Showing papers on "Antenna (radio) published in 1983"

The resonant cylindrical dielectric cavity antenna

Abstract: An experimental investigation of the radiation and circuit properties of a resonant cylindrical dielectric cavity antenna has been undertaken. The radiation patterns and input impedance have been measured for structures of various geometrical aspect ratios, dielectric constants, and sizes of coaxial feed probes. A simple theory utilizing the magnetic wall boundary condition is shown to correlate well with measured results for radiation patterns and resonant frequencies.

Rectangular dielectric resonator antenna

Abstract: An antenna which consists of a resonant rectangular parallelepiped dielectric on top of a ground plane is described. Calculated radiation patterns and measured impedances are presented, and the effects of feed probe length variations are discussed.

System for controlling body implantable action device

Abstract: The system includes a sensor assembly comprising a body implantable physiological sensor for controlling a body implantable action device operable to act upon the body in response to changes in a physiological parameter sensed by the sensor. The body implantable action device can be a heart pacing device, a drug infusion pump, or other device which acts upon a human body. The sensor assembly includes a transmitter for transmitting coded signals to the action device which has programming circuitry for deciphering the signals received from the sensor assembly generated by the sensor which is in a location away from the location of the action device. Once these signals have been deciphered, the programming circuitry can adjust the output from the action device, such as the rate and A-V delay of pacing pulses from the pacing circuitry. In one embodiment, the transmitter is a radio transmitter and the programming code transmitted therefrom is picked up by an output terminal, such as a distal electrode of a pacing lead, which acts as a pickup antenna.

Endotract antenna device for hyperthermia

Abstract: An endotract antenna used for hyperthermia treatments. A microwave radiation antenna is surrounded by a balloon-like member made of a thin polymeric film. Tubes for feeding and draining a cooling liquid to and from the inside of the balloon-like member enable the device to effectively warm an endotract lesion such as a tumor by effectively supplying the energy of the microwaves emitted from the antenna to the endotract lesion.

Direction finding with an array of antennas having diverse polarizations

Abstract: The advantages of using diversely polarized antennas to determine bearings of multiple cochannel narrow-band signals are shown Three bearing estimation algorithms-maximum likelihood (ML), adapted angular response (AAR), and Music (multiple signal classification)-are extended to handle antenna arrays with diverse polarizations; the maximum entropy method does not readily extend The proposed algorithms are applicable to arbitrary antenna locations and directional characteristics and arbitrary noise correlations between the antenna outputs The algorithms are compared on the basis of multiple signal resolution and bearing accuracy in the presence of noise The Music algorithm exhibits superior performance at moderate to low signal-to-noise ratio (SNR)

Least-squares methods for the extraction of surface currents from CODAR crossed-loop data: Application at ARSLOE

