Showing papers on "Antenna (radio) published in 1985"

Antennas and Radiowave Propagation

Abstract: Antennas and radiowave propagation , Antennas and radiowave propagation , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Gain enhancement methods for printed circuit antennas

Abstract: Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.

Method and apparatus for high frequency catheter ablation

Abstract: A medical procedure for treatment of tachycardia (rapid heartbeat) or cardiac disrhythmia uses a catheter which includes a flexible coaxial transmission line (coax) terminated by an antenna. The antenna and coax are introduced into a chamber of the heart. The antenna is brought into contact with a wall of the heart. Action potentials generated by the heart are coupled through the antenna and the coaxial cable to a standard electrocardiograph apparatus for display. Other electrodes placed about the body also produce action potentials which are displayed by the electrocardiograph. The position of the antenna in the chamber of the heart is adjusted with the aid of the displayed action potentials until the antenna is in contact with the region to be ablated or injured as indicated by its characteristic electrical signature. When the antenna is adjacent to or in contact with the desired location, radio frequency or microwave frequency electrical energy is applied to the proximal end of the coax and through the coax to the antenna. The action potentials may be viewed while the electrical energy is applied. The power of the electrical energy is slowly increased until the desired amount of blockage of the bundle of His or damage to the ectopic focus has been achieved.

A radial line slot antenna for 12 GHz satellite TV reception

Abstract: The analysis and design of novel planar antennas which can radiate circularly polarized pencil beams in x -band are presented for the application of receiving direct broadcast from a satellite (DBS). This antenna belongs to a class of slotted waveguide antennas and high efficiency is expected in principle. A circular two-dimensional aperture is located on the top plate of a twofold radial waveguide and is excited by a radially inward traveling transverse electromagnetic (TEM) mode in the upper waveguide. Slots are arrayed on the aperture spirally in such a way that they can couple with the radial currents flowing over the aperture plate to produce a circularly polarized broadside beam. Promising performances of the antenna are predicted theoretically. Experiments are performed with respect to basic characteristics of the antenna and they show the validity of the design and analysis.

The MU radar with an active phased array system: 1. Antenna and power amplifiers

Abstract: The MU (middle and upper atmosphere) radar of Japan is a 46.5-MHz pulse-modulated monostatic Doppler radar with an active phased array system. The nominal beam width is 3.6° and the peak radiation power is 1 MW with maximum average power of 50 kW. The system is composed of 475 crossed three-subelement yagi antennas and an equivalent number of solid state power amplifiers (transmitter-receiver modules). Each yagi antenna is driven by a transmitter-receiver module with peak output power of 2.4 kW. This system configuration enables very fast and almost continuous beam steering that has not been realized by other mesosphere-stratosphere-troposphere radars. Also, a variety of sophisticated operations are made feasible by dividing the antenna array into several independent subarrays. A brief description of the system, particularly its antenna and power amplifiers, is presented herein.

Dual polarized sinuous antennas

Abstract: A sinuous antenna having N identically generally sinuous arms extending outwardly from a common point and arranged symmetrically on a surface at intervals of 360°/N about a central axis. Each antenna arm comprising cells of bends and curves. Each cell being interleaved without touching between adjacent cells of an adjacent antenna arm.

Factorization of the feed efficiency of paraboloids and Cassegrain antennas

Abstract: The first approximation to the aperture efficiency of a paraboloidal reflector antenna is called the feed efficiency. The factorization of the feed efficiency into subefficiencies which account for losses due to spillover, cross polarization, nonuniform aperture illumination, and phase errors is considered. The relations between the radiation patterns of circularly and linearly polarized feeds are also derived.

A multidirectional feed and flush-mounted surface wave antenna

Abstract: The present invention relates to a multidirectional feed which can be used by itself or preferably incorporated within a surface wave structure to form a flush-mounted antenna on, for example, a mobile unit. The feed arrangement comprises a ground plane including an annular cavity with a smaller annular slot. The annular slot is connected by multiple, spaced-apart, leads to an associated transceiver. The annular cavity is also formed to prevent both a shorting of the radio waves therein and the radio waves from propagating away from the cavity in a direction opposite the slot. A surface wave structure is disposed preferably with the feed centrally mounted and can comprise any suitable structure including annular corrugations and/or a dielectric layer to provide a flush-mounted antenna arrangement which provides radiation in azimuth in all directions with moderate elevation gain.

