Showing papers on "Dipole antenna published in 1998"

Wide-band planar monopole antennas

Abstract: The circular disc monopole (CDM) antenna has been reported to yield wide-impedance bandwidth. Experiments have been carried out on a CDM that has twice the diameter of the reported disc with similar results. New configurations are proposed such as elliptical (with different ellipticity ratios), square, rectangular, and hexagonal disc monopole antennas. A simple formula is proposed to predict the frequency corresponding to the lower edge of the bandwidth for each of these configurations. The elliptical disc monopole (EDM) with ellipticity ratio of 1.1 yields the maximum bandwidth from 1.21 GHz to more than 13 GHz for voltage standing wave ratio (VSWR)<2.

Design and experiments of a high-conversion-efficiency 5.8-GHz rectenna

Abstract: A high-efficiency rectenna element has been designed and tested at 5.8 GHz for applications involving microwave-power transmission. The dipole antenna and filtering circuitry are printed on a thin duroid substrate. A silicon Schottky-barrier mixer diode with a low breakdown voltage is used as the rectifying device. The rectenna element is tested inside a waveguide simulator and achieves an RF-to-DC conversion efficiency of 82% at an input power level of 50 mW and 327 /spl Omega/ load. Closed-form equations are given for the diode efficiency and input impedance as a function of input RF power. Measured and calculated efficiency results are in good agreement. The antenna and circuit design are based on a full-wave electromagnetic simulator. Second harmonic power levels are 21 dB down from the fundamental input power.

Microstrip-fed quasi-Yagi antenna with broadband characteristics

Abstract: A compact and uniplanar antenna with broadband characteristics is presented. The novel Yagi-like printed dipole array antenna is fed by a microstrip-to-coplanar strip transition, and uses the truncated microstrip ground plane as its reflecting element. An X-band prototype measures a bandwidth of 17%. With 6.5 dB gain, 18 dB front-to-back ratio, and lower than -15 dB cross-polarisation level at 10 GHz.

Simulation of light emission from thin-film microcavities

Abstract: In light-emitting devices based on thin-film technology, light waves that are partially or totally reflected at interfaces between different materials interfere and influence the angular distribution of the emitted light. For an electrical dipole transition, the radiation pattern is equivalent to that of an electrical dipole antenna. New theoretical expressions are provided for the radiation, discriminating for polarization, emission angle, absorption, and transmission; and the numerical calculation of discrete modes, narrow modes, and evanescent waves near absorbing media is discussed.

Bipolar electrostatic structures in the shock transition region: Evidence of electron phase space holes

Abstract: We present observations of intense, bipolar, electrostatic structures in the transition region of the terrestrial bow shock from the Wind spacecraft. The electric field signatures are on the order of a tenth of a millisecond in duration and greater than 100 mV/m in amplitude. The measured electric field is generally larger on the smaller dipole antenna, indicating a small spatial size. We compare the potential on the two dipole antennas with a model of antenna response to a Gaussian potential profile. This result agrees with a spatial scale determined by convection and gives a characteristic scale size of 2–7 λd. We interpret the observations as small scale convecting unipolar potential structures, consistent with simulations of electron phase space holes and discuss the results in the context of electron thermalization at strong collisionless shocks.

Double resonance antenna structure for several frequency ranges

Abstract: The invention relates to small-sized antenna systems, especially planar antenna structures operating on several frequency bands. The antenna structure of the invention comprises a radiating antenna element with at least two lips. Thus, the antenna structure has two basic resonance frequencies, which are defined by the dimensions of the lips of the antenna element, gaps between them, and the other dimensions of the antenna structure. The radiating antenna structure is connected to the ground plane at least at one place. The radiating antenna element comprises at least two connection points, which are used for connecting the feed lines of the transmitter and receiver, and for connecting special tuning elements. The resonance frequencies of the antenna structure may be adjusted by connecting the said tuning elements to the connection points and antenna feed lines so that the antenna structure is operable on more than two frequency bands. The switches may be conventional semiconductor switches, such as FET switches or PIN diodes. Various optionally connectable tuning element or antenna feed arrangements may be used for carrying out an antenna arrangement which may be tuned in on all reception and transmission bands of an arrangement with several frequency ranges and mobile phone systems.

