Showing papers on "Dipole antenna published in 1985"

Microstrip antenna aperture-coupled to a microstripline

Abstract: A new technique for feeding printed antennas is described A microstrip antenna on one substrate is coupled to a microstripline feed on another parallel substrate through an aperture in the ground plane which separates the two substrates A simple theory explaining the coupling mechanism is presented, as well as measurements of a prototype aperture-fed antenna

Endfire tapered slot antennas on dielectric substrates

Abstract: Endfire tapered slot antennas are suitable for many integrated circuit applications, imaging and phased arrays. We report on an investigation of single elements of such antennas, including slots which are exponentially tapered (Vivaldi), linearly tapered (LTSA) and constant width (CWSA). For antennas of all types, a good general agreement is obtained for curves of beamwidth versus length, normalized to wavelength, when one compares the data with that for traveling-wave antennas published by Zucker. An important condition for this agreement is that the effective dielectric thickness, defined in the text, is in a certain optimum range. This condition is qualitatively explained in terms of the theory for traveling-wave antennas.

The MU radar with an active phased array system: 1. Antenna and power amplifiers

Abstract: The MU (middle and upper atmosphere) radar of Japan is a 46.5-MHz pulse-modulated monostatic Doppler radar with an active phased array system. The nominal beam width is 3.6° and the peak radiation power is 1 MW with maximum average power of 50 kW. The system is composed of 475 crossed three-subelement yagi antennas and an equivalent number of solid state power amplifiers (transmitter-receiver modules). Each yagi antenna is driven by a transmitter-receiver module with peak output power of 2.4 kW. This system configuration enables very fast and almost continuous beam steering that has not been realized by other mesosphere-stratosphere-troposphere radars. Also, a variety of sophisticated operations are made feasible by dividing the antenna array into several independent subarrays. A brief description of the system, particularly its antenna and power amplifiers, is presented herein.

Dipole and slot elements and arrays on semi-infinite substrates

Abstract: The printed dipole or slot antenna on a semi-infinite substrate and infinite phased arrays of these elements are investigated. The solution is based on the moment method in the Fourier transform domain. The generalized impedance or admittance matrix can be expressed in rapidly converging infinite-integral or infinite-summation forms, allowing the accurate determination of the current distributions. Using the present formulation, the input impedance, resonant length, and radiation pattern for the isolated antennas, and the reflection coefficient for infinite phased arrays, are calculated.

Electric surface current model for the analysis of microstrip antennas on cylindrical bodies

Abstract: An approach to the analysis of microstrip antennas on cylindrical bodies is presented. The printed radiator is replaced by as assumed surface current distribution, and the fields are solved taking into account the presence of the dielectric layer and the metallic cylinder. Calculation takes place in the Fourier domain. The far field, calculated asymptotically from this solution, is used to get the radiation patterns of the wraparound antenna for any dielectric and the half-wavelength patch for \epsilon_{r} = 1 .

Adaptive array antenna

Abstract: A small linearly polarized adaptive array antenna for communication systems is disclosed. The directivity and pointing of the antenna beam can be controlled electronically in both the azimuth and elevation planes. The antenna has low RF loss and operates over a relatively large communications bandwidth. It consists, essentially, of a driven λ/4 monopole surrounded by an array of coaxial parasitic elements, all mounted on a ground plane of finite size. The parasitic elements are connected to the ground plane via pin diodes or equivalent switching means. By applying suitable biasing voltage, the desired parasitic elements can be electrically connected to the ground plane and made highly reflective, thereby controlling the radiation pattern of the antenna.

Input impedance of annular ring microstrip antenna using circuit theory approach

Abstract: Input impedance and bandwidth of an annular ring microstrip antenna have been determined by modeling the antenna as a section of radial line loaded with wall admittances. The effect of mutual coupling between the radiating apertures has been taken into account. The theoretically calculated values of input impedance for TM 12 -mode are compared with measurements. The agreement is good. Higher order modes have been found to be present in the vicinity of TM 12 -mode. The reactance due to these modes can be utilized to increase the voltage standing-wave ratio (VSWR) bandwidth of the antenna.

