Showing papers on "Dipole antenna published in 1999"

Calibration and integrated beam control/conditioning system for phased-array antennas

Abstract: A near-field calibration arrangement for an antenna array determines the phase shifts or attenuation of the elemental control elements of the array. The calibration system includes a probe located in the near field, and a calibration tone generator. The tone generator is coupled to the probe in the case of calibration of a receive antenna, and to the signal port of the array in the case of calibration of a transmit antenna. A code generator generates sets of values, with each set being orthogonal to the others. The codes are applied to the control input port of the array antenna, so that the codes encode the tone passing through the antenna. The encoded tones are applied to a decoder and processor, which processes the signals to determine the phase shift or attenuation associated with each bit of the control signal. A transmit antenna attitude determination or pointing arrangement uses the calibration tone generator in conjunction with a plurality of remote sites.

A parameter study of stripline-fed Vivaldi notch-antenna arrays

Abstract: A parameter study of Vivaldi notch-antenna arrays demonstrates that the wide-band performance of these antennas can be improved systematically. Stripline-fed Vivaldi antennas are comprised of: (1) a stripline-to-slotline transition; (2) a stripline stub and a slotline cavity; and (3) a tapered slot. The impedances of the slotline cavity and the tapered slot radiator combine at the transition to yield an equivalent series impedance on the feedline. The stripline stub can be represented by a series reactance. The resistance and reactance of the antenna impedance yield insights into the effects of various design parameters. In particular, it is found that the minimum operating frequency can be lowered primarily by increasing the antenna resistance through a change of design parameters. However, beyond a limit for each design parameter, the in-band performance begins to deteriorate. Plots of antenna impedance versus frequency for several parameter variations have been obtained by using a full wave method of moments analysis of infinite arrays. These plots provide a means for designers to systematically improve array performance with bandwidths in excess of 6:1 having been achieved.

Eddy current error-reduced AC magnetic position measurement system

Abstract: A device is disclosed for measuring the position (location and orientation) in the six degrees of freedom of a receiving antenna with respect to a transmitting antenna utilizing multiple frequency AC magnetic signals. The transmitting component consists of two or more transmitting antenna of known location and orientation relative to one another. The transmitting antenna are driven simultaneously by an AC excitation, with each antenna occupying one or more unique positions in the frequency spectrum. The receiving antennas measure the transmitted AC magnetic field plus distortions caused by conductive metals. A computer then extracts the distortion component and removes it from the received signals providing the correct position and orientation output to a high degree of accuracy.

Printed twin spiral dual band antenna

Abstract: The present invention overcomes the above-identified deficiencies in the art by providing a miniature, built-in dual band antenna which is suitable for use in future compact mobile terminals. According to exemplary embodiments, a built-in antenna is provided which includes two spiral conductor arms which are of different lengths and capable of being tuned to different frequency bands. The spiral arms are mounted on the mobile terminal's printed circuit board via a substrate. Matching of the antenna is performed by a matching bridge which is positioned between a feeding pin and grounded post. By adjusting the length of the matching bridge, the matching of the antenna can be changed. In an alternative embodiment, a loading resistor is attached to the matching bridge in order to enhance the bandwidth of the antenna.

Light scattering from dipole and quadrupole nanoshell antennas

Abstract: Metal nanoshells are nanoscale optical components that allow for the controllable redirection of electromagnetic radiation via careful engineering of their multilayer structures. By varying the core size and shell thickness of these nanoparticles, nanoscale “antennas” are constructed that can be selectively driven into a dipolar or quadrupolar oscillation pattern. With scattering cross sections many times larger than their physical cross section, these antennas efficiently couple to the incident electromagnetic wave. These structures can focus, redirect, or split the incident light with subwavelength precision, and may find useful applications in the remote coupling of electromagnetic signals into nanoscale machines or devices.

