Showing papers on "Dipole antenna published in 1992"

Theoretical and experimental development of 10 and 35 GHz rectennas

Abstract: A 35-GHz rectenna has been developed with 39% conversion efficiency. The rectenna uses a microstrip dipole antenna and a commercially available mixer diode. Over 60% conversion efficiency was demonstrated using this diode at 10 GHz. A theoretical analysis was derived to predict the performance of the rectenna. The analysis is a useful tool for device and circuit design. The theoretical and experimental results should have many applications in microwave power transmission and detection. >

Energy absorption mechanism by biological bodies in the near field of dipole antennas above 300 MHz

Abstract: The energy absorption mechanism in the close near field of dipole antennas is studied by numerical simulations. All computations are performed and validated applying the three-dimensional multiple multipole software package. The numerical model of the plane phantom is additionally checked by accurate as possible experimental measurements. For the plane phantom, the interaction mechanism can be described well by H-field induced surface currents. The spatial peak specific absorption rate can be approximated within 3 dB by a formula given here based on the incident H-field or antenna current and on the conductivity and permittivity of the tissue. These findings can be generalized to heterogeneous tissues and larger biological bodies of arbitrary shape for frequencies above 300 MHz. The specific absorption rate is mainly proportional to the square of the incident H-field, which implies that in the close near field, the spatial peak specific absorption rate is related to the antenna current and not to the input power. >

Double-slot antennas on extended hemispherical dielectric lenses

Abstract: An investigation of the coupling efficiencies to a gaussian-beam of a double-slot antenna on a hyperhemispherical lens is presented. It is shown that both lenses couple equally well to an appropriate gaussian beam (about 80 percent). The radiation patterns of both lenses with a double-slot antenna are computed using the ray-tracing method. The experimental radiation patterns are presented and show close agreement to the theoretically computed patterns.

Active reflectarray antenna for communication satellite frequency re-use

Abstract: An antenna suited for a communications satellite includes two separately located, mutually orthogonally polarized feed antennas such as vertically and horizontally polarized linear horns. The horns feed an active reflector antenna array. The array includes a plurality of mutually orthogonally polarized antenna elements such as crossed dipoles or square patch antenna with cross feeds for two independent orthogonal polarizations. The feeds of the antenna elements are coupled to amplifier modules. Each module includes a circulator for each polarization, coupled to a processor including a low noise amplifier, controlled phase shifter, variable gain amplifier and power amplifier. The output of the power amplifier feeds the antenna element through the circulator. The large number of radiating elements allows high power using power amplifier with relatively modest capabilities. The phase shifters of each module independently control the reradiation phase of the vertical and horizontal signals, so that a collimated beam can be independently focused to the two feed points, one for each polarization.

Electronically agile dual beam antenna system

Abstract: The present invention provides an improved antenna system that, in one embodiment, includes an antenna array comprised of a plurality of elements, each of which is capable of providing a signal. Also included in the improved antenna system is, a multi-beam beamformer for producing two spatially independent overlapping beams from the signals provided by two different subsets of the antenna array. The phase of the two beams is compared to realize an interferometer that can provide high or fine resolution data on the position of an object relative to the antenna system. The amplitude of the two beams can also be compared to obtain coarse data on the position of the object. The beamformer includes a switching network for selecting which elements of the antenna array form the two subsets. This permits, for example, the position of the beams to moved, the baseline of the two beams to be varied, and/or the beam width of the beams to be altered. To reduce adverse aerodynamic effects in certain applications, the antenna array is located conformal to the exterior surface of the body on which the array is mounted. Further, to reduce temperature related problems associated with high speed movement of the body on which the array is located, the array is located on the side of the body, as opposed to the front of the body. The side location also provides space for other types of sensors that are preferably located adjacent to the front surface of the body.

System including spiral antenna and dipole or monopole antenna

Abstract: A broadband antenna system includes a frequency-dependent antenna and a frequency-independent antenna rotatably coupled to the frequency-dependent antenna. The antenna system may be arranged such that a dipole or monopole antenna is rotatably coupled to the inner or outer termination points of a spiral antenna, which is, in turn, movably coupled to a base. When the dipole antenna is coupled to the outer termination points of the spiral antenna, the elements of the spiral antenna may be extended.

