Showing papers on "Antenna (radio) published in 1986"

An overview of near-field antenna measurements

Abstract: After a brief history of near-field antenna measurements with and without probe correction, the theory of near-field antenna measurements is outlined beginning with ideal probes scanning on arbitrary surfaces and ending with arbitrary probes scanning on planar, cylindrical, and spherical surfaces. Probe correction is introduced for all three measurement geometries as a slight modification to the ideal probe expressions. Sampling theorems are applied to determine the required data-point spacing, and efficient computational methods along with their computer run times are discussed. The major sources of experimental error defining the accuracy of typical planar near-field measurement facilities are reviewed, and present limitations of planar, cylindrical, and spherical near-field scanning are identified.

A reciprocity method of analysis for printed slot and slot-coupled microstrip antennas

Abstract: A method is presented for the analysis of slot-type discontinuities in microstripline. The approach is based on the reciprocity theorem and uses the exact Green's functions for the grounded dielectric slab in a moment method solution for the unknown antenna currents. The method is applied to two specific geometries: a radiating slot in the ground plane of a microstripline, and an aperture coupled microstrip patch antenna. Results for antenna impedance are compared with measurements, and far-zone patterns are calculated. The method is shown to be quite versatile, and should find application to related problems.

A technique for an array to generate circular polarization with linearly polarized elements

Abstract: A method is presented for generating circularly polarized radiation from an array composed of linearly polarized elements having unique angular and phase arrangements. With this technique the complexity, weight, and RF loss of the array feed can be significantly reduced, especially in a large array. This uniquely formed array has the capability of generating excellent circular polarization (CP) over a relatively wide frequency bandwidth. In addition, the array is capable of scanning its main beam in the principal planes to relatively wide angles from its broadside direction without serious degradation to its CP quality. Another feature of this uniquely arranged array is a reduction in the occurrence of mutual coupling. The discussion in this paper places special emphasis on the microstrip type of radiator, although the technique presented can be adapted to most types of linearly polarized antenna elements.

The Handbook of Antenna Design

Abstract: These books present the fundamental background, theory and analytical techniques of antenna design, dealing with a very wide range of antenna types from very low frequencies to millimeter waves.

Analysis of an aperture coupled microstrip antenna

Abstract: A microstrip patch antenna that is coupled to a microstripline by an aperture in the intervening ground plane is analyzed. Coupled integral equations are formulated by using the Green's functions for grounded dielectric slabs so that the analysis includes all coupling effects and the radiation and surface wave effects of both substrates. A Galerkin moment method solution of the coupled integral equations agrees quite well with measured data. Design data are contained in parameter studies, many of which are verified by experimental results.

A spiral antenna backed by a conducting plane reflector

Abstract: An Archimedean planar spiral antenna is numerically analyzed in the presence of a conducting plane reflector. The analysis shows that the spiral antenna backed by the plane reflector has two distinct regions in the current distribution, which explain the radiation of a circularly polarized wave for the outer circumference C ranging over about 1.3 \lambda and C > 2.9 \lambda , where \lambda is a free-space wavelength. Further consideration is given to a truncated spiral antenna whose outer circumference is on the order of 1.4 \lambda . The truncated spiral antenna maintains a decaying current distribution and radiates a circularly polarized wave over a 1:1.2 frequency bandwidth. It is also demonstrated that a power gain on the order of 8.5 dB is realized over the same frequency range.

An experimental investigation of electrically thick rectangular microstrip antennas

Abstract: The electromagnetic properties of electrically thick rectangular microstrip antennas were investigated experimentally. Antennas were fabricated with different patch sizes and with electrical thicknesses ranging from 0.03 to 0.23 wavelengths in the dielectric substrate. The resonant frequencies were measured and compared to existing formulas. The bandwidth was calculated as a function of electrical thickness and the antenna radiation patterns were measured.

Analysis of the tapered slot antenna

Abstract: A method for calculating the radiation pattern of end-fire tapered slot antennas with or without dielectric substrate is presented. The method involves a two-step procedure: 1) determine the field distribution of a traveling wave along the tapered slot, and 2) compute the radiation from this slot field by using the half-plane Green's function to account for termination effects. Acceptable estimates of the slot field usually can be obtained from a stepped approximation to the tapered geometry. The method has been verified by comparisons to measured patterns for various dielectric substrates and antenna dimensions. However, the effect of lateral truncation has not yet been successfully modeled. Experimental patterns showing this effect are presented.

