Relationship between group delay and stored energy in microwavefilters

In this paper, an expression for the time average stored energy (t.a.s.e.) in a passive lossless two-port is derived in terms of its scattering parameters. In particular, it is shown that the t.a.s.e. in a passive lossless reciprocal symmetrical or antimetrical two-port is proportional to the group delay. One implication of this result is that the t.a.s.e., which is linked to the power-handling capability in many passive filters used in practice, is proportional to the group delay of the filter. This rigorous derivation is based on a variational theorem, which has been used in the past to prove energy storage results for passive lossless one-ports and periodic two-ports     

Comments on “Relationship between group delay and storedenergy in microwave filters”

For original paper, see ibid., vol.49, no.1, p.192-6 (2001). In the original paper, it is shown that the time-averaged stored energy in a passive lossless reciprocal symmetrical or antimetrical two-port is proportional to the group delay. The authors point out that some of their results were previously reported in a book by Penfield et al. (1970) and apologize for claiming credit for the work     

Analytical behavior of the noise resistance and the noiseconductance for a network with parallel and series feedback

An analysis is presented of the changes of the noise parameters of a two-port network when noisy series and parallel feedback immittances are applied. Exact formulas for the noise parameters R_n, g _n, and ρ_n are given as functions of the feedback for a given network. It is proved that R_n always reaches a minimum when a reactive series feedback is considered. The same results are demonstrated for g_n since a duality principle is pointed out. The results are valid for a wide range of linear microwave two-port networks, either passive or active, and they are used to confirm the data from previously published work     

Calculated microwave breakdown voltages in nitrogen,oxygen and air from DC data

The general microwave breakdown characteristic in nitrogen, oxygen and air is calculated from the DC dependence of the rimary ionization coefficient and the electron mean energy on the reduced electric field using basic equations reviously obtained by the authors. Specific breakdown characteristics are then obtained using the effective electric field concept and experimental mean electron collision frequencies; these calculated characteristics agree excellently with experimental values. This has application for microwave cavities operating at altitudes up to 100 km     

Intrinsic dielectric strength of dense pure hydrocarbons including polythene

Starting from the origin of ionisation by electrons colliding with gaseous hydrocarbons using the traditional Townsend approach, straight forward expressions are derived and illustrated graphically for the uniform field electric strength characteristic of dense methane and ethylene at their critical point, which exhibit the expected Paschen minimum though now at micrometer electrode spacings. Turning then to the more modern concept of molecule number density, further expressions for the intrinsic dielectric strength of all dense pure hydrocarbons, including polythene, are obtained which become independent of polymeric chain length for large molecules and these are also illustrated. Comparison between these two sets of characteristics show that whilst in gaseous/liquid methane and ethylene the electric field strengths are in the region of 100 MV/m. In dense/solid hydrocarbons like polythene these materials should be capable of withstanding fields of 1,000MV/m, which represent an upper limit. Some of the pitfalls preventing these high intrinsic dielectric field strengths from being reached, for instance the occurrence of high field electron emission from the cathode, are considered. With present day interest in short-fast-HV pulses, these high dielectric insulation strengths should become routinely achievable in modern electrical equipment.     

Design of waveguide E-plane filters with all-metal inserts by equalripple optimization

An optimization based approach to the design of E-plane filters is described. An optimization procedure based on Cohn's equal ripple optimization is developed. This vector procedure has several advantages over the general purpose optimization routines previously applied to the design of F-plane filters. The problem of local minima does not arise. Optimization is carried out with respect to the Chebyshev (or minimax) criteria. Less frequency sampling and therefore less calculation of the electrical parameters of E-plane discontinuities is required. The design of a symmetrical F-plane filter is considered. Higher order mode interaction between E-plane discontinuities is not included in the design. For the design example considered this is shown not to be significant. A numerically efficient method, requiring only real scalar arithmetic, for calculating the insertion loss of a symmetrical cascade of lossless symmetrical 2-ports is employed. Measurements on a fabricated filter confirm the accuracy of the design procedure     

Classical interpretation of single electron emission rates (SEERS) at the origin, from oxide covered cathodes in compressed gas and vacuo insulation

In order to quantitatively interpret the previous experimental single electron emission rates (SEERS) obtained by Guile et al (1997), the Richardson/DushmanSchottky (1914) expression is extended by invoking the concept of multiple images of the emitted electron in the naturally occurring or grown oxide layer covering the metal cathode, first proposed by Silvester (1968) in another application. This leads to a new expression for the Schottky barrier lowering term being obtained, involving a converging infinite series of terms, solvable on a computer, and enables the SEERS to be computed for cathodes covered with varying thicknesses of oxide. Numerical agreement between applied theory and experiment is excellent and requires the postulated presence of electron multiplication-avalanching-in the oxide layer. This method can be further applied to the presence of liquid and/or solid dielectric insulation between oxide covered metal electrodes and can take into account the presence of the anode for small electrode spacings.     

Optimum noise-source reflection-coefficient design with feedbackamplifiers

The issue of designing a low-noise microwave feedback amplifier for a given optimum noise-source coefficient Γ_Sopt is addressed and a set of original formulas is presented. These expressions define a new procedure which does not rely on computer optimization in order to get the required noise performance of the low-noise amplifier stage. The technique permits the design of a circuit which is simultaneously noise and power matched at its input port without an input matching circuit. This method can be used to screen devices for an optimum noise performance and it provides the essential mathematical tool for designing the core of a feedback amplifier     

Design and characterization of a microwave feed-forward amplifier with improved wide-band distortion cancellation

A new approach to the design of a wide-band feed-forward amplifier (FFAMP) is presented in this paper. Phase equalizers are employed in an FFAMP to match the nonlinear delay/phase characteristics of the main and error amplifiers, improving phase balances within the cancellation loops and providing improvement in signal cancellations over a wide bandwidth. The proposed 1.7-1.9-GHz FFAMP was fabricated and characterized. The conventional FFAMP obtains an average of 15-dB third-order intermodulation (IM3) distortion cancellation over the whole bandwidth. With the phase equalizers, the proposed FFAMP achieves a further 6-dB reduction on IM3 level.     

Classical Interpretation of Conduction Currents in Crosslinked Polyethylene (XLPE) and a Comparison with Ideal Polyethylene

Recent experimental conduction current data are numerically analyzed in terms of the established Richardson/Dushman-Schottky (1914) expression for electron emission rates, from a metal cathode, multiplied by the traditional Townsend (1915) derived electron avalanche sizes due to electron-molecule collision ionization in the bulk insulating dielectric for electric fields up to in excess of 1000 MV/m. Agreement between applied theory and experiment limited to 70 MV/m is excellent. Deduced Townsend primary ionization coefficients in ideal, low and high density polyethylene, in solid, liquid and gaseous ethylenes, air, solid Al₂O₃ and Nb₂O₅ are shown diagrammatically. From these it is postulated by calculation that 1.5 - 6% of the interelectrode gap distance in practical XLPE is occupied by air filled space rather than by total ideal polyethylene and that this free space is responsible for considerable ionization in the region of 30 MV/m which prevents 1000 MV/m to be attained. Such high dielectric strength should be achievable if in addition a low electron field emitter cathode such as ultra-pure aluminum is used. It is concluded from this and previous work that bonds between atoms/molecules in polymers are as important as the individual discrete particles by themselves in determining dielectric properties.