Antenna problems in RFID systems

Abstract: As the frequency of choice for RFID devices rises into the microwave region, the problem of designing antennas to match the devices on the protected object becomes more acute. The objective of any such antenna must be to maximise the transfer of power into and out of the device on the protected object. This requires careful design to match the antenna to free space and to the following ASIC. The frequency bands considered in this paper are 435 MHz, 2.45 GHz and 5.8 GHz and the usage is for retail goods only. The major considerations in choosing an antenna are: the type of antenna; its impedance; RF performance when applied to the object; and RF performance when the object has other structures around it. Antennas which are omnidirectional should be avoided and, wherever possible, directional antennas should be used because they have the advantage of less disturbance to the radiation pattern and to the return loss. (5 pages)

Design of unequally spaced arrays for performance improvement

Abstract: Classical antenna array synthesis techniques such as Fourier, Dolph-Chebyshev and Taylor synthesis efficiently obtain array current distributions for equally spaced arrays that generate a desired far-field radiation pattern function or keep important parameters like beamwidth and sidelobe level within prescribed performance bounds. However, the concept of optimization of the field pattern (e.g., by decreasing sidelobes or beamwidth) of an given equally spaced array realization by altering its element spacings still represents a challenging problem having considerable practical advantages. These include reduction in size, weight, and number of elements of the array. This paper describes a new approach to synthesis of unequally spaced arrays utilizing a simple inversion algorithm to obtain the element spacings from prescribed far-zone electric field and current distribution, or current distributions from prescribed far-zone electric field and element spacings.

Beam scanning antennas with plurality of antenna elements for scanning beam direction

Abstract: An array antenna is formed of a plurality of antenna elements, each of which scans a beam in the direction of an angle θ to a boresight of the antenna and electrically varies the direction of a rotation angle φ of the beam. The antenna elements are disposed so that the optical path difference of radio waves transmitted or received by two adjacent antenna elements in the directions of a plurality of direction angles φ on the plane tilted for an angle θ to the boresight of the antenna is nearly a multiple of the wave length of the radio waves.

Method and apparatus for mitigating array antenna performance degradation caused by element failure

Abstract: An array antenna (10) having a plurality of antenna elements (12) keeps only a subset of elements active during normal antenna operation. When a failure of one of the active elements in the array (10) is detected, one of the previously inactive elements (46) is activated to operate as a replacement for the failed element (50). The number of elements that are active during normal operation is selected to achieve a level of antenna performance required by an underlying antenna application. Thus, a desired level of antenna performance is maintained during the life of the array antenna (10) without the consumption of excess power by spare elements in the antenna. Redistributions of inactive element locations are periodically performed during the life of the array antenna (10) to enhance antenna performance in light of failed element locations.

Application of plasma columns to radiofrequency antennas

Abstract: Plasma offers a promising alternative to metal for a wide variety of radiofrequency antenna applications. In this letter we report measurements of efficiencies up to 50% and radiation patterns for plasma column antenna elements. It is demonstrated that the current distribution along the antenna can be controlled by the plasma density. Plasma columns can be used instead of metal elements in communications antennas.

A broad-band microstrip-to-waveguide transition using quasi-Yagi antenna

Abstract: A novel microstrip-to-waveguide transition utilizing a coplanar-strip Yagi-like antenna is presented. The compact and single-layered quasi-Yagi antenna fabricated on high dielectric-constant substrate has end-fire radiation patterns. This monolithic-microwave integrated-circuit (MMIC)-compatible antenna is inserted in the E-plane of the rectangular waveguide to launch the TE/sub 10/ dominant mode. With this new scheme of excitation, compact design and low-cost fabrication is achieved without requiring multilayered substrate or backshort hermetic sealing. This transition, in addition, achieves very broad bandwidth and relatively low insertion loss. The transition's broad-band characteristics are analyzed, and optimization guidelines for individual components of the transition are discussed in detail. A tolerance study proves that the transition is robust in mechanical alignment. The X-band transition with alumina substrate demonstrates 35% bandwidth with return loss better than -12- and -0.3-dB insertion loss at the center frequency. This transition should find wide applications due to its high compatibility with microwave-integrated-circuit/MMIC technology and very low fabrication cost.

