Showing papers on "Antenna (radio) published in 1977"

Phased array antenna

Abstract: An antenna system for producing from a fixed array of active antenna elements which are each omnidirectional in a plane, a sensitivity pattern that is directional in said plane and which pattern can be rotated around the array. The system consists of at least three antenna elements located at the corners of a regular polygon and are excited with substantially equal magnitudes of current that are in the same phase at two adjacent corners and different in phase by substantially 90 electrical degrees at the third corner. The antenna system further includes an electrical power dividing and phasing network as well as electrical switching means to effect proper rotation.

Resonant frequency of a circular disc, printed-circuit antenna

Abstract: The resonant frequency is obtained in analytical form for a planar, circular disc antenna which is etched on a printed-circuit board so that the low-profile antenna is separated from the ground plane only by a thin layer of dielectric material. The formula is found to have an error of less than 2.5 percent when compared with experimental data.

Multifrequency antenna system integrated into a radome

Abstract: An antenna system that comprises two or more linear arrays within close pimity which can be integrated into a conical dielectric radome. The elements of each array are wedge shaped open-ended cavity radiators plated on the outside of the radome structure. The bottom edge of each element is shorted to an inside conducting surface. Each array is designed to be operated in a different frequency band. A simple coaxial line feeds each of the radiators.

Antenna array for a cellular RF communications system

Abstract: An array of antennas for a cellular RF communications system for providing communications to randomly placed transceivers in a given area. The antenna array includes a plurality of antenna sites located in the centers of cells. Each antenna site has a plurality of sectored antennas for providing a plurality of communication channels. A predetermined number of sites are used to constitute a subarray of cells to provide a set of communication channels and channel allocations are repeated from subarray to subarray. Channels are also so allocated as to minimize channel interference and optimize channel utilization. An omnidirectional antenna may be provided for each antenna site for signalling purposes.

Radio propagation for vehicular communications

Abstract: Radio propagation is affected by many factors including the frequency, distance, antenna heights, curvature of the earth, atmospheric conditions, and the presence of hills and buildings. The influence of each of these factors at frequencies above about 30 MHz is discussed with most of the quantitative data being presented in the series of nomograms. By means of three or four of these charts an estimate of the received power and the received field intensity for a given point-to-point radio transmission path ordinarily can be obtained in a minute or less. The theory of propagation over a smooth spherical earth is presented in a simplified form that is made possible by restricting the frequency range to above about 30 MHz where variations in the electrical constants of the earth have only a secondary effect. The empirical methods used in estimating the effects of hills and buildings and of atmospheric refraction are compared with experimental data on shadow losses and on fading ranges.

Antennas for VHF/UHF personal radio: A theoretical and experimental study of characteristics and performance

Abstract: A theoretical analysis of the characteristics of small personal radio antennas for the 68- to 470-MHz frequency range is given. Representing the human body by a simplified lossy dielectric structure, the influence of the body on the performance of the antenna is investigated in detail, and it is shown how antenna impedance, gain, and radiation patterns can be calculated taking the presence of the body into account. For very short antennas the results indicate that radiation from the body may dominate over the radiation contributed by the antenna itself, and that the presence of the body can increase the antenna efficiency considerably, indicating that even very short antennas may provide acceptable radiation efficiencies. The results of the theoretical work are supported by measurements on practical antennas. Quarter-wave and short antennas of the helical type are compared with respect to efficiency and radiation patterns at 80, 160, and 450 MHz, and it is demonstrated how the physical length of the antenna affects the antenna performance. The design of a very short and compact personal radio antenna is described.

Built-in miniature radio antenna

Abstract: A miniature radio antenna formed integral with a molded plastic housing comprising a body 1 and a cover 2. The antenna 1', 1", 2', 2" includes sheets, foils or films of electrically conductive metal or coats of conductive paint laid on the inside surfaces of the opposing housing sections, or conductors embedded therein. The antenna is free from adverse acoustic effects due to resonant vibrations in sympathy with a speaker mounted in the housing, and the housing may be molded into any desirable external shape, including fully rounded corners, without increasing the size.

