Passband Transmission Research Articles

Performance evaluation study of signal design and equalization options for high-bit-rate digital subscriber line transceivers

This paper analyses different equalization, coding and signal constellation alternatives for the proposed high-bit-rate (800 kb/s) digital subscriber loop transmission interface. The simulation results presented in the paper demonstrate that bit rates above 1000 kb/s at acceptably low bit-error rates (≤ 10−7) are feasible, if baseband transceivers with appropriate equalization and simple trellis coding are used. It is also shown that baseband transmission and Tomlinson precoding provide a significant performance advantage over bandpass transmission and decision-feedback equalization, respectively.

Periodic Structure Studies

It has previously been noted by numerous writers that the propagation characteristics of a uniform waveguide are profoundly modified by means of periodically spaced obstacles. Basically, periodic loading causes the hyperbolic dispersion diagram of the empty waveguide to be broken up into transmission passbands such that the phase and group velocities are no longer simply related. With the increase in applications of electromagnetic theory the former technique of solving every boundary value problem anew each occasion was abandoned as repetitious. While physical fields are three dimensional, in transmission lines the two transverse components may be integrated out, and thereby concealed, leaving a one dimensional wave equation of general engineering use.

Specular reflectance of optical-black coatings in the far infrared

Far-infrared specular reflectance spectra of seven optically black coatings near normal incidence are presented. Seven photometric spectra were obtained using eleven bandpass transmission filters in the wavelength range between 12 and 500 μm, and three interferometric spectra were obtained for corroboration. Data on the construction, thickness, and rms surface roughness of the coatings are also presented. The chemical composition of three coatings can be distinguished from that of the others by a strong absorption feature between 20 and 40 μm, which can be largely attributed to amorphous silicate material. At 100 μm, the most and least reflective coatings differ by nearly 3 orders of magnitude. Inverse relationships observed between the spectra and the roughness and thickness of the coatings led to development of a reflecting-layer model for the measured reflectance. The model successfully describes the spectra at wavelengths outside the silicate absorption, and optical constants are deduced from a nonlinear least squares fit to the data. Parametric errors are estimated by chi-square analysis, and sensitivity tests are performed to determine which parameters control reflectance in different spectral regions.

Practical two-wavelength multi–demultiplexer: design and performance

A two-wavelength multi–demultiplexer for practical use is discussed. An internal-filter microoptic-type multi– multi–demultiplexers have been experimentally fabricated based on the specified branching characteristics, i.e., wide pass-bandwidth, low passband transmission loss, and high cross-talk attenuation. All demultiplexer is attractive for practical use due to its compactness and coaxial structure. Sixteen multi–demultiplexers satisfy the specified branching characteristics in initial performance, and stability tests confirm that this type of multi–demultiplexer has stable performance.

Synthesis and Realization of Narrow-Band Canonical Microwave Bandpass Filters Exhibiting Linear Phase and Transmission Zeros

The present study is concerned with the synthesis and realization of narrow-band canonical microwave bandpass filters exhibiting additional couplings between nonsuccessive resonant circuits. These bypass couplings effect, on the one hand, attenuation poles at finite frequencies and, on the other hand, make the bandpass filter nonminimum-phase, and therefore offer degrees of freedom for group delay equalization in the passband. The realization of canonical network structures with bypass couplings is possible by extracting from the chain matrix an ideal transformer, the input of which is connected, for example, in shunt with and its output in series with the remainder two-port. The extraction is associated with the reduction by 2 of the degree of the denominator polynomial of the chain matrix elements. To realize a clear correlation between the bypass elements and the electrical performance, canonical structures with sections that are bypassed only once or twice are proposed. Theoretical and measured curves of the examples of realization for 1235 MHz, consisting of coaxial cavities, and for 4000 MHz, consisting of dual-mode cavities, are seen to be in close agreement.

Single mesh narrow bandpass filters from the infrared to the submillimeter region

Narrow bandpass filters from i.r. to Submillimeter have been investigated utilizing the bandpass transmission characteristic of an electroformed metal mesh around the wavelength near the grid constant ( ɡ). The bandwidth was narrowed by controlling the strip breadth of the mesh. It was found experimentally that the mesh having the strip breadth equal to half the grid constant was best. Filters with 25 mesh ( ɡ = 1016 μ), 50 mesh ( ɡ = 508 μ), 100 mesh ( ɡ = 254 μ), 250 mesh ( ɡ = 101.6 μ). 500 mesh ( ɡ = 50.8 μ), 1000 mesh ( ɡ = 25.4 μ) and 1500 mesh ( ɡ = 16.9 μ) have been measured, keeping each strip breadth at the best condition, and narrow bandpass filters from i.r. to submillimeter have been constructed. Most of these filters have maximum transmittance around 70% and Q-value of about 4. These filters have some advantages over Reststrahlen filters and are useful for many spectroscopic studies.

Multi-element mesh interference filters for the infrared

This paper discusses the development of infrared filters of both lowpass and bandpass types for the wavelength region λ>40 μm. The design techniques of multilayer filters have been extended to mesh filters. Bandpass filters at wavelengths near 50 and 100 μm with bandwidths between 5% and 10% and up to 90% transmission have been made using either double-halfwave or Fabry-Perot systems. Lowpass filters of high performance, passband transmission 70% and rejection greater than 103 are shown with edges near 100 μm. Narrowband filters for the HCN laser line at 30 cm−1 are also shown.

Simple RC active filters using controlled sources

The letter outlines a method of synthetising RC active filters by a cascade of simple second-order stages isolated by voltage-or current-controlled current sources of low gain. Second-order stages are described having bandpass, lowpass and highpass responses and transmission zeros at finite frequencies. All the active circuits are based on simple parallel or series LC resonant circuits.

