Waveguide Load Research Articles

Highly localized mode in a pair structure made of epsilon-negative and mu-negative metamaterials

In this paper, the tunneling phenomenon occurring in a pair structure made of epsilon-negative (ENG) and mu-negative (MNG) metamaterials is experimentally studied. The ENG and MNG metamaterials are fabricated using coplanar waveguide loading with lumped-element series capacitors and shunt inductors. The properties of the tunneling mode are investigated by means of the transfer-matrix method, based on the experiment parameters of effective permittivity and permeability. The results show that the tunneling frequency is independent of the pair length and the electric field is highly localized at the interface of the ENG-MNG pair. These features illustrate that the pair behaves as a cavity with strongly enhanced electric field and with dimensions beyond the half-wavelength limit.

Radiometric-Waveguide Calibrators

We describe the electromagnetic and thermal design, performance, and fabrication for two types of radiometric- waveguide load calibrators. A simple theory is presented and used to minimize the total volume of the absorber structure. These devices have been used from room temperature to below 4 K in microwave to millimeter wavebands. The estimated precision of the calibrator is better than 1 mK absolute at temperatures near 2.7 K.

Frequency-Sensitive Characteristics of a Screen Having Rectangular Apertures and Waveguide Loads

Frequency-Sensitive Characteristics of a Screen Having Rectangular Apertures and Waveguide Loads

Efficiency Optimization for Systems and Components in Microwave Power Engineering

The paper is concerned with one aspect of optimization of microwave thermal processing, namely, with optimization of energy coupling interpreted as a numerical characteristic of system efficiency. Since in computer-aided design coupling can be evaluated through the computed reflections, an optimization scheme is presented that is particularly suitable for minimizing the reflection coefficient in typical systems and elements of microwave power engineering. Based on response surface methodology and the sequential quadratic programming for constrained optimization, the procedure is linked with the full-wave 3-D FDTD electromagnetic simulator QuickWave-3D. Credibility and effectiveness of the method is illustrated by four examples: dimensional optimization is performed for a dry waveguide load, a waveguide T-junction with a partial-height post, a water cylinder in a cavity, and a slotted waveguide-backed radiating element.

Cutoff frequencies of an asymmetrically loaded cylindrical waveguide

The cutoff characteristics of an asymmetrically loaded cylindrical waveguide are analyzed using the null-field method. The fields in the metallic waveguide and dielectric loading are expressed in their corresponding guided-wave modes. The addition theorem of the Bessel function is used to relate the fields across the air-dielectric boundary.

A nearly monochromatic cavity for high current storage rings

A strong damping of the higher order mode (HOM) spectrum of an RF cavity can be obtained by coupling appropriate waveguides directly to the cavity. This type of HOM suppression has been investigated at S.T. After studies and tests on different shapes of cavities, particularly on bell-shaped cavities, it has been decided to design a pill-box cavity for the ELETTRA Storage Ring. A prototype of this cavity has been produced with two waveguide suppressors coupled to it. The suppression effect on the HOM spectrum is described along with discussions on the vacuum window design and on the shape and the material for the waveguide load. The effects on the accelerating mode are shown as well.

A High Power Low Cost S-Band Waveguide Load for Accelerator Applications

The design and constructional aspects of a dissipative wall waveguide load in S-band are described. The load is fabricated for the high power microwave transmission line of 20 MeV Microtron. A mixture of cement and graphite is used as an attenuating material. A low VSWR could be obtained by providing linear taper along the length of the waveguide. Power dissipation per unit length in the load is kept almost constant and the dissipated heat is removed by circulating water. The load can be operated up to peak power of 5 MW and average power of 500 W. The VSWR of the load is better than 1.1 at the operating frequency of 2.856 GHz.

Rf power calculations for the NRL buncher/converter microwave generator

Simple formulas are derived for the rf power output from NRL’s novel buncher/converter microwave source. These equations emphasize the physics of the converter and explicitly demonstrate the effects of waveguide and coaxial-line loading, the positions of the tuning stubs, system dimensions, etc. Numerical examples show that capacitive loading of the coaxial line can significantly affect the level of radiated power. They also indicate that the output power is usually not limited by the radiation resistance or radiative coupling of the coaxail and rectangular sections.

Long-term stability and verification period of type �9-123 to 127 waveguide loads

Long-term stability and verification period of type �9-123 to 127 waveguide loads

Evaluation of calculated temperature distributions for a 27 MHz ridged waveguide used in localized deep hyperthermia.

The computational model developed by van den Berg has been used to perform two-dimensional simulations of tissue-equivalent phantoms heated by a 27 MHz ridged waveguide. The program is able to calculate temperature distributions for realistic inhomogenous tissue configurations (as derived from CT scans) in about 20 min on a PDP 11-44. Results for tissue-equivalent phantoms are evaluated with respect to their accuracy in predicting actual temperature distributions by comparing them with measured temperature distributions. In general the computer simulation tends to overestimate the depth of penetration; this can be ascribed to the two dimensional approach followed which does not take into account the divergence of the electric field in the third dimension. This effect can to a certain degree be compensated by assigning a higher value for the electrical conductivity of the medium. For homogenous phantoms this results in a satisfactory agreement between measured and calculated temperature distributions. Furthermore, a correct approximation for the electric field distribution over the aperture appears to be of importance, since it significantly influences the calculation results, especially for waveguide loads whose size exceeds the width of the ridge area. For inhomogeneous media the simulation results, using realistic (literature) values for the electrical conductivity, can be used with these limitations in mind, as a best-case estimate of the absorbed power distribution at depth. For more accurate simulations a three-dimensional computer model is ultimately needed.

