Evanescent Waveguide Research Articles

Field analysis of rectangular waveguide open junction

The problem of a rectangular waveguide open junction is investigated using field theory and the relevant model of two normally intersected, infinite parallel-planes waveguides. Evanescent waveguide modes generated by waveguide wall edges and/or the discontinuity in dielectric are taken into account; an infinite set of equations is derived, where the mode coupling is given by the dielectric slab modes. Proper pole handling is discussed, and a solution for the system is given. Expressions are derived for the reflected, transmitted, and radiated power, which are shown to be sufficiently reliable in the domain of practical interest, regarding the width and the dielectric loading of the gap. The analysis shows that a substantial fraction of the microwave power leaks from the dielectric gap, confirming the absolute necessity of using a choke-flange at the waveguide junction.

Transitional combline/evanescent-mode microwave filters

Traditional combline-filter theory based on TEM-mode coupling results in bandwidths which are too large-the increase being a function of the ground-plane spacing to wavelength ratio b//spl lambda/. As the b//spl lambda/ ratio increases from 0.05 to 0.35, the bandwidth ratio (BWR), defined as actual bandwidth/TEM bandwidth, increases from unity to over 2:1. This bandwidth increase has now been confirmed by calculation of the coupling coefficient between combline resonators using mode matching. Accompanying the increased bandwidth is a considerable increase in the unloaded Q in accordance with the higher Q of the evanescent waveguide modes. A similar study carried out in the case of interdigital filters shows that these effects are much less significant.

Deposition Conditions for Large Area PECVD of Amorphous Silicon

ABSTRACTThe production of amorphous silicon devices usually requires large area, high-deposition-rate plasma reactors. Non-uniformity of the film thickness at high power and deposition rate is found to be an important factor for large area deposition.Increasing the radio frequency from the conventional 13.56 MHz up to VHF has demonstrated advantages for the deposition of a-Si:H films, including higher deposition rates and lower particle generation. The use of VHF for large area deposition leads to the generation of standing waves and evanescent waveguide modes at the electrode surface and on the power feeding lines. Thereby increasing the non-uniformity of the film thickness. The uniformity of the film thickness for an excitation frequency strongly depends on the deposition parameters e.g. pressure, input power, silane flow and the value of load impedances. With increasing exciting frequencies the range of deposition parameters for obtaining uniform films narrows.Subsequently it is shown that for a large-area plasma-box reactor (500 × 600 mm2 plate size) with a double-sided RF electrode, the non-uniformity of the film decreases due to a homoge-neization of the electrode voltage distribution by using multiple power supplies and load impedances on the end of the RF electrode. The uniformity errors decrease from ±20% to ±2.4% (27.12MHz) and from ±40% to ±5.9% (54.24MHz). Experimental results of the film uniformity will be discussed in dependence on excitation frequencies and the deposition parameters.

Comparison of experimental microwave tunneling data with calculations based on Maxwell's equations

We compare microwave tunneling experiments using three types of potentials with calculations describing these systems, using only Maxwell's equations. The values obtained are identical within a very narrow error limit. Thus, microwave tunneling through evanescent waveguide regions, including superluminal tunneling velocities, is described by Maxwell's equations. The dispersion relation yields purely imaginary, complex, or real k-values. As an analogy, microwave tunneling presents an ideal tool for studying quantum mechanical tunneling.

Microwave active filter in integrated waveguide technology

A new configuration for the microwave active filter based on integrated waveguide technology is described. A filtering structure is formed by an evanescent mode rectangular waveguide loaded with dielectric slabs. A Gunn diode is used to compensate for dissipative losses. The transmission matrix model has been used to determine a configuration of the microwave active filter and complex admittance of the active element providing full compensation of insertion loss. The measured results have confirmed theoretical predictions.

Sensitivity optimization of a grating coupled evanescent wave immunosensor

The sensitivity of a grating coupled evanescent wave step index slab waveguide sensor for ultra-thin films is given by a single normalized expression.