Multifrequency operation of microstrip antennas using aperture-coupled parallel resonators

Abstract: A microstrip antenna composed of parallel dipole resonators of different lengths fed by a rectangular slot cut in the ground plane of a microstrip line is analyzed using an integral equation technique solved in the spectral domain using the Galerkin method of moments. Multifrequency operation of this antenna is demonstrated using two different configurations. Experimental data are shown to be in good agreement with predicted results. The fundamental parameters influencing the realization of multifrequency operation, as well as impedance matching of the different resonances, are studied. Lastly, the radiation patterns of the antenna at different frequencies and the relative contribution of the dipoles to the radiation are investigated. >

Frequency-independent antennas and broad-band derivatives thereof

Abstract: The principles used in the development of frequency-independent antennas are reviewed. Examples of log-periodic (LP) geometry and the additional requirements that must be met for practical success are given. The evolution of unidirectional, wire-outline, and dipole arrays is presented. Analytical results for LP dipole arrays led to the concept of an active region that remains almost fixed in size relative to the wavelength. Periodic structure theory serves as an aid to understanding LP structures. The analysis of periodically loaded lines shows the problems that may arise from the existence of stop regions on LP antennas and provides procedures for eliminating them. This has led to successful LP monopole and cavity-backed slot arrays. Planar and conical log-spiral antennas are discussed. Frequency-independent, circularly polarized patterns-bidirectional, unidirectional, omnidirectional, and conical-can be provided from log-spiral antennas with two or more arms. Recently, the LP design principles have been applied to low-profile antennas: patches, thin cavities, and spirals over ground. They have also produced flush-mounted aircraft antennas that can respond simultaneously to two different linear of circular polarizations. >

Finite-difference time-domain method for antenna radiation

Abstract: The finite-difference time-domain (FDTD) method is used to model and predict the radiation patterns of wire and aperture antennas of three basic configurations. A critical step in each is the modeling of the feed. Alternate suggestions are made and some are implemented. The first antenna is a quarter-wavelength monopole and the second is a waveguide aperture antenna. In both bases the antenna is mounted on ground planes, either perfectly conducting or of composite material. The results obtained using the FDTD technique are compared with results obtained using the geometrical theory of diffraction (GTD) and measurements. The third configuration of interest is a pyramidal horn antenna. To model the flared parts of the horn, a staircase approximation was applied to the antenna surface. The computed radiation patterns compared well with measurements. >

Properties of electromagnetic beams generated by ultra-wide bandwidth pulse-driven arrays

Abstract: Analytical bounds on the characteristics of beams generated by an arbitrary pulse-driven array are derived and supported with numerical calculations. These bounds extend the meaning of near-field distances or diffraction lengths to the situation where the array driving functions can be broad-bandwidth signals. Particular attention is given to transmitting and receiving array systems which consist of elements that are not large in comparison to the shortest wavelength of significance contained in the signals driving them. Their output signals constitute higher-order beams whose coherence properties are degraded more slowly by diffraction than lower-order beams. It is shown that for certain measures of performance involving these beam characteristics, a localized wave pulse-driven array can outperform similar continuous-wave-driven arrays. An array with independent addressable elements is required to realize these localized wave effects. The enhanced localization effects are intimately coupled to the proper spatial distribution of broad-bandwidth signals driving the array. >

Waveguide-fed parallel plate slot array antenna

Abstract: A novel planar antenna in which radiating slots are arrayed on one side of a square parallel plate waveguide and coupling slots occupy the other side is proposed. The antenna is excited via the coupling slots by a rectangular waveguide. In order to suppress unwanted reflections and to assure the purity of the transverse electromagnetic traveling-wave mode in the parallel plate waveguide, all the slots are arrayed in pairs. An X-band model antenna was fabricated, and uniform aperture illumination was demonstrated with 48% antenna efficiency. These results demonstrate the feasibility of antennas of this type. >