Abstract: Least-squares methods are demonstrated that extract surface current radial velocities from first-order Coastal Ocean Dynamics Applications Radar (CODAR) sea-echo Doppler spectra for the compact crossed-loop/monopole antenna system. Based on the known physics of first-order sea scatter at HF, these techniques, implemented as software, are objective and automatic in that they: a) determine from the sea-echo phase and amplitude correction factors for the antenna elements; b) separate the first-order spectrum from the surrounding continuum for arbitrarily varying current conditions; c) using statistical hypothesis testing, select and use either a single or dual-angle model for radial current patterns, whichever best fits the data; d) calculate angles associated with given radial velocities; e) combine the data into a polar-coordinate map of radial velocity versus position; and f) calculate radial velocity uncertainties at each point on the map. In addition, as interpretive aids, two methods are evaluated and compared that provide total current vectors from single-site CODAR data, along with their uncertainties: model fitting and the application of the equation of continuity. It is shown how these methods can be applied to the older, CODAR 4-element antenna system, however, the following advantages of the crossed-loop/monopole system are discussed: it is physically more compact; analysis procedures are more efficient; resulting current velocities are more accurate, because there are no side-lobe problems; and finally, it also gives the ocean wave-height directional spectrum. These methods are tested and optimized against data taken during the Atlantic Remote Sensing Land Ocean Experiment (ARSLOE) storm (October 23-27, 1980), when surface currents varied in speed between 0-50 cm/s and over nearly 300° in angle. Current velocities were measured to a range of 36 km from the radar. Standard deviations in angle are typically 1°-3°; these translate to 2-3 cm/s rms radial velocity uncertainties over most of the coverage area, with decreased accuracy in angular sectors nearest the coast. Total current velocity vectors in strips parallel to shore obtained from model fitting have typical speed and angle uncertainties of 4 cm/s and 12°, respectively. Of the several formulations for the equation of continuity evaluated here, the best gave uncertainties of 5 cm/s, 12° at the closest range cells; these values increase rapidly with range to exceed 20 cm/s, 30° for distances greater than 20 km. The surface currents were observed to follow the wind throughout most of the storm at ARSLOE, but the current was almost always more closely parallel to the shore than the wind. An interesting exception occurred when the onshore storm wind that had prevailed for two days ceased; there was a rush of surface current directly offshore as the storm-surge sea level dropped. The surface current speed measured by CODAR in the upper meter of the ocean was, on the average, 2.1 percent of the windspeed.

An introduction to NMR imaging: From the Bloch equation to the imaging equation

Abstract: The emerging technology of NMR imaging is introduced here as a problem in system identification. We show how selected families of signals may be input into the system ("system," in this case, is almost synonymous with "patient") in order that the system's responses to these inputs may be directly interpreted in terms of the system parameters. Once identified, a raster display of the system parameters provides an internal image of the patient. Inputs to the system age four-component functions of time. One component describes the strength of an RF signal, and the other three components govern the strength of three spatially varying, independently controlled magnetic fields (the gradient fields) in which the patient is immersed. In response to these inputs some of the protons in the patient, acting in concordance with the Bloch equation, give rise to local fluctuations in the magnetization which are detected with a tuned antenna and a sensitive receiver. The relationship between this output signal and the system parameters is summarized in the imaging equation.

Design of Dielectric Grating Antennas for Millimeter-Wave Applications

Abstract: At theoretical procedure well suited for generating design data on dielectric grating antennas for the millimeter-wave region is presented. The procedure utilizes the effective dielectric constant (EDC) method to determine the phase constant of the leaky modes supported by the antenna structure of finite lateral width. The radiation or leakage constant of these modes is obtained from the relatively simple boundary value problem of dielectric grating antennas of infinite width. For single-beam radiation, the practicably interesting case, the phase and leakage constants completely determine the field distribution in the antenna aperture, from which the directivity gain and radiation pattern are then calculated. The dependence of the antenna characteristics on the dimensions of the radiating structure is presented and discussed for epsilon = 12, the dielectric constant of typical millimeter-wave materials, such as silicon and GaAs.

Geodesic dome-lens antenna

Abstract: An antenna of the geodesic lens type is disclosed. The antenna structure is based on optical principles and provides wide angle scanning of a narrow base. The exact shape of the domed structure is found by solving an integral equation and results in nearly perfect focus in the scan plane. A dielectric loaded flared horn is attached to the feed circle of the domed structure and focusses energy in the plane orthogonal to the scan plane. The cross sectional shape of the outer curvature of the dielectric is elliptical. Since the structure is circularly symmetrical, constant beam shape, wide angle scanning, and a rapid scan rate are possible.

Considerations for Millimeter Wave Printed Antennas

Abstract: Absiruct4alculated data are presented on the performance of printed antenna elements on substrates which may be electrically thick, as would he the case for printed antennas at millimeter wave frequeneies. Prioted dipoles and microstrip patch antennas on polytetrafluoroethylene (PTFE), quartz, abd gallium arsenide substrate are considered. Data are given for resonant length, resoriant resistance, bahdwidth, loss due to surface waves, loss due to dielectric heating, and mutual coupling. Ah presented is an optimizatidn procedure for maximizing or minimizing power launched into surface waves from a multielemerit printed antenna array. The data are calculated by a moment method solution.

