Showing papers on "Dipole antenna published in 1997"

Multiple antenna ablation apparatus and method

Abstract: A multiple antenna ablation apparatus includes an electromagnetic energy source, a trocar including a distal end, and a hollow lumen extending along a longitudinal axis of the trocar, and a multiple antenna ablation device with three or more antennas. The antennas are initially positioned in the trocar lumen as the trocar is introduced through tissue. At a selected tissue site the antennas are deployable from the trocar lumen in a lateral direction relative to the longitudinal axis. Each of the deployed antennas has an electromagnetic energy delivery surface of sufficient size to, (i) create a volumetric ablation between the deployed antennas, and (ii) the volumetric ablation is achieved without impeding out any of the deployed antennas when 5 to 200 watts of electromagnetic energy is delivered from the electromagnetic energy source to the multiple antenna ablation device. At least one cable couples the multiple antenna ablation device to the electromagnetic energy source.

Method of manufacturing an enclosed transceiver

Abstract: The present invention teaches a method of manufacturing an enclosed transceiver, such as a radio frequency identification (“RFID”) tag. Structurally, in one embodiment, the tag comprises an integrated circuit (IC) chip, and an RF antenna mounted on a thin film substrate powered by a thin film battery. A variety of antenna geometries are compatible with the above tag construction. These include monopole antennas, dipole antennas, dual dipole antennas, a combination of dipole and loop antennas. Further, in another embodiment, the antennas are positioned either within the plane of the thin film battery or superjacent to the thin film battery.

Optical antenna: Towards a unity efficiency near-field optical probe

Abstract: We demonstrate that an antenna can be used to realize a near-field optical probe that combines spatial resolution well below the diffraction limit with transmission efficiency approaching unity. The probe consists of a planar bow-tie antenna with an open-circuited gap at its apex. We present proof-of-principle measurements using microwave radiation and discuss scaling the antenna to the visible optical spectrum.

Antenna characterization in the time domain

Abstract: A theory for a complete far-field transmit-receive system characterization of short-pulse antennas is derived in the time domain. The transmit-receive antenna system is characterized by a set of cascaded operators, which transform the source waveform and power into similar quantities at the receiving antenna terminals. Two such sets are defined. The first one is phrased in terms of the wave-type "time-dependent effective-height" operator, while the second one is defined in terms of the energy-type "gain operator". Both definitions fit within a complete transmit-receive system description, the latter being equivalent to the frequency-domain Friis equation. However, these operators are derived entirely in the context of the time-domain field equation. The starting point in the time-domain analysis of the effective height is the slant stack transform (SST) of the time-dependent current distribution in a manner equivalent to the spatial Fourier transform used in the frequency domain. The vector autocorrelation of the transmitting effective height is then used to define the time-dependent gain operator under impulsive source excitation. Time-domain reciprocity leads to the definitions of antenna parameters under receiving conditions and the corresponding equivalent circuit. The parameters defined in this way fit within a consistent transmit-receive convolution operator, operating on the autocorrelation of the input signal. This independent time-domain representation is thus similar to the frequency-domain representation. However, unlike the conventional frequency-domain circuit parameters, which relate voltage and current amplitudes, the time-domain circuit representation is based on incident and reflected wave-type constituents. In addition, the use of appropriate norms facilitates the transformation of our operators to stand-alone figures of merits. The general concepts developed are demonstrated for a short dipole antenna.

Generation of coherent terahertz radiation by photomixing in dipole photoconductive antennas

Abstract: We demonstrate the generation of continuous-wave terahertz radiation at frequencies up to 3.5 THz by photomixing in LT-GaAs photoconductors with printed dipole antennas. The expected resonance peak was clearly observed in the radiation spectrum of a 50 μm dipole antenna, and the radiation property was discussed in terms of the antenna impedance. The spectral bandwidth was greater than the electrical bandwidth of the photoconductor determined by the carrier lifetime of the material. The quality of the resonance, however, was not as high as expected because of the imperfect geometry and ohmic loss of the antenna.