Compact broadband microstrip antenna

Abstract: Arrangements of compact broadband microstrip antennas are disclosed. Each arrangement comprises a dielectric material (32, 62) with the microstrip antennas mounted to one side and a ground surface (GP) on the opposite side. A first arrangement comprises a closed array of antenna elements (63-70) electrically driven out of phase from one another to excite one or more spiral modes. A second arrangement comprises one or more antenna elements arranged on a magnetic substrate (73) which has a relative permittivity approximately equal to its relative permeability. In a third arrangement, the microstrip antenna operates in a single mode and radiation from other modes is suppressed by varying the spacing above the ground plane (GP) in the radiation zones so that only radiation in the desired zones is fostered. In a fourth arrangement, a spiral mode antenna element (21) is spaced between 1/60 and 1/2 wavelengths from the ground surface (GP) throughout a multioctave operating frequency range. The substrate (32) has er³1.0 and the antenna is driven by a near-perfect impedance-matched feed network.

High performance antenna for hand-held and portable equipment

Abstract: An antenna system for portable electronic apparatus, particularly for the handset of a cordless telephone system, and comprising two antenna, a first (shown) mounted on a flap (2) and comprising a groundplane 5 and active monopole 4 fed by a coaxial feed 6 from electronic circuitry (not shown) in the main section of the handset 1. The flap is pivotally connected to the main section of the housing 1, and is folded down against the main section when not in use. Another similar antenna is fitted in the main section, and both antennae are connected to the transceiver circuitry via the same node. The two antennae are specially designed so as to introduce deliberate mismatch so as to provide an effective switching system between the two antenna without the need for separate circuit elements.

Highly efficient planar antenna on a periodic dielectric structure

Abstract: Efficient transmission and reception of electromagnetic radiation are achieved by an antenna on a substrate. An antenna (100) is fabricated on the top surface (102) of a substrate (104) which includes a periodic dielectric sturcture (106). The antenna (100) operates at a frequency within the band gap of the periodic dielectric structure (106). Radiation emitted by the antenna (100) cannot propagate through the structure (106) and is therefor emitted only into space away from the substrate. When the antenna is receiving, radiation striking the device does not propagate through the substrate but is concentrated at the antenna. A phased array with isolated elements is achieved by fabricating the array elements on top of a substrate having a periodic dielectric structure and by surrounding the circuits associated with each antenna element with the periodic dielectric structure. Radiation from an element or associated circuitry at a frequency within the band gap of the structure cannot propagate into the substrate to interfere with other elements.

Monolithic microwave integrated circuit receiving device having a space between antenna element and substrate

Abstract: The receiving device according to this invention includes one or more patch or helical antennas and one or more receiving units formed monolithically on a single substrate. In order to widen the receiving frequency band, antenna elements are formed not directly on a compound semiconductor substrate but with a space between the antenna element and the substrate. In the patch antenna embodiment, patch elements are supported by dielectric posts, whereby there is provided a void between most of the patch antenna and the underlying semiconductor substrate.

Lens-coupled imaging arrays for the millimeter- and submillimeter-wave regions

Abstract: The authors have been developing four kinds of lens-coupled antenna imaging arrays for operation at millimeter- and submillimeter-wave frequencies. Dipole antennas, Yagi-Uda trap-loaded antennas, and microstrip patches are compared from the viewpoint of matching with detectors and optical systems. The radiation patterns and input impedance of each antenna have been calculated and measured to attain the optimum matching using model experiments. The trap-loaded antenna arrays have been successfully applied to plasma diagnostics at the Tsukuba GAMMA 10 tandem mirror. >

Directional scanning circular phased array antenna

Abstract: A directional scanning antenna includes a circular array of a plurality of antenna elements extending several wavelengths in diameter. The number of antenna elements are sufficient to form a plurality of directionally-oriented subsets of active antenna elements and associated subsets of parasitic antenna elements. An antenna feed system provides connections to each one of the plurality of antenna elements that include connections to electronically variable reactances and connections to a source or receiver of electromagnetic energy. The antenna feed system is controllable to provide connections between the subsets of active antenna elements providing wave propagation and reception in one or more directions and to provide connections between a plurality of the remainder of antenna elements in associated subsets of parasitic antenna elements to assist the directionality of the antennas.