Array signal processing

Abstract: Array signal processing (ASP) represents a class of antenna system where the output from an array is subjected to various forms of signal processing (e.g. phase and amplitude control, time delay or frequency translation) in order to produce outputs which can simultaneously provide angular information relating to several different directions. A different aspect of ASP which has received considerable attention over the last few years is adaptive arrays and null steering antennas. Here, instead of defining a number of wanted directions for receiving signals we can specify some wanted and some unwanted directions; the latter may contain high-level interfering signals which must be minimised by means of directional nulls in the patterns. In some cases the directions of these nulls may be fixed or pre-programmed, but in many cases the antenna response must be adaptive. This means that the shape of the directional pattern is determined in response to the angular distribution of received signals in order to try to meet some desirable criterion. The simplest form of adaptive and null steering antenna is probably the sidelobe canceller. This can steer a single directional null within the sidelobe region of a normal directional pattern. Multiple null adaptive arrays in general define a 'wanted direction' and then introduce one or more feedback controls to minimise the signals from all other directions. Null steering systems have applications in radar, sonar and communication systems. In the latter case, there may be additional complications if it is not possible to specify the direction of the wanted signals.

School of Electrical Engineering.

Abstract: The possibility of making the antenna of an MST radar too large is pointed out. It is not that the signal ceases to become stronger beyond some critical antenna size; the received scattered signal actually becomes weaker as the antenna size is increased whenever the target is in the near field, Fresnel region of the antenna. The Arecibo antenna is a case in point. It is supposed that MST work would benefit to use a feed which illuminated only a portion of the dish.

An efficient computational method for characterizing the effects of random surface errors on the average power pattern of reflectors

Abstract: Based on the works of Ruze and Vu, a novel mathematical model has been developed to determine efficiently the average power pattern degradations caused by random surface errors. In this model, both nonuniform root mean square (rms) surface errors and nonuniform illumination functions are employed. In addition, the model incorporates the dependence on F/D in the construction of the solution. The mathematical foundation of the model rests on the assumption that in each prescribed annular region of the antenna, the geometrical rms surface value is known. It is shown that closed-form expressions can then be derived, which result in a very efficient computational method for the average power pattern. Detailed parametric studies are performed with these expressions to determine the effects of different random errors and illumination tapers on parameters such as gain loss and sidelobe levels. The results clearly demonstrate that as sidelobe levels decrease, their dependence on the surface rms/ \lambda becomes much stronger and, for a specified tolerance level, a considerably smaller rms/ \lambda is required to maintain the low sidelobes within the required bounds.

Cylindrical-rectangular microstrip antenna

Abstract: Resonant frequencies f_{r} of a cylindrical-rectangular microstrip antenna are theoretically calculated. Comparison is made to f_{r} for a planar rectangular patch antenna, including the simplest planar patch modes having no field variation normal to the patch surface. The validity of using planar antenna patches to characterize microstrip antennas is examined.

Broadband isotropic probe system for simultaneous measurement of complex E- and H-fields

Abstract: A broadband isotropic probe system simultaneously measuring the E- and H-field intensities of rf complex, near-field electromagnetic radiation comprises a set of three mutually orthogonal dipole antennas and a set of three mutually orthogonal loop antennas located within the same volume of space. Each antenna has associated circuitry comprising a frequency-response-shaping filter and diode detector to provide a frequency response which is flat over the desired frequency bandwidth. The lengths of the dipoles are kept electrically small so that the EM fields are not perturbed. The diameters of the loops are kept electrically small so that the E-field pickup will be negligible. Coupling between any of the probe's antennas is also minimized by the use of electrically small antennas. Circuit means based on the use of square law detectors is also provided, the circuit including an arrangement of analog or digital data processing portions leading into a display means and a data recorder.