Wire-antenna designs using genetic algorithms

Abstract: There is a large class of electromagnetic radiators designated as wire antennas. As a rule, an inductive process is used to design these antennas. Either an integral equation is formulated or a simulator is used that gives the current distributions on the wires of the antenna, from which the electromagnetic properties of the antenna can then be determined. Once the antenna properties are known, the parameters are optimized, using guides such as intuition, experience, simplified equations, or empirical studies. However, using an electromagnetics simulator in conjunction with a genetic algorithm (GA), it is possible to design an antenna using a completely deductive approach: the desired electromagnetic properties of the antenna are specified, and the wire configuration that most closely produces these results is then synthesized by the algorithm. In this paper, we describe four antennas designed using GAs. The first is a monopole, loaded with a modified folded dipole that was designed to radiate uniform power over the hemisphere at a frequency of 1.6 GHz. The second antenna consists of seven wires, the locations and lengths of which are determined by the GA alone, that radiates waves with right-hand-circular polarization at elevation angles above 10/spl deg/, also at 1.6 GHz. The last two antennas are modified Yagis. One is designed for a broad frequency band and very low sidelobes at a center frequency of 235 MHz. The other is designed for high gain at a single frequency of 432 MHz. We have built and tested these antennas.

Planar phased array antenna assembly

Abstract: A new planar phased array antenna is disclosed having M by N antenna cells with only M+N phase shifters A grid of M+N feed lines with the M feed lines at a first frequency having a uniquely controllable phase and N feed lines at a second frequency with each feed line having a uniquely controllable phase are provided separating adjacent cells in the matrix By coupling an antenna element through a mixer to one row and column feed, a phase for each antenna element in the array can be uniquely controlled through a scan, thereby providing a simplified planar array to be implemented as a patch antenna

Patch antenna equivalent to simple monopole

Abstract: Properties of a circular patch antenna with radiation characteristics similar to those of a resonant monopole are presented. The TM/sub 01/ mode excited patch on a small ground plane radiates a null on boresight and is easy to match to a 50 /spl Omega/ line. Applications include mobile vehicle applications and wireless LANs.

Variable pitch angle, axial mode helical antenna

Abstract: Optimization of the exchange of energy between a free space wave and current flowing in the conductive helix of an axial mode, helical antenna is achieved by varying the pitch angle of successive turns of the antenna along the axis of the antenna, from a relatively small pitch angle at the base, feed location of the antenna, to a relatively large value at the distal end of the antenna. Pitch angles of successive turns of the antenna are varied in a non-linear manner to correspond to the non-linear manner in which the phase velocity of a wave propagating through the antenna varies relative to the phase velocity of a free space electromagnetic wave. For the case of an axial mode, helical antenna operating at C-band, the pitch angle of said antenna may be varied between 3-8 degrees at the antenna feed point to a 20-30 degrees at its free space-interfacing distal end. The variable pitch angle antenna has a gain versus bandwidth characteristic that contains a plurality of spaced apart peak regions, one of which has a peak gain slightly less than the other. This dual peak gain behavior permits application design trade off between a smaller sized antenna with slightly reduced performance versus a larger sized antenna with slightly higher performance.

Method of making antenna array panel structure

Abstract: A tapered notch antenna structural panel array that can serve both as a structural member and an antenna is made from an injection molded monolithic three dimensional grid of thermoplastic material. The notch and feed line is in the form of microstrip or stripline circuitry formed to the sidewalls of adjacent cells. Dielectric sheets of material are bonded to the upper and lower edges of the grid. Interconnect circuitry on the antenna ground plane is supported by the sheet bonded to the lower edge and connected to the antenna circuitry of the sidewalls.

Voltage controlled variable tuning antenna

Abstract: A catheter shaft carries a coaxial cable, the terminal end of which contains a dipole antenna with opposing first and second helical elements. The first and second helical elements originate from a common connection to an outer conductor of the coaxial cable. The first and second helical elements are formed by winding flat wire around an outer insulator of the coaxial cable near a terminal end of the coaxial cable. A variable, controllable impedance is connected between an inner conductor of the coaxial cable and a point on the second helical element where the resistive component of the antenna's impedance matches the characteristic impedance of the coaxial cable. The impedance match minimizes reflective losses of the antenna, thereby maximizing power transferred to the antenna. The antenna has an effective electrical length which is equal to one-half the wavelength of the radiation emitted, independent of the physical length of the antenna. The antenna also has a radiation length which can be adjusted by varying the number in pitch and turns of the flat wire and the location of the impedance matching point.