Phase array calibration by orthogonal phase sequence

Abstract: Methods and systems for calibrating an array antenna are described. The array antenna has a plurality of antenna elements each having a signal with a phase and an amplitude forming an array antenna signal. For calibration, the phase of each element signal is sequentially switched one at a time through four orthogonal phase states. At each orthogonal phase state, the power of the array antenna signal is measured. A phase and an amplitude error for each of the element signals is determined based on the power of the array antenna signal at each of the four orthogonal phase states. The phase and amplitude of each of the element signals is then adjusted by the corresponding phase and amplitude errors.

Frequency-scanned end-fire phased-aray antenna

Abstract: A frequency-scanned end-fire phased-array antenna includes a board, a sinuous transmission line formed on the board, a plurality of end-fire antennas, and a plurality of couplers corresponding to the end-fire antennas, such that the transmission line is selectively coupled to the plurality of end-fire antennas via the plurality of couplers, for selectively coupling energy within the transmission line to the end-fire antennas. By varying the input frequency to the antenna over a narrow range, the direction of a main radiation beam emitted by the antenna can be scanned ±90 degrees from broadside. A single antenna board produces a frequency-scanned fan beam. Stacked antenna boards can produce a frequency-scanned pencil beam, or several independent frequency-scanned fan beams at different frequencies. The present antenna can operate in the microwave, millimeter-wave, terahertz, infrared, or optical frequency range. Because this frequency-scanned phased-array can be mass produced by planar fabrication techniques, it can be much smaller and less expensive than conventional "hollow pipe" waveguide frequency-scanned phased-array antennas.

Double U-slot rectangular patch antenna

Abstract: A rectangular microstrip antenna with two U-shaped slots on the patch is described. Using a foam layer of thickness /spl sim/8% wavelength as the supporting substate, an impedance bandwidth of 44% is achieved. The radiation patterns are stable across the passband.

Design and Experiments of a High-Conversion-Efficiency

Abstract: A high-efficiency rectenna element has been designed and tested at 5.8 GHz for applications involving microwave- power transmission. The dipole antenna and filtering circuitry are printed on a thin duroid substrate. A silicon Schottky- barrier mixer diode with a low breakdown voltage is used as the rectifying device. The rectenna element is tested inside a waveguide simulator and achieves an RF-to-dc conversion efficiency of 82% at an input power level of 50-mW and 327- load. Closed-form equations are given for the diode efficiency and input impedance as a function of input RF power. Measured and calculated efficiency results are in good agreement. The antenna and circuit design are based on a full-wave electromagnetic simulator. Second harmonic power levels are 21 dB down from the fundamental input power.

On-chip antenna, and systems utilizing same

Abstract: One or more antennas are formed on an integrated circuit (IC) chip and connected to other circuitry on the IC chip. Antenna configurations include loop, multi-turn loop, square spiral, long wire, or dipole. The antenna may be formed to have two or more segments which can selectively be connected to one another to alter an effective length of the antenna. Two antennas may be formed in two different metallization layers separated by an insulating layer. Additionally, an antenna may be incorporated in a heat sink structure that is joined to the IC chip. IC chips having antennas are suitably included in a system or subsystem having electrical functionality, such as general purpose computers, telecommunications devices, and the like.

Measuring the impedance of balanced antennas by an S-parameter method

Abstract: The input impedance of a balanced antenna is conventionally measured by using a balun that forces opposite currents in each part of the radiator. In this paper, balanced antennas are viewed as two-ports, the S-parameters of which are determined by standard network-analyzer techniques. Simple formulas then lead to the differential input impedance. The method is illustrated by measurements on a dipole antenna, which are compared to the results for monopoles over a ground plane.

Ultra-wideband magnetic antenna

Abstract: An ultra-wideband magnetic antenna includes a planar conductor having a first and a second slot about an axis. The slots are substantially leaf-shaped having a varying width along the axis. The slots are interconnected along the axis. A cross polarized antenna system is comprised of an ultra-wideband magnetic antenna and an ultra-wideband dipole antenna. The magnetic antenna and the dipole antenna are positioned substantially close to each other and they create a cross polarized field pattern. The present invention provides isolation between a transmitter and a receiver in an ultra-wideband system. Additionally, the present invention allows isolation among radiating elements in an array antenna system.

Antenna unit and digital television receiver

Abstract: An antenna unit comprising a conductor base plate and an antenna element arranged near the conductor base plate. The antenna element includes a predetermined portion as a coil or zigzagged conductor and has one end grounded through the conductor base plate. The antenna element may include the coil or zigzagged conductor at its one end in such a manner that the coil or zigzagged conductor is connected with the other part of the antenna element on an insulator provided on the conductor base plate.