Rectangular microstrip patch antennas with infinite and finite ground plane dimensions

Abstract: The rectangular microstrip patch antenna has been extensively analyzed with regard to its input impedance and resonant frequency, both for infinite and finite ground plane dimensions. For infinite ground planes existing formulas have been compared and improved parameters presented. The influence from the side current radiation has been discussed as well. For finite ground plane dimensions the contribution from the ground plane edge diffraction has been accounted for in an equivalent radiation conductance and an equivalent diffraction susceptance. Formulas for these parameters have been developed on the basis of different theories. They are valid under the condition that only one of the ground plane dimensions are finite at the same time. Experimental investigations are carried out to test the accuracy of the developed formulas, showing good accuracy under the given conditions.

A Quasi-Optical Polarization-Duplexed Balanced Mixer for Millimeter-Wave Applications

Abstract: An integrated planar antenna-mixer structure for use at millimeterwave frequencies is described. A simple but accurate theory of the slot-ring antenna is applied to several experimental devices. Mixer conversion loss of about 6.5 dB was obtained from an X-band model. Measured radiation patterns of structures designed for 65 GHz agree reasonably well with theory.

Homotropic antenna system for portable radio

Abstract: An adaptable homotropic antenna system for use with a portable communication transceiver is described. The antenna system can be used for reception or transmission and can be completely enclosed within the portable transceiver housing. The homotropic antenna system evaluates the quality of a received signal and if the signal is below a predetermined threshold level, an alternate antenna will be selected. The antenna system will continue to sample the available antennas until an antenna produces a signal of acceptable quality.

Quadrifilar helix antenna tuning using pin diodes

Abstract: An antenna is tuned in separate discrete frequency bands by changing the ctrical length of the antenna. PIN diodes are placed at predetermined locations on the antenna coaxial cable radiating elements. When it is desired to shorten the antenna for a higher frequency band use, the diodes are biased short circuiting segments of the antenna. When the lower frequency band use is desired, diodes are unbiased so that the diodes act like a very small capacitance shunted by a large resistance which is essentially an open circuit permitting the entire length of the antenna to operate.

Time domain sensors for radiated impulsive measurements

Abstract: Discussion of various sensors and radiators commonly used for time domain antenna measurements is presented. The sensors and radiators discussed here are passive and analog devices which convert the electromagnetic quantity of interest to a voltage or current at their terminal ports. Moreover they are primary standards in the sense that their transfer functions can be calculated from their geometries and are flat (constant) across a wide frequency range. One of the major requirements for these sensors and radiators is that the electromagnetic far field, transmitted or received, is a replica or high fidelity derivative of the original pulse. Note that the transmitting transfer function of an antenna is proportional to the time derivative of the receiving transfer function of the same antenna, which follows from the reciprocity theorem. For electric field strength measurements, linear antennas loaded nonuniformly and continuously with resistance, or with both resistance and capacitance are discussed. Also, a conical antenna and an asymptotic conical antenna are discussed from the standpoint of improved characteristics. For an improved directivity, various types of transverse electromagnetic (TEM) horns are considered, e.g., a conducting TEM horn, and a resistively loaded TEM horn.

Electronic proximity identification system with simplified low power identifier

Abstract: An identification system comprising a reader (10) including a first signal generator (12) for generating a first signal (F1) which is radiated by an antenna (17). An identifier (11) includes an antenna (20) receiving the first signal for transmission to a signal modulator (32) which operates to modulate the signal in accordance with a preassigned code for the identifier. The modulated signal is then used to periodically unload or change the reactance of the antenna (20) which action in turn changes the reactance of the reader antenna and consequent voltage on the reader antenna (17). By detecting the change in the voltage on the reader antenna the code of the identifier is determined. Power drain is minimized and power is used efficiently by unloading during modulation and by changing reactance without changing load.