Two new forms of waveguide load

Two new forms of waveguide load

Certification of waveguide loads for phase of the reflection coefficient

In order to shorten the time and improve the accuracy of the checks on panoramic impedance meters for waveguide equipment, one must have standards that have been certified both for the standing-wave ratio and for the phase of the reflection coefficient. It is technically possible to use waveguides that have been constructed along the narrow wall as the standard waveguide loads. This construction is calculated to a first approximation from the standing-wave ratio which is equal to b/b~, where b and bl are the dimensions of the narrow wall for the normal and the constructed waveguides, respectively.

Installation for certifying waveguide loads in the 8–12-GHz range

The reflection-factor modulus and phase measurements are based on the methods of comparing tested load 7 to reference reflection standard 8, whose reflection-factor modulus is similar to that of the load. The comparator (denoted by a dashed line) consists of a doublechannel circuit with an amplitude-modulated measuring channel. The shf signal of generator 1 with a phase-controlled automatic frequency trimming which provides a l-h stability of 10 -7 [2] is split by means of the directional coupler DCI into two channels. The reference channel incorporates phase shifter 2, waveguide switch 3, and ferrite gate 4~ The measuring channel comprises variable attenuator ii, amplitude modulator I0 with a p--i--n diode, gates 4, and tuned reflectometer consisting of directional coupler DC3 and the matching transformers 9. Low-frequency 10-kHz generator 13 is used for modulation purposes. The signals from both channels are fed to detector 5 through directional coupler DC2. If the signals are in quadrature, low-frequency, narrow-band amplifier 6, which is tuned to the modulation frequency, will have zero output signal. In order to raise the circuit sensitivity and to eliminate the • ~ ambiguity in measuring the reflection-factor phase, synchronous detector 12 is used.

Comments on “A new waveguide flow calorimeter for levels of 1–20 W”

In the December 1974 issue, a paper <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> described a recently developed dual-flow microwave calorimeter with very high precision and accuracy. A control and coolant circulation console was described as operating with a series of dual waveguide loads where precision was achieved by the inherent balance between one load heated by the unknown microwave power and the other by an accurately measured dc power while the errors were estimated by the use of an auxiliary thermocouple measuring the temperature difference between the waveguide bodies.

Program for Processing Standing Wave Measurements (Program Descriptions)

This subroutine processes standing wave measurements with or without line loss on a transrnission-line or waveguide load leading to its one-port characterization.

Approximation Technique for Dielectric Loaded Waveguides

An algebraic procedure is described which yields approximate values for the cutoff frequencies and propagation constants of dielectric-loaded waveguides. The procedure is demonstrated for a waveguide completely filled with an anisotropic dielectric and for waveguides partially filled with isotropic dielectrics. For the latter case results are tabulated for five types of waveguide loading. The symmetrically loaded waveguide is used to show the accuracy which may be expected. This procedure is shown to be identical with the Rayleigh-Ritz variational method but with the advantage that it provides a systematic approach to improve the accuracy and to handle a multitude of waveguide geometries.

Thermoelectric cooling applied to the absolute measurement of microwave power

The development of efficient thermoelectric semiconductors such as p and n type bismuth telluride has given rise to a variety of applications of thermoelectric cooling in the field of instrumentation.3,4This paper is concerned with the application of thermoelectric cooling to a load in which the heat produced, by the microwave power absorbed, is balanced by the heat extracted thermoelectrically. By this means the load may be maintained at the temperature of its surroundings, in which case extraneous heat transfer is reduced to zero. A restriction is applied to the temperature drop across the thermoelements used, and it is shown that the cooling power required to balance the microwave power may then be evaluated from the Peltier coefficient and two values of direct current.A simple form of waveguide termination is described to which distributed cooling is applied. It is concluded that the type of waveguide load required, to approach the inherent accuracy of the method, will be closely approached as the wavelength decreases into the millimetre band.

Helium-Cooled Reference Noise Source in a 4-kMc Waveguide

We describe a 4-kMc waveguide load which radiates an effective noise temperature (approximately 5°K) known to within a small fraction of a degree Kelvin. The absorber is immersed in liquid helium and the temperature distribution along the guide is measured by means of an array of germanium diode thermometers.

Thermoelectric cooling applied to the absolute measurement of microwave power

The development of efficient thermoelectric semiconductors such as p and n type bismuth telluride has given rise to a variety of applications of thermoelectric cooling in the field of instrumentation.3,4This paper is concerned with the application of thermoelectric cooling to a load in which the heat produced, by the microwave power absorbed, is balanced by the heat extracted thermoelectrically. By this means the load may be maintained at the temperature of its surroundings, in which case extraneous heat transfer is reduced to zero. A restriction is applied to the temperature drop across the thermoelements used, and it is shown that the cooling power required to balance the microwave power may then be evaluated from the Peltier coefficient and two values of direct current.A simple form of waveguide termination is described to which distributed cooling is applied. It is concluded that the type of waveguide load required, to approach the inherent accuracy of the method, will be closely approached as the wavelength decreases into the millimetre band.

Circularly polarized slot radiators

A pair of narrow slots crossed at right angles and located at the proper point in the broad wall of a rectangular waveguide will radiate a circularly polarized wave. Some of the results of a study of the properties of such slots is presented. The study was undertaken with the aim of obtaining information useful in design of a circularly polarized linear array. Some of the properties of the slot pairs are as follows: 1) They are inherently matched, independent of the slot length. 2) When the slot arms are made resonant, approximately 75 per cent of the incident power is radiated, with a vswr of 1.12. 3) When fed from one end of the waveguide, the slots radiate right-hand circular polarization; from the other end, left-hand. In using these slots in linear arrays the power radiated is varied by changing slot length, since position and orientation are fixed by the requirements of circular polarization. The slots must be separated by a guide wavelength, so waveguide loading or other complicated schemes must be used to reduce the slot spacing.