Showing papers on "Antenna (radio) published in 1979"

An improved theory for microstrip antennas and applications

Abstract: An improvement to a recently reported theory for the analysis of the pattern and impedance loci of microstrip antennas is developed. It yields a theory which is simple and inexpensive to apply. The fields in the interior of the antennas are characterized in terms of a discrete set of modes. The poles corresponding to these modes are complex and depend on the losses in the antenna. The representation of the fields in terms of these modes is rigorous only for a bona fide cavity with no copper loss. The proper shift in the complex poles due to the addition of copper and radiative losses is approximated by lumping the latter two together with the dielectric loss to form an effective loss tangent. By so doing, it is found that the resulting expressions for impedance of the microstrip antenna are in good agreement with measured results for all modes and feed locations. The theory is applied to the evaluation of impedance variation with feed location, to multiport analysis, and to the design of circularly polarized microstrip antennas.

Electromagnetic waves and antennas above and below the surface of the earth

Abstract: The well-known electromagnetic fields generated by infinitesimal dipoles in the presence of the earth are reviewed briefly with special reference to contributions by H. Bremmer. The fields due to currents in extended conductors can be expressed in terms of an integral over the occupied volume but its evaluation is possible only when the currents are known in their dependence on the properties of the earth. This is true of the horizontal-wire antenna quite close to the earth both when driven by a localized emf and when acting as a scatterer in an incident field. It is also true of horizontal antennas in the earth not too close to the surface. Expressions for the most useful component of the radiated or scattered field are formulated for an end-driven Beverage-type antenna, for the horizontal wire as a scatterer in the presence of the earth, and for the embedded insulated traveling-wave antenna.

Quantum limits on resonant mass gravitational radiation detectors

Abstract: The methods of quantum detection theory are applied to a resonant-mass gravitational-radiation antenna. Quantum sensitivity limits are found which depend strongly on the quantum state in which the antenna is prepared. Optimum decision strategies and their corresponding sensitivities are derived for some important initial states. The linear detection limit (${E}_{min}\ensuremath{\sim}\ensuremath{\hbar}\ensuremath{\omega}$) is shown to apply when the antenna is prepared in a coherent state. Preparation of the antenna in an excited energy eigenstate or in a state highly localized in position or momentum space leads to increased sensitivity. A set of minimum-uncertainty states for phase-sensitive detection is introduced.

Design of a dichroic Cassegrain subreflector

Abstract: The design of a dichroic subreflector for a dual-frequency reflector antenna is described. This antenna consists of a Ku -band Cassegrain feed requiring the subreflector surface to be highly reflective at 13-15 GHz and a primary focus S -band feed requiring the subreflector to be transparent at 2.0-2.3 GHz. Such a performance is achieved by a surface of crossed dipoles printed on a dielectric sheet. The influence of parameters, dipole length, width and spacing, and the dielectric constant and thickness of the sheet on the reflection and transmission coefficients is experimentally evaluated. An analysis based upon the Floquent mode theory is shown to correctly predict the experimental results. The construction of a hyperbolic subreflector using the selected surface parameters is briefly described. As compared to a solid subreflector of identical shape, this dichroic subreflector produced a negligible loss (less than 0.1 dB) over a 13-15 GHz band. At the S band the loss was less than 0.2 dB over narrow selected bands and the axial ratio deterioration was also no more than 0.2 dB.

Analysis of the microstrip disk antenna element

Abstract: The circular microstrip antenna element is formed by a radiating disk closely spaced above a ground plane. It is modeled as a cylindrical cavity with magnetic walls which can be resonant in the transverse magnetic (TM) modes. The far fields and the radiation conductances for different mode structures have been calculated assuming a magnetic line current flowing along the perimeter of the disk. The directivity of a disk antenna excited in the dominant mode is between 4.8 dB and 9.9 dB, depending on the size. Losses, due to imperfect supporting dielectrics and to the finite conductivity of the conductors, have been derived by means of a perturbation technique. Graphs are given for design purposes showing the input impedance, the Q factor, and the radiation efficiency at resonance for different modes and thicknesses. The air-filled microstrip antenna has the highest efficiency and the broadest bandwidth at a given resonant frequency.