Compact antenna structures including baluns

Abstract: An antenna structure includes a center feed dipole antenna having first and second radiating sections that extend along a substrate from a center feed point. A feed section is electrically coupled to the center feed point. The feed section includes a radio frequency input line and a ground line extending along the substrate adjacent one another. A balun extends along the substrate between the first radiating section and the ground line. The first radiating section, the radio frequency input line, the ground line and the balun preferably extend along the substrate in parallel. A tuning shunt may also be provided across the balun for dual band operation. Accordingly, compact dual band antenna structures including baluns may be provided.

Performance of a meandered line as an electrically small transmitting antenna

Abstract: For antennas to radiate at maximum efficiency, their dimensions must be on the same order as the radiated wavelength At frequencies below 30 MHz, antennas with efficient radiation are often too large for mobile and portable applications Smaller antennas can be made to radiate efficiently by use of matching networks For installation convenience and ease of adjustment, these networks are usually placed between the transmitter and the antenna input; but it has been found that for best radiation efficiency, matching network elements should be placed at points on the antenna structure Unfortunately, such matching networks must be tuned for each transmitting frequency and, when mounted on the antenna, they cannot easily be tuned A meander element antenna was found to present some electrical and mechanical properties allowing convenient placement of tuning elements when configured as an electrically small transmitting antenna Some simplified design guidelines were derived from experimental data

Dipole configurations with strongly improved radiation efficiency for hand-held transceivers

Abstract: In this paper the design criteria for antenna structures with improved radiation efficiency while operating in close vicinity to a biological scatterer are investigated. The study is performed using a simple /spl lambda//2 dipole combined with a directive or reflective element. The optimization criteria are the effective radiation efficiency, the spatial peak specific absorption rate (SAR), and the sensitivity of the input resistance to the distance from the scatterer. It is demonstrated that the primary design criterion to improve the radiation efficiency is not directivity but the reduction of the maximum incident magnetic field strength in the exposed skin area of the user's head. For the reflectively coupled dipole, all performance parameters are improved by several decibels compared to a standard, /spl lambda//2 dipole, whereas for some other directive structures, the performance is impaired. The study is conducted with the generalized multipole technique (GMT) numerical simulation method, the results of which are validated by measurement methods.

Rfid conveyor antenna

Abstract: An RFID antenna system is described, comprising an elongated antenna (12) proximate an interrogation path (A1-A4) for interrogating transponders (10) moving along the interrogation path. The antenna (12) is oriented such that the longitudinal axis of the antenna is substantially perpendicular to said interrogation path. The antenna provides an active RF interrogation zone that intersects at least 40 % of the horizontal longitudinal plane of the interrogation path.

Microstrip antennas for SAR applications

Abstract: This paper discusses various methods of implementing a shared-aperture dual-frequency dual-polarized array antenna for spaced-based synthetic aperture radar (SAR) applications. After evaluating the use of several potential array architecture concepts and radiating elements, a design using interlaced C-band microstrip patches and X-band printed slot elements was chosen as the best choice for the present system requirements. Layout considerations for the two arrays and their associated feed networks are addressed in terms of a practical design. A dual-frequency (C- and X-band), dual-linear polarized SAR array antenna prototype was designed, fabricated, and tested. The principal goal of this effort was to demonstrate the viability of the dual-band dual-polarized array concept, and this has been accomplished. Test results are shown with good correlation between measured and predicted results, validating the design approach used. This work demonstrates that a dual-frequency dual-polarization SAR antenna within a single aperture is a feasible approach to meeting user requirements in future SAR spacecraft.

Adjustable array antenna

Abstract: A passive reflective antenna (75) located near an active receiving antenna (71) is used to change the energy at the receiving antenna (71). The change in energy may be such as to remove a null created by multipath or to provide directionality, or both. The receiving antenna (71) is permanently connected to a single receiver (73). When the receiver's output signal degrades below an acceptable level of quality, the reflective phase of the passive antenna's load is changed to change the phase of the reflected energy and achieve a desired effect (remove a null, change directionality, etc.) at the receiving antenna (71). In the simplest embodiment, the termination of the passive antenna (75) is switched from an open circuit to a short circuit, or vice versa, to invert the phase of the reflected energy.

