Showing papers on "Slot antenna published in 1980"

Electromagnetic transmission through narrow slots in thick conducting screens

Abstract: The general formulas for electromagnetic transmission through an infinitely long slot in a perfectly conducting screen of finite thickness are specialized to the case of a narrow slot. The slot may be filled with a homogeneous isotropic material. A simple equivalent circuit for the narrow slot is developed. It is found that for certain screen thicknesses the slot becomes resonant, and exceptionally large transmission of energy may occur. In fact, as the slot width approaches zero, the transmission width at resonance becomes 1/\pi wavelengths regardless of the actual slot width. The effect of loading the slot with a lossy dielectric is also considered. Computations are given to illustrate the validity of the equivalent circuit model and the accuracy of transmission characteristics computed from it.

Antennas and waveguides for far-infrared integrated circuits

Abstract: Antennas and waveguides for the wavelength range 0.1-3 mm are considered. Emphasis is placed on those designs which lend themselves to integration with each other and with other components such as diodes. The general properties of FIR antennas are reviewed. A novel silicon waveguide antenna is discussed, and its design, simulation, fabrication, and performance at 119 μm are described. This antenna has a highly symmetrical, single-lobed beam with 3 dB beamwidths of 35 and 38° in the E - and H -planes, respectively. The gain (measured in microwave simulation) is 12.8 dB. This antenna is well suited for integration with Schottky diodes. The related subject of FIR waveguides is discussed. Experiments with metal transmission lines at 119 μm are described and dielectric guides related to the waveguide antenna are also considered. Using components such as these it may soon be possible to construct receiver front ends for this wavelength range in integrated-circuit form.

Near-field pattern analysis of airborne antennas

Abstract: Results of a newly formulated analysis for computing patterns of an aperture or monopole antenna mounted on the fuselage of an aircraft are presented. Approximate models of the aircraft structure are employed in conjunction with the geometrical theory of diffraction (GTD) to obtain the computed fields. A major feature of the analysis is that it can accommodate receiver range specifications varying from as close as a wavelength to the aircraft surface to the true far field. This feature is especially useful in that computed on-aircraft pattern performance can be compared with measurements taken at any convenient range, including the near field. Further, after such crucial checks between computations and measurements have been made, the numerical solution can be employed to predict accurately the far-field performance of the on-aircraft antenna system. The accuracy of the numerical solutions obtainable with the analysis is demonstrated by comparison with model measurements.

Power combining antenna structure

Abstract: Low-loss power combining-transmitting antenna arrangements are disclosed which are suitable for use in power distribution systems employing RF transmission of the energy being distributed and other applications in which it is necessary to coherently combine and transmit several RF signals. The disclosed arrangements utilize slot radiators that are excited at each end by separate feed lines. Narrow, nonradiating slots extend outwardly from the ends of each radiating slot to provide impedance matching. One modular arrangement includes amplifier circuitry for supplying the antenna excitation signals and phase error correction circuits for maintaining proper signal phase through the antenna module.

Theory of dielectric-filled edge-slot antennas

Abstract: A theory has been developed for dielectric-filled edge-slot (DFES) antennas which belong to a class of circumferential slot antennas that are suitable for conformal mounting on conducting bodies of revolution. The specific antenna considered consists of a disk of dielectric substrate mounted between the two halves of a conducting cylinder and is excited at its center by a coaxial stub. It can be tuned for a desired operating frequency with the help of a number of axially oriented passive metallic posts located inside the dielectric region. For analysis, the antenna is modeled as a symmetrically excited E -type radial waveguide loaded with the metallic posts and terminated by an equivalent admittance appropriate for the radiating aperture. Circuit parameters for the metallic posts in the radial waveguide are obtained by detailed field analysis using mode matchng techniques. These are then used, along with the equivalent transmission line circuit for the antenna, to obtain the input reflection coefficient as a function of frequency for various DFES antennas. The results of computations based on the theory developed are compared with available measured values.

Spiral slotted phased antenna array

Abstract: A flush mounting, cavity-backed, dual orthogonal slot antenna in which improved radiation pattern characteristics are obtained by making the spiral slot pattern elliptical in the aperture plane. A cavity (11) and a flanged aperture plate (11a) are shown in which one slot pair (12 and 13) is orthogonal with respect to another slot pair (14 and 15) within the aperture plate (11a). Coaxial split-tube baluns (12a and 14a) are used to drive the junctions between corresponding slot pairs. Optional cavity dielectric (18) is provided and a drive coupling arrangement includes a four port comparator hybrid (30) having ≦ and Δ ports (17 and 16) respectively, for alternate excitation to produce a single lobe or a double lobe pattern with null. Switching apparatus is provided to connect a common terminal (26) to either of the ports (17 or 16).

