Showing papers on "Antenna (radio) published in 1978"

Reactively controlled directive arrays

Abstract: The radiation characteristics of an N -port antenna system can be controlled by impedance loading the ports and feeding only one or several of the ports. Reactive loads can be used to resonate a real port current to give a radiation pattern of high directivity. The theory of resonance is extended to include complex port currents and impedance loads. The initial design of an array is obtained by resonating a desired port current vector, which is then improved by an optimum seeking univariate search method. The direction of maximum gain can be controlled by varying the load reactances. Several numerical examples are given for a circular array of seven dipole elements.

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.

Basic theory of probe-compensated near-field measurements

Abstract: The general problem concerning the interaction of a probe antenna with the near field of an arbitrary antenna is considered. The application of the Lorentz reciprocity theorem to the problem of determining antenna characteristics, including the far-field pattern, is presented. The data required to correct for the directional effects of the probe, the effect of probe correction on the measured data, and the attendant mathematical computations in rectangular systems are described. Extensions to cylindrical and spherical systems are discussed.

Offset-parabolic-reflector antennas: A review

Abstract: Although used for some decades, the offset-parabolicreflector antenna's electrical properties and performance were not accurately modeled and optimized until the 1960's. This paper reviews, in a tutorial fashion, the state of the art of this important antenna for readers who are not necessarily experts in antenna theory and technology. After a discussion of fundamentals, the performances of both single- and double-reflector configurations are treated and compared, and practical primary feeds are described. Comments are given on the present status of analysis and design and on problems to be solved.

Evidence for specular reflection from monostatic VHF radar observations of the stratosphere

Abstract: The received signal obtained on the vertical antenna of the 40 MHz Sunset radar often reveals an order-of-magnitude enhancement over the received signal obtained nearly simultaneously on an antenna pointed 30° from the zenith. The enhancement is most pronounced in regions of the atmosphere which are hydrostatically very stable. The enhanced vertical echoes are consistent with specular or partial reflection from thin stable laminae of radio index of refraction. An order-of-magnitude calculation is used to show that the expected reflectivity from a thin stable layer would easily be detected by the radar.

Plane-Wave Scattering-Matrix Theory of Antennas and Antenna-Antenna Interactions

Abstract: From Abstract: "This monograph is distinguished by the use of plane-wave spectra for the representation of fields in space and by the consideration of antenna-antenna (antenna-scatterer) interactions at arbitrary separation distances." From Preface: "The primary objective of this monograph is to facilitate the critical acceptance and proper application of antenna and field measurement techniques deriving more or less directly from the plane-wave scattering matrix (PWSM) theory of antennas and antenna-antenna interactions. A second objective is to present some recent and some new theoretical results based on this theory."

Apparatus for localized heating of a living tissue, using electromagnetic waves of ultra high frequency, for medical applications

Abstract: An apparatus for thermal treatment of the human body, using electromagnetic waves (200 to 2500 Mc/s) and radiometric receivers for monitoring and possibly controlling the temperature reached by the living tissues A generator at ultra high frequency delivers a power of about one Watt into a coaxial cable terminated by a probe emitting electromagnetic waves in the organ to be heated by dielectric losses in the medium A multichannel receiver, switched at intervals, analyzes the radiation reemitted by the living tissues through the probe, then utilized as a receiving antenna The temperature reached in a region surrounding the probe is deduced therefrom and can be utilized for controlling the power emitted through a servocontrol system

Method for automatically matching a radio frequency transmitter to an antenna

Abstract: A plurality of series inductors and shunt capacitors are provided between a radio transmitter and an antenna The inductors and capacitors are arranged in binary increments and are inserted in, or withdrawn from the circuit via provided reed relays A microprocessor activates the relays in one of several modes until the required degree of match is provided The status of the relays is stored in provided memory such that upon tuning of the transmitter to the same channel a proper match condition can be established without resort to the matching program

Estimates of brightness temperatures from scanning radiometer data

Abstract: In the analysis of antenna temperature maps of the earth obtained by satellite-borne microwave radiometers, estimates of brightness temperatures or averages of brightness temperatures over areas considerably smaller than the region sensed at a given position of the radiometer antenna are often needed. An application of the Backus-Gilbert methodology is made to obtain an objective criterion of the best resolution (in a least squares sense) obtainable from a given system and to investigate the trade-off between resolution and noise in the derived average brightness temperatures. The mathematically related problem of simultaneously analyzing antenna temperature measurements made at different frequencies by antennas with noncoincident antenna patterns is also considered.

