Showing papers on "Dipole antenna published in 1977"

Design of a stripline log-periodic dipole antenna

Abstract: A procedure is given for designing a two-layer stripline log-periodic dipole (LPD) antenna array. Measured input impedance and far-field characteristics are demonstrated for a 12-element array for 1-2 GHz operation that are in good agreement with design specifications.

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.

Radio frequency ring-shaped slot antenna

Abstract: An array antenna is disclosed wherein each one of the antenna elements includes at least two concentric slots formed in a conductive sheet. The conductive sheet is disposed on a dielectric support and a ground plane is found on the opposite surface of such support. The inner one of the slots enables the outer slot to radiate radio frequency energy having a wavelength greater than the circumference of such outer slot. When such antenna includes an additional concentric slot the antenna is adapted to operate over a pair of frequencies separated by greater than twenty percent while enabling the array antenna to have satisfactory grating lobe characteristics.

Flush-mounted piggyback microstrip antenna

Abstract: A dual radiating system where one radiating element is placed atop the ot in a piggyback fashion. The elements can be a pair of microstrip or dielectric-loaded parallel plate radiators, or it can be a combination of the two. Separate coaxial lines feed each of the radiators, and there is a minimum of coupling from one antenna to another. The antenna can be used alone or more effectively in a linear or planar conformal array.

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.

Evaluation of an implantable electric‐field probe within finite simulated tissues

Abstract: A set of miniature isotropic probes has been used experimentally to map electric fields within two small spheres of simulated muscle tissue (3.3-cm and 8-cm radii) that were irradiated by 450-, 915-, and 2450-MHz plane waves. Good agreement was obtained with the theoretically predicted spatial distribution of fields in both spheres, even in the immediate proximity of the boundaries. The absolute calibrations of the probes were found to be moderately to significantly dependent upon the dielectric constant of the medium (1 ≤ ∈r ≤ 50) in which the probe was implanted, with the least dependence occurring at 2450 MHz (±2.25 dB), and the greatest dependence occurring at 450 MHz (±4.25 dB). A set of design criteria is presented that are necessary for proper performance of such a dipole/diode probe. Of particular importance are the thickness of the insulation surrounding the dipole antenna, and the dimensions of the dipole. Both must be small compared to the wavelength of the field in the biological media. The validity of the design criteria has been experimentally demonstrated, illustrating the feasibility of producing an improved probe whose response to an electric field of given strength would be relatively constant regardless of the dielectric constant of the media and independent of boundary-proximity effects. Preliminary results of in vivo measurements are presented; improved, biologically compatible designs are discussed.

Design of Printed Resonant Antennas for Monolithic-Diode Detectors

Abstract: Model experiments at 10-GHz band have been performed to obtain optimum structures of printed resonant antennas for monolithic GaAs Schottky-diode detectors in the submillimeter-wave region. Design charts for antenna structures, which are also useful for a thin-film metal-to-metal diode structure on a dielectric substrate, are presented.

Triband vehicle antenna

Abstract: An antenna for simultaneous connection to a citizen's band transceiver, an AM receiver and a FM receiver, particularly suitable for use on a vehicle such as an automobile. The antenna proper is a center-loaded upstanding rod which, in the preferred form, telescopes downwardly to a retracted position where it does not protrude above the ground plane. The antenna proper is connected to a T-connected open stub transmission line and to a FM resonant relatively high impedance signal-carrying transmission line. The former has inductive reactance in the FM band which offsets the capacitive reactance of the relatively short effective length of the antenna proper in the FM frequencies. The signal-carrying transmission line is substantially half wave in length in the FM band so as to reflect impedance at its far end substantially equal to the impedance present at the T-connection. The signal-carrying transmission line is also of length that provides resonant action transforming the relatively low impedance at the T-connection or base of the antenna in the CB band to a higher impedance, such as 50 ohms, at the end of that transmission line. Finally, the signal-carrying transmission line, because of its relatively high characteristic impedance, has very low capacitance and therefore does not tend to load the AM radio. The end of the signal-carrying transmission line is connected to the input terminal of splitter containing resonant circuits which are in turn connected to two transmission lines, one leading to the CB transceiver and the other leading to the AM/FM radio.

