Small Flare Angle Research Articles

Electrothermal Design of Bidirectional Wide-Boom Log-Periodic Antennas

A wide-boom, microstrip-fed planar bidirectional log-periodic (LP) antenna is proposed and improvements in its impedance match, radiation, and thermal performances are demonstrated. The boom width of each arm is increased by moving its virtual apexes into the other arm while preserving the small flare angle and self-complementarity. This modification widens the ground plane for the microstrip feed line and results in enhanced impedance match and gain. In addition, electrothermal multi physics analysis demonstrates that the wide-boom mitigates hot spots logarithmically developed on LP’s active regions. The impedance and far-field measurements show that the fabricated antenna achieves VSWR ≤ 2 and flat gain around 5 dBi over a decade bandwidth. A non contact thermal imaging system is used to measure temperature response of the antenna under a ~5 W input power over 1.71–1.85 GHz range. The measured temperature images correlate well with the multi physics simulations, therefore validating the conclusions obtained via electrothermal analysis.

Suppression of Low-Frequency Shock Oscillations over Boundary Layers by Repetitive Laser Pulse Energy Deposition

The effect of repetitive energy deposition on low Strouhal number oscillations of the shock wave induced by boundary-layer interaction over a cylinder-flare model was studied. The fluctuation of the energy deposition frequency was induced in the flow, because the bubble generated by the energy deposition flowed downstream along the surface repeatedly. The region before the bubble size was affected by the energy deposition directly, so the fluctuation frequency was equal to the energy deposition frequency. However, the flare shock behavior at a position farther from the surface than the bubble size was also affected strongly by the energy deposition. For low-frequency unsteadiness and the effect of energy deposition on its unsteadiness, two categories have been observed. In the relatively small flare angle case, the flare shock was oscillated owing to the fluctuation induced by the boundary-layer interaction at the shock foot, and its oscillation occurred at 2.1 kHz with a small amplitude. The amplitude of this oscillation was decreased by highly repetitive energy depositions, and its amplitude could not be detected at a highly repetitive energy deposition. In the longer cylinder section case, the region of the shock-wave interaction was widened, and the amplitude of the flare shock oscillation was increased. In this case, the amplitude drastically decreased because of energy deposition.

The Design for WR-06 Corrugated Conical Horn Antenna and its Application in Emissivity Measurement of Microwave Radiator

This paper presents the design for a corrugated conical-horn antenna working in WR06 frequency band and its application in emissivity measurement of microwave radiator. For a calibration target of microwave radiometer, we consider design the corrugated conical-horn antenna to satisfy its measurement requirements of the emissivity of calibration target. The antenna is designed with small flare angle and low VSWR in a frequency range of 150±10GHz. The measurement results for electrical properties of antenna and emissivity of microwave radiator are presented in this paper. The results show that the performance of antenna is fit to the emissivity measurement of radiator of radiometer calibration target.

Simple analytical relations for ship bow waves

Simple analytical relations for the bow wave generated by a ship in steady motion are given. Specifically, simple expressions that define the height of a ship bow wave, the distance between the ship stem and the crest of the bow wave, the rise of water at the stem, and the bow wave profile, explicitly and without calculations, in terms of the ship speed, draught, and waterline entrance angle, are given. Another result is a simple criterion that predicts, also directly and without calculations, when a ship in steady motion cannot generate a steady bow wave. This unsteady-flow criterion predicts that a ship with a sufficiently fine waterline, specifically with waterline entrance angle 2αEsmaller than approximately 25°, may generate a steady bow wave at any speed. However, a ship with a fuller waterline (25°<2αE) can only generate a steady bow wave if the ship speed is higher than a critical speed, defined in terms of αEby a simple relation. No alternative criterion for predicting when a ship in steady motion does not generate a steady bow wave appears to exist. A simple expression for the height of an unsteady ship bow wave is also given. In spite of their remarkable simplicity, the relations for ship bow waves obtained in the study (using only rudimentary physical and mathematical considerations) are consistent with experimental measurements for a number of hull forms having non-bulbous wedge-shaped bows with small flare angle, and with the authors' measurements and observations for a rectangular flat plate towed at a yaw angle.