Tuning fractal antennas and fractal resonators

Abstract: A first fractal antenna of iteration N≧2 in free space exhibits characteristics including at least one resonant frequency and bandwidth. Spacing-apart the first fractal conductive element from a conductive element by a distance Δ, non-planarly or otherwise, preferably ≦0.05λ for non-planar separation for frequencies of interest decreases resonant frequency and/or introduces new resonant frequencies, widens the bandwidth, or both, for the resultant antenna system. The conductive element may itself be a fractal antenna, which if rotated relative to the first fractal antenna will alter or tune at least one characteristic of the antenna system. Forming a cut anywhere in the first fractal antenna causes new and different resonant nodes to appear. The antenna system may be tuned by cutting-off a portion of the first fractal antenna, typically increasing resonant frequency. A region of ground plane may be formed adjacent the antenna system, to form a sandwich-like system that is readily tuned. Resonator systems as well as antenna systems may be tuned using is disclosed methodology.

Matching circuit and antenna apparatus

Abstract: A matching circuit (10) and an antenna apparatus which, though small-sized, can be used in a radio apparatus which transmits and receives radio waves having a wide range of frequencies. A matching circuit (10) includes an inductance element (12) formed of a chip inductor connected in series with an antenna body (11), a first capacitance element (13) formed of a trimmer capacitor, and a second capacitance element (14) formed of a chip capacitor, which capacitance elements are connected between respective ends (A, B) of the inductance element (12) and a ground terminal, and thus in parallel to the antenna body (11). One end (A) of the inductance element (12) is connected to the power supply terminal (15) of the antenna body (11), and the other end (B) is connected to a power source for applying a voltage to the antenna body (11). The first capacitance element (13) is connected between a ground and the connection point (A) of the power supply terminal (15) of the antenna body (11) and the inductance element (12). The second capacitance element (14) is connected between a ground and the connection point (B) of the inductance element (12) and the power source.

Coplanar waveguide-fed uniplanar bow-tie antenna

Abstract: The design of coplanar waveguide (CPW)-fed bow-tie antenna for the 2.4-GHz ISM band is described. A coplanar waveguide-to-coplanar strips (CPW-to-CPS) balun is used to obtain the balanced feed line for the printed bow-tie. An analysis method based on the mixed potential integral equation method is used to characterize the input characteristics of the bow-tie antenna. The numerical results obtained are in good agreement with the experimental data. Through experiments with bow-tie antennas of various extended angles, the bow-tie antenna with a 90/spl deg/ extended angle exhibits the widest bandwidth in the desired frequency band which has a bandwidth of 17% for a VSWR <1.5:1.

Equivalent circuit of dipole antenna of arbitrary length

Abstract: The purpose of this letter is to derive an equivalent circuit for a dipole of any length and to compare the input impedance versus frequency of the resulting equivalent circuit with published analytical and experimental data.

Modeling near-field GPR in three dimensions using the FDTD method

Abstract: Complexities associated with the theoretical solution of the near‐field interaction between the fields radiated from dipole antennas placed near a dielectric half‐space and electrical inhomogeneities within the dielectric can be overcome by using numerical techniques. The finite‐difference time‐domain (FDTD) technique implements finite‐difference approximations of Maxwell's equations in a discretized volume that permit accurate computation of the radiated field from a transmitting antenna, propagation through the air‐earth interface, scattering by subsurface targets and reception of the scattered fields by a receiving antenna. In this paper, we demonstrate the implementation of the FDTD technique for accurately modeling near‐field time‐domain ground‐penetrating radar (GPR). This is accomplished by incorporating many of the important GPR parameters directly into the FDTD model. These variables include: the shape of the GPR antenna, feed cables with a fixed characteristic impedance attached to the terminals...

Comparative study of high-performance GPS receiving antenna designs

Abstract: The FAA decision allowing the use of the global positioning system (GPS) as a radio navigation and landing help system in the United States commercial airports boosts the need for a high-performance GPS receiver which provides the demanded precision. The design of the receiving antenna is one of the most important parts in the design process, as it has to face significant challenges including uniform coverage of all satellites and the rejection of the multipath signals. The rejection of the multipath signals is accomplished by specifying restrictive criteria to the GPS antenna. This includes a high rejection of the cross-polarized signals and a radiation pattern with a sharp slope for low-elevation angles; that is, near the horizon. The feasibility of using different types of antennas to satisfy restrictive criteria such as dual-frequency coverage (L1 and L2 frequencies), -15 dB cross-polarization rejection, and a beamwidth of more than 130/spl deg/ is discussed. The antenna designs examined in this study include patch antennas, helical antennas, and conical spiral antennas. Two different receiver designs were also examined including a single-antenna system with a hemispherical coverage and an antenna array which may provide independent sectoral coverage or the desired beamwidth. It is shown that a design based on a conical spiral antenna backed with absorbing material may be used to satisfy all the desired specifications. This result was confirmed experimentally.

