Showing papers on "Antenna (radio) published in 1988"

Spherical near-field antenna measurements

Abstract: * Chapter 1: Introduction * Chapter 2: Scattering matrix description of an antenna * Chapter 3: Scattering matrix description of antenna coupling * Chapter 4: Data reduction in spherical near-field measurements * Chapter 5: Measurements * Chapter 6: Error analysis of spherical near-field measurements * Chapter 7: Plane-wave synthesis * Appendix 1: Spherical wave functions, notation and properties * Appendix 2: Rotation of spherical waves * Appendix 3: Translation of spherical waves * Appendix 4: Data processing in antenna measurements * Appendix 5: List of principal symbols and uses

Definition of artificially soft and hard surfaces for electromagnetic waves

Abstract: The widely used transversely corrugated surfaces and other alternative surfaces having the same anisotropic surface impedance deserve a common name. Here it is proposed to call them soft surfaces by analogy with the soft surfaces in acoustics. In the same way artificially hard surfaces are defined. Cylindrical hard waveguides of any cross-sectional shape can support TEM waves.

A leaky-wave analysis of the high-gain printed antenna configuration

Abstract: A leaky-wave analysis is used to explain the narrow-beam resonance-gain phenomenon in which narrow beams may be produced from a printed antenna element in a substrate-superstrate geometry. It is demonstrated that the phenomenon is attributable to the presence of both transverse electric and transverse magnetic-mode leaky waves, that are excited on the structure. Asymptotic formulas for the leaky wave are compared with the exact patterns to demonstrate the dominant role of the leaky waves in determining the pattern. Results are presented as a function of frequency, the scan angle, and the permittivity of the superstrate. >

Comparison of three methods for the measurement of printed antenna efficiency

Abstract: Three methods for the measurement of antenna efficiency are evaluated: (1) the Wheeler cap method, (2) the radiometric method, and (3) the directivity/gain method. Each of these methods was used to measure the efficiency of four different printed antennas (three microstrip patches with various feeds, and an eight-element series-fed microstrip array). These methods and the experimental results which were obtained are discussed. >

Distributed antenna system

Abstract: The present invention provides a distributed antenna system comprising a primary antenna (14A, 16A) and a plurality of secondary antennas (36, 40), a . .fibre.!. .Iadd.fiber .Iaddend.optic network (20, 22) connected between the primary antenna (14A, 16A) and the secondary antennas (36, 40), first means (. .16.!. .Iadd.24.Iaddend., 44) associated with a first one of the antennas (16A, 40) which transmits signals received by that antenna (16A, 40) into the . .fibre.!. .Iadd.fiber .Iaddend.optic network (20, 22), and second means (32, 50) associated with a second one of the antennas (14A, 36) which causes that antenna (14A, 36) to transmit signals received by the second means (32, 50) from the . .fibre.!. .Iadd.fiber .Iaddend.optic network (20, 22). Preferably, the use of a heterodyne circuit is avoided and the light signals travelling within the . .fibre.!. .Iadd.fiber .Iaddend.optic networks (20, 22) are modulated at radio frequency.

Microstrip transmission line excitation of dielectric resonator antennas

Abstract: A systematic investigation of the excitation of a cylindrical dielectric resonator antenna was undertaken to illustrate the possibility of such a feed structure and to characterise the coupling behaviour and radiation patterns of the system.

Near-field probe used as a diagnostic tool to locate defective elements in an array antenna

Abstract: Results of an experimental study are presented in which the near-field probe was used as a diagnostic tool to locate the defective elements in a planar array. The near-field data were processed not only to obtain the far-field patterns of the array under the test, but also to reconstruct the aperture field for diagnostic purposes. The backward transform enables the near-field probe to identify accurately aperture faults at a distance, free of interactions and couplings with the array elements. In practice, to recover the aperture field properly from the near-field distribution, the evanescent components in the computed far-field spectrum must be excluded from the inverse process with fast-Fourier-transform (FFT) techniques. For low-gain array antennas, a correction on the far-field spectrum is required to remove the contribution of the probe and the element factor before the inverse transform, strongly enhancing the resolution. >

On carrier signal multipath effects in relative GPS positioning

Abstract: Discusses errors in GPS carrier phase observations resulting from multipath interference. A mathematical model for multipath induced carrier phase errors is derived. It is shown that multipath can be monitored over short baselines by analyzing dual frequency measurements. Two related experiments are reported. The first example demonstrates that extreme multipath interference can render useless GPS observations for precise positioning applications. The 2nd example shows the danger of occurrence of long periodic multipath errors caused by conducting material in the immediate vicinity of the receiver antenna.