Integrated horn antennas for millimeter-wave applications

Abstract: The development of integrated horn antennas since their introduction in 1987 is reviewed. The integrated horn is fabricated by suspending a dipole antenna, on a thin dielectric membrane, in a pyramidal cavity etched in silicon. Recent progress has resulted in optimized low- and high-gain designs, with single and double polarization for remote-sensing and communication applications. A full-wave analysis technique has resulted in an integrated antenna with performance comparable to that of waveguide-fed corrugated-horn antennas. The integrated horn design can be extended to large arrays, for imaging and phased-array applications, while leaving plenty of room for the RF and IF processing circuitry. Theoretical and experimental results at microwave frequencies and at 90 GHz, 240 GHz, and 802 GHz are presented. >

Reconfiguration of passive elements in an array antenna for controlling antenna performance

Abstract: Disclosed is an array antenna (10) that may be reconfigured to point in multiple directions. The array antenna includes a driven element (12) coupled to a transmission line (14) and a pair of passive elements (22) and (24). The passive elements (22) and (24) each include three antenna segments that are coupled together by a pair of optoelectronic switches (26) and (28), respectively. When the optoelectronic switches coupled to a particular passive element are closed the element functions as a reflector; when the switches are open, the element functions as a director. Other reconfigurable antennas are also disclosed, including antennas with reconfigurable gain and field pattern characteristics.

Multiport scattering analysis of general multilayered printed antennas fed by multiple feed ports. I. Theory

Abstract: A general solution is given for a class of printed antenna geometries composed of multiple dielectric layers or ground planes, radiating patches, dipoles, or slots, and an arbitrary configuration of multiple transmission lines proximity-coupled or aperture-coupled to the radiating elements. The solution uses a full-wave spectral-domain moment method approach, and a new generalized multiport scattering formulation to model the excitation from the multiple feed lines. This method treats infinite phased arrays as well as isolated elements. The general theory using the new multiport scattering formulation is elaborated, with details of the key analytical and numerical aspects. Considering the unified nature of the multiport scattering analysis, and its simplicity, this analysis is appropriate for computer simulation of a large variety of multilayered microstrip antennas involving radome layers, dual polarized feeds, proximity-coupled or aperture-coupled elements, multifeed stacked or parasitic patches, and several related configurations for integrated phased array applications. >

Optoelectronically reconfigurable monopole antenna

Abstract: A monopole antenna is reconfigured for 200 or 375 MHz bands by optoelectronically switching two segments together. Light levels of much less than 1 mW significantly change the antenna pattern and gain. >

Electronically reconfigurable antenna

Abstract: An electronically reconfigurable antenna includes individual antenna elements which can be reconfigured as active or parasitic elements in the process of variable mode operation. In the antenna, an active subset of antenna elements excites a Wave on a parasitic subset of antenna elements, which are controlled by a plurality of electronically variable reactances. The plurality of electronically variable reactances. is used to provide the reconfigurable array, which may operate in a plurality of modes of wave propagation. Furthermore, the plurality of variable reactances allow compensation for the inherently narrow operating bandwidth of the high-gain surface wave antennas.

Self-focusing antenna array

Abstract: A phased array for transmitting to a microwave powered aircraft is focussed and steered by feedback from the aircraft. Each antenna of the array is phase modulated in turn, and the resulting amplitude modulation of the field at the aircraft is used to calculate a correction to the antenna phase, which is telemetered back to the array system and applied to the antenna phase shifter.

Conventional explanation for 'crossed field antenna'

Abstract: Recent papers have described the ‘crossed field antenna’, and have offered an explanation of its properties in terms of ‘Poynting vector synthesis’. In this Letter the antenna is analysed in a more conventional manner, providing an alternative explanation of its operation. The importance of the alternative is its compatibility with the Wheeler criteria for electrically small antennas. Extrapolation to very small antennas then encounters the expected efficiency-bandwidth limitations.