Correlative Data Transmission with Coherent Recovery Using Absolute Reference

A new data-transmission method that has twice the speed capability of the duobinary technique over an identical bandpass transmission medium is presented. Advantages of this method include promising performance and completely digital manner of signal generation, thus considerably reducing the circuit complexity. The system is based on correlative techniques in which the digital encoding forms an integral part of the carrier modulation. The process is sufficiently general to be applicable to both voice anti broadband communication channels.

Far Infrared Bandpass Filters and Measurements on a Reciprocal Grid

Transmittance and reflectance measurements on wirecloth and electroformed metallic meshes are presented in the region 0.01 <or= lambda/d <or= 5. The results were obtained under equal geometric optical conditions with a vacuum grating spectrometer. The measurements are used for the construction of a transmission bandpass filter in the wavenumber region nu > 18 cm(-1). In order to be able to construct a bandpass filter in the entire far ir, a reciprocal grid is investigated and found to be suitable as a transmission low pass filter characterized only by geometrical parameters.

Direct Synthesis of Band-Pass Transmission Line Structures

Realizable band-pass (zero of transmission, i.e., infinite loss, at dc) equiripple gain functions are constructed which permit exact physical realization of systems consisting of cascaded lines and stubs. The problem of the realization of a prescribed load resistance is solved when a dc zero of transmission is present due to a shunt short-circuiting stub. The exact limits of realizable load resistance are given for equiripple band-pass gain functions and a straight-forward method is presented to synthesize any desired value of load between the predetermined limits. The basis of the synthesis technique is the choice of location of the shunt stub in the cascaded chain.

Matching into Band-Pass Transmission Structures

This paper describes a method for broad banding the matching transition from a low-dispersion transmission line to a high-dispersion iterated filter structure. A good match can be obtained over essentially the entire pass band of the filter structure. To accomplish this the band at the end of the structure is widened beyond both nominal cutoff frequencies. It is narrowed down to the regular structure bandwidth in a taper extending over a few filter elements. In the comb structure used for traveling wave masers, a return loss of 20 db (VSWR = 1.2) or better is realized over 90 per cent of the pass band with a taper including four comb fingers. Several examples of suitable taper designs are given. Each of these, however, requires empirical adjustment in order to produce an optimum match.

Band-pass filters with linear phase

A set of techniques has been developed which permits the simultaneous realization of flat pass band transmission (±0.15 db experimental) linear phase (to within ±5° experimental) over most (1 - 1/N) of the nominal pass band, where N is the number of in-band poles. Outside the pass band, the attenuation skirts are steep; experimentally, 40 db has been obtained within 1/N of the nominal filter bandwidth. Shunt L and/or stray capacitance are easily taken into account in the design; in particular, crystals as well as lumped LC have been used. The procedures can accommodate any amount of series resistance in inductors at the expense of flat loss, without any essential change in the computed values of inductors, capacitors, or resonant frequencies. The sensitivity of the network transmission to component errors is modest; discrepancies in the impedance level or tuning of a given constituent resonance in the network branches affect the characteristic mainly in the vicinity of that resonance.

Identification of Certain Networks with Reflection Coefficient Zero Locations

In this paper, the coefficients of return loss expansions are found for certain low-pass, LC ladder networks which have n lossless elements and which exhibit Tchebycheff (or equal ripple) pass band and monotonic stop band transmission behaviors. The return loss expansion is the Taylor expansion of In ( 1/\rho_{1}(s) ) about s equal to infinity, the variable s being the familiar complex frequency variable s = \sigma + j{\omega} , and \rho_1 being the reflection coefficient between a resistive termination and the remainder of the network. The return loss coefficients are tabulated according to reflection zero locations for odd and even n . Methods for synthesizing low-pass, LC ladder networks from return loss coefficients are available. A presentation of the modifications necessary to adapt these methods for use with the particular coefficients discussed above is given. Thus, it is possible to synthesize certain Tchebycheff networks through use of return loss coefficients which are, in turn, directly identified with reflection zero locations. The paper concludes with a brief discussion of the extension of existing tables of Tchebycheff network element values for finding the element values for several reflection zero distributions and LC ladder arrangements.

The Design of Two-Section Symmetrical Zobel Filters for Tchebycheff Insertion Loss

It is shown that the complete Tchebycheff insertion-loss function giving equal valley heights in the stop band and equal ripple heights in the pass band can be realized with two Zobel m-derived sections by suitable choice of the m values and the terminating resistance. The limitation in comparison with more general synthesis techniques is that for each width of the cutoff region only one Tchebycheff-Zobel filter is possible, having a fixed value of passband ripple. The ripple levels obtained, however, are in the range of interest and the filters are of practical value. Data are given in chart and tabular form so that the design procedure is very simple. The results show that prototype sections do not appear in the optimum designs, and that terminating half sections need not be used to obtain flat pass-band transmission.

Low-Q Microwave Filters

Waveguide bandpass transmission filters, each stage of which is composed of two similar irises spaced a distance s apart, are considered. The distance between stages for effectively quarter-wave coupling is shown to be s±1/4λ g/ g. The loaded Q of one stage is computed, and the frequency consciousness of the iris susceptance is shown to have no effect on the spacing condition, but to have a substantial effect upon the loaded Q, especially for low values of Q.

A Frustrated Total Reflection Filter for the Infra-Red

The Frustrated Total Reflection filter is a transmission band pass filter. It can be constructed for any part of the spectrum for which there exist transparent materials of different indices of refraction. Measurements are shown of a filter which was designed for the rocksalt infra-red region. This filter has two oppositely polarized pass bands which, at a particular angle of incidence, are at 412 and 5 microns, respectively. Both the pass bands are approximately 110 of a micron wide. They can be shifted over a range of approximately half a micron by tilting the filter.