Crossed beam high frequency anti-theft system

Abstract: An article surveillance system employs a label or tag containing a non-linear impedance element, such as a semiconductor diode, connected to a metal antenna loop configured to pick up two distinct radio frequency transmissions displaced on either side of a selected center frequency. The non-linear impedance element connects opposing sides of a closed loop section at one end of the antenna to form a tuned tank circuit having a resonant frequency twice that of the selected center frequency. A first transmitter generates a tone modulated radio frequency displaced on one side of the center frequency, and a second transmitter generates a continuous wave radio frequency displaced from the center frequency on the other side. Both transmitter signals are fed separately to respective radiating antennae located adjacent to a surveillance area. The antennae are chosen to produce circularly polarized transmission of both frequencies within the surveillance area. The two different frequencies picked up by the transponder antenna are mixed by the non-linear impedance causing the tank circuit to resonate at a single higher frequency equal to their sum, which is double the center frequency; that resonant frequency is reradiated to be picked up by a receiver antenna or antennae suitably placed with respect to the surveillance zone to be detected by a very narrow band receiver responsive to the sum frequency. The modulating tone signal is derived from the received signal to produce a gradually increasing charge that is compared against a preselected threshold level to trigger an alarm for a fixed interval only when the detected signal is of a sufficient strength and duration.

Integrated receiver antenna device

Abstract: An integrated receiver antenna device comprising a pair of antenna elements providing a spiral antenna for receiving radio frequency signals over a broadband of frequencies with an extended high frequency limit and providing high sensitivity over the broadband of frequencies. The elements each have first and second ends and provide a pair of interwound conductive windings with their first ends positioned proximate to each other at the center of the antenna for providing sensitivity at the high frequency limit of received radio frequency signal, while the second ends of the elements are displaced from the first ends and positioned at the periphery of the antenna. A detector mixer unit is connected between and positioned proximate to the first ends of the antenna elements for deriving radio frequency signals received by the antenna elements and receiving an input signal for providing an oscillating signal at the detector mixer unit for producing an output signal.

Electric positioning motor control system, particularly automatic vehicle antenna extension system

Abstract: A commutator-type d-c motor has its line current connected through a sensing resistor (18) or transformer (18'), the pulses of which, upon energization, are counted in a counter (C) and also passed to a speed sensing circuit (S) in a control circuit (30), energization of the motor being disconnected if the frequency of undulations or waviness of the motor current drops, thus indicating that the positioned element, for example an antenna, window, or sliding roof of an automobile has reached a limiting position. The counter can be used to establish intermediate positions, upon suitable control by a selector switch (27) or a reference count number stage (C-Ref) controlled, for example, by a potentiometer (P) or from the selector switch (27). A timing circuit (T) prevents short-circuit through the motor upon manual sudden reversal of command of direction of rotation. The main switch can be coupled to a car radio to extend the car radio antenna upon energization thereof, retract the antenna upon de-energization, the selector switch also permitting manual retraction or projection, and disabling of the system if, for example, the radio is used for stored, e.g. tape reproduction.

Analysis of microstrip wraparound antennas using dyadic Green's functions

Abstract: The radiation pattern of microstrip wraparound antennas was obtained here using a theory based on dyadic Green's functions for concentric-cylindrical layered media. The dielectric layer that is usually neglected as a first-order approximation was considered here. An asymptotic expression for the dyadic Green's function that takes into account only the space wave is first obtained. Radiation patterns for various radii, permittivities, and thicknesses of the dielectric layer of a microstrip wraparound antenna were obtained using as a source a uniform annular magnetic current obtained by means of a cavity model with conducting magnetic walls. The calculated values of the percent pattern coverage decreases as the thickness and the permittivity of the dielectric layer increase. The influence of the dielectric layer is more pronounced for radiation direction near that of the axis of the cylindrical surface. It is also shown that the radiation patterns at a frequency of 2.0 GHz are not much dependent on the diameter of the antenna for values from 3 to 120 in.