Measurements of the impressed electric field inside a coaxial electron cyclotron resonance plasma source

The magnitude and spatial variation of the impressed electric-field patterns inside a compact electron cyclotron resonance ion/plasma source are experimentally measured for argon and nitrogen feed gases. This ECR plasma source consists of several components: a resonant coaxial coupling section, an evanescent circular waveguide section, coupling loop, and the ECR discharge load itself. The electric fields inside the coaxial and circular waveguide sections are measured as the operating pressure and input power and are varied from 0.2 to 2.0 mTorr and 100 to 170 W, respectively. The measured fields verify that a standing wave with a maximum of 20–40 kV/m exists inside the coaxial section of length l. For matched conditions the length of this section varies only slightly between 0.6 and 0.7λ as pressure, power, and gas type vary. However, the evanescent impedance-matching circular waveguide section of length d changes from 2.5 for argon to 3.2 cm for nitrogen, indicating that the gas type influences the plasma impedance. Field pattern measurements in the ECR section of the source demonstrate the presence of nonevanescent fields in the discharge region. Measured plasma loaded and unloaded quality factors varied from 220 to 1800, respectively, indicating that 87% of the net input power is coupled into the discharge load. Additional calculations of conductive wall losses show that about 6% of the input power is lost in the cavity walls, and the remaining 7% is lost in the coupling loop.

Dual-mode dielectric or air-filled rectangular waveguide filters

An accurate design technique of dual-mode microwave dielectric or air-filled rectangular waveguide filters is described. Dual-mode coupling is realized by a section of rectangular waveguide with square-corner-cut. The unequal couplings between dual-mode pairs of the cavities is provided by a section of evanescent mode waveguide. Rigorous analyses are applied to characterize the microwave junctions and to obtain the design parameters for the filter. The design procedure used to determine the dimensions of the waveguide junctions with a minimum of computational effort is described. The design is demonstrated by four-pole and six-pole dual-mode rectangular waveguide elliptic function filters. Excellent agreement between computer simulation and experimental results with absolutely no tuning justifies the design.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A new aperture admittance model for open-ended waveguides

A new model for the aperture admittance of open-ended waveguide structures radiating into a homogeneous, lossy dielectric is presented. The model is based on the physical and mathematical properties of the driving point admittance of passive, stable one-port networks. The model parameters, which depend upon the geometry of the waveguide and aperture, are determined from a relatively small number of computed admittances. This computed data is obtained by a full-wave moment method solution and, hence, includes the effects of radiation and energy storage in the near field and the evanescent waveguide modes. The accuracy of the numerical method is demonstrated by comparison with measured values. As an example, the model parameters are determined for the coaxial-line geometry. The accuracy of the model, for both the direct and inverse problem, is verified and a rigorous sensitivity and uncertainty analysis is performed. The new model has important applications in the field of dielectric spectroscopy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Evanescent-mode propagation and quantum tunneling.

The tunneling of particles is in direct analogy with the transmission of evanescent electromagnetic waveguide modes as has been shown quite recently. We compare experimental data of an electromagnetic wave packet traversing an evanescent waveguide region with theoretical values derived for particle tunneling through a rectangular potential barrier. The transmission time was deduced by transformation of the experimental frequency data to the time domain. The data are in agreement and reveal superluminal wave-packet velocities for opaque evanescent regions.

Dual mode coupling by square corner cut in resonators and filters

A method for realization of dual-mode coupling in rectangular waveguide cavities is described and analyzed. The method completely replaces the coupling screw, and therefore can be used to eliminate the need for tuning in dual-mode waveguide cavity filters. It also offers a wide range of coupling values and can achieve higher power-handling capability than coupling screws. Mode matching is used to calculate the mode chart of the infinitely long square corner cut rectangular waveguide (SCCRW), the field distributions of each mode, and the resonant frequencies of the cavity. An evanescent mode rectangular waveguide is used to provide dual-mode couplings between adjacent cavities. The junction discontinuity between the SCCRW and the rectangular waveguide is modeled by a double mode-matching method, yielding modal scattering parameters of the junction. A four-pole dual-mode elliptic-function rectangular waveguide cavity filter using the coupling method was constructed. The experimental filter results showed excellent agreement with theory.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Resonant tunneling in a quasi-one-dimensional wire: Influence of evanescent modes.

We calculate the transmission coefficients through two point scatterers in a quasi-one-dimensional wire as the Fermi energy and distance between scatterers are varied. At a subband minimum the standard wave-interference pattern between propagating modes, characteristic of a Fabry-Perot interferometer, is completely suppressed. Instead, we find that the shape of the lowest evanescent waveguide mode determines the electron transmission so that a different pattern of conductance oscillations emerges. If either of the scatterers is attractive, the transmission is suppressed abruptly near the ``quasidonor'' levels formed in the scatterer below each subband minimum.