Portable radio antenna

Abstract: PORTABLE RADIO ANTENNA ABSTRACT OF THE DISCLOSURE An antenna for a hand-held radio transceiver includes first and second elements extending from the radio's case. The first element is comprised of a pair of series coupled members having electrical lengths of one-half and one-quarter wavelength, respectively, with the free end of the second member being coupled to the transmitter output. The second element couples to the radio's electrical ground and is configured to form a transmission line with the second member. The effective electrical length of the second element, including the influence of the elements parasitic coupling to the radio, is adjusted to be one-quarter wave-length. The resulting antenna structure minimizes surface currents across the radio's body, thereby substantially eliminating power loss caused by absorption in the user's body.

Missile base mounted microstrip antennas

Abstract: Proof of the feasibility of aft mounting low-profile antennas on reentry vehicles is presented. This is an application of state of the art antenna hardware. Aft mounting presents the best reentry environment to antenna hardware, and its practicality has been demonstrated. Microstrip antenna principles can be used to produce very rugged antennas. Their low profile reduces many interface, mechanical, and survival problems. The pattern coverage for these vehicles must be toward the fore direction. This type of pattern requires an interaction between the vehicle and the antenna when the antenna is effectively shadowed from that direction. This paper describes the results obtained by actual experimental hardware. Contoured elements were used, as were foreshortened elements. These elements demonstrated ability to be fit around other aft equipment. The versatility of these elements were further demonstrated by tailoring them for two different types of coverage to accommodate different vehicle operational requirements.

Transmission line theory of antenna impedance in a magnetoplasma

Abstract: Transmission line theory for the impedances of wire antennas immersed in a cold magnetoplasma is proposed The theory is applicable to antennas which are not necessarily small in terms of a wavelength measured along the antenna wire The transmission line theory for the impedance of a very thin cylindrical dipole antenna leads to the Balmain quasi-static theory when the antenna length reduces to zero New impedance resonances which would be observed for antennas of finite length in a magnetoplasma in the frequency region below and near the electron cyclotron frequency are predicted by the present theory

Isotropic transmission-line antenna and its toroid-pattern modification

Abstract: The far-field strength of the \lambda/4 transmission-line antenna is derived as a complex vector containing amplitude, phase, and direction of the E vector. The product of this phasor-vector and its conjugate is constant and proves that the transmission-line antenna is an isotropic radiator with respect to the powerflow density of coherent electromagnetic waves. Folding of the line conductor parallel to the symmetry plane reduces the pattern to toroid shape analogous to radiation of a short dipole. While the unbalanced straight transmission-line antenna is used on rockets and vehicles, the unbalanced folded type is suitable as efficient transmit antenna at VLF, LF, or MF.

Amplitude responsive detector

Abstract: Disclosed are apparatus and method for detecting the presence, or absence, of material at a predetermined location. A crystal controlled oscillator generates a constant-frequency, constant-amplitude signal which is fed through a load resistor to an antenna sensor circuit, including an antenna probe positioned at the sensing location. The amplitude of the signal fed to the sensor circuit varies as the impedence of the antenna probe is affected by material in its environment, or the lack thereof. The signal amplitude is converted to a d-c voltage level, which is added to a reference d-c voltage level preset with the antenna probe free of impedance-affecting material. The difference voltage level value thus obtained, and which reflects the environment of the antenna probe, is used to control a switching circuit whose output assumes one value or another, depending ultimately on the antenna probe's environment. The output from the switching circuit may be used to operate one or more devices indicating the environment of the antenna probe, and/or affecting the environment by adding to, and/or removing therefrom, material affecting the impedance of the antenna probe.

AM-FM-CB Disguised antenna system

Abstract: A vehicle-mounted antenna simultaneously coupled via a passive electrical network to a 40-channel Citizens band transceiver and to an AM-FM receiver is disclosed. A non-loaded whip antenna, sized to be electrically short at Citizens band frequencies, is cowl-mounted in a conventional manner to present the dimensions and generaly appearance of a standard broadcast band car radio antenna. The passive electrical coupling network includes a broadband compensated, quarter-wave transmission line transformer for impedance matching the electrically short antenna to the Citizens band transceiver, and associated L-C circuits for selectively blocking, bypassing and separating AM and FM band signals relative to each other and to Citizens band signals. The disclosed antenna with its associated network provides excellent AM-FM radio receiver reception while presenting to the Citizens band transceiver a voltage standing wave ratio of 1.5:1 or better.