Methods for null control and their effects on the radiation pattern

Abstract: Several methods for synthesis of array antenna patterns with prescribed nulls are reviewed. Methods based on full amplitude/phase control at each array element and methods with a restricted number of degrees of freedom are compared, with attention focused on the characteristic features of the resultant patterns. These features are largely independent of any algorithm for achieving the nulls, and therefore they also provide a perspective on the performance of adaptive antenna systems, which employ these various control architectures.

Crosscorrelation between the envelopes of 900 MHz signals received at a mobile radio base station site

Abstract: An experimental investigation is reported of the crosscorrelation of 900 MHz signals received by two spatially separated antennas at a base station. The investigation embraced vertical, horizontal and combined horizontal and vertical separation of the antennas, for transmission from test routes 1.3 km from the base station. It was found that a crosscorrelation ≤0.7 (i.e. when diversity improvement becomes significant) can best be achieved using vertical separation of the antennas of between 11 λ and 13 λ for the 1.3 km cell radius. At 900 MHz such an antenna separation is easily obtained and, in addition, the roof space required is small. Moreover, the crosscorrelation using vertically spaced antennas is independent of the incoming arrival angle (unlike horizontally spaced antennas), and hence low correlation can be achieved while maintaining omnidirectional coverage.

A dielectric hybrid mode antenna feed: A simple alternative to the corrugated horn

Abstract: A hybrid-mode horn antenna has been analyzed theoretically and experimentally. It consists of a conical metal horn with a dielectric core inside, separated from the metal wall by another dielectric layer with lower permittivity than for the core material. It is characterized by a very simple design and excellent electrical performance. The horn can support the balanced hybrid HE 11 -mode, and exhibits low cross polarization and low sidelobes over a wide frequency range. Compared to corrugated horns, the new horn has a simpler design, is easier to analyze, and has the potential of similar cross-polar bandwidth as for corrugated horns with ring-loaded corrugations. Drawbacks are the effects of dielectric losses. Thus the new horn represents an attractive alternative to the corrugated horn antenna.

Broadband microstrip antenna

Abstract: An antenna assembly which comprises a first laminar structure which includes a sheet of dielectric material having on one side a contiguous metal sheet and on the other side a strip transmission line adapted to be coupled with signal feeding means, and a second laminar structure, one side of which is in contact with the transmission line, and having on the other side, at least one region but preferable at least two concentrically arranged regions of a coated or cladded metal which serves as a radiator, characterized in that the transmission line is non-symetrically disposed with respect to the radiator.

Differential navigation system for remote mobile users

Abstract: A differential navigation system applicable to mobile users and covering a wide range geographic area, including remote regions. A reference receiver of known location tracks a navigation information service, computes differential data with respect to that information and communicates the data to a transmitting unit. The transmitting unit transmits differential data via a commercial geosynchronous earth satellite relay to a mobile user located no more than 500 miles from the reference receiver, but possibly located in a remote region. The mobile user receives the relayed signal with a non-directional, circularly polarized, non-stabilized antenna. Reception at a sufficient data rate with sufficient reliability is made possible by formatting the differential data using spread spectrum techniques.

Microwave plane antenna simultaneously receiving two polarizations

Abstract: Multi-element microwave plane antenna for receiving satellite television signals with two simultaneous polarizations. The antenna is provided with two systems of lines (1) whose ends (3, 30) form probes emerging into wave-guides (2). The probes of one system (3) are perpendicular to those of the other system (30). Between the two systems of lines there is placed only a thin sheet (150) bored with cross-shaped cut-outs (6), and provided with separating studs made from a silk-screen-printed insulating material.

Transmitting and receiving apparatus

Abstract: PURPOSE:To perform the simultaneous use and change-over use of a radio wave and a light wave without lowering the functions of both radio wave and light wave systems, by providing an optical system to the peripheral space part of a radio wave array antenna arranged in a planar state. CONSTITUTION:The radio wave signal from a transmitter 3 is supplied to an array antenna 1 by a duplexer 2 to be emitted to a space. The reflected signal from a target passes through the route reverse to that at the time of transmission to be sent to a receiver 4 by the duplexer 2 and the detection of a target signal is performed by a signal processor 5. The light wave allowed to radiate from the target is converted to an electric signal by a light wave detector 7 through the optical system 6 provided to the space part 10 of the peripheral part of the antenna 1. The light signal from the target converted to the electric signal is sent to a signal processor 9 through an amplifier 8 to perform the detection of a target signal. As mentioned above, by allowing the radio wave system and the light wave system to function independently each other, the effect exerted on the capacity of the radio wave system such as the lowering in the gain of the antenna 1 or the deterioration of side robe capacity becomes min. and, even when both radio wave and light wave systems are arranged in parallel, the lowering in the functions of both systems can be prevented.

