Improving the characteristics of rectangular waveguide branchings by cylindrical obstacles

quency in the range of the first, second, and third harmonic components of the signal. It is of the greatest interest to measure the relationship to frequency of the readings of a wattmeter with a complex structure of the sensing elements of its input transducer, when the computation of its sensitivity is very difficult. Therefore, we selected as objects of our investigation a waveguide multielement bolometric wattmeter [i], a wattmeter based on a multielement directional coupler with a thermistor head, and a double-element ponderomotive wattmeter [2]. The bolometric transducer consists of a rectangular waveguide section with butt-end flanges. The waveguide carries inside it perpendicularly to its wide wall 16 tungsten-wire bolometers whose length coincides with the waveguide height. The two bolometer rows are located along the waveguide axis. The uhf signal power is measured by means of the substitution method with an automatic bolometric bridge. The directional coupler of the thermistor wattmeter consists of two parallel rectangular waveguides with a common wide wall, with 16 identical holes located in two rows along the waveguide axis serving as coupling elements. The transition loss of a hole amounts, in the waveguide frequency range, to ~40 dB with a directivity exceeding 40 dB. A waveguide thermistor head is connected to the lateral arm of the directional coupler. The uhf power is also measured by means of the substitution method. The waveguide ponderomotive wattmeter consists of a rectangular waveguide with two sensing elements in the shape of rings at an angle of 45 ~ to the waveguide axis and a system for indicating the rotation angle of both ring suspensions. The ring centers are located at a distance of equal to one-fourth the working wavelength along the waveguide axis. The wattmeter scale used for indicating the suspension deflections is calibrated in watts by means of the method described in [2]. The frequency as well as the dynamic ranges of the wattmeters were chosen to be similar for comparison purposes. Thus, the working frequency ranges of the bolometric wattmeter amounts to 3.94-4.85 and 4.85-6.64 GHz, of the wattmeter with the directional coupler to 3.94-5.64 GHz, and of the ponderomotive wattmeter to 4.75-5.25 GHz. The dynamic range of the bolometric wattmeter amounts to 0.3-10 W, of the wattmeter with the directional coupler to 0.1-50 W, and of the ponderomotive wattmeter to 1-20 W. The input transducers of all the wattmeters have waveguide cross sections amounting to 48  24 mm. The frequency characteristic of each wattmeter was repeatedly measured in the working range in the course of their calibration and periodic testing, and it was found that the measured data is in good agreement with the computation results. In addition to the basic wave type H1o others arise in the waveguide with a rising frequency, therefore, their fre

Two metallic or lossy dielectric cylinders placed in one cross section of a rectangular waveguide are investigated by the orthogonal expansion method. Resonances are shown by frequency responses of the transmission coefficient. They are discussed by patterns of the magnetic field and diagrams of the Poynting vector. Physical explanations of the resonances are given. The structure may be used as a filter element. With two small dielectric posts, a frequency characteristic with two stopbands can be obtained. Center frequencies are tunable by moving the posts. Using one large metallic and one small dielectric post, a tunable passband characteristic can be realized.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

In Chapter 2, a method is presented to study a substrate integrated waveguide circuit with metallic posts inserted inside a homogeneous substrate. Although this type of circuit is the most widely adopted so far, a substrate integrated waveguide circuit with inhomogeneous substrate gives more freedom in the circuit design, and it may give some compact designs. This chapter generalizes the method presented in Chapter 2 to deal with a substrate integrated waveguide circuit with both dielectric and metallic cylinders. Herein, the field expression in each dielectric regions are required, and the boundaries conditions at all the material discontinuities including the boundaries of both metallic and dielectric cylinders should be enforced. The method is presented in a similar manner to that in Chapter 2, and two examples of inhomogeneous substrate integrated waveguide circuits are shown at the end of the chapter.

Based on the mutual coupling coefficient between two identical structure parallel rectangular waveguides and the scalar integral method for analyzing the mutual coupling factor between two nonparallel waveguides, the coupling characteristic between two nonparallel straight rectangular single mode waveguides is discussed, and a computing instance is introduced for showing the crosstalk characteristic between two nonparallel output rectangular waveguides in the Y branch optical switch. These works provide some theoretical support for ascertaining the fundamental parameters of a Y branch MQW waveguides optical switches.

A new high efficiency and large volume microwave plasma source has been developed. The microwave plasma source consists of a 1–10kW 2.45GHz magnetron power supply, microwave transmission and monitoring system, microwave power splitter, adjustable short-circiut plunger and two parallel straight waveguide components with slots on its inner sides. Microwave eletronmagnetic energy is coupled from the parallel rectangular waveguides through regularly positioned slots into the plasma rectangular chamber of 460mm in length, 64mm in width and 118mm in height, shaped by a quartz glass cube to enclose the space of work gas. The location and size and direction of slots and the distance between the two parallel metal waveguides were determined by the electromagnetic numerical simulation. The design parameters of the microwave plasma source were optimized to produce high-amplitude and uniform electromagnetic field distribution. The calculated fields distribution fit perfectly to those measured inside the plasma chamaber without plasma. The stable microwave plasma of different gases (He, Ar) at atmospheric pressure is produced at low-power inside the entire quartz glass cube. The operational characteristics of microwave plasma source in different experimental condition is discussed.