A Multislotted Waveguide Antenna for High-Powered Microwave Heating Systems

Abstract: A method of microwave power application is described for large industrial heating systems in which a preselected temperature distribution may be specified for typical work loads. This goal is approached through the use of a discrete number of fieldradiating slots cut in the broad side of an S-band waveguide. Uniform or graded distributions of microwave power are obtainable through design data that were experimentally determined and empirically recorded. Individual slot power is determined by the waveguide input power, the number of slots, and the location of the slots on the surface of the waveguide. In a system using 30 slots, work-load temperatures at 60-kW input levels were noted to meet a five-percent variation around a 100°C requirement.

New microstrip slot radiator for medical applications

Abstract: A microstrip slot radiator for local heating of biological tissue operating at 2.45 GHz was designed and tested. The radiator is well matched within a relatively wide range of frequencies (v.s.w.r. < 1.5 for 2.45 ± 0.3 GHz) and provides energy deposition within an area of about 1.5 cm × 1 cm.

Annular slot antenna

Abstract: The antenna comprises an open-mouthed cylindrical cavity 1 defined by side 11 and bottom 12 walls. A conductive coating 5 on an insulative substrate 4 lies on the bottom wall 12. The coating 5 is spaced from the side wall 11 by an annular space 2. A coaxial line 7, 8 feeds microwave energy to the zone between the coating 5 and the wall 12. That zone acts as a radial transmission line which couples the coaxial line to the cavity.

Antenna for radio equipment

Abstract: PURPOSE:To obtain a high-efficiency magnetic field type incorporated antenna, by providing a slot antenna and a cavity resonator as one body on the housing of a radio equipment to constitute the antenna compactly. CONSTITUTION:A conductor plate 2 is provided closely to one face 1 on a metallic housing 10 of a rectangular parallelepiped structure for a radio equipment, and edges other than a slit 4 are earthed to the face of the housing 10 to obtain a cavity resonator. The length of the slit 4 is set to about lambda/2 (lambda is the wavelength of a used frequency), and the longitudinal length of a cavity resonator 3 is set to about 1/4, thus resonating the resonator as a slot antenna. In this slot antenna, a power is fed across the housing 10 and the slit 4 of the conductor 2, and the impedance near the resonance frequency in the center of the slit 4 is very high and reaches several hundreds OMEGA. Therefore, for impedance matching between the slot antenna and the radio equipment, a feed point 5 of the slot antenna is shifted from the center to perform the offset feed.

A cavity-backed resonant slot array--Theory and measurement

Abstract: An antenna is described which consists of a broadside array of half-wavelength slots backed by a single cavity containing a filter that allows resonance with a mode suitable for the excitation of the array. A formula for the input resistance at resonance is derived using a mathematical model which is valid only if the cavity is highly underdamped and if the individual slot spacings exceed half a free-space wavelength. By proper choice of dimensions it is shown that the antenna can be matched to an external power source. Measurements were made on two arrays at 10 GHz, and results are consistent with calculations. The observed radiation patterns agree with expected field distributions provided there are no metallic projections on the plane of the array.

Design of collinear longitudinal slot arrays fed by boxed stripline

Abstract: An analytical design method is presented which enables determination of the length of each slot in a collinear array and the tilt angle of the strip relative to each slot for a specified aperture distribution and input impedance, in the presence of external mutual coupling. The theory uses an extension of Stevenson's approach to relate the TEM mode current in the boxed stripline to the slot-voltage, and a geometrical theory of diffraction (GTD) expression for the external coupling between slot elements. A novel method is introduced to constrain resonant slot lengths to practical values. An array constructed to validate the theory has given good results.

Strip and line source synthesis with a quality factor constraint

Abstract: Rhodes' antenna synthesis method is extended and modified to include strip source antenna systems that are optimized for a given value of a quality factor. A set of biorthogonal aperture functions, which happen to minimize the quality factor functional of the antenna, are shown to have a finite Fourier transform that is doubly orthogonal over the invisible and visible ranges of the radiation pattern. The biorthogonality properties of the above functions as well as the double orthogonality properties of the finite Fourier transforms of these functions are shown to lead to a synthesis method that is numerically identical to Rhodes' but which handles a more general class of antennas.

Crow's-nest antenna

Abstract: An experimental system of a phased array with 3π coverage is described, whose core component is the newly developed crow's-nest antenna, a phased-array antenna with spatially randomly distributed loop antennas.

Analysis of radiation pattern and G/TA for shaped dual-reflector antennas

Abstract: An accurate calculation of the radiation pattern from shaped Cassegrain-type dual-reflector antennas is given. In the forward axial region this is achieved by using the classical methods of physical optics and aperture field. Elsewhere we use the g.t.d. in the analysis, utilising a recent solution for the double knife-edge diffraction phenomenon between the two reflector edges. The result is used to compute the antenna temperature TA at a number of frequencies in the 1–100 GHz region commonly used for radio astronomy and space communications. The use of shaped reflector profiles to maximise G/TA consistent with other requirements such as acceptable sidelobe levels is discussed.