Parabolic antenna for directional-radio systems

Abstract: A radome (6) having a cylindrical collar (7) is placed in front of the reflector (1) of the antenna. The collar is clad internally with a ring (9) consisting of metal foil and a ring (10) of absorber material placed above it. The side of the rings (9, 10) facing away from the reflector (1) is provided with a tooth system (Z).

Automobile antenna system

Abstract: The present invention provides an autombile antenna system for detecting surface currents induced on the vehicle body by radio waves. The antenna system includes an electrostatic shielding case mounted on the vehicle body and having an opening formed therein. The opening in the case faces a metallic plate in the vehicle body and a loop antenna is housed within the case and disposed in close proximity to the opening thereof. The loop antenna has a plane of the loop positioned relative to the surface of the metallic vehicle plate at an angle in the range of 90 degrees to 135 degrees or 225 degrees to 270 degrees, whereby the antenna system can more efficiently detect the surface currents induced on the vehicle body by radio waves and can be miniaturized and improved in performance without any externally protruding member.

A low noise receiver for millimeter and submillimeter wavelengths

Abstract: A broadband, low noise heterodyne receiver, suitable for astronomical use, has been built using a Pb alloy superconducting tunnel junction (SIS). The RF coupling is quasioptical via a bowtie antenna on a quartz lens and is accomplished without any tuning elements. In this preliminary version the double sideband receiver noise temperature rises from 205 K at 116 GHz to 375 K at 349 Ghz, and to 815 K at 466 GHz. This is the most versatile and sensitive receiver yet reported for sub-mm wavelengths.

Nuclear magnetic resonance imaging antenna subsystem having a plurality of non-orthogonal surface coils

Abstract: An NMR antenna subsystem has a plurality of co-planar surface coils, each comprised of a plurality of segments and elements for tuning the coil to resonance at the Larmor frequency of a nuclei specie to be investigated. Each coil has circuitry for selectively detuning that surface coil when at least one other one of the plurality of surface coils is in use. One of a pair of co-planar surface coils can be utilized for signal reception and includes a parallel-resonant detuning circuit which operates only when a relatively large magnitude RF signal is induced by an excitation signal in a second surface coil. The second surface coil includes a circuit for detuning that coil except when an externally-provided signal is present; this signal may be the RF excitation signal itself or another signal provided simultaneously with the RF excitation signal.

Implantable apparatus for localized heating of tissue

Abstract: With the object of repetitively treating deep-seated, inoperable tumors by hyperthermia as well as locally heating other internal tissue masses repetitively, a receiving antenna, transmission line, and electrode arrangment are implanted completely within the patient's body, with the receiving antenna just under the surface of the skin and with the electrode arrangement being located so as to most effectively heat the tissue to be treated. An external, transmitting antenna, driven by an external radio-frequency energy source, is closely coupled to the implanted receiving antenna so that the energy coupled across the air-skin interface provides electromagnetic energy suitable for heating the tissue in the vicinity of the implanted electrodes. The resulting increase in tissue temperature may be estimated by an indirect measurement of the decrease in tissue resistivity in the heated region. This change in resistivity appears as a change in the loading of the receiving antenna which can be measured by either determining the change in the phase relationship between the voltage and the current appearing on the transmitting antenna or by measuring the change in the magnitude of the impedance thereof. Optionally, multiple electrode arrays may be activated or inactivated by the application of magnetic fields to operate implanted magnetic reed switches.

Dual-band microstrip antennas with monolithic reactive loading

Abstract: The design and experimental measurement of a dual-band, monolithic microstrip antenna is presented. The structure utilises a short-circuited length of microstrip transmission line to provide reactive loading and, thereby, retains the low-profile characteristic of a normal microstrip patch radiator.

The receiving antenna as a linear differential operator: Application to spherical near-field scanning

Abstract: The general receiving antenna is represented as a linear differential operator converting the incident field and its spatial derivatives at a single point in space to an output voltage. The differential operator is specified explicitly in terms of the multipole coefficients of the antenna's complex receiving pattern. When the linear operator representation is applied to the special probes used in spherical near-field measurements, a probe-corrected spherical transmission formula is revealed that retains the form, applicability, and simplicity of the nonprobe-corrected equations. The new spherical transmission formula is shown to be consistent with the previous transmission formula derived from the rotational and translational addition theorems for spherical waves.

The Effects of Driving Frequency and Antenna Length on Power Deposition Within a Microwave Antenna Array Used for Hyperthermia

Abstract: The theory of the linear, insulated antenna embedded in an electrically dense medium is applied to microwave antennas used for hyperthermia cancer therapy. The pattern of power deposition is computed for a square array of four antennas with a side length of 3 cm under the assumption of no coupling among antennas. The driving frequency is set to seven values between 300 and 915 MHz, and the antenna halflength is set to three values: 3 cm, 6 cm, and the resonant value.