Microwave time delay spectroscopic methods and apparatus for remote interrogation of biological targets

Abstract: Remote interrogation of biological targets is accomplished in accordance h the present invention by method and apparatus wherein a microwave signal is generated which varies in frequency from a first frequency to a second frequency in a predetermined time period. The signal is divided into two signals, one of which is propagated through a test channel comprising a transmitting antenna for transmitting the signal through the target, and a receiving antenna for receiving the signal transmitted through the target, and the other of which is propagated through a reference channel providing a fixed time delay of propagation. The propagated signals are detected and mixed to produce a time delay spectrum wherein the frequency of each spectral line represents the instantaneous difference in the frequencies of the detected signals.

Kalman estimator tracking system

Abstract: A radar tracking system having a Kalman estimator is disclosed. The estimator is provided with angle and range track error measurements in a coordinate system that is aligned with and normal to the antenna line of sight, commonly referred to as the LOS coordinate system. This estimator implementation uses less computing resources in converting the measurements provided relative to the antenna LOS coordinate system, to predict target position referenced to a stable coordinate system such as geographic, wander azimuth, or inertial.

Underground pipe detector

Abstract: An apparatus and method wherein an electrical impulse source transmits a radar-type signal through an antenna into the ground and is reflected by a target. The reflected signal or echo is detected by the antenna and an analog-to-digital converter converts it to a digital form which may be readily operated on, stored and recalled. A memory stores the information until recalled for comparison with a subsequent signal to give an indication of the location of metallic and non-metallic buried targets.

Adjustable antenna arrangement for a portable radio

Abstract: An extendable half-wave dipole is capacitively coupled to a driven resonant helical antenna for use as on a hand-held, two-way portable radio, the helix being end fed. The dipole may be mounted adjacent to or collinear with the axis of the helix. The collinear mounting requires non-conductive portions on each end of the dipole. Optimum dimensional and performance characteristics are available without switching.

Directional antenna system including pattern control

Abstract: A directional antenna system is disclosed which selectively couples two radiating antenna elements to a transceiver through a selective phase, magnitude and matching network which is controlled by the output of a logic circuit. The network provides for equal magnitude current coupling between the transceiver and the two antennas while simultaneously selectively producing either positive or negative approximately 90° phase shifts between the two antennas to produce either of two discrete directive cardioid radiation patterns directed in substantially opposite directions. The logic circuit, in conjunction with a manual step switch, provides for a manually selecting either of the two cardioid radiation patterns, as well as producing a figure eight or an omnidirectional radiation pattern. For generating a transceiver omnidirectional pattern, one antenna is used and the other is connected to a standard broadcast band receiver. Matching networks are simultaneously selectively connected between the two antennas and the transceiver such that maximum power transfer and impedance matching is maintained for different radiation patterns. An automatic scanning switch is coupled to the logic circuit and provides for automatically selecting one of the cardioid radiation patterns as an optimum pattern in which the signal from the remote site is most strongly received by the transceiver. Indicating lights are provided to indicate which one of the radiation patterns is generated for the transceiver.

High-efficiency microwave reflector antennas—A review

Abstract: The paper provides a review of current research on microwave reflector antennas with particular regard to those antennas which produce pencil-beam radiation patterns. After a preliminary examination of microwave antennas of different types attention is focused on circularly symmetric antennas with axially symmetric feed systems. This class of antenna accounts for the largest number of applications which include microwave point-to-point communication, satellite communication, and radio astronomy. The choice of optimum feed is considered in more detail and it is demonstrated that metallic feeds with corrugated walls represent the best choice in most cases. Brief reference is also made to dielectric cone feeds which may find a place in future systems. The design of dual-reflector systems is considered in depth and different computer optimisation techniques are reviewed. These include the latest methods of diffraction optimization in which more than one of the antenna specifications is involved. An example is given where efficiency and VSWR are simultaneously optimized.

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.