Patient tracking system

Abstract: A patient tracking system is employed to determine when an occupant leaves the confines of a nursing home or similar institution. Each patient has a transmitter strapped to his or her wrist which emits a signal having a distinctive radio frequency. The corridors of the nursing home include a plurality of sharp receiving antenna elements connected together in series by a coaxial cable. A scanning radio receiver is attached to the antenna system. The scanning radio receiver determines when the strength of the signal received by the antenna elements falls below a predetermined level at which point an alarm is sounded. If the alarm sounds, an attendant uses a second, directional receiver to track the patient who may have wandered away before the patient hurts himself or herself.

System and method for communicating signals in a cased borehole having tubing

Abstract: A system and method are disclosed for wireless two-way communication in a cased borehole having tubing extending therethrough. A downhole communications subsystem is mounted on the tubing. The downhole subsystem includes a downhole antenna for coupling electromagnetic energy in a TEM mode to and/or from the annulus between the casing and the tubing. The downhole subsystem further includes a downhole transmitter/receiver coupled to the downhole antenna, for coupling signals to and/or from the antenna. An uphole communications subsystem is located at the earth's surface, and includes an uphole antenna for coupling electromagnetic energy in a TEM mode to and/or from the annulus, and an uphole receiver/transmitter coupled to the uphole antenna, for coupling the signals to and/or from the uphole antenna. In accordance with a feature of the invention, the annulus contains a substantially non-conductive fluid (such as diesel, crude oil, or air) in at least the region of the downhole antenna and above.

Electronic proximity identification system

Abstract: An identification system in which power drain is minimized is disclosed. The system comprises a reader (10) including a first signal generator (12) for generating a first signal (F1) which is then radiated by an antenna (17). An identifier (11) is shown which includes an antenna (20) for receiving the first signal for transmission to a signal modulator (32) which operates to modulate the first 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 (17) and the consequent voltage on the reader antenna. By detecting the change in the voltage on the reader antenna the code of the identifier is determined. Power is used efficiently by low frequency oscillation within the signal modulator, by unloading during modulation, and by changing circuit reactance without changing the circuit load.

Self monitoring/calibrating phased array radar and an interchangeable, adjustable transmit/receive sub-assembly

Abstract: The invention relates to a self monitoring/calibrating phased array radar in which the operating path for transmission and the operating path for reception may be monitored/calibrated by the addition of a corporate calibration network coupled at the plural end to the antenna elements and at the singular end to the exciter/receiver, and switching means to selectively route the monitoring/calibrating signal derived from the exciter in a transmit path to calibration path sequence or in a calibration path to receive path sequence. In one embodiment of the invention, a phase shifter common to transmit and receive paths is adjustable in increments under active logical control for calibration, while power and gain performance is monitored but not actively controlled. A novel T/R sub-assembly houses the operating electronics for four antenna elements in the form of four T/R modules with a one to four divider network in the transmit/receive path and in the calibration path. The four antenna elements are an integral part of the T/R sub-assembly.

Planar dual polarization antenna

Abstract: A microwave-frequency microstrip antenna (10) simultaneously usable for both transmitting and receiving microwave-frequency signals that have dual orthogonally polarized components. The components may be either linearly or circularly polarized. A radiating patch (26) is mounted on a first dielectric (12). A ground plane (20) abuts the first dielectric (12) and has two elongated coupling apertures (32,31) at right angles to each other. A second dielectric (22) abuts the ground plane (20) and has embedded thereon two substantially identical conductive planar feed networks (52,51) that are disposed at right angles to each other. At least one additional optional dielectric layer (16,18) having a conductive patch (36,34) may be interposed between the first dielectric (12) and the ground plane (20) for purposes of broadening the bandwidth of the antenna (10). A meanderline polarizer (45) or a 3 dB 90° hybrid coupler (40) may be used for converting from linear polarization to circular polarization.

Dielectric or magnetic medium loaded antenna

Abstract: A loaded antenna (11) comprises a wave source (12) of an arbitrary polarized wave, a reflector (13) disposed near the wave source (12), with the surface opposite to the wave source (12) limited in area, and a dielectric (14) disposed on the opposite side of the reflector across the wave source (12), at least with the surface opposite to the reflector (13) formed parallel to the reflector (13). By properly selecting the mutual interval among the dielectric (14), wave source (12) and reflector(13), the dimension and the dielectric constant of the dielectric (14), the vibration component in the running direction of the wave within the dielectric (14), the vibration component in the direction vertical to the running direction, and the vibration component between the reflector and dielectric are superposed, so that the electromagnetic field distribution in the vicinity of the dielectric (14) is made uniform. Thereby, high gain and high efficiency are realized, and the structure may be notably reduced in size.