Wide-band multiport antenna characterization by polarimetric RCS measurements

Abstract: A theoretical description of the scattering of multiport antennas is derived in accordance with the polarimetric radar target characterization. For two-port antennas with dual linear orthogonal polarization, a procedure for the determination of the antenna mode scattering parameters and the structural scattering parameters of the complete polarimetric antenna scattering matrix [S] is given. A measurement setup and experimental results of wide-band polarimetric radar cross section (RCS) antenna measurements are presented. For two-port antennas, in total, 24 unknowns have to be determined. The load variation method is used. The polarimetric RCS antenna measurement is especially advantageous over a wide bandwidth; for example 2-40 GHz with only one single calibration. From the antenna scattering matrix [S], the antenna parameters like polarimetric gain, optimum gain, gain bandwidth, wave admittance, structural scattering, etc., are derived. Results are shown for an X-band horn antenna and a 2-18-GHz dual linearly polarized horn. The measurement technique and evaluation gives the most complete and very accurate information about antenna radiation, antenna characteristics, and scattering obtainable with one single measurement setup. Some quantities determined here, like the maximum available gain and the polarization characteristics, are difficult to access with standard transmission measurements. No cable from the antenna to the receiver is necessary. This helps avoid some difficulties usually experienced at low signal levels.

A biconical multibeam antenna for space-division multiple access

Abstract: The biconical antenna is well known as an easy to build broad-band antenna with omnidirectional radiation. In this paper, the biconical antenna is modified for selective radiation in the azimuth direction. By enlarging the diameter of the coaxial feed to the biconical antenna, a set of higher order modes can be excited. In addition to the angle independent TEM mode, higher order TE-modes are also allowed for propagation, which result in an angle-dependent far-field pattern. Several features of this multimode excitation are of interest. Applying multiple input feed connectors allows simple rotation of the antenna beam by switching or, when independently operated, transmission and reception for communication in different angular directions for real-time space division multiple access (SDMA). As with conventional antenna arrays, adaptive pattern synthesis can also be realized by using multiple input feed connectors in combination with an appropriate amplitude and phase shifting network. The antenna allows an extremely flexible design of its characteristics at low cost, both requisites for SDMA communication.

Transmit diversity by antenna selection in CDMA downlink

Abstract: We study transmit diversity concepts in DS/CDMA wireless networks with multiple transmit antennas. The previously proposed diversity techniques are reviewed and their performance is compared to a selective transmit diversity (STD) concept, proposed here for CDMA systems. In all the competing concepts the encoded bits are distributed to all transmit antennas, whereas in the proposed concept bit are transmitted only from the best antenna as indicated by a closed loop antenna selection (CL-AS) subchannel from the terminal to the base. We quantify the achievable gains for these transmit diversity concepts with Monte-Carlo simulations.

On modeling and personal dosimetry of cellular telephone helical antennas with the FDTD code

Abstract: A novel method to model helical antennas working in the normal mode, as well as helix-monopole antennas with finite-difference time-domain (FDTD) code is presented. This method is particularly useful to model antennas used for personal wireless communication handsets, where the fairly small dimensions of the helical antennas with respect to wavelength and the grid cell size do not allow an appropriate description of the antennas by the use of metal wires. By observing that a helix working in the normal mode is equivalent to a sequence of loops and dipoles, it is possible to model the helix as a stack of electric and magnetic sources with relative weights calculated using information obtained from analytical expressions for the far fields. Dosimetry associated with wireless telephones using helical antennas is then considered by calculating the specific absorption rates (SARs) induced by two actual devices in a 1.974/spl times/1.974/spl times/3.0-mm resolution model of the human head based on MRI scans of a male volunteer. Comparison of the computed results with experimental measurements in the near field, the far field, and the induced SARs shows good agreement.

Radio antenna system

Abstract: The invention relates to an apparatus and a method for simultaneously generating, with the same radio antenna apparatus (10), a number of narrow beams and a wide beam, covering substantially the same area covered by the individual pointed beams together. The radio antenna apparatus (10) comprises an antenna array (3), a Butler matrix (2) connected to the antenna array and a set of amplifying modules (1a,...,1h). The activation of each of the inputs (L1,...,L8) of the radio antenna apparatus corresponds to a radiation pattern characterized by a narrow beam with a high antenna gain from the antenna array (3). By simultaneously activating the beam ports with the same signal with suitable phase relationships a superimposition of the radiation patterns to which the activated beam port corresponds is achieved in such a way that a wide beam is generated. Since all amplifying modules (1a,...,1h) are used simultaneously, the lower antenna gain of the wide beam will be compensated by a corresponding higher amplification. The wide beam will therefore have substantially the same range as the narrow beams.