Plane-wave expansion for arrays of arbitrarily oriented piecewise linear elements and its application in determining the impedance of a single linear antenna in a lossy half-space

Abstract: An infinite array of arbitrarily oriented identical elements with arbitrary identical currents is considered. The field from this array is expanded into plane inhomogeneous waves, and the mutual impedance between the array elements and an exterior arbitrarily oriented element is derived. The formulation is particularly useful when the array is located adjacent to a dielectric interface. Numerical examples are given and the relationship to earlier formulations pointed out. It is further shown that the impedance of a single element can be obtained as the average of the scan impedance taken over the entire hemisphere (called the array scanning method (ASM)). This technique has a clear physical interpretation which greatly facilitates its uses, which include the moment method solutions of wire antennas as applied to the Sommerfeld integral. Numerical evaluation is straightforward when the dipole is in the lossy half-space, and the utility of the method is demonstrated by the presentation of results for the input impedance of dipoles in a variety of half-space environments. Solution is by Galerkin's method with a piecewise sinusoidal expansion for the current. Computer time is proportional to d^{-1} , where d is the distance of the dipole to the interface. For conducting media and low frequencies an approximation is made to reduce computation time. The moment method solution of a dipole buried at a depth as small as 1/150000 wavelength in the earth is presented.

Hybrid mode waveguide or feedhorn antenna

Abstract: The present invention relates to a hybrid mode waveguide or feedhorn antenna for transforming the TE 11 mode into the HE 11 mode. The waveguide or antenna comprises a first waveguide section of uniform cross-section at the TE 11 mode entrance port which in the antenna arrangement changes to a second section which flares outward toward the antenna mouth, and a spiro-helical projection bonded with a dielectric layer to the inner surface of the waveguide or antenna. The spiro-helical projection comprises a closely spaced helically wound wire structure formed of dielectrically coated wires which in the first section decrease in gauge size in small adjacent portions thereof as the helix progresses away from the TE 11 mode entrance port and in the remainder of the helical projection, the same or decreasing gauge wire in adjacent portions can be used.

Helmet-mounted sighting system

Abstract: An electromagnetic system for determining the orientation including position of a helmet worn by a pilot is disclosed, having a transmitting antenna for transmitting electromagnetic field vectors, a receiving antenna for sensing the electromagnetic field vectors, a control apparatus responsive to the sensed electromagnetic field vectors and the transmitted electromagnetic field vectors for determining the orientation including location of the helmet, the control apparatus having a first output for supplying the orientation to a utilization apparatus and a second output, a driver for supplying driving energy to the transmitting antenna coils, and a selector switch connected to the second output of the control apparatus and to the driver for sequentially energizing the coils of the transmitting antenna.

Array of annular slots excited by radial waveguide modes

Abstract: OF THE DISCLOSURE A high gain antenna suitable for use in satellite or similar communications systems having low profile, low weight and which does not interfere with dynamics during movement through space. The antenna has variable radiation patterns by the excitation of one or several radial modes. Basically the antenna is a simple radial open or closed waveguide with a slotted wall and transmission line to the radial waveguide at one or several places to launch the desired mixture of radial waveguides modes. The antenna may also be used as a filtering device in couplers and multi-feed systems.

Antennas for use with optical and high-frequency radiation

Abstract: Disclosed is an antenna for use in transmitting and/or receiving both optical, including infrared, and high-frequency electro-magnetic radiation. The antenna is comprised of a hollow conductor in the interior of which is arranged a light conductor as a dielectric. Arranged in the wall of the hollow conductor is at least one slot which acts as an input and/or output coupling opening for the hollow conductor and as an inlet and/or outlet window for optical radiation. Also disclosed is an antenna assembly unit consisting of a plurality of the individual antennas arranged to give omni-directional capabilities for receiving and transmitting of optical and high-frequency electro-magnetic radiation.

On natural noises detected by antennas in plasmas

Abstract: A formal generalization of the Nyquist formula for an antenna in a possibly anisotropic equilibrium plasma is presented along with practically useful expressions derived from it. It is shown that this can explain some preliminary results of the recent three-dimensional radio mapping experiment (SBH) on the ISEE 3 spacecraft.

Small antenna location synthesis using characteristic modes

Abstract: It is shown that the efficiency of a small antenna can be substantially increased by properly locating it on its support structure Characteristic modes are used to determine the optimum location and frequency

A plane-polar approach for far field reconstruction from near-field measurements

Abstract: It is well-known that the far field of an arbitrary antenna may be calculated from near-field measurements. Among various possible nearfield scan geometries, the planar configuration has attracted considerable attention. In the past the planar configuration has been used with a probe scanning a rectangular geometry in the near field, and computation of the far field has been made with a two-dimensional fast Fourier transform (FFT). The applicability of the planar configuration with a probe scanning a polar geometry is investigated. The measurement process is represented as a convolution derivable from the reciprocity theorem. The concept of probe compensation as a deconvolution is then discussed with numerical results presented to verify the accuracy of the method. The far field is constructed using the Jacobi-Bessel series expansion and its utility relative to the FFT in polar geometry is examined. Finally, the far-field pattern of the Viking high gain antenna is constructed from the plane-polar near-field measured data and compared with the previously measured far-field pattern. Some unique mechanical and electrical advantages of the plane-polar configuration for determining the far-field pattern of large and gravitationally sensitive space antennas are discussed. The time convention exp ( j \omega r ) is used but is suppressed in the formulations.