The ISEE-1 and ISEE-2 Plasma Wave Investigation

Abstract: The ISEE-1 and ISEE-2 plasma wave investigation is designed to provide basic information on wave-particle interactions in the earth's magnetosphere and in the solar wind. The ISEE-1 plasma wave instrument uses three electric dipole antennas with lengths of 215, 73.5, and 0.61 m for electric-field measurements, and a triaxial search coil antenna for magnetic-field measurements. The ISEE-2 plasma wave instrument uses two electric dipoles with lengths of 30 and 0.61 m for electric-field measurements, and a single-axis search coil antenna for magnetic-field measurements. The ISEE-1 plasma wave instrumentation provides a comprehensive determination of wave characteristics over a broad frequency range, including high-frequency resolution spectrum scans, simultaneous high-time resolution electric- and magnetic-frequency-spectrum measurements, wave normal and Poynting flux measurements, and wide-band waveform measurements. The basic frequency range of the ISEE-1 measurements is 5.62 Hz-311 kHz, although wide-band waveform measurements can be made in selected frequency ranges up to 2.0 MHz using a special long baseline interferometer mode of operation. The ISEE-2 plasma wave instrumentation consists of a 16-channel spectrum analyzer covering the frequency range from 5.62 Hz to 31.1 kHz and a wide-band waveform receiver with the capability of making waveform measurements in selected frequency ranges up to 2.0 MHz.

Antenna measurements—1978

Abstract: This paper discusses the techniques in antenna measurements and facilities which have evolved over the last decade. The facilities include the tapered anechoic chamber, the compact range, and the near-field probing range. The significant advances in obtaining improved measurement accuracy for power gain, polarization, and swept-frequency techniques are also discussed.

VHF radar studies of tropospheric velocities and irregularities using spaced antenna techniques

Abstract: Observations of the troposphere with a VHF radar using a large antenna for transmission and small spaced antennas for reception show that atmospheric velocities measured by the drifts method agree well with balloon winds. Many of the echoes from the middle troposphere appear to come from horizontally stratified layers. Studies of the irregularity structure by measurement of the spatial coherence of these echoes and of their angular spectra by interferometric techniques show that many echoes are caused essentially by specular reflection.

A relatively short cylindrical broadband antenna with tapered resistive loading for picosecond pulse measurements

Abstract: A relatively short cylindrical antenna with continuously tapered resistive loading has been studied for the purpose of picosecond pulse measurements. The antenna considered is a nonconducting cylinder with continuously deposited varying-conductivity resistive loading. The current distributions on the antenna were numerically calculated using the method of moments. Using these current distributions, other quantities such as input admittance, near-field and farfield radiation patterns, and radiation efficiency, were also numerically calculated and compared with the results using the Wu-King's approximate current distribution. Agreement is relatively good except at high frequencies kh > \pi/2 where the method of moments appears to give better results. To verify the theoretical results, several resistively loaded antennas were fabricated, and their picosecond pulse receiving characteristics were analyzed for the frequency range between 5 kHz and 5 GHz. The experimental results indicate excellent linear amplitude and phase response over the frequency range. This provides the unique capability of this antenna to measure fast time-varying electromagnetic fields with minimal pulse-shape distortion due to nonlinear amplitude or phase characteristics.

Partially adaptive array techniques

Abstract: The selection of auxiliary elements for partially adaptive antenna arrays for the purpose of optimizing performance in a multiple narrow-band jammer environment is studied. An explicit solution for the two-jammer problem is derived. This case is sufficient to illustrate the interaction of multiple jammers and at the same time affords a degree of understanding of more complex problems. Computer solutions are also presented and discussed for several line array and planar array configurations.

Nonuniformly spaced linear and planar array antennas for sidelobe reduction

Abstract: The material discussed can be divided into two parts. In the first part, an iteration method is presented for calculating the distances between the elements of a symmetrical nonuniformly spaced linear array antenna for sidelobe reduction. The amplitude of the excitation is assumed to be constant. The iteration method is applied to linear array consisting of 24 elements. After a few iterations, the sidelobe-to-mainlobe power ratio was reduced to over 22 dB from its value of 13.2 dB for uniform array spacing. In the second part, several symmetrical nonuniformly spaced planar array antennas have been designed, using the nonuniform linear array spacings of part one. The planar arrays include square-shaped and circular structures, with the number of elements ranging from 284 to 576. The iteration method discussed can be applied to linear arrays with any number of elements to obtain nonuniform grid spacings for sidelobe reduction. A number of planar grid structures can be constructed using the nonuniform linear grids. The nonuniform linear and planar arrays utilize fewer radiating elements and result in desirable sidelobe structures.