Dual polarized cross bow tie dipole antenna having integrated airline feed

Abstract: A dual polarization antenna for transmitting/receiving polarized radio frequency signals includes a reflector plate that reflects the polarized radio frequency signals and one or more dipole assemblies. Each dipole assembly has two cross bow tie dipoles having radiating arms for transmitting/receiving the polarized radio frequency energy signals at two polarizations, and having U-shaped air-filled transmission feedlines for supporting respective radiating arms and providing the radio frequency signals between the reflector plate and the respective radiating arms. Each U-shaped air-filled transmission feedline includes two legs and respective feed rods arranged in respective legs. Each leg has a rectangular shape with three sides for isolating undesirable radio frequency energy. The radiating arms are triangularly-shaped and have notches dimensioned for minimizing radiation pattern distortion due to undesirable radio frequency coupling between the two cross bow tie dipoles. The dual polarization antenna also has an RF isolation device for coupling RF energy back in a proper phase and magnitude to cancel the undesirable RF energy of the respective opposite polarization. The RF isolation device includes an isolation tree or bar, isolation rails, small thin isolation rods or wires arranged in relation to the dipole assembly, or an isolation strip between positive and negative arms of the cross bow tie dipoles; or a combination of one or more of the above.

Microwave phase conjugation using antenna arrays

Abstract: A technique has been developed and tested for achieving phase conjugation in the microwave and millimeter-wave regime. The effective nonlinearity required for this phase-conjugation process is provided by electronic mixing elements feeding an array of antennas. Using these balanced mixing circuits in conjunction with a one-dimensional array antenna, we have demonstrated two-dimensional free-space phase conjugation at 10.24 GHz. A critical factor of this technique is the delivery of a 2/spl omega/ pump signal to each array element with the same phase. Two types of interconnects, electrical and a more versatile optical technique, have been implemented to distribute the pump signal in our demonstrations. In both systems, two-dimensional free-space phase conjugation was observed and verified by directly measuring the electric-field amplitude and phase distribution under various conditions. The electric-field wave-fronts exhibited retro-directivity and the auto-correction characteristics of phase conjugation. Furthermore, these experiments have shown amplified conjugate-wave power up to ten times of that of the incoming wave. This amplifying ability demonstrates the potential of such arrays to be used in novel communications applications.

Broadband direct fed phased array antenna comprising stacked patches

Abstract: A broadband phased antenna is comprised of multiple patches which are dirly feed. The multiple patches provide the broadband patch antenna having overlapping narrow frequency bands and comprise a ground-plane element, multiple antenna elements, multiple dielectric layers, an RF feed line, and a feed arrangement. The ground-plane element has predetermined length and width dimensions and an aperture therein at a predetermined location near its center. The multiple antenna elements have an uppermost antenna element. The multiple dielectric layers are respectively interposed between and separate the multiple antenna elements into a stacked arrangement having odd and even numbered antenna elements.

Integrated modified rectangular loop slot antenna on substrate lenses for millimeter- and submillimeter-wave frequencies mixer applications

Abstract: A coplanar waveguide (CPW)-fed rectangular-loop slot antenna with built-in tuning and DC-return capabilities on extended hemispherical lenses is examined. The proposed configuration is scalable up to the submillimeter-wave frequencies. For designing and analyzing the impedance characteristics of the proposed antenna, a multilayer method of moments (MoM) solver has been developed based on the mixed potential integral equation (MPIE) formulation. The corresponding patterns through the lens are obtained using geometrical optics and the surface equivalence principle. Three models have been simulated and one of them has been built and tested at 65 GHz. The integrated antenna exhibits tuning capability, rotationally symmetric patterns, high directivity, good Gaussian coupling efficiency, and a reasonable bandwidth. In addition, computed results agree well with measurements and are used to characterize the input impedance and pattern behavior of the antenna.

An improved FDTD model for the feeding gap of a thin-wire antenna

Abstract: In calculations using the finite-difference time-domain (FDTD) method, the feeding gap of a thin-wire antenna is often modeled by a so-called "one-cell gap" which lets the feeding gap to be one interval of Yee's lattice. This is often inconsistent with the actual situation and it causes error in FDTD calculation results. This work shows that the error due to the one-cell gap model is strongly dependent on the cell size, and we present an improved FDTD model which assumes an infinitesimally narrow feeding gap. We show that the antenna input impedance calculated with the new gap model is barely affected by the cell size and agrees well with the method of moments (MoM) calculation results for an infinitesimal gap. Furthermore, we clarify the dependence of error of a one-cell gap on the cell size on the basis of the proposed model.