The tab monopole

Abstract: A new, compact, broadband printed antenna called the tab monopole is described The tab monopole is a small antenna designed primarily for applications requiring antennas that can be readily integrated with printed circuit boards The tab monopole is smaller than a quarter wavelength in size but provides a 2:1 VSWR bandwidth of greater than 50% Measured S/sub 11/ and gain patterns are provided

Wire antenna with optimized impedance for connecting to a circuit

Abstract: An antenna used as a voltage and power source is designed to operate with arbitrary load, or front end. The antenna has one or more (number of) loading bars that are placed adjacent to the elements of the antenna at a spacing distance. The real part of the antenna input impedance is changed by adjusting the loading bar length, width, and/or spacing distance and/or the number of loading bars. These changes are implemented to reduce the real part of the antenna input impedance to make it small enough to develop an adequate voltage, Vp, to operated the front end and connected circuitry. In a preferred embodiment, the real part of the antenna input impedance is reduced to the point at which Vp no longer increases. One or more stubs is added to one or more of the antenna elements. The stubs act as two-conductor transmission line and is terminated either in a short-circuit or open-circuit. The short-circuit stubs act as a lumped inductor. The open-circuit stub acts as a lumped capacitor. The magnitude of these lumped capacitors and inductors (reactances) is affected by a stub length, a stub conductor width, and a stub spacing. Zero or more short-circuit stubs and zero or more open-circuit stubs are added to one or more of the antenna elements to change the reactive (imaginary) part of the antenna input impedance. In a preferred embodiment, the reactive part is changed to be equal to the negative magnitude of the reactive part of the front end input impedance. For a given real part of the antenna impedance, Ra, this approach maximizes both the DC voltage generated from the input and maximizes the power transferred between the antenna and the front end.

Doppler spectrum in mobile-to-mobile communications in the presence of three-dimensional multipath scattering

Abstract: This paper provides analytical expressions for the time-autocorrelation function and the Doppler spectrum in a mobile radio channel in the presence of three-dimensional (3-D) multipath scattering. Mathematical modeling of the transmission channel is based on the assumption of wide-sense stationary (WSS) scattering. This paper deals with the case of a mobile-to-mobile radio link and derives formulas for the mobile-to-radiobase link as a special case. The Doppler spectrum examples provided are typical when assuming mobile terminal(s) located in densely built-up urban areas and simple dipole terminal antenna(s). Furthermore, the Doppler spectrum for transmission between a nongeostationary satellite and a mobile terminal located on the ground is analyzed. If different antenna patterns are to be considered and detailed knowledge is available on the multipath distribution, realistic Doppler spectra may be calculated using the approach presented in this paper.

Flat three-dimensional antenna

Abstract: A flat three-dimensional antenna is built in three planes. In the first plane is a base plate, in the second plane is a slot divider bent in a U-shape, and in the third plane is resonant structure above the slot divider. The slot divider has a middle part with a length of preferably λ/4 and two limbs of λ/8 of the same length. With the base plate the slot divider forms a λ/2 antenna slot, while the resonant structure with the slot divider defines a shorter second antenna slot. The antenna is characterized by a large bandwidth and omnidirectional radiation characteristic. Perpendicular to the base plate there is essentially no radiation. Feeding takes place preferably via a stripline which is routed between two limbs to a middle part. Impedance matching of the antenna is achieved by suitable dimensioning of the stripline. The antenna can be built equally well in air as well as in a dielectric such as a ceramic block. Several of these antennas can be combined into an ultracompact diversity antenna system.

Portable communication device with optimized transmission loss

Abstract: A portable electronic apparatus is disclosed having an antenna and a communication circuit. The antenna impedance is chosen to be a predetermined value which is deliberately mismatched to the impedance of the communication for a predetermined frequency band. This mismatch is chosen to optimize the signal loss between the antenna and the communication circuit when the antenna is far and near a disturbing source. The imaginary part of the antenna impedance has a sign opposite to the sign of the circuit impedance when the antenna is a predetermined distance from the disturbing source.

Tunable microstrip patch antenna and feed network therefor

Abstract: A patch antenna is provided with one or more tuning strips spaced therefrom and RF switches to connect or block RF currents therebetween. When a conducting path for RF current is connected between the tuning strips and the patch, the tuning strips increase the effective length of the patch and lower the antenna's resonant frequency, thereby allowing the antenna to be frequency tuned electrically over a relatively broadband of frequencies. If the tuning strips are connected to the patch in other than a symmetrical pattern, the antenna pattern of the antenna can be changed. A feed network couples RF to the antenna and includes two hybrid couplers, one for providing the correct amplitude and phase of excitation at the feed probes, and the second for effectively dissipating reflected power due to antenna impedance mismatch.

