM response of a laser diode using passive filters are noted. An error has occurred as a result of assuming a constant C as a positive instead of negative. When C is negative and large, the equalization network cannot be realized with passive networks. Also the simulated time waveform shown in the article for the optical frequency of an equalized laser does not show some spikes which are expected theoretically. The spikes occur as a result of an imperfect equalization provided by the proposed passive filters that were realized assuming C as positive. In replying the original author feels that the comments and observations result simply from attempting to extend the simple FM transfer-function model far beyond its limits while trying to introduce unnecessary theoretical rigor