Magnetic tuning of a microstrip antenna on a ferrite substrate

Abstract: The operating frequency of a microstrip antenna on a ferrite substrate can be tuned by varying the DC magnetic bias field applied to the ferrite. The letter reports experimental work where a 40% tuning range has been obtained, with usable patterns and return loss over this band.

Characteristics of the equilateral triangular patch antenna

Abstract: The results of a comprehensive analysis of this antenna based on the cavity model with a coaxial feed source are given. The theoretical formulas are given, and the characteristics obtained from them are presented, including radiation patterns, percentages of power radiated, total Q-factors, input impedances, and their variations with feed position. A number of disagreements with previously published results are noted. The theoretical and experimental results are compared. The results of the comparison indicate that the equilateral triangular patch can be designed to function as a triple frequency antenna. A method for correcting for the nonperfect magnetic wall is suggested. >

High bit rate communication system for overcoming multipath

Abstract: A communication system for relatively high data bit rate RF communication overcomes multipath interference by employing relatively narrow beam antenna sectors and by selecting the best communication path established between two terminals, at least one of which has narrow beam antenna sectors. The communication path selection process includes determining the signal integrity of data communicated between the terminals. One implementation includes the narrow beam antenna sectors at each terminal.

Measurements of path loss at 910 MHz for proposed microcell urban mobile systems

Abstract: Measurements of propagation path loss at 910 MHz were made in an urban area (Ottawa, Canada), using transmission from an antenna at street-lamp height (8.5 m) to a mobile receiving antenna at a height of 3.65 m. The received power was sampled about once per meter. On the same street as the transmitter, the received power was found to approximate the free-space value, with occasional 10 dB fades. On other streets, the signal was in most places less than the free-space value by 20 dB or more. The received power was found to depend in a detailed way on the distribution of buildings and the open areas between them. >

Opto-electronic vivaldi transceiver

Abstract: A planar integrated opto-electronic transceiver apparatus having a pair of broadband tapered slot line antennas which are monolithically integrated on an ion implanted silicon on sapphire substrate. An optical pulse which is applied to the narrow slot of the transmitting antenna, generates an electromagnetic transient to the antenna aperture from which it is radiated to receiver slot line antenna. The received electromagnetic transient is detected at the narrow slot and is time resolved by an optical sampling signal.

Extendable antenna for portable cellular telephones with ground radiator

Abstract: An antenna for a portable cellular telephone includes a quarter-wavelength ground radiator and a helical coil capacitively coupled to an extendable half-wavelength radiator. The extendable half-wavelength radiator includes a metallic coil molded in plastic. The ground radiator includes a serpentined transmission line on a flexible circuit board. The helical coil and ground radiator are coupled by a transmission line to a duplexer. The duplexer couples transmitter signals from a radio transmitter to the antenna and receiver signals from the antenna to a radio receiver. The antenna may be advantageously utilized in any portable radio applications where small size and immunity to hand induced radiation losses are desired.

Satellite communications system employing frequency reuse

Abstract: A satellite communications system employs separate subsystems for providing broadcast and point-to-point two-way communications using the same assigned frequency band. The broadcast and point-to-point subsystems employ an integrated satellite antenna system which uses a common reflector (12). The point-to-point subsystem achieves increased communication capacity through the reuse of the assigned frequency band over multiple, contiguous zones (32, 34, 36, 38) covering the area of the earth to be serviced. Small aperture terminals in the zones are serviced by a plurality of high gain downlink fan beams (29) steered in the east-west direction by frequency address. A special beam-forming network (98) provides in conjunction with an array antenna (20) the multiple zone frequency address function. The satellite (10) employs a filter interconnection matrix (90) for connecting earth terminals in different zones in a manner which permits multiple reuse of the entire band of assigned frequencies. A single pool of solid state transmitters allows rain disadvantaged users to be assigned higher than normal power at minimum cost. The intermodulation products of the transmitters are geographically dispersed.

Two-port higher mode circular microstrip antennas

Abstract: For circular microstrip antennas, single-mode design techniques work well for the dominant mode (n=1, where n is the azimuthal dependence of the fields in the antenna), but this is not the case for zero-order (n=0) and higher order (n>1) modes, where a modal expansion is necessary. The design of higher order dominant mode circular microstrip antennas is addressed, with an example and measurements for the n=3 case. Measurements for the n=3 modes show reasonable agreement with theory in the forms of the impedance loci, but the frequency dependence is in error by the order of the bandwidth of the antenna. A design example is given for a roof-mounted circular patch for vehicular communications. The example indicates that an n=3 dominant mode patch can be used as a two-port antenna for diversity applications or with a 90 degrees phase shifter and adder as a single-port antenna for omnidirectional coverage with (essentially) circular polarization. >