A numerical approach is described for the analysis of scattering from dielectric obstacles in a rectangular waveguide. The approach is a combination of the finite-element method and the analytical solution. In order to save computer memory, the substructure method is introduced in the finite-element method. To combine the uniform waveguide region with the finite-element-method region, evanescent modes and propagating modes are considered in the analytical solution. Spurious fields like the spurious solutions generated in the finite-element analysis of three-dimensional eigenvalue problems can appear in the three-dimensional discontinuity problems when the variational expression in terms of three components of the magnetic field is used. To suppress and eliminate the spurious fields, the penalty function method is also introduced. To confirm the validity and usefulness of the approach, numerical examples are shown for a rectangular dielectric scattering obstacle in a waveguide.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Scattering from a cylindrical metallic object placed centrally in a waveguide so that its axis is parallel to the transverse magnetic field of the dominant mode is shown to give rise to two field types in the scattered waves, which are dipole and isotropic in nature. On the other hand, a dielectric rod similarly placed shows only dipole scattering. A method is presented which uses a potential theory to describe dipole scattering from metallic, dielectric and magnetic obstacles, and it is further shown that the theory may be used to derive in a simple manner the dipole scattering from a coaxial obstacle which may consist of a metal rod with a dielectric or magnetic sleeve, or coaxial combinations of dielectric and magnetic materials. Isotropic scattering is important in a coaxial system only when the core is a good conductor, and it is shown by an electromagnetic solution that its magnitude is associated only with the radius of the metal core, any dielectric outer sleeve having negligible effect, provided that the overall radius is sufficiently small.

The theory developed in the companion article for obtaining rigorous bounds on cotη, where η the phase shift, is applied to scattering by dielectric obstacles in rectangular waveguides. For the obstacles considered here, bounds are also obtained on the phase shifts directly and on the elements of the equivalent T network. The exact solution for a dielectric slab of finite length, which extends to the conducting boundaries of the waveguide and completely encloses the obstacle, is introduced as a convenient trial function. The permittivity of the slab is retained as a parameter which is varied to improve the bounds. In the expressions for the bounds on cotηe and cotη0, the particular obstacle configuration appears only in certain integrals of relatively simple form. Numerical results are obtained for large and small obstacles of various shapes, including some truly three-dimensional cases. The upper and lower bounds on the phase shifts and on the elements of the equivalent circuit are found to be quite close to one another. In one case, the bounds obtained by using the simple trial function are compared with the bounds obtained by using the trial function which generates the Schwinger integral variational principle.

A rigorous approach combining the orthogonal expansion method for modeling cylindrical posts in rectangular waveguides and the extension of the three short plane technique is introduced to obtain the S-matrix for a general coaxial probe in a rectangular waveguide. A cascading procedure is applied to solve the problem of a probe near a waveguide discontinuity and to obtain the response of a probe-excited band pass filter. The computed results are in excellent agreement with the measured results showing the usefulness of this method.

Doppler spectra from broadside 77 GHz plane wave radar illuminated dielectric and metallic cylinders are investigated under static and dynamic target conditions. The classical formulae of modulation theory are reviewed and verified empirically using measured data containing AM and PM components manifested as discrete sideband imbalances. Particular emphasis is placed on the phasor representation of the Doppler and on the practical understanding of the intrinsic AM/PM ambiguities. Techniques used in the analysis could be applicable to the problem of AM and PM conversion in oscillators and sources. In particular ambiguities are represented and bound using a vector in a box approach.

The substrate-integrated waveguide (SIW) is an artificial waveguide structure that is fabricated in planar dielectric substrate with periodic metallic cylinders, and can be analyzed as an equivalent rectangular waveguide (RW). In this letter, the formula of the conductor loss in SIW has been derived from the conductor loss formula of conventional RW. In addition, the equality condition at which the conductor losses in SIW and RW are exactly equal has been found. The conductor losses in SIW and RW have been investigated and compared, good agreement has been observed between the theoretical calculations and HFSS numerical simulations.

Theory of scattering by conducting, lossy dielectric, ferrite and/or pseudochiral cylinders is investigated using a combination of a modified iterative scattering procedure and the orthogonal expansion method. The addition theorems for vector cylindrical harmonics, which transform harmonics from one coordinate system to another, are presented. The scattered field patterns for open structures and frequency responses of the transmission coefficients in a rectangular waveguide describing the resonances of the posts on the dominant waveguide mode are derived. The validity and accuracy of the method is verified by comparing the numerical results with those given in literature.

The theory of TE- and TM-wave scattering by an array of conducting and dielectric cylinders is investigated using a combination of an iterative scattering procedure and the orthogonal expansion method. Polarization parameters of the scattered plane wave are derived in the near and the far fields.

A planar antenna comprised of parallel feed waveguide circuit and sub-arrays of four aperture elements have been proposed. First, we describe a fundamental concept of planar antenna employing parallel feed waveguide. Next, a parallel feed circuit using rectangular waveguide, a subarray with four aperture elements, new T-junction which is made by casting in one body and L-bend is designed, and characteristics of the planar antenna is investigated experimentally. The antenna, proposed here, has the feature of a good aperture efficiency, broadband, high heat-resistance and small size. The aperture efficiency is over 90% in frequency ratio bandwidth of 5.8% and is over 80% in frequency ratio bandwidth of 11.0%.

A numerical implementation and generalized conservation properties of a formulation for calculating wave propagation through stacked gratings comprising metallic and dielectric cylinders are presented. The basic formulation of the method was given in a companion paper [J. Opt. Soc. Am. A. 17, 2165 (2000)]. Here, details of the numerical implementation of the method are discussed and are illustrated for the ensemble average of a strongly scattering structure with refractive index and radius disorder. Also presented are a comprehensive treatment of energy conservation and generalized phase relations, as well as reciprocity.