An Investigation of Corrugated Groove Conical Horns with Small Flare Angle

Including space harmonics in the interior region of the waveguide, the fields radiated by a \( HE^{{{\left( 1 \right)}}}_{{11}} \) mode in an aperture of a corrugated groove conical horn are described, and theoretical radiation patterns of the horns are given. Experimental results in support of our theory have also been presented.

On the propagation of electromagnetic waves through parabolic cylindrical chiroguides with small flare angles

AbstractWith the use of Maxwell's field equations, an analytical investigation of the propagation of electromagnetic (EM) waves through a three‐layer parabolic cylindrical chirowaveguide is presented; different regions of the guide have different values of chirality admittance. The analytical approaches to derive the dispersion relations and the eigenvalue equations for cutoff are discussed under the assumption of small flare angles of the parabolic cylindrical boundaries. However, more emphasis is given on the modal field cutoffs. It is observed that the bunching tendency of field cutoffs, which is seen in the cases of parabolic cylindrical dielectric guides, is greatly affected in this case, which is attributed to the presence of chirality in the medium. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 33: 414–419, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10338

Partial electromagnetic wave guidance by a parabolic cylindrical chiroboundary with small flare angle

Summary Propagation of electromagnetic (EM) waves through an unbounded medium with two regions, having different values of chirality admittances separated by a parabolic cylindrical surface, is dealt with. The dispersion relations and cutoff conditions for such a chiroguide are described under the assumption of small flare angle of the parabolic cylindrical boundary. More emphasis is, however, given on the field cutoffs. A kind of mode bunching phenomenon is reported which is, however, partially localized in this case.

On primary incident wave models for pyramidal horn gain calculations

A few widely used primary incident wave models for pyramidal horn antenna analysis are compared on the basis of gain calculations. The analysis is based on edge-wave diffraction theory, as presented in a previous publication, with some modifications made to the underlying theory. It is shown that these models agree well for high-gain horns with small flare angles, but that the differences are more profound for lower gain horns, where the flare angles are larger. The accuracy of the various models are studied by comparing the results to actual measurements. The respective effects of amplitude and phase variation in the primary incident wave are also illustrated.

A mode matching-integral equation technique for the analysis and design of corrugated horns

A hybrid mode matching-integral equation method is presented for the analysis and design of corrugated horns. By applying a particular formulation of the equivalence principle, which implies covering the horn aperture with a metallic plate, the original issue is divided into an exterior and an interior problem. The former is formulated by using a combined field integral equation, the latter by employing a modal expansion. The separation of the two problems allows running an optimization procedure to meet all the requirements needed in high performance radiating systems. The technique has been used for the design of a small flare angle and a discrete-section profiled horn. The theoretical predictions remarkably agree with experimental data.

Broadbanding of feed horn utilizing corrugated waveguide with two kinds of slots

This paper presents an analysis of the dual corrugated waveguide, consisting of two kinds of slots with arbitrary shapes and a technique for broadbanding of a conical horn with a small flare angle made of this waveguide. First, the characteristic equation for the dual corrugated waveguide was derived under an assumption that the admittances of the two kinds of slots are known. By this arrangement, the propagation characteristics of the waveguide can be easily determined once the admittances of the slots are substituted into the equation when the shapes of the slots are modified. Next, the results were applied to the dual corrugated waveguide with two kinds of parallel slots. The effective frequency, ranges, not previously clear, of the dual corrugated conical horn were found out when the width ratio of the two slots was modified. Hence, the design data for a conical horn were provided. Next, for broadbanding of the dual corrugated conical horn, a ring-loaded dual corrugated waveguide, made of shallow parallel slots and deep ring-loaded slots, was proposed. When this waveguide is applied to a horn, the bandwidth can be increased 1.3 times. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(3): 12–21, 1997