Radio frequency antenna with controllably variable dual orthogonal polarization

Abstract: A controllable dual input/output port power divider coupled with a controllable phase shifter feed a dual ported dual polarized microstrip antenna structure. By controlling the power divider and phase shifter, arbitrary orthogonal polarization (e.g., linear, circular or elliptical) radiated r.f. fields are obtained. Virtually the entire structure comprising the dual port power divider, phase shifter and microstrip radiator may be formed of shaped photo-chemically etched microstrip conductors disposed a very short distance (e.g., less than one-tenth wavelength) above a conductive reference surface.

Furniture antenna system

Abstract: An antenna system for an article of furniture in which a panel of the article of furniture is sealed by a low loss dielectric material to isolate the panel from impurities which affect its electrical integrity. An antenna structure is applied thereon by silk screening, painting or otherwise marking of a conductive ink, or by vacuum deposition techniques, or by application of stamped or die cut foil, or by metallic tape, all by way of example. Connections to the antenna structure are made by compressing a conductive elastomeric material against terminations of the antenna structure so as to avoid temperature or other initiated dimensional changes of the panel which could effect the contact resistance to the terminations of the antenna structure, and also to avoid damaging the antenna structure. A specific connection arrangement is disclosed.

Frequency independent shielded loop antenna

Abstract: An antenna is disclosed that is especially useful for radiating and receiving non-sinusoidal electromagnetic waves. The antenna is an efficient and distortion-free radiator of electromagnetic pulses that do not use a sinusoidal carrier. The antenna's size is independent of frequency and the antenna, therefore, can be of small size relative to the wavelength of the radiated electromagnetic waves. When used for reception of electromagnetic wave energy, the antenna performs with low distortion. The basic concept underlying the invention is the modification of the Hertzian electric dipole into an antenna structure that can carry large currents without requiring a large driving voltage. Antennas for the transmission or reception of sinusoidal waves achieve that goal by employing resonant structures. The invention achieves the same result by changing the Hertzian electric dipole into a loop that forms a Hertzian magnetic dipole and preventing the undesirable magnetic dipole radiation by shields of conducting and absorbing materials.

Multifrequency HF radar observations of currents and current shears

Abstract: Techniques have been developed for using high-frequency (HF) surface-wave radar to measure ocean currents and vertical current shears in the upper 1 or 2 m of the ocean surface. An HF radar can precisely measure the phase velocity and direction of propagation of ocean waves whose wavelength is one.half the radar wavelength. In the absence of a current, the speed of the waves is given by the still-water dispersion relation. An underlying current will modify this speed. The radar measures the actual phase velocity through a Doppler shift, and the wavelength of the ocean wave is known through the first-order Bragg scattering relation, so a difference between observed and theoretical stillwater phase velocity can be calculated. In addition, longer ocean waves are affected by currents at deeper depths than are shorter ocean waves. By measuring the phase velocity at several different wavelengths, it is possible to measure a vertical current shear in the top 1 or 2 m of the ocean surface. This is a measurement that is very difficult to make by any other means. A portable coherent pulsed-Doppler HF radar system was developed at Stanford and used in several experiments, both on land on the California coast and on board a ship during the Joint Air-Sca Interaction (JASIN) experiment. The land-based experiments demonstrated that a current could be measured by an HF radar, and that its value agreed well with that measured by in-situ drifting spar buoys. In addition, there was evidence of a vertical current shear, both from the radar measurements and from the buoy measurements. The JASIN experiment was an attempt to apply these techniques to the measurement of surface current and current shear in the open ocean. The radar system was installed on board a ship, along with a receiving antenna consisting of a steerable phased array of eight wide-band loops. The steerable antenna was quite rugged and performed as expected. It produced antenna patterns consistent with the physical aperture of the array. The wind velocity during the JASIN experiment was quite low, so wind- and wave-generated currents were quite small. Nevertheless, there is some evidence of a current shear. Its magnitude is small and near the resolution limit of the radar, but it appears to be somewhat higher than estimates based on either the wind or wave conditions alone, but less than the estimates based on the sum of the two components.