Apparatus for emitting high-frequency electromagnetic waves

Abstract: Apparatus for emitting high frequency electromagnetic waves comprises a low-voltage power supply, an emitter and an antenna comprising at least one conductor on a thin flexible insulating support and including a length of conductive material formed into a pattern and having interconnected ends in the region of which the conductor is connected to the output of the emitter by a single connector. This not only enables the whole antenna to be flexible so that it can be applied to areas difficult of access, e.g. parts of the human body and even be rolled into a tube for insertion in a body cavity, or wrapped around a limb, for example, but the emitter operates at a voltage of less than 50 volts, the antenna is athermic and the apparatus is significantly small. This is in contradistraction to the high voltage, bulky equipment hitherto used for therapeutic treatment of the body of a patient, both human and animal. The antenna may be associated with current-emitting electrodes and such current may be emitted alternately or simultaneously with the emission from the antenna. The emitter may be caused to emit trains of waves at frequencies between 1 HZ and 100 MHz, and the energy strength may be less than 100 MW per square centimeter.

Energy deposition in simulated human operators of 800-MHz portable transmitters

Abstract: The measured values of energy deposited in simulated human tissue exposed for one minute in the immediate vicinity of 800 MHz portable radio transmitters are presented. The deposited RF energy was evaluated by temperature measurements. The portable radio used in the tests had a 6-W experimental transmitter operating at 840 MHz. Two different antennas were tested for energy deposition: a sleeve dipole and a resonant whip. The two antennas have given substantially different results indicating different field structures near the two radiators. The experiments with flat slabs have shown that the sleeve dipole deposits higher levels of power density than the resonant whip in the near field although the length of the latter radiator is about half the size of the former. The temperature profiles generated by both antennas inside the head of the simulated operator indicate the presence of a "hot spot" about 1 in below the surface of the temporal bone. This phenomenon was not detected previously at lower frequencies. The short antenna exposes the eye of the operator to more intense power deposition than the sleeve dipole. The temperature increases measured during the investigation are so small that no thermal damage to tissue should be caused by normal use of the portable radio.

Decametric survey of discrete sources in the northern sky

Abstract: The paper describes the antenna system, principles of the electrical beam steering, checks of the pattern parameters and the receiving facilities of the UTR-2 radio telescope. Principal characteristics of the instrument are given and possible errors analysed for the operating frequencies of 10, 12.6, 14.7, 16.7, 20 and 25 MHz. The methods of survey work on discrete radio sources are described with an analysis of the flux measurement errors specific for the decametre band. A computer algorithm of data processing is presented.

Windshield mounted half-wave communications antenna assembly

Abstract: A half-wave length communications antenna assembly especially adapted to be mounted on non-conductive surfaces, such as on a window of a vehicle. The antenna assembly desirably includes an electrically shortened half-wave inductively loaded radiating whip loaded at its base end by a loading capacitor plate to be fixed to a non-conductive surface. The whip is coupled through the non-conductive surface to a transmission line internally of the vehicle by a coupling capacitor plate which, with the loading capacitor plate, forms a coupling capacitor. A tuned circuit which is tuned to the nominal resonant frequency of the whip is connected to the coupling capacitor plate and serves as an impedance matching circuit between the half-wave whip and the transmission line. The tuned circuit also affects the radiation pattern of the whip to produce a pattern more typical of a five-eighths wave length antenna to provide somewhat greater gain.

Spurious radiation from microstrip

Abstract: The method of an earlier paper is applied to calculate the disturbances due to a number of discontinuities encountered in typical antenna feed and network structures, such as impedance changes, power dividers, T-junctions, open and short circuits etc., and these are compared for relative radiation. Error estimates due to some secondary effects are calculated and shown to be generally negligible. The process of radiation from an open circuit is studied in detail and it is shown that, although most of the radiation comes from the tip, a substantial amount is radiated and also absorbed to. about a free-space wavelength behind the discontinuity. A method analogous to the induced e.m.f. method is formulated and shown to confirm existing results for radiated power. A distinction is made between the phase centre for radiation, which is usually located at a discontinuity, and the source region for radiation. The two are not coincident and the latter may be quite extensive for microstrip radiations. The results are applied to show how the disturbances can affect the performance of a comb antenna and how they can also be utilised to enhance the efficiency of a strip-end radiator on a thin substrate.