Comparison of real gas simulations using different numerical methods

Two different numerical simulation codes (the SPLIT/NE code and the PoliTo code) are examined in this paper by comparing results for non-equilibrium flow cases using two different geometries, a hemisphere-cylinder-flare (axisymmetric) and a hyperbola-flare-cylinder configuration (axisymmetric and 2-D plane). The solution methods implemented in the codes are essentially different (finite difference, bow shock fitting, matrix splitting and Runge-Kutta high accuracy schemes for SPLIT/NE and finite volume, shock capturing, flux difference splitting and E.N.O. high accuracy schemes for PoliTo). The flow simulations are done employing physical models of different complexity (inviscid and viscous flows, chemically reacting flows in vibrational equilibrium and non-equilibrium, steady and unsteady flows). Comparing the solutions for the different codes, a very good agreement is obtained for both the hemisphere-cylinder-flare flow and the 2-D plane hyperbola-flare-cylinder flow. For relatively small flare angles, this is also true for the axisymmetric hyperbola-flare-cylinder flow; however, for larger flare angles, differences in the solutions can be detected which can be addressed to the formation of a strong recirculation bubble behind the detached flare shock.

Comments on "GTD analysis of the near-field patterns of conical and corrugated conical horns"

For original paper see ibid., vol.AP-25, no.3, p.447 (1977) which presents a novel technique for the analysis of the principal plane near-field patterns of conical and corrugated conical horns with small and wide flare angles excited in the dominant mode using the uniform theory of diffraction (UTD). The authors apply a slope diffraction correction, which is necessary in cases where the incident field is rapidly varying at the edge

Longitudinally slotted conical horn antenna with small flare angle

Longitudinally slotted conical horn antenna with small flare angle

Radiation Characteristics of Dielectric-Coated Conical Horn

The results of the analytical and experimental study of the propagation and radiation behaviour of dielectric-coated conical horns with small flare angles are reported. The analysis of the fields in such a horn is made using spherical hybrid modes. The characteristic equation for the separation constant is obtained. The radiation characteristics are derived using vector diffraction formula with the assumption of no phase variation over the aperture of small-angle cones. Analytical results are in good agreement with experimental results. Axial directivity and beamwidth of conical horns have been found to improve due to dielectric coating.

Scattering coefficients at a waveguide-horn junction

Schwarz's iterative procedure of overlapping regions, which has been previously employed in the solution of polygonal waveguides and similar problems, is employed here to solve for the scattering matrix coefficients at the sharp junction of a sectoral and parallel-plate waveguides. It is shown that by dividing the junction into semi-infinite rectangular and sectoral subregions, and using the Green's functions of each, the problem is reduced to the solution of a system of integral equations of the Fredholm type. The scattering-matrix coefficients are computed and presented graphically as a function of kb, together with the previously published data. The solution is relatively simple and the method is shown to be efficient since the fields are described in terms of rapidly convergent series (especially for a sectoral region of small flare angle), and accurate results are typically obtained after two or three iterations. It is shown that the method is applicable for sectoral regions of arbitrary flare angle, but a third circular subregion is particularly required for flare angles exceeding 180°.

H-plane multimode waveguide transition sections with large flare angles: radial and rectangular modal analyses

Waveguide transition sections that connect standard single-propagating-mode waveguides to multimode waveguides are designed using a quasioptical approach, as well as fullwave techniques based on both radial and rectangular modal analyses. The three different approaches to the problem result in the derivation of the coupled wave equations for the wave amplitudes, which are solved numerically using an iterative method as well as the Runge-Kutta method. These numerical solutions are compared with experimental results. The advantages and disadvantages of the different approaches are discussed in detail. The quasioptical approach is found to be very suitable for transition sections with small flare angles. For transition sections with large flare angles, the fullwave solutions must be used. It is shown that the radial modal analysis is here more efficient.