Useful coordinate transformations for antenna applications

Abstract: General coordinate transformations which are commonly encountered in many antenna applications are presented. Neither the feed coordinates nor the far-field pattern coordinates in general coincide with the antenna coordinates. Transformations discussed allow one to relate the spherical and Cartesian components of one system to the spherical and Cartesian compoents of the other system. In particular, attempts are made to use unified notations to assist the reader in a straightforward application of the transformations.

A new travelling-wave antenna in microstrip

Abstract: The radiation characteristics of the first higher order mode of microstrip lines are investigated. As a result, a simple travelling wave antenna element is scribed, having a larger bandwidth compared with resonator antennas. A method to excite the first higher order mode is shown. A single antenna element is treated theoretically and experimentally, and an array of four antenna elements is demonstrated.

Imaging reflector arrangements to form a scanning beam using a small array

Abstract: To obtain the performance of a large aperture phased array, a small phased array is combined with a large main reflector and an imaging arrangement of smaller reflectors to form a large image of the small array over the main reflector. An electronically scanable antenna with a large aperture is thus obtained, using a small array. An attractive feature of the imaging arrangement is that the main reflector need not be fabricated accurately, since small imperfections can be corrected efficiently by the array. As an application, a 4.2-m diameter antenna is discussed for a 12–14 GHz satellite with a field of view of 3 degrees by 6 degrees required for coverage of the continental United States.

High-frequency behaviour of microstrip open-circuit terminations

Abstract: The extensive use of open-circuit microstrip terminations as tuning stubs and, more recently, as antenna elements, demands design data on the frequency-dependent characteristics of the termination A variational solution for the end admittance is formulated using discrete and continuous mode distributions to represent the radiation, evanescent and substrate surface-wave fields Computed results for a variety of line widths on polyguide and alumina substrates are compared with available experimental and theoretical data It is established that useful admittance curves can be readily calculated using a simple trial aperture field, and the functional form of the curves is independently predicted by a Hilbert-transform relationship The frequency-dependent end admittance reveals the lower frequency range over which a given substrate is suitable for unshielded high-Q circuit applications and the higher-frequency region for microstrip antenna applications The generation of substrate surface waves increases with frequency, and sets an upper frequency limit for microstrip antenna applications Other practical issues of interest such as radiation patterns, intercircuit coupling and resonator losses are briefly considered and the usefulness of this approximate analysis, which represents the most complete treatment to date, is evident

Cellular mobile radiotelephone system using tilted antenna radiation patterns

Abstract: In cellular mobile radiotelephone systems employing reuse of a predetermined set of channels in adjacent iterations of a pattern of cells (FIG. 1), average signal-to-interference ratio in at least one cell region of interest is improved by tilting the antenna (11,12) gain pattern center-beam line of an antenna serving that region below the horizontal (FIG. 3). In one embodiment the tilt (θ) is sufficient to create a reduced-gain notch (FIG. 8) in the center-beam portion of the pattern.

Automatic vehicle identification system and method

Abstract: An automatic vehicle identification system for use in identifying and routing vehicles, such as railway cars or other vehicles which routinely travel a given track or path. A passive electronic device or electrical circuit is employed to intersect an energy field and respond thereto by generating a code in accordance with energy received and converted to coded electrical signals. Connected to the passive device is a short wave transmitter for transmitting signals generated by the electrical device when so energized. The electrical device may also comprise a plurality of different induction coils or antenna which serve to modify an energy field in a given manner, which modification may be detected by short wave sensing and converted to a coded electrical signal which is employed to identify the vehicle. In another form, a coded array of antenna or induction coils, is provided which modify energy fields generated at check points or scanning locations along a trackway or roadway, wherein such energy field modifications are sensed at each such scanning location, resulting in the generation of an electrical code at each location and identification of the vehicle.

Superresolution of uncorrelated interference sources by using adaptive array techniques

Abstract: By using adaptive techniques an antenna array can achieve an angular resolution of uncorrelated interference sources substantially greater than the aperture of diffraction limit. The antenna beam is scanned over the interference source locations, and for each scan condition the adaptive processor is allowed to reach its steady state. It is shown that for realistic ratios of interference strengths to system thermal noise, resolutions in excess of 0.25 times the Rayleigh limit can be achieved.

Optimum antenna polarizations for target discrimination in clutter

Abstract: The concept of Stokes vectors and Stokes target operators is used to obtain optimum antenna polarizations for target discrimination in the presence of background clutter. The analysis involves a constrained maximization of the ratio of two bilinear forms, representing the signal-to-interference power ratio.