Adaptive electronically steerable phased array

Abstract: An adaptive antenna system which enhances the desired signal in the output of the system while reducing the interference from signals arriving from directions other than that of the desired signal The antenna system operates in conjunction with a modulation/demodulation system for spreading and despreading the spectrum of the desired signal By a series of deterministic perturbations of phase shifters or other signal varying devices attached to the antenna elements, the system measures the effects of these perturbations: (1) on the wide-band energy in the output of the antenna, prior to spectrum despreading, and (2) on the narrow-band energy following despreading, and then adjusts the phase shifters or other signal varying devices so as to enhance the desired signal while reducing the interfering signals

Multiple band, multiple resonant frequency antenna

Abstract: An antenna (10) suitable for multiple frequency band utilization includes three impedance elements (11,12 and 13). The second impedance element (12), which may also be called a network (12), includes a coil (L 2 ) and at least one other conductor (17) in operative association therewith. The second impedance element may be electrically connected to both a first impedance element (11), which may include a linear conductor (14) coupled to a radio, and a third impedance element (13), which may include a coil (L 1 ). By constructing the network (12) so as to have appropriate dimensions, antenna 10 will have a plurality of natural resonant frequencies substantially within or nearby at least each higher band of frequencies of interest.

Impedance of a circular-disc printed-circuit antenna

Abstract: The driving-point impedance of a printed-circuit antenna consisting of a circular disc separated by a dielectric from a ground plane is investigated experimentally. The impedance is measured as a function of the operating frequency for various disc diameters, thicknesses and permittivities of the dielectric and feed point positions. In addition, a theoretical parallel RLC circuit model is proposed and compared with the experimental data.

Spring tunable helical whip antenna

Abstract: A spring tunable antenna for mounting to the frame of a vehicle. The antenna includes a base adapted to be mounted on the vehicle, a flexible rod supported at its lower end in the base, and a low-resistance wire conductor wound helically around the rod. The conductor windings in the tip region of the rod are selectively movable, whereby the antenna may be tuned.

Large element antenna array with grouped overlapped apertures

Abstract: An antenna for transmitting or receiving, for limited fine scan or wide angle scan, or for producing multiple beams has a plurality antenna radiators or receivers (apertures) in a linear array, coupled to a smaller plurality of antenna networks so that many of the antenna apertures are coupled to two of the networks and the networks are all coupled to a common transmission line. For a spatial scanning system, each network is coupled to the common transmission line through a variable phase shifter so that the radiation patterns of the apertures combine to define a beacon of predetermined fine pointing direction that can be used to spatially sweep a sector by varying the phase shifters according to a predetermined schedule. Furthermore, by shifting the point of feed to the networks, the pointing direction is caused to switch in relatively large steps, from one sector to another sector.

Electrically short monopole antennas with dielectric or ferrite coatings

Abstract: A comprehensive analysis of the electrically-small material-clad monopole is performed by representing the various fields by discrete and continuous eigenvalue spectrums. The cladding creates a dominant quarter-wavelength resonant-cavity effect whereby the leakage of radiation at the terminal plane is transformed into a low impedance at the annular feed. The mode coupling taking place at both feed and terminal plane is solved by variational methods to yield the antenna radiation pattern, bandwidth, efficiency and input impedance as a function of electrical size and frequency. The agreement between the computed and measured results establishes the usefulness of the analysis, and design curves are presented; other factors that influence the system performance of the antennas in practice are discussed. It is concluded that the optimisation of this type of antenna centres on the choice of suitable low-loss material with comparable relative permeability and permittivity values at the frequency of interest. In general, this calls for research into improved materials, but useful antennas can be made with commercially available materials.

Variable support apparatus

Abstract: This specification discloses an apparatus and method for supporting and moving an antenna load when tracking a satellite in a synchronous orbit. The apparatus includes three elongated supports all of which are attached to the antenna with couplings having a two degree of freedom of movement and two of which supports are attached to the ground with couplings having a two degree of freedom of movement. A stabilizing member coupled between the two supports having a two degree of movement connection with the ground rigidifies the support apparatus. Adjusting the longitudinal length of the elongated supporting members permits the antenna to be simply and effectively positioned over a wide angular range.

Low power system and method for communicating audio information to patrons having portable radio receivers

Abstract: Low power apparatus and method for tuning portable receivers of patrons of an establishment (such as an auditorium) to a predetermined frequency and communicating audio frequency information to the patrons via the portable receivers An audio signal is derived from an audio frequency public address sound system and inputted to a modulator to modulate a radio frequency carrier signal The modulated carrier signal is amplified and transmitted by means of a loop antenna surrounding the region of the establishment wherein the patrons and their portable receivers are situated A very low power modulated radio frequency signal is derived from a transmitter including a modulator and an amplifier and is inputted to a receiver tuning aid circuit positioned near the entrance of the establishment The tuning aid circuit drives a small ferrite core antenna which radiates a signal which enables the patrons to easily tune their portable receivers to the carrier signal frequency by positioning the receivers close to the ferrite core antenna and tuning the receivers for the loudest audio signal