Carrier with antenna for radio frequency identification

Abstract: An object identification system (100) includes a monitor (124) and a plurality of transceivers (114) that communicate over a common medium. The monitor includes a first transmitter (2424), a first receiver (2416), and a processor (2402). Each transceiver includes a resonant circuit (204), a transmitter (210), a receiver (208), and an antenna (202) coupled to the resonant circuit. The processor performs a method for performing transceiver communication (500) that includes the steps of: (a) transmitting (604) from the first transmitter a first frequency (170) for a first duration; (b) after lapse of the first duration, receiving (608) via the first receiver a response signal (172) from at least one of the resonant circuits; (c) determining (510) a second frequency from the received response signal; and (d) performing (512) transceiver communication using the second frequency. Transceivers of the type having a resonant circuit coupled to an antenna, when operating in close proximity to each other, may interfere with the response from a single transceiver by absorbing the energy intended to be received by the transceiver, absorbing the energy transmitted by the transceiver, or altering the resonant frequency of the resonant circuit. By determining the second frequency for transceiver communication, the monitor may establish communication with the single transceiver at a frequency better suited for transferring operative power (1593, 1597) to the transceiver, conducting an interrogation protocol (912, 1140, 1130) for identifying the transceiver, or for data transfer (914, 916, 918, 920).

Asymmetric dipole antenna assembly

Abstract: An asymmetric dipole antenna assembly is provided for wireless communications devices, and includes separate upper and lower conductor traces and a low impedance feedpoint at the junction of the conductor traces. The upper conductor trace may include a matching network and may be printed on a planar printed circuit board mounted proximate the top of the a hand-held wireless transceiver. The upper conducting trace provides ¼ wave resonance over a desired frequency range and a 50 ohm input impedance for the antenna. The lower conductor trace may be provided by the ground trace of the wireless device circuitry, requiring only a minimum effective trace length of ¼ wavelength at the lowest frequency of operation. Polarization of the antenna is determined by the orientation of the longest dimension of the lower conductor.

Log-periodic staggered-folded-dipole antenna

Abstract: A folded-dipole antenna element, that is modified so that the two matching conductors are located on opposite sides of the main conductor Such staggered folded dipoles are superior for constructing log-periodic antennas, because they allow relatively small and straight feeder conductors and they allow the whole antenna to be grounded

Radio frequency tag with miniaturized resonant antenna

Abstract: An RF transponder is provided with a miniature resonant antenna that can fit on a small form factor the size of a button or coin. More particularly, the RF transponder comprises a substrate and an RF integrated circuit disposed thereon. An antenna is provided on the substrate and is electrically connected to the RF integrated circuit. The antenna has a contorted shape that permits it to fit into the limited available space on the substrate, while having an electrical length that is greater than a maximum length dimension of the substrate. Possible shapes for the antenna may include a meander antenna, a non-uniform meander antenna, a bent dipole antenna, a spiral antenna, a z-shaped dipole, a squeezed dipole antenna, or a combination of any of the antenna types. The RF transponder may further include at least one loading bar spaced from the antenna and/or at least one tuning stub coupled to the antenna.

Magnetic resonance antenna

Abstract: A magnetic resonance antenna has at least five antenna elements, each of, which extends essentially radially from an inner element beginning to at least one outer element end with respect to a center axis. The antenna elements are at least magnetically coupled with one another.

Characteristics of single- and double-layer microstrip square-ring antennas

Abstract: A method for miniaturization of microstrip patch antennas without degrading radiation characteristics is investigated. It involves perforating the patch to form a microstrip square-ring antenna, which is investigated numerically and experimentally. The ring geometry introduces additional parameters to the antenna that can be used to control its impedance, resonance frequency, and bandwidth. For a single square ring increasing the size of perforation increases its input impedance, but decreases the resonance frequency and bandwidth. It has a small effect on directivity of the antenna. To match the antenna to a transmission line and also enhance its bandwidth, the ring is stacked by a square patch or another square ring. The computed results are compared with experimental data and again good agreement is obtained.

Dual band antenna for radio terminal

Abstract: A dual band antenna for a radio terminal consists of a retractable whip antenna (10) and a helical antenna (30) with irregular pitches, wherein the whip antenna (10) is independent of the helical antenna (30). The helical antenna (30) includes first and second helical portions (35) having first and second pitches, respectively and the first and second helical portions (35) are operable at different frequency bands independently. The whip antenna (10) includes a conductive core line (12), a conductive substance (13) covering a first portion of the conductive core line (12) to serve as a choke and an isolation element extending from an upper end of the conductive core line (12), for filling a gap between the conductive core line (12) and the conductive substance (13). Here, only the first portion of the conductive core line is operable at a first frequency band and the entire conductive core line (12) is operable at a second frequency. A fixing element (40) fixes the helical antenna (30) and the whip antenna (10) to the radio terminal (60). The fixing element (40) has an upper end connected to a lower end of the helical antenna (30) and a through hold via which the whip antenna (10) is inserted into an interior of the radio terminal (60).