Superconducting superdirectional antenna arrays

Abstract: Electrically and physically small antenna arrays in a superconducting state can be used to obtain a radiation pattern of moderate directivity with high radiation efficiency. The loss resistance is reduced by several orders of magnitude, and superdirectivity is achieved with a loop antenna array. Radiation beamwidth depends upon only the number and relative phase of the loops and is independent of array size. Experimental results show efficiency of an electrically small two loop antenna array increases 250 times when placed in a liquid helium environment. Its directive properties compare well with theoretical predictions.

Effects of a human body on a dipole antenna at 450 and 900 MHz

Abstract: The VSWR and pattern characteristics of a dipole held close to or touching a human body have been experimentally determined and the results are reported. Two choke-sleeve dipoles, tuned for the two test frequencies of 450 and 900 MHz, were used for this study. The measurements were made with the antenna held at a person's waist, chest, and shoulder levels and also held above the head. The radiation characteristics of the combined body and antenna were compared with the dipole characteristics in free space. Propagation shadowing by the body and the effects of the body on the VSWR characteristics are illustrated.

Coupling between a dipole antenna and an infinite cable over an ideal ground plane

Abstract: A formulation is given for the fields radiated by an electric or magnetic dipole of arbitrary orientation in the presence of a cable suspended above a flat and perfectly conducting ground. The cable can be a solid conductor, a leaky coaxial cable, a CATV cable, or a surface-wave transmission line. Illustrative numerical results for both the far-field radiation pattern and excitation of the modal currents on the cable are given for the case of a vertical electric dipole source. Among other things, we find that the resultant radiation or far fields are not markedly influenced by the presence of the cable unless the dipole source is very near the cable. However, there is a significant cross-polarized component produced by the presence of cable that could have important consequences in producing bearing errors in low frequency beacon navigation systems.

Short-pulse characteristics of the conical spiral antenna

Abstract: The short-pulse charactersitics of the conical spiral antenna are examined in detail. The antenna is anlyzed using a time-domain integral equation. Various peculiarities associated with the numerical solution procedure are discussed, including the effects of a high Q , low-frequency resonance and impedance loading of the antenna. Special attention is directed to the radiated-pulse properties of the antenna for different types of time-varying excitation. Also presented is a quantitative assessment of the antenna's fidelity under pulsed conditions and an approach for obtaining the desired radiated-pulse shape by tailoring the time variation of the applied antenna voltage.

Three band monopole antenna

Abstract: A three band monopole antenna with such length as to be of greater electrical length than a quarter wavelength of the two highest frequency bands and shorter than a quarter wavelength of the lowest frequency band. The antenna system includes a matching network at its base matching the antenna on three frequency bands related by, substantially, the progression 1, 2, 4, and with the matching network including a shunt inductor and an inductor and capacitor in series with the signal feedpoint.

Theory of an insulated linear antenna in a dissipative medium

Abstract: The theoretical model of an insulated antenna in a general ambient medium is reviewed briefly. Attention is then directed to the solution of the integral equation for the current distribution in the antenna. The properties of the kernel are discussed in detail, and approximate solutions for the complex wave number are obtained. The evaluation of the kernel and other related numerical problems are discussed and a numerical method of computation is presented. A discussion of approximate solutions is included. A comparison of the theoretical results with measured data and numerical computations is made to check the applicable range of the theory.

Radio frequency array antenna system

Abstract: A radio frequency array antenna system wherein an array of antenna elements in a multibeam array antenna is coupled to one of a pair of beam forming networks and a portion of such antenna elements is coupled to another one of the pair of beam forming networks. Radio frequency amplifiers are coupled between the array of antenna elements and the pair of beam forming networks. The beam forming network which is coupled to only a portion of the antenna elements is used in the transmission of continuous wave radio frequency energy and the other beam forming network is used in the transmission of pulsed radio frequency energy. During transmission of the continuous wave energy only the portion of the radio frequency amplifiers coupled to the corresponding beam forming network is powered and during transmission of pulse modulated radio frequency energy all of the radio frequency amplifiers are supplied with power. With such arrangement the power required for the multibeam array antenna system is reduced and activation of the radio frequency amplifiers which are used to transmit pulsed energy produces minimum intermodulation of continuous wave energy being transmitted.