Phase retrieval in the radio holography of reflector antennas and radio telescopes

Abstract: Methods of phase retrieval from simulated intensity information have been tested for use in the radio holography of reflector antennas In numerical simulations the Misell algorithm has been used successfully to retrieve the aperture phase distribution from two numerically simulated power polar diagrams, one in focus and the second defocused The technique uses no auxilliary reference antenna However, it does need a high signal to noise ratio, typically 50 dB if a 60 \times 60 array is to be measured to a precision such that the gain is within 1 percent of ideal It should be most useful where no direct phase measurements are possible and ground-based or satellite transmitters can be used as sources The use of astronomical maser sources (22 GHz) can give information on large scale deformations

Apparatus for microwave glow discharge deposition

Abstract: Apparatus for microwave energized glow discharge deposition of materials, onto a substrate including electronic structures having a plurality of layers of amorphous semiconducting alloys of varying conductivity types. The apparatus includes at least one deposition chamber in which a novel antenna coupled to a source of microwave energy to form a microwave energy excited glow discharge plasma is disposed. The antenna has coaxial conductors approximately one half wavelength long that are electrically connected to each other at their respective distal ends. A multiple integer of one half wavelength of a coaxial transmission line coupling the antenna energy and source may also form part of the antenna. The respective outer conductors of the transmission line and antenna are separated by an electrically small gap, but the respective center conductors are electrically connected. The apparatus may provide for continuous glow discharge deposition on a moving substrate web that passes through a number of deposition chambers for deposition of various layers to form a desired electronic device structure. Each chamber may include an antenna according to the invention.

Directivity optimization of a reflector antenna with cluster feeds: A closed-form solution

Abstract: The directivity of a reflector antenna deteriorates as the feed moves away from the focal point for beam scanning. This deterioration can be substantially reduced if a cluster feed instead of a single feed is used to control a beam. A closed-form solution is presented for the cluster excitation to achieve the optimum directivity. For an offset 108 \lambda parabolic reflector scanning 10 beamwidths, the optimum-directivity achieved by a 19-element (seven-element) cluster is 12 dB (8 dB) higher than that of a single element. Comparison of the optimum-directivity design and the popular conjugate field matching design is made. When the cluster spacing d is greater than 1 \lambda , it is found that the optimum directivity is higher than that of conjugate field matching (CFM) scheme by an insignificant amount, although the excitations of two designs can be quite different. For d , the optimum design may exhibit the supergain phenomenon, namely, extremely high directivities achieved by an oscillatory cluster excitation.

Microwave holography of large reflector antennas--Simulation algorithms

Abstract: The performance of large reflector antennas can be improved by identifying the location and amount of their surface distortions and then by correcting them. Microwave holography techniques are finding considerable applications as viable tools for performing this task. In these techniques, the complex (amplitude and phase) far-field pattern of the antenna is measured, using a reference antenna. Then, the Fourier transform relationship, which exists between the far field and a function related to the induced current, is invoked to result in the identification of the surface distortions. To critically examine the accuracy of the constructed surface profiles, simulation studies are required to incorporate both the effects of systematic and random distortions, particularly the effects of the displaced surface panels. In this paper, different simulation models are investigated with emphasis given to a model based on the vector diffraction analysis of a curved reflector with displaced panels. The simulated far-field patterns are then used to reconstruct the location and amount of displacement of the surface panels by employing a fast Fourier transform (FFT)/iterative procedure. The sensitivity of the microwave holography technique based on the number of far-field sampled points, level of distortions, polarizations, illumination tapers, etc., is also examined. In addition, the relationships between Az-El and u-v spaces are addressed in the Appendix. Most of the data are tailored to the dimensions of the NASA/JPL Deep Space Network (DSN) 64-m reflector antennas for which the result of a recent measurement is also presented.

Switchless external antenna connector for portable radios

Abstract: A portable radio transceiver and mobile mount housing are disclosed which utilize a switchless connector for connecting the portable unit to an external antenna which is electrically coupled to the mobile mount. In the preferred embodiment, the portable radio is equipped with an internal antenna which is either coupled to an electrical contact on the exterior of the portable unit adaptable to making electrical contact with a similar contact on the inside of the mobile housing when the portable radio is inserted therein. The internal antenna in the portable unit is shielded by the metallic mobile mount housing which obviates the need to disconnect the same. In one embodiment the contact disposed on the portable unit exterior is connected to a predetermined point on the internal antenna for impedance matching with the external antenna when the portable unit is inserted into the mobile mount housing. Similar switchless contacts can also be utilized for connecting the portable unit to external microphones, speakers, battery chargers and the like.