Radiation characteristics of corrugated<tex>E</tex>-plane sectoral horns

A study of the radiation characteristics of corrugated <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</tex> -plane sectoral horns is described. Assuming the corrugations to be infinitely thin and sufficiently close packed, impedance boundary conditions are imposed on the fields in the axial region of the horn and it is established that a separable modal solution of fields in terms of TE to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</tex> modes is possible for this geometry. The horn aperture field is determined in terms of cylindrical wave functions and the vector diffraction formula is used to analyze the far-field radiation patterns. Excellent agreement is obtained between the theoretically derived pattern with experimental results for horns supporting the balanced <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">HE_{11}</tex> mode with small flare angles ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2_{\alpha 0} \leq 30\deg</tex> ), designed using the theory presented. Bandwidth properties of the horn have been studied which may be used to advantage in designing a corrugated <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</tex> -plane sectoral horn without much degradation of its radiation characteristics corresponding to the balanced <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">HE_{11}</tex> made over a wide frequency bandwidth (1.5:1).

Eigenvalues of a class of spherical wave functions

An analytically simple and sufficiently accurate solution for the eigenvalues of a class of spherical wave functions is presented. The class of spherical wave functions considered are modes in conical and quasipyramidal waveguides with perfectly conducting walls and hybrid modes in corrugated conical and quasipyramidal horns with an impedance boundary. The indicated solution has been first used to obtain in closed form eigenvalues of the class of spherical wave functions considered which are subsequently used as the starting values for evaluating the exact eigenvalues with a simple digital-computer based iterative algorithm. The digital-computer evaluation of the eigenvalues has been found to be very fast, since the starting values are close to the exact solution, irrespective of the flare angle of the radial waveguides considered. Further, some mathematical insight has been provided in order to explain why the asymptotic solution, which appears to be valid only for small flare angles, yields eigenvalues close to the exact one even for wide flare angle(s) of the radial waveguides.

Engineering approach to the design of tapered dielectric-rod and horn antennas

The taper profile of optimized dielectric-rod and horn antennas is synthesized as a series of non-interacting planar radiating apertures. The method is semi-empirical, straightforward to apply, enables the dielectric-rod antenna to be satisfactorily optimized and provides a means of evaluating and optimizing a dielectric-horn antenna with variable wall thickness. The optimum profiles are taken as those which smoothly transform the surface-wave power from the launcher to the radiating aperture. The optimization of the dielectric-rod antenna considerably improves the radiation pattern while computations supported by measurements confirm earlier reports that a dielectric-horn can have a higher gain than a metal horn of similar dimension but side-lobe level is seen to be an important issue. Wide flare-angle horns give ideal E-plane patterns at the expense of a high side-lobe level in the H-plane; for small flare angles the dielectric horn gives similar patterns to the tapered rod antenna and thus preserves rotational symmetry. Calculations throughout are restricted to cylindrical geometry but other geometries and variations on the dielectric-horn principles are described. Useful engineering design data have been compiled for both the dielectric-horn and rod antennas and curves are given which determine near-optimum parameters for gains up to about 20 dB which is seen to be a practical operating limit for these surface wave devices. A unified impression of dielectric antennas emerges with the important conclusion that, when optimized, dielectric-rod and horn antennas are in fact competitive with small metal horns for some applications; furthermore the dielectric-horn antenna, used singly or in arrays, is an ideal device for producing a low side-lobe level in the E-plane.

Modes in a conical horn: new approach

An analytically simple, sufficiently accurate, and self-consistent solution for modes in a conical horn is presented. The eigenfunctions and eigenvalues derived from the simpler solution for the TE and TM modes of different orders are close to the exact solution. Application of the simpler solution for obtaining the aperture field and, subsequently, the far-field-radiation patterns of conical horns of arbitrary flare angles excited in the TE11 mode, with the aid of a vector diffraction formula, yields results in close agreement with experiment. The new approach provides a simple and accurate solution for the balanced hybrid modes in corrugated conical horns with small and wide flare angles, emphasising the more general validity of the technique adopted.