Tunable microwave and millimeter-wave band-pass filters

The authors present an overview of tunable microwave and millimeter-wave bandpass filters realized in different technologies. Some general design principles are described. Recent progress in the performance of various tunable filters is reported. The authors survey magnetically tunable filters (ferrimagnetic resonance filters, magnetostatic-wave filters, evanescent waveguide filters, E-plane printed circuit filters), electronically tunable filters, and mechanically tunable filters. The typical performance parameters are summarized. This comparison shown that none of these devices can simultaneously satisfy all requirements for perfect tunable filters. For microwave systems where multioctave tuning is essential, a YIG filter is an obvious choice. In systems where the requirement of high power handling capability combined with low insertion loss, predominates, mechanically tunable filters and magnetically tunable E-plane filters are recommended. If the tuning speed is a crucial requirement, varactor-tuned filters or E-plane filters with ferrite toroids are devices of choice. For millimeter-wave design, the most promising structures are ferrimagnetic resonance filters utilizing hexagonal ferrite resonators or, up to 60 GHz, magnetically tunable E-plane printed circuit filters.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Raman and photon scanning tunnelling microscopy of optical waveguides

Recent results from our laboratories on the design and characterization of optical waveguides are reviewed. Modelling of the design of channel optical waveguides is discussed and two means of experimental characterization that provide spatially local information are presented. Raman microprobe spectroscopy is used to explore the role of stress induced by a thin dielectric overlayer used to form channel waveguides in GaAlAs, and thus the role of photoelastic effects on waveguide behaviour. Photon scanning tunnelling microscopy is used to investigate local surface and index variations by probing the evanescent waveguide field.

An Evanescent Mode Waveguide Bandpass Filter at Q-Band (Comments)

It was with considerable surprise that I discovered my results published in the above paper. The design, development of the Craven (Evanescent waveguide)-type filter published in the forementioned paper was solely my effort. The required testing was done mainly by M. Noyes, presently with RCA Astro Eletronics, Princeton, NJ. Mr. Noyes also contributed to the mechanical changes necessary for both the ease of tuning, the reduction of loss from tbe filter. The work was completed on April 16, 1982.

Complex permittivity of soil and water mixtures at 9 GHz

Measurements of the complex permittivity of many soil samples were conducted using the evanescent waveguide technique at 9 GHz. The complex permittivity was taken as a function of moisture content. The experimental results were interpreted using Wiener's theory for dielectric mixtures to evaluate the degree of binding of water in soils.

New Application of Evanescent Mode Wave-Guide to Filter Design

Evanescent waveguide (rectangular or round) sections are used in conjunction with an admittance inverter synthesis technique incorporating frequency variable turns ratios to realize wide-band microwave (up to 1 octave) and low-frequency (60-MHz) low-loss bandpass filters. This work extends and corrects previous published information.

The measurement of the permittivity of sheet materials at microwave frequencies using an evanescent waveguide technique

Based on a method first proposed by Barlow (1962) the paper discusses how the complex permittivity of a sheet material can be determined by measuring the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> and frequency change produced by a sample when it is placed in a circular evanescent waveguide which is coupled to a resonant cavity. The method appears to be satisfactory for dielectric materials with loss tangents above about 0.01. Measurements on two mixtures of polystyrene and carbon, taken at 9 GHz, are reported.

Measurement of the complex permittivity of lossy fluids at 9 GHz

A new technique is described to measure the complex permittivity of high loss fluids at 9 GHz. Measurements on methyl alcohol and ethylene glycol are reported. The permittivity and loss tangent are calculated from changes in the resonant frequency and Q-factor of a resonant cavity which is coupled to an evanescent waveguide which contains the fluid sample.

The Design of Evanescent Mode Waveguide Bandpass Filters for a Prescribed Insertion Loss Characteristic

A design theory for evanescent dominant mode waveguide filters is presented. The cutoff guide is represented by its equivalent /spl pi/-section network, the elements of which closely approximate lumped inductances. Resonators may be formed by introducing appropriate capacitive obstacles at suitable intervals along the guide. The filter that results is a microwave analog of lumped filters with series coupling, the magnitude of the series inductance being controlled by the separation between capacitive obstacles. The theory derives the equivalent ladder network from the low-pass prototype and is accurate up to at least 20 percent band-widths. Filters may be designed to couple into other cutoff waveguide components using the same basic principles, a propagating guide, and coaxial terminations. The filters are normally constructed in standard production waveguide and are simple and cheap to manufacture. A considerable size and weight reduction, compared with orthodox waveguide filters, is possible at the cost of a small increase in insertion loss.