Subsurface inspection radar

Abstract: A radar system for subsurface inspection comprising a short pulse transmitter, an antenna for radiating signals to and receiving external reflections from the surface and from below the surface being inspected, a receiver connected to the antenna for generating an output signal in response to the external reflections, and a clutter cancellation circuit for eliminating internal reflections developed in the system to prevent interference by such internal reflections with the desired external reflections to enhance the system detection capability and reliability of evaluation of such external reflections. Clutter cancellation is accomplished by storing the internally generated clutter and subsequently subtracting it from each incoming radar range sweep consisting of surface and subsurface signals plus unwanted clutter. An internal signal recognition circuit rejects all return signals except that generated internally to the radar by the antenna structure, and this internal antenna echo is used as an internal reference signal whereby the radar system is relatively insensitive to wide variations in external reflection characteristics caused by wide variations in the nature of materials present in the surface being inspected. This in turn provides for a reliable control of the receiver sampling process which is indpendent of external signals and of their amplitude variations. A circuit for compensating for thermal drift permits long term cancellation of the internally generated clutter. The drift compensation circuit, the internal signal recognition circuit and the receiver provide a closed loop stabilization to allow the internal clutter to remain correlated on a range sweep by range sweep basis.

Voltage-controlled optical/RF phase shifter

Abstract: A new fiber-optic device designed to steer the radiation beam of a phased-array antenna has been demonstrated. A radiofrequency (RF) signal at 125 MHz is generated via photomixing at the output of a single-mode fiber-optic interferometer. The phase of the electrical signal is shifted over several cycles in direct proportion to a voltage applied to an optical controller. The controller consists of a Pockels-type optical phase modulator located in one arm of the heterodyne interferometer. Rapid changes in RF phase are feasible. A miniature low-voltage version of the device, based upon integrated optics, is proposed.

Tactile localisation: the function of active antennal movements in the crayfish Cherax destructor.

Abstract: Video recordings and single frame analysis were used to study the function of the second antennae of crayfish (Cherax destructor) as a sensory system in freely behaving animals. Walking crayfish move their antennae back and forth through horizontal angles of 100 degrees and more, relative to the body long axis. At rest, animals tend to hold their antennae at angular positions between 20 and 50 degrees. Movements of the two antennae are largely independent of each other. Before and during a turn of the body the ipsilateral antenna is moved into the direction of the turn. Solid objects are explored by repeatedly moving the antennae towards and across them. Both seeing and blinded crayfish can locate stationary objects following antennal contact. On antennal contact with a small novel object, a moving animal withdraws its antenna and attacks the object. When the antenna of a blinded crayfish is lightly touched with a brush the animal turns and attacks the point of stimulation. The direction taken and the distance covered during an attack can be correlated with: the angle at which the antenna is held at the moment of contact and the distance along the antennal flagellum at which the stimulus is applied. From behavioural evidence we conclude that crayfish use information about the angular position of their antennae and about the position of stimulated mechanoreceptors along the antennal flagellum to locate objects in their environment. We suggest ways in which an active tactile system-like the crayfish's antennae--could supply animals with information about the three-dimensional layout of their environment.

Design formulas for an asymmetrical coplanar strip, folded dipole

Abstract: The planar folded dipole is an appealing choice as a radiating element due to the properties that it can be constructed using printed circuit technology and its input impedance can be adjusted over a wide range of values. The input impedance of this type of antenna depends on three quantities: the impedance of the transmission line mode, the impedance of the dipole mode, and the impedance step-up ratio. The solution to three problems associated with these three quantities is developed and design formulas for a planar folded dipole are presented.

Microwave plane antenna

Abstract: A microwave plane antenna in which antenna bodies carrying thereon respectively at least a pair of microstrip lines are mounted to a supporting frame through means for movably positioning the antenna bodies along a plane including an axis perpendicular to the plane of the antenna body and another axis in the width direction of each pair of the microstrip lines, whereby the main beam direction of the plane antenna is made settable optionally in three-dimensional zone to be in the optimum direction with respect to a geostationary broadcasting satellite for remarkably improving the reception gain.

Dipole antenna with parasitic elements

Abstract: A dipole antenna system includes a driven dipole element and two parallel parasitic dipole elements equally spaced from the driven dipole element. Dual polarization can also be achieved by using two such systems arranged orthogonally.