Microstrip radiator with folded resonant cavity

Abstract: A resonant microstrip radiator wherein the size of the radiator is reduced in the resonant or non-resonant dimensions, or both, without reducing the effective resonant dimension or substantially lowering the efficiency of the radiator. Reduction of the resonant dimension is provided by folding the resonant cavity, while reduction of the non-resonant dimension is facilitated by utilization of a low density, low loss dielectric, such that the loss resistance of the element is appreciable with respect to the radiation resistance of the element. Also disclosed are interdigitated antenna structures and provisions for circularly or elliptically polarized radiation.

Probe correction of spherical near-field measurements

Abstract: Probe correction has been implemented in a computer program which calculates antenna far fields from spherical nearfield measurements. The computer program has been applied to near-field measurements on a satellite model, and the accuracy of the computed far field is significantly improved, compared with the results obtained without probe correction.

Directional antenna system with end loaded crossed dipoles

Abstract: An electrically directable antenna system is provided which is tunable to individual stations in the FM band. The antenna system includes a pair of crossed, forshortened dipole components which are arranged to be mutually perpendicular. Each of the dipole components includes a pair of longitudinally aligned arms which are flared at their outer ends so as to be shaped generally like an arrow. At their inner ends, these arms are connected to a narrow bandwidth tuner network which is designed to resonate the dipole components at a frequency corresponding to a selected station and to impedance match each of the dipole components to the input of the FM receiver. The tuner network includes a bandwidth control, which is operable to produce a predetermined impedance mismatch between the dipole components and the receiver input so that, without changing the frequency to which the antenna system is tuned, the overall antenna system gain can be made substantially constant over the entire FM band. The signals from the four dipole arms, as coupled through the tuner network, are selectively combined in a direction selector switch so that the signal provided from the switch to the receiver input is either: one of the dipole component signals, the sum of the two dipole component signals, or the difference between the two dipole component signals. The particular signal applied to the receiver determines the directionality of the antenna system.

Electronic theft detection system for monitoring wide passageways

Abstract: An electronic theft detection system has a transmitting antenna and a receiving antenna located on the floor and overhead of a passageway being monitored. The antennas have conductors extending along and crossways of the passageway in staggered arrangement to provide system sensitivity for different paths of egress and different planes of orientation of resonant circuits to be detected. The transmitting antenna consists of a plurality of overlapping loops connected in phase, whereas the receiving antenna consists of a plurality of overlapping loops connected with alternating phase to provide cancellation of extraneous electrical disturbances.

Efficiency of electrically small antennas combined with matching networks

Abstract: The efficiency of an antenna combined with a matching network constructed from elements with finite Q is determined by applying the principle of conservation of energy. The conditions which must be satisfied to obtain maximum efficiency are examined. An analysis shows that for many electrically small antennas the conditions for maximum efficiency can be met using a simple L section as the matching network. Examples are presented to show the importance of including the matching network in efficiency calculations for electrically small antennas.

Broadband quasi-taper helical antennas

Abstract: A unique approach is described for widening the bandwidth of a helical antenna with improved gain, pattern, and axial ratio characteristics. The antenna may be described as a nonuniform or quasi-taper helix, which consists of a combination of uniform and tapered helix sections. Measured patterns, gain, axial ratio, and VSWR for various helical antenna configurations are presented and compared. It is shown that a nonuniform quasi-taper helix can provide an operating bandwidth twice that of a conventional uniform-diameter helix.