Method and apparatus for signal strength measurement and antenna selection in cellular radiotelephone systems

Abstract: A method and apparatus for determining which sector antenna of a sectorized cellular radiotelephone system is receiving the strongest radio signal is disclosed. The signal strength of sector antennas is sequentially sampled, converted to digital representations, and stored according to which antenna received the signal. The digital representations are recalled from storage and the strongest signal along with an identification of the receiving antenna are determined. This determination may be used in the handoff process or in detecting when a remote unit requires a handoff.

The effect of various parameters of circular microstrip antennas on their radiation efficiency and the mode excitation

Abstract: The numerical solution of circular microstrip antenna is carried out using the method of moment. The effect of the probe position, The dielectric permittivity of the substrate, and the substrate thickness on the radiation pattern and the mode excitation efficiency are studied. It is found that the probe position and the patch size can be used to control the mode excitation efficiency, and heigher order modes can be generated using only one feed location. Also, the finite ground plane can be used to improve the symmetry of the radiation patterns. The technique is general and can be used to investigate other scattering and antenna problems involving axisymmetric geometries.

Electronic monitoring system

Abstract: A system for monitoring the location of an individual is disclosed and includes a band to be strapped to the individual's wrist or ankle. A trigger, transmitter, and antenna are incorporated into the band. The trigger controls operation of the transmitter and activation is effected by a portable authority-retained control unit. The trigger deactivates the transmitter under predetermined conditions (such as removal of the band) and reactivation requires utilization of the control unit.

Comparison of Quasi-Static and Exact Electromagnetic Fields from a Horizontal Electric Dipole Above a Lossy Dielectric Backed by an Imperfect Ground Plane

Abstract: In most microstrip transmission lines, analysis is made assuming that a quasi-TEM mode exists and propagates down the line. The primary objective of this paper is to obtain the region of validity of this assumption. The second objective of this paper is to derive the expressions for the fields for a horizontal electric dipole over a Iossy dielectric medium backed by an imperfect ground plane. It is shown that, to a first approximation, fields at the air-dielectric interface are independent of the ground plane conductivity. Since we are interested in coupfing between lines, our interest is in the computation of the fields primarily at the air-dielectric interface. Finally, numerical results are presented to show where the quasi-static approximations deviate from the exact solution for a given microstrip geometry as the frequency of operation or the observation point is changed.

Single-block dual-passband ceramic filter useable with a transceiver

Abstract: A single-block ceramic filter (100) providing both pass and stop bands couples an RF signal from transmitter (180) to an antenna (190) and an RF signal from the antenna (190) to a receiver (170). The ceramic filter (100) includes seven holes (102, 104, 106, 108, 110, 112 and 114) each having an elongated cross section and being surrounded by capacitive strips (e.g. 130, 131, 140 and 141 for hole 106), and electrodes (120, 122 and 124) coupled to receiver (170), transmitter (180) and antenna (190), respectively. A bracket (150) may be soldered to the ceramic filter (100) for holding cables coupled to the receiver, transmitter and antenna and for mounting the ceramic filter in a radio transceiver.

Electromagnetic structure and method

Abstract: An electrically small, efficient electromagnetic structure, that may be used as an antenna or waveguide probe, having an electromagnetically closed, velocity-inhibiting conducting path, for supporting a standing, inhibited-velocity wave in response to the flow of an electrical current through the path and a process for establishing the standing wave. Use of the structure is particularly advantageous at the lower end of the electromagnetic spectrum, where various embodiments produce purely vertically polarized radiation in directional and omnidirectional patterns. Various embodiments of the structure include multiple conducting paths and image means to complete the conducting path. Embodiments of the structure may be used to excite the earth-ionosphere cavity at the Schumann resonances.

Drive system and filament for a twistable septum in a feedhorn

Abstract: A drive system for a twistable septum in a feedhorn for use in satellite communications antenna systems. The drive system includes a flexible drive rod, coupled to a drive motor, which bends to accommodate off-center coupling with the septum drive wheel.