A 94-GHz aperture-coupled micromachined microstrip antenna

Abstract: This paper presents an aperture-coupled micromachined microstrip antenna operating at 94 GHz. The design consists of two stacked silicon substrates: (1) the top substrate, which carries the microstrip antenna, is micromachined to improve the radiation performance of the antenna and (2) the bottom substrate, which carries the microstrip feed line and the coupling slot. The measured return loss is -18 dB at 94 GHz for a 10-dB bandwidth of 10%. A maximum efficiency of 58/spl plusmn/5% has been measured and the radiation patterns show a measured front-to-back ratio of -10 dB at 94 GHz. The measured mutual coupling is below -20 dB in both E- and H-plane directions due to the integration of small 50-/spl mu/m silicon beams between the antennas. The micromachined microstrip antenna is an efficient solution to the vertical integration of antenna arrays at millimeter-wave frequencies.

A broadband microstrip-to-waveguide transition using quasi-Yagi antenna

Abstract: A novel microstrip-to-waveguide transition utilizing a coplanar strips Yagi-like antenna is presented. The X-band transition demonstrates about 40% bandwidth with return loss better than -12 dB. This transition should find wide applications due to its high compatibility with MIC/MMIC technology at very low fabrication cost.

A method for designing broad-band microstrip antennas in multilayered planar structures

Abstract: The narrow bandwidth of a microstrip antenna is one of the important features that restrict its wide usage. A simple and practical method for the design of broad-band microstrip antennas is presented in this paper. Utilizing this design technique, several two-layer microstrip antennas have been proposed. To confirm the applicability of the method for the designs of antennas at L-band, experiments have been carried out. The measured results show that the proposed antennas have a bandwidth of up to 25.7%. Also, the method proposed in this paper is applicable to the design of other types of multilayered planar antennas.

A uniplanar quasi-Yagi antenna with wide bandwidth and low mutual coupling characteristics

Abstract: We report for the first time a planar quasi-Yagi antenna printed on a single layer of high dielectric constant substrate (Durold, /spl epsiv//sub r/=10.2) which measures 48% bandwidth (VSWR 15 dB and cross-polarization level below -12 dB across the entire frequency band. A very low mutual coupling level of below -22 dB has been measured for a two-element array with /spl lambda//sub 0//2 separation.

Subsurface fracture measurement with polarimetric borehole radar

Abstract: A full-polarimetric borehole radar system is presented with combinations of dipole antennas and axial slot antennas and is applied to subsurface fracture measurement. First, to determine a scattering matrix from measurements with antennas having different antenna transfer functions between orthogonal polarizations, the authors present an antenna compensation algorithm that is achieved by an inverse filtering method with the antenna transfer functions experimentally determined by crosshole measurements. The results of crosshole and single-hole measurements carried out in granite at the Kamaishi Mine are shown to verify the proposed method. In the crosshole measurement, the authors find that the used dipole and slot antennas have almost the same radiation pattern and frequency dependency from 50 to 120 MHz. The transmission matrices through the host rock are the unit matrix for most paths, while depolarization is observed in some sections. Reflections from subsurface fractures show significant depolarization in the polarimetric single-hole reflection measurements. Using the scattering matrix, it is evaluated that subsurface fractures have a randomly isotropic rough surface for wavelengths between 1 and 2 m on the rotation of polarization basis.

Apparatus and method for radio frequency transponder with improved read distance

Abstract: A radio frequency identification transponder (RFID tag) in accordance with the principles of the present includes a tag antenna having a gain and an input impedance. The tag also includes RFID circuitry, which may be in the form of an RFID tag integrated circuit, the RFID circuitry also being characterized, in part, by an input impedance. According to the principles of the present invention the tag's read distance is maximized by tuning the tag antenna impedance and gain. In general, the imaginary part of the antenna impedance is chosen as the negative of the imaginary part of the RFID circuitry's impedance. Additionally, the real part of the tag antenna's impedance is selected by tuning those geometrical antenna parameters that affect both the antenna's gain and impedance. For RFID tags wherein the geometrical parameters of the tag antenna do not affect the gain G a of the tag antenna, the antenna input impedance may tuned to establish an antenna input impedance which is the complex conjugate of the RFID circuitry's input impedance.