Canonical sources and duality in chiral media (antenna arrays)

Abstract: The authors examine the characteristics of antenna arrays embedded in unbounded chiral media using the Green's dyadic for electric sources and the Green's vector for magnetic sources. The purpose is to bring to light the new characteristics of sources, both point and extended, which interact with this medium and to examine general characteristics of sources located in a medium with handedness. Very simple quality relations are presented that are characteristic of chiral media when the results are written in terms of the circular eigenmodes. Appropriate measures of chirality such as the chirality admittance and impedance and a dimensionless chirality factor are introduced as needed. It is shown that, in the far field, both point and extended sources, whether electric or magnetic, radiate two electromagnetic eigenmodes which are of opposing handedness. Sources that access only one of the eigenmodes of the medium are demonstrated. Several applications of the results and array performance in chiral media are noted. >

Simple model for the input impedance of coax-fed rectangular microstrip patch antenna for CAD

Abstract: We present a simple model for the input impedance of a rectangular microstrip patch antenna. This model is well suited for computer aided design (CAD). It is based on classical methods: (a) the cavity model determining the frequency and the input resistance at resonance, (b) the dynamic permittivity of a rectangular microstrip patch antenna (to take into account the influence of the fringing field at the edges of the rectangular patch antenna) and (c) the resonant parallel RLC circuit with an inductive reactance. This model is valid for electrically thick substrates. The theoretical results are in good agreement with experimental data.

A linearly polarized radial line slot antenna

Abstract: A design for linearly polarized radial line slot antenna (RLSA) is proposed. A novel slot arrangement is presented which couples to the rotationally symmetric guided waves to produce a uniform aperture distribution with linear polarization. Basic characteristics were measured in the 12-GHz band on a model antenna. The radiation patterns indicate a reasonable cross-polarization level more than 15 dB below the copolarization. The poor VSWR response is typical for waveguide broadside arrays. A technique to suppress this reflection is to tilt the beam from the boresight. >

Antenna and its electronic circuit combination

Abstract: An antenna and its electronic circuit combination is presented to comprise a ground conductor plane 30, a radiating conductor plane 40 disposed in parallel spaced relation to the ground plane 30 and shorted at its one end to the ground plane 30. A ground plane 30 is preferably formed on a printed board 10 which is disposed in parallel relation to the radiating plane 40 to define therebetween an open air space. Mounted on the printed board 10 and received within the open air space are electronic components which form a receiving or transmitting electronic circuit 60 associated with the antenna structure and electrically coupled by means of a feed element 20 to a feed point 44 on the radiating plane 40. Consequently, a number of electronic components forming the electronic circuit for the antenna can well be incorporated within the antenna structure by better utilization of the open air space formed between the radiating and ground planes, giving a space saving compact arrangement to the antenna and its electronic combination suitable for installation in a limited space.

Beam powered antenna

Abstract: The invention relates to an antenna for receiving and modulating transmitted signals having a very low power density on the order of below 1 watt per meter squared, at a selected center frequency above 2,000 MHz The antenna uses a folded planar dipole section having two separated oppositely disposed U-shape elements, each of said elements having a pair of ends A capacitor is series-coupled between two of the oppositely disposed ends of the elements, and a diode having a high impedance at the selected center frequency is series-coupled between the other two oppositely disposed ends of the U-shape elements A metallic backplane is mounted parallel to the planar folded dipole section and spaced from the dipole section a predetermined distance selected to reduce the antenna impedance The impedance of the diode, the shape of the folded planar diode section and the predetermined amount of spacing of the backplane from the planar folded dipole section are all selected to increase the dc power output of the antenna

Theory of Bernstein wave coupling with loop antennas

Abstract: Coupling to ion Bernstein waves near the first harmonic of the ion cyclotron resonance with coil antennas is investigated by using a plane layered model of a tokamak plasma. The boundary conditions in vacuum are solved analytically for arbitrary orientation of the antenna and Faraday screen conductors, in terms of the surface impedance matrix of the plasma for plane waves. The latter is evaluated by solving the wave equations in the plasma by taking into account finite Larmor radius and finite electron inertia effects, cyclotron and harmonic damping by the ions, and Landau and collisional damping by the electrons. – Applications to the Alcator C tokamak give reasonable agreement between the calculated and measured radiation resistance when the first ion cyclotron harmonic is just behind the antenna; outside this range, the calculated resistance is lower than the experimental one. In general, the coupling efficiency is found to be very sensitive to the edge plasma density, good coupling requiring a low density plasma layer in the vicinity of the Faraday screen. Coupling also improves with increasing ion temperature in the scrape-off layer and is appreciably better for antennas with antisymmetric than with symmetric current distribution in the toroidal direction.