Slot-coupled DR antenna for dual-frequency operation

Abstract: To achieve dual-band operation or wider bandwidth, a new configuration of dielectric resonator antenna is proposed. This structure consists of two rectangular dielectric resonators displaced near two edges of a single slot in the ground plane of a microstrip line. The measured impedance and radiation patterns for two cases are presented. The results for typical examples indicate that an impedance bandwidth twice that of a single element or dual-frequency operation at two separate bands can be achieved.

Small omni-directional, slot antenna

Abstract: This invention discloses a small slot antenna incorporated within a flat circuit board and having a three dimension omni-directional radiation pattern. In one embodiment, the antenna is formed as an L shaped slot along two edges of the circuit board of a miniature radio transceiver. The antenna is ideally suited for use in applications where radio frequency inventory tags (operating in the high VHF to low UHF frequency ranges of 400 to 500 mHz) are associated with items for which a high level of inventory control is required. It is important that such tags be able to communicate with vertical and horizontal polarized signals with reasonable gain. This invention features a low cost for manufacture and has application in radio communications in general wherever there is a requirement for a small transceiver with an integrated, orientation insensitive antenna.

Antenna Model for Conductive Omega Particles

Abstract: Analytical models for small Ω-shaped conductive particles in free space or embedded in isotropic materials are presented and discussed. The electromagnetic analysis is based on the antenna theory for circular loop antennas and dipole wire antennas. Analytical expressions for the polarizabilities valid in the frequency area covering the two lower resonances are given. Mutual coupling between two portions of the particle: the loop and the straight wire is considered in terms of the mutual impedance, which is analytically calculated with the use of the induced electromotive force method. Approximate analytical expressions are compared with numerical simulations and are seen to be in good agreement. The results can be used in analytical modeling of omega and chiral composite materials and in the antenna theory.

Twin Vivaldi antenna fed by coplanar waveguide

Abstract: The authors describe twin Vivaldi antennas directly fed by a coplanar waveguide. They have been designed and measured for various angles between the radiating slots. All the designs show a centred zero in the E plane with a low cross-polarisation. In the H plane they provide zeros for phis = 90° and 270° and are omnidirectional for other values.

Antenna system for an RF data communications device

Abstract: An RF data communications device antenna system (10) is shown that includes a dipole and an electromagnetic coupler (16) that provides coupling between each dipole arm (22, 24) to establish a desired resonant bandwith. An LC matching circuit (30) is provided for matching the dipole to the impedance of the RF data communications device and for transforming the RF signal between the dipole arms of the antenna system.

Bandwidth and gain enhancement of a dielectric resonator antenna with the use of a stacking element

Abstract: The stacked structure of an aperture-coupled cylindrical dielectric resonator (DR) antenna is studied experimentally The effects of the offset and the air gap between the driven and parasitic DR elements are investigated It is found that the bandwidth of the stacked structure can increase from the single-element value of 9% to 37% The voltage standing-wave ratio, the radiation patterns, and the antenna gain are also reported © 1997 John Wiley & Sons, Inc Microwave Opt Technol Lett 14: 215–217, 1997

Design of a loaded monopole having hemispherical coverage using a genetic algorithm

Abstract: A genetic algorithm is used to design a monopole loaded with a modified folded dipole so that it radiates uniform power over the hemisphere. Each of the wires that make up the antenna are given a range of possible lengths. The genetic algorithm randomly selects a sample population of possible antenna configurations from the total population of all configurations. The radiation pattern of each sample configuration is computed using the numerical electromagnetics code (NEC). The solutions are compared with the desired pattern and ranked in terms of performance. The best solutions are retained and mated with one another and the process is repeated until an optimal solution is obtained. The genetic algorithm quickly produced an antenna that has a nearly uniform power over the hemisphere. Although the antenna was designed to operate at a frequency of 1.6 GHz, it performed satisfactorily over the frequency range from 1.4 to 1.8 GHz. The antenna was fabricated and the computational results were verified experimentally. We have shown that the genetic algorithm is a very powerful tool for designing wire antennas; it is expected that this process can be used to design any antenna that can be analyzed using an electromagnetic code.