FDTD analysis of resistor-loaded bow-tie antennas covered with ferrite-coated conducting cavity for subsurface radar

Abstract: This paper presents a full-wave analysis of a ground penetrating radar (GPR) using the finite-difference time-domain (FDTD) method. The antenna treated here consists of a resistor-loaded bow-tie antenna, which is covered with a rectangular conducting cavity of which inner walls are coated partially or fully with ferrite absorber. Some techniques are introduced into the FDTD analysis to obtain the accurate results and to save the computer resources. The validity of the FDTD analysis is confirmed experimentally. Furthermore, the effects of the ferrite absorber on the GPR characteristics are theoretically investigated in detail. The FDTD results indicate that the remarkable improvement of the antenna characteristics for the GPR system cannot be attained by the ferrite absorber.

Planar trapezoidal and pentagonal monopoles with impedance bandwidths in excess of 10:1

Abstract: A planar disc monopole antenna has been developed for the Japanese TV band (90-770 MHz) in 1991. A model for determining the input impedance of a circular disc monopole has been proposed in 1993. In 1998, a simple formula for predicting the frequency corresponding to the lower edge of the bandwidth was proposed. The planar monopole may be realised by replacing the cylindrical element of a conventional monopole with a planar element.

A high-gain 58-GHz box-horn array antenna with suppressed grating lobes

Abstract: A low-profile high-gain antenna array of box horns for the frequency band 57.2-58.2 GHz is presented. The antenna consists of 256 radiating elements divided into two subgroups of 128 elements fed by a rectangular waveguide feed network. The radiating elements are fed in parallel and the waveguides are connected with T-junctions. The matching of the T-junctions is improved with a matching pin and a splitter. Because of the waveguide feed network, the element spacing is larger than one wavelength, which causes grating lobes. The grating lobes and sidelobes in the H-plane have been suppressed by the use of a combination of subarrays, a special characteristic of the box horn, and an array amplitude tapering. The measured sidelobe levels in the H-plane are below -30 dB at angles larger than 8/spl deg/ from boresight. A gain higher than 35.7 dBi and a return loss higher than 14.4 dB have been measured for the antenna over the band 57.2-58.2 GHz.

Dual-polarized dipole antenna

Abstract: The invention relates to a dual-polarized dipole antenna which consists of several separate dipoles. Said dipoles are preferably arranged in front of a reflector (33) and form a dipole square when viewed from above, whereby each dipole (111-114) is supplied with current via a symmetrical line (115-118). The invention is characterized by the following features: The dual-polarized dipole antenna transmits electrical radiation in a polarization at an angle of +45° or -45° in relation to the constructively predetermined alignment of the dipoles (111-114); the ends of the symmetrical or approximately symmetrical lines which lead to the respective dipole halves (111a to 114b) are interconnected in such a manner that the corresponding line halves (115a to 118b) of the adjacent dipole halves (114b and 111a; 111b and 112a; 112b and 113a; 113b and 114a) which are vertical in relation to one another are electrically connected; and the supply of electric power to the diametrically opposite dipole halves results for a first polarization and decouples a second polarization which is orthogonal thereto.

Array antenna having multiple independently steered beams

Abstract: An array antenna system for forming multiple independently steered beams is described. The antenna system includes series or parallel feed circuits and phase shifters which are not disclosed directly in the signal path between the feed circuits and antenna elements included in the array antenna system.

A 77-GHz FM/CW radar front-end with a low-profile low-loss printed antenna

Abstract: Design and results of a 77-GHz frequency-modulation/continuous-wave radar sensor based on a simple waveguide circuitry and a novel type of printed, low-profile, and low-loss antenna are presented. A Gunn voltage-controlled oscillator and a finline mixer act as transmitter and receiver, respectively, connected by two E-plane couplers. The folded reflector-type antenna consists of a printed slot array and another planar substrate, which, at the same time, provides twisting of the polarization and focusing of the incident wave. The performance of the radar is described, together with the initial results of a scanning of the antenna beam.