Subarray pattern control and null steering for subarray antenna systems

Abstract: Improved performance of an electronically scanned subarray antenna system is realized by tailoring the subarray pattern in a manner that reduces the undesirable effects of illumination truncation at the edge of the main array. This is accomplished by introducing variable attenuators into individual feed elements to effect an illumination intensity taper of the feed element array output. The improvement permits effective utilization of deterministic and adaptive nulling at both the main array and the subarray levels and further provides a system ability to scan over wide spatial angles with wide bandwidths and low sidelobes. The technique is adaptable to both space fed and constrained subarray antenna systems.

Accurate determination of gain and radiation patterns by radar cross-section measurements

Abstract: Using a two-port network and geometrical interpretation of equations involved in antenna scattering, it can be derived that antenna characteristics may be determined in properly designed scattering measurements. As an alternative to this approach it is shown that measurement procedures for gain and radiation pattern can be developed from simple considerations of the receiving, transmitting, and scattering properties of antennas. The main advantages of the technique are that no gain standard is required and a disturbing feedline to the antenna can be avoided. In addition to this the technique seems to be highly accurate. These general conclusions are well corroborated by experimental data on a standard gain horn. Sources of errors are outlined and compared with sources of errors in conventional techniques.

Multiple band circularly polarized microstrip antenna

Abstract: Disclosed is a multiple band antenna assembly for communicating electromagnetic radiation. An antenna element stack is constructed of a plurality of elliptical lamina antenna elements mutually separated by layers of dielectric material, and separated from a ground plane by dielectric material. The antenna assembly is coupled through a feed line in contact with the top antenna element. A conductor joins the remaining antenna elements to the ground plane. Each individual antenna element is operable for communication reception and transmission within a frequency band determined by the size of the particular antenna element. The antenna elements are arranged in order of decreasing size with the largest antenna element closest to the ground plane. The sizes of the antenna elements may be selected to provide electromagnetic radiation communication over several distinct frequency bands, or to connect the individual bands into a broad band.

Slotted cavity antenna

Abstract: A resonant cavity having at least one radiating antenna slot formed in a wall of the cavity includes an electrically conducting plate 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.

A model for calculating the radiation field of microstrip antennas

Abstract: Starting from the equivalence principle, an aperture model is developed for calculating the radiation field of microstrip antennas. In this communication the model is applied to the rectangular microstrip resonator antenna. Antenna characteristics, like patterns and radiation resistance, are computed and compared with experimental results. The model and the calculations include the higher order modes as well as the fundamental mode of the resonator antenna.

Temperature-sensing probe structure for wireless temperature-sensing system

Abstract: A sensing element is adapted to monitor a temperature of a foodstuff placed within an oven cavity of a cooking utensil such as a microwave oven. The sensing element comprises a thermally-responsive element, an antenna, a double choke, and a trimmer condenser. The double choke is bent so as to provide a double compartment for causing choke operations. The double compartment contains a material the dielectric constant of which is higher than the air. A capacity of the trimmer condenser is adjustable. A resonance circuit or an oscillation circuit may be formed with the thermally-responsive element and the trimmer condenser. A metallic member is disposed adjacent to the antenna. The length of the antenna is selected as an integral multiple of about λ/2 (λ is the wavelength of the microwaves).

Water-Immersed Microwave Antennas and Their Application to Microwave Interrogation of Biological Targets

Abstract: This paper describes a method of significantly improving the resolution of systems used for interrogating the spatial variation of permittivity of biosystems at S band. The basic principle employed is to contract the wavelength of the interrogating radiation and to reduce the physical aperture of the interrogating probes by immersing the transmitting antenna, receiving antenna, and the target into a material with a high dielectric constant, namely water. The antenna design is described, and line scans employing transmitted and reflected energy are presented.

Ultra-high-frequency diode phase shifter usable with electronically scanning antenna

Abstract: A four-state phase shifter for UHF waves comprises two O-π phase-shifting elements of planar structure on a common substrate, these phase-shifting elements including a symmetrical and an asymmetrical transmission line which can be selectively coupled in one of two ways by the alternate blocking and unblocking of respective diodes for a relative phase reversal. The two phase-shifting elements are linked by two further transmission lines of different propagation constants which can be selectively activated, again with the aid of diodes, and which may be disposed on opposite faces of the substrate or may form part of a coplanar conductor array on the same substrate face.

Coaxial dual antenna connection arrangement for communications apparatus

Abstract: Apparatus having an integral coaxial antenna coupled via a coaxial connector to its internal circuitry has a coaxial switch/connector for alternatively coupling an external coaxial signal source to the internal circuitry, thus reducing impedance mismatch to a minimum with no impedance matching network required.