Clutter and multipath suppressing sidelobe canceller antenna system

Abstract: An improved antenna and interference-cancelling system for improving signalampling, particularly in side-lobe canceller system operating in a multiple-interference-source environment An antenna is constructed as a circularly symmetric lens having loosely coupled feed elements disposed around the periphery of the lens Each feed element acts as a high-azimuth-gain antenna which permits signal reception from all directions The lens, when connected to couple the receiving feed elements to a side-lobe canceller, permits the canceller to discriminate against clutter and scattered signals and resolve interference sources in angle so that all canceller loops do not receive signals from all other interference sources, while still providing interference samples from all directions

Phased power switching system for scanning antenna array

Abstract: A system for a phased array antenna including a set of power amplifiers for amplifying the power of a signal to be transmitted by radiating elements of the antenna. A set of hybrid couplers are connected between the power amplifiers and the radiating elements with individual ones of the hybrid couplers being cross-connected for sharing the power of each amplifier among a set of radiating elements. The coupling of power is selectively varied between the amplifiers and the radiating elements by shifting the phase of the signal applied to each power amplifier.

An analysis of the Wheeler method for measuring the radiating efficiency of antennas

Abstract: A model problem is formulated to evaluate the limitations imposed by the assumptions in the Wheeler or cap method for measuring the radiating efficiency of antennas. The antenna in the model is a circular loop and the radiation shield is a spherical metal shell. Calculated values of the actual efficiency of the antenna and the efficiency that would be measured using the Wheeler method are compared to determine the accuracy of the method and set guidelines for its application.

Antenna‐coupled infrared detectors

Abstract: A theoretical study has been made of the use of antennas to couple radiation to infrared detectors. It is shown in general that for any detector characterized by a specific detectivity D, noise‐equivalent power (NEP) can be reduced until the background blackbody fluctuation limit is reached. The reduction in NEP is expected to be on the order of b/λ, where b2 is the area of the detector. In the case of far‐infrared bolometers away from the blackbody limit, significant reductions of NEP appear to be possible. Alternatively the antenna may be used to increase the temperature at which the bolometer can be operated or to reduce its response time. The possible use of antennas with various other infrared detectors is also considered, and some criteria for suitability are described.

A scanning spot-beam satellite system

Abstract: We propose a satellite with a high gain, movable spot beam to communicate with individual earth stations time-sharing a single channel in the tdma (Time-Division Multiple Access) mode It is estimated that this approach could readily save some 20 dB in the link budget while still providing full US coverage When this 20 dB is apportioned with the objectives of reducing the earth-station antenna size, increasing the satellite capacity, and reducing transmitter power, the effects are dramatic This technique can be combined with a fixed-spot beam system serving major traffic areas This combination can provide both full area coverage as well as multiple reuse of the frequency band A tdma burst organization is proposed, and estimates of burst lengths, beam switching intervals, and buffer storage size are made for a 100-earth-station network operating on a 600 Mb/s channel A phased array antenna with each element irradiating the entire US is employed to form the movable spot-beam This provides an attractive solution even though a closed-loop beam-forming algorithm may be required It appears feasible to construct such an antenna with nearly 50-dB gain capable of forming a spot beam toward any position within the continental United States with a switching time of a few nanoseconds

Migrating Birds Respond to Project Seafarer's Electromagnetic Field

Abstract: Radar tracking of individual migrating birds flying over a large alternating-current antenna system showed that the birds turned or changed altitude more frequently when the antenna system was operating than when it was not. These results suggest that birds sense low-intensity alternating-current electromagnetic fields during nocturnal migratory flight.

Multi-band directional antenna

Abstract: A multi-band multi-element directional antenna array having a driven element and at least one parasitic element with a network at the center of each element interconnecting element opposite side radiators. While some of these would be a driven element and either a reflector or director parasitic element array most applications call for at least three elements, a driven element, a reflector element and a director element, and for some applications, additional parasitic director elements are added. While antenna arrays embodying features hereof may be adapted as two band f 1 f 2 , f 2 f 3 , or f 1 f 3 antenna arrays, primary useage would be in a three radio band f 1 , f 2 , f 3 version with band nominal center frequencies related, approximately by the progression 1, 1.5, 2 (example 14, 21, and 28 MHz). Reflector and director elements with their center networks as parasitic elements are structured to resonate at frequencies up to ten percent displaced from respective band operating frequencies--reflector elements at lower frequencies and directors at higher frequencies. Some of the arrays employ folded elements for improved unidirectional radiation patterns and structural advantages.