Compact omnidirectional antenna array

Abstract: An omnidirectional antenna array comprising a ferrite antenna inductively coupled to one leg of a loop antenna that lies in a plane parallel to the long axis of the ferrite antenna The output signal may be taken from either of the antennas

Antenna mounted tuning indicator

Abstract: A device facilitating the tuning of an antenna system comprising a body having an opening accommodating its mount to and operative connection with a whip, wire or rod type antenna, incorporating means which in the mount thereof inherently forms the secondary of a transformer, the primary of which is provided by the antenna or its loading coil The secondary is electromagnetically coupled to the primary to have induced therein a RF voltage and a resulting current actuates a signal means connected across the secondary The signal means signals the tuned or untuned condition of the antenna to which the body is applied in accordance with the level of the sensed current

Coupling between small thin-wire antennas and a biological body

Abstract: Coupling between the electromagnetic (EM) field of a small thin-wire antenna and an adjacent finite biological body is investigated analytically. Proximity effects of the body on the impedance and radiated power of the antenna are studied; the induced field and dissipated power in the biological body are determined. Radiation fields of the antenna-body system are evaluated.

Properties of dielectrically loaded antennas

Abstract: An analysis is made of the effect of dielectric loading on electric dipole antennas. Theoretical and experimental evidence is reviewed and an overview of properties in several distinct regimes obtained. The possible use of dielectrically loaded antennas for (a) broadband and (b) narrowband applications is assessed.

Broadband isotropic antenna with fiber-optic link to a conventional receiver

Abstract: A broadband active isotropic receiving antenna for use with a conventionallectromagnetic interference receiver to measure weak near-zone electric fields of unknown polarization. The antenna consists of three mutually orthogonal active dipoles, including RF amplifier circuitry and light emitting diode means, located therein coupled to fiber optic waveguide means. The frequency range of each of the three field components is amplified and used to modulate respective light emitting diodes whose modulated infrared or visible signals are guided through the fiber optic waveguide means to photo-detectors at the far end of the fiber optic guides. These photo-detectors recover the RF modulation from the IR carrier which is then time multiplexed for input to the electromagnetic interference receiver. The DC output from the receiver is processed to provide an output voltage proportional to the square root of the sum of the squares, i.e. the Hermitian magnitude of the three mutually orthogonal electric field components.

Apparatus and method for improving r.f. isolation between adjacent antennas

Abstract: Method and apparatus for improving the r.f. isolation between a transmitting and receiving antenna disposed at respectively corresponding spaced apart but relatively adjacent locations. A special compensation radiator is provided at the transmitting and/or receiving antenna site and fed from the same r.f. input/output which feeds the main antenna. The direction, magnitude and phase of r.f. energy radiated and/or received from the compensating radiator are chosen so as to substantially cancel the undesirable r.f. energy otherwise directly received by the receiving antenna from the transmitting antenna.

The horizontal-wire antenna over a dissipative half-space: Generalized formula and measurements

Abstract: It is shown and verified by experiment that a horizontal resonant or traveling wave antenna placed in air close to a dense halfspace with the properties of lake or sea water or earth behaves like a terminated lossy transmission line. The terminal impedance is related to the radiation of the antenna into the air and the complex wavenumber and characteristic impedance are those of an infinitely long line. The complex wavenumber takes account of both dissipation in and radiation into the dense half-space.

Dual asymmetrically fed electric microstrip dipole antennas

Abstract: Circularly polarized microstrip antennas consisting of thin electrically ducting, square-shaped radiating elements formed on one surface of a dielectric substrate and having a ground plane on the opposite surface of the substrate. Two feed points are used to provide a circular polarized radiation pattern. The feed points are located along the centerlines of the antenna length and width or along the diagonal lines of the element and the input impedances can be varied by moving the feed points along both centerlines or both diagonal lines from the centerpoint of the element. The antennas can be notched in from the edges of the radiating element along the centerlines of the element width and length, or along opposite diagonal lines of the element, to the optimum input impedance match feed point.