Numerical simulation of annular-phased arrays of dipoles for hyperthermia of deep-seated tumors

Abstract: The authors have used the finite-difference-time-domain (FDTD) method to calculate the specific absorption rate (SAR) distributions from an annular-phased array of eight dipole antennas coupled through water 'boluses' in anatomically based three-dimensional models of the human body. They evaluated the effect of tapered bolus chambers, frequency (100-120 MHz), dipole length (17-30 cm), and phase and amplitude of power to the various dipoles on the ability to focus energy in the region of deep-seated tumors in the prostate and the liver. Assuming tumor conductivity and permittivity to be similar or slightly higher than surrounding normal tissues, calculations indicate that adjustment of the noted parameters should result in considerable improvement in focusing of SAR distributions in tumor-bearing regions. If such calculations can be shown to correctly predict empirical measurements from complex inhomogeneous (although not necessarily anatomically correct) phantoms, they may be useful for hyperthermia treatment planning based on patient-specific anatomic models. >

Scanning characteristics of infinite arrays of printed antenna subarrays

Abstract: The analysis and scanning characteristics of several different types of infinite arrays composed of subarrayed printed dipole and microstrip patch elements are presented. The analysis is based on full-wave moment method theory, and includes mutual coupling between elements in the subarray as well as between subarrays. The effect of subarraying on scan blindness is demonstrated for arrays using two-element subarrays of printed dipoles and microstrip patches. Results are also given for the amount of power radiated in grating lobes. The effect of a subarray composed of one driven element and one parasitic element, and the use of a four-element synchronous subarray of microstrip patches to generate circular polarization are also considered. Data are given for impedance mismatch, power radiated into grating lobes, and the axial ratio; both square and rectangular patches area considered. Results are also shown for an infinite array of seven-element hexagonal subarrays of printed dipoles, and it is found that the large spacing between subarrays leads to a limited scan range. >

Dual frequency, dual polarized, multi-layered microstrip slot and dipole array antenna

Abstract: An antenna array system is disclosed which uses subarrays of slots and subarrays of dipoles on separate planes. The slots and dipoles respectively are interleaved, which is to say there is minimal overlap between them. Each subarray includes a microstrip transmission line and a plurality of elements extending perpendicular thereto. The dipoles form the transmission elements and the slots form the receive elements. The plane in which the slots are formed also forms a ground plane for the dipoles--hence the feed to the dipole is on the opposite side of this ground plane as the feed to the slots. HPAs are located adjacent the dipoles on one side of the substrate and LNAs are located adjacent the slots on the other side of the substrate. The dipoles and slots are tuned by setting different offsets between each element and the microstrip transmission line.

Multiport scattering analysis of general multilayered printed antennas fed by multiple feed ports. II. Applications

Abstract: For Part I, see ibid., vol.40, no.5, p.469-481 (1992). The general analysis of part I is applied to several practical geometries of multilayer/multifeed printed antennas. These examples include a dual-feed circularly polarized geometry; a stacked patch geometry; a stripline-aperture coupled geometry with a radome; an open-end proximity-coupled patch; and dipole and slot geometries inclined or perpendicularly coupled to different feedlines. Features of the selected geometries cover many practical aspects of multilayer integrated phased arrays. Experimental results for several geometries are compared with the analytical results to demonstrate the accuracy and versatility of the analysis used. Various design considerations for the use of these multilayered printed antenna geometries in integrated phase array applications are discussed. >

Radio communication device having a microstrip antenna with integral receiver systems

Abstract: A radio communication device (600) comprises a microstrip antenna (300) having a planar antenna element (302) and a ground plane (314) coupled to the planar antenna element (302). The microstrip antenna further comprises a dielectric material (304) positioned between the planar antenna element (302) and the ground plane (314), and a primary receiver element (325, 326, 328) mechanically coupled to the ground plane (314). The microstrip antenna (300) further comprises a feeder (308, 310) electrically coupled between the planar antenna element (302) and the primary receiver element (325, 326, 328) for feeding an intercepted radio signal therebetween for down conversion by the primary receiver element (325, 326, 328). The radio communication device (600) also comprises a secondary receiver element (828) coupled to the primary receiver element (325, 326, 328) for demodulating the intercepted radio signal after down conversion by the primary receiver element (325, 326, 328).