Antenna with lumped reactive matching elements between radiator and groundplate

Abstract: Between a circular conductor plate and a grounding conductor plate, lumped constant elements such as coils and capacitors are connected. As a result, the resonance frequency of an antenna can be changed in a wide range.

Multiple antennae breast screening system

Abstract: A method and apparatus for cancerous tumor detection employing a plurality of microwave antennae supported in an array conforming substantially in size to the breast that is being screened. In one embodiment of the invention a single array is used and another embodiment for larger breasts a pair of arrays are used. A microwave radiometer is used for detecting temperature readings corresponding respectively to the breast temperature at sites underlying the receiving antennae. Also, in accordance with the invention compression is employed so as to reduce tissue thickness enabling far more rapid reading of antenna sites.

Retractable helical antenna

Abstract: A retractable antenna assembly is disclosed for tuning an antenna having a helical section to frequency by selectively positioning an appropriate tuning core within the helix. The antenna frequency can either be raised or lowered through the use of conductive or permeable tuning core compositions. The core positioning mechanism is implemented by affixing the tuning core to a portion of the antenna supporting rod slideably located within the helix. This helical antenna/tuning core configuration is readily adaptable to miniature portable radios by providing a helical antenna assembly which is retractable within the radio housing in the receive-only or standby mode, and which is outwardly extendible from the radio housing for use in the active transmit/receive mode. A unique barrel-cam latching mechanism is also described.

Specific Absorption Rates of Energy in Man Models Exposed to Cellular UHF Mobile-Antenna Fields

Abstract: Thermography, nonperturbing temperature probes, and E-field sensitive diodes were used to quantify the SAR patterns in human models exposed to UHF mobile-antenna fields. The exposure conditions include man, woman, and child models in the standing position close to roof- and trunk-mounted antenna; man sitting in the back seat near a trunk-mounted antenna; child kneeling in the back seat and looking through the rear window. Incident power densities near the antennas were also measured. Based on the current ANSI radio-frequency protection guide, the exemption of 7-W input power will violate the ANSI primary exposure criterion, but satisfies the 8-W/kg exclusion clauses. A maximum power of 3.5 W would satisfy all of the ANSI guides.

The Alfvén wave spectrum as measured on a tokamak

Abstract: The detailed experimental data obtained on the TCA tokamak [Proceedings of the 11th Symposium on Fusion Technology (CEC, Luxembourg, 1981), Vol. I, p. 601] concerning the antenna loading and wave fields as a function of the Alfven wave spectrum are presented. The plasma density, plasma current, working gas, toroidal magnetic field, and frequency were varied systematically and the detailed results are compiled and discussed. In addition the phasing of the antenna currents was varied systematically, thereby exciting different combinations of modes, including pure traveling waves. The conclusions relevant to the design of an antenna system have been stressed.

Axial mode helical antennas

Abstract: The radiation characteristics of helical antennas operating in the axial mode are evaluated on the basis of the theoretical current distributions and are verified by experimental work. A comparison between monofilar helix and bifilar helix antennas is made, and a helical antenna with a parasitic helix (HAP) is proposed in order to enhance the power gain. It is found that the gain of the HAP in which the parasitic helix is wound from a point diametrically opposite to that of one and one-half turns of the driven helix is about 1 dB higher than that of the monofilar helix. The ratio of the frequency band in which the HAP radiates a circularly polarized wave within an axial ratio of 3 dB is calculated to be 1:1.8.

Monolithic antenna with integral pin diode tuning

Abstract: Antennas chiefly intended for microwave and millimeter-wave use include geometric-shaped conductive patches on one broad surface of a planar semiconductor substrate. The other broad side of the substrate bears a conductive ground plane. Monolithic PIN diodes are formed by doping the substrate at various points between the conductive patch and the ground plane. Biasing arrangements affect the conduction of the PIN diodes thereby affecting or tuning the optimum operating frequency, the radiation pattern, and/or the impedance of the antenna. In a particularly advantageous configuration, the PIN diodes have lateral dimensions greater than or equal to one-tenth wavelength (λ/10) at the operating frequency. Distributed diodes have lower resistance and reactance than discrete or discrete monolithic diodes, thereby providing improved radiating characteristics, and have a relatively large power-handling capability which makes them useful for power transmission.