Crossed slot cavity antenna

Abstract: A resonant cavity (10) having at least one radiating antenna slot (18,20) formed in a wall (12) of the cavity includes an electrically conducting plate (22) disposed within the cavity and substantially spaced from all internal cavity walls so as to effectively lengthen the electrical resonant dimensions of the cavity for a given physical size. This slotted cavity antenna permits the use of simplified feeding structures, provides a more efficient antenna structure and reduces the necessary physical dimensions of the structure for operation at a given frequency.

Offset Cassegrain Earth Station Antenna for the Japanese Domestic Satellite Communication System

Abstract: Offset reflector antennas have advantages for communication systems because they are not severely subject to blocking. Difficulties mainly arising from structual asymmetries have inhibited the realization of an offset reflector antenna with a large aperture for commercial use. This paper describes the design of an offset Cassegrain earth station antenna for the Japanese domestic satellite communication system. Antenna measurements showed 76 and 69 percent aperture efficiencies at 20 and 30 GHz, respectively, less than -20 dBi wide angle directivity and an 18 K noise temperature in operating conditions. Performances are far superior to conventional axisymmetrical earth station antennas. The antenna was reassembled on a telephone office building after the measurements. The antenna gain was reconfirmed there, using the sun as a radio frequency source. Experiments show that the earth station antenna and a terrestrial antenna can be placed on the same building without serious interference.

Pattern shaping with a metal plate lens

Abstract: The metallic parallel plate lens is a viable alternative to both the shaped reflector and the array antenna for beam shaping. A C -band antenna using this lens is designed to provide a csc^{2} \theta (cos \theta)^{1/2} power pattern over the angular limits of 60\deg-80\deg below horizontal. The Woodward-Levison synthesis technique is applied to determine the required amplitude and phase distribution across the aperture. Initial plate positions and lengths of the lens are determined from geometrical optics and infinite waveguide theory. The positions and lengths of the lens plates are adjusted experimentally until a satisfactory pattern is obtained.

Radiation characteristics of annular-slot arrays fed by radial waveguides

Abstract: A method is established which gives the field solution for an annular slot array fed by a radial waveguide. The exciting source is placed in the central area of the feeding waveguide and its field is assumed as a summation of the radial waveguide modes. The dielectric constant of the waveguide region could be lossy or lossless. To obtain a solution, the aperture electric field is expanded into a finite series of suitable basis functions with unknown coefficients, the number of which is directly related to the electrical dimensions of the slots. The complex constants are then obtained by employing the appropriate Green's functions and an application of the boundary conditions over the aperture. It is shown that, in general, higher order modes of the radial waveguide region excited by the slot discontinuities may have a significant effect on the solution and for a precise evaluation of the field their contribution must also be included. The possible application of the method for the design of arrays with directive beams is also discussed.

Coupling between closely spaced back-to-back paraboloidal antennas

Abstract: Using the geometrical theory of diffraction (GTD), a method of calculating the power coupling between closely spaced back-to-back paraboloidal antennas is presented. The method is illustrated by considering the coupling between two identical front-fed symmetric paraboloids, each of which is fed by a TE 11 mode circular waveguide.

New technique for efficient pattern computation of aperture and reflector antennas

Abstract: A new and efficient technique for computing secondary patterns of antennas with known aperture distributions is described. The method is extendable to parabolic reflector antennas with given surface current distribution. The fast Fourier transform (f.f.t.) algorithm is used to compute the coefficients of expansion of a series representing the radiation pattern.

A new interpretation of the VLF impedance measurements of island slot antennas

Abstract: It was first suggested by Morgan in 1960 that an island might serve as a naturally resonant VLF slot antenna. However, theoretical studies by Galejs and Staras suggest that the principal current path would not be, as hoped, the ocean looping around the ends of the island. Rather the current would be confined to a region of the order of 1 skin depth radius centered on the conductor coupling the VLF power to the island. This is in conflict with the recent observations of Morgan, who claims to have observed resonances in the impedance of Deception Island. It is suggested here that these resonances are in fact resonances of the transmission lines used to connect power to the island. A similar explanation is also offered for the peninsula resonances observed by Gould. With this interpretation the experimental data on island antennas is fully in agreement with the current theoretical predictions of Galejs and Staras.

Crosspolarisation characteristics of linear comb-line microstrip antennas

Abstract: Microstrip antennas are a subject of increasing interest in the microwave antenna field, and the comb-line antenna is particularly attractive for medium to low sidelobe level operation. However, the crosspolarisation properties of such structures have not been discussed previously, although these are of importance where the suppression of sidelobes in all polarisation planes is required. A mainly experimental investigation is described into the crosspolarisation characteristics of comb-line antennas, and criteria for crosspolarisation suppression are derived for particular board characteristics at 4.3 GHz.