Electric surface current model for the analysis of microstrip antennas with application to rectangular elements

Abstract: An approach to the analysis of microstrip antennas which is applicable also to relatively thick substrates using the relevant Green's function is presented. The Green's function is derived and closed form expressions for various antenna characteristics which explicitly take into account the presence of the dielectric material are obtained in terms of the electric surface current density. For rectangular microstrip elements near resonance the current distribution is approximated using lossless transmission line analysis, thus enabling the complete evaluation of the characteristics of the element near resonance. The results obtained in this approach for the radiation resistance, surface wave resistance, radiation pattern, directivity, and bandwidth are presented in a detailed set of graphs for a representative set of parameters.

The Effects of Driving Frequency and Antenna Length on Power Deposition Within a Microwave Antenna Array Used for Hyperthermia

Abstract: The theory of the linear, insulated antenna embedded in an electrically dense medium is applied to microwave antennas used for hyperthermia cancer therapy. The pattern of power deposition is computed for a square array of four antennas with a side length of 3 cm under the assumption of no coupling among antennas. The driving frequency is set to seven values between 300 and 915 MHz, and the antenna halflength is set to three values: 3 cm, 6 cm, and the resonant value.

Parasitically coupled, complementary slot-dipole antenna element

Abstract: A parasitically coupled, complementary slot dipole antenna element includes a driven, cavity-backed slot antenna element and a parasitic dipole element transverse to the slot of the cavity-backed slot antenna element. The cavity-backed slot and parasitic dipole antenna elements resonate at about the center frequency of the excitation signals supplied to the cavity-backed slot antenna element in order to generate a relatively symmetrical electromagnetic signature and an increased bandwidth.

Shortened wideband decoupled sleeve dipole antenna

Abstract: A shortened wideband decoupled sleeve dipole antenna is disclosed in which a helically wound upper radiating element and an inductively loaded lower radiating sleeve element reduce the linear size of the antenna. Substantial decoupling is provided by a helically wound feed coaxial transmission line within the sleeve element. A matching network at the antenna feed point provides capacitive reactance above the antenna resonant frequency and inductive reactance below the antenna resonant frequency such that an impedance match between the feed coaxial transmission line is obtained at frequencies above and below the resonant frequency and dual-band performance may be obtained.

Crossed-drooping dipole antenna

Abstract: A first planar printed circuit board and a second planar printed circuit board are assembled to intersect each other at right angles to each other. Each board includes a microstrip realization of a drooping dipole antenna. The realization comprises, for each planar board, two vertical parallel feed lines with a radiating element extending from each feed line. Each of the feed lines is fed 90° out of phase with the other feed line on the same board.

Dipole antenna with parasitic elements

Abstract: A dipole antenna system includes a driven dipole element and two parallel parasitic dipole elements equally spaced from the driven dipole element. Dual polarization can also be achieved by using two such systems arranged orthogonally.

A bandwidth enhancement method for microstrip antennas

Abstract: Bandwidth enhancement methods for electromagnetically coupled microstrip dipoles are discussed. It is demonstrated that if parasitic metallic strips are incorporated in the structure either co-planar and parallel to the embedded microstrip transmission line open end, or between the transmission line and the microstrip dipole, then substantial bandwidth enhancement results. Experimental verification of this model is introduced for a bandwidth definition based on the frequency range which satisfies a voltage standing-wave ratio (VSWR) \bar{E} - and \bar{H} -plane patterns verify the theoretical model which accounts for radiation from the microstrip dipole, the parasitics, and the transmission line.

Measurement of the electrical constitutive parameters of materials using antennas, part II

Abstract: A general technique is presented for measuring the electrical constitutive parameters of a material using a monopole (dipole) antenna A normalized impedance that is only a function of the dimensionless parameter kh (wavenumber length) is defined for the antenna The normalized impedance is expressed as a rational function, and the coefficients in this function are determined from a measurement of the impedance in a standard medium The impedance measured in a material with unknown constitutive parameters is used with the rational function to form a polynomial in kh The constitutive parameters of the medium are determined from a root of this polynomial The measurement technique is implemented for a rational function of order three The constitutive parameters of the alcohol 1-butanol and saline solutions were measured over a range of frequencies using the technique with cylindrical and conical monopole antennas The measured constitutive parameters are in good agreement with those determined by previous investigators

General relations for a phased array of printed antennas derived from infinite current sheets

Abstract: Simple and general relations characterizing the behavior of infinite phased arrays of printed antenna elements are derived from a model based on infinite current sheets. The Green's function of an electric current source on a grounded dielectric slab is used in various limiting forms to treat arrays in free space, arrays above a ground plane, arrays on a semi-infinite substrate, and arrays on a grounded dielectric slab. Current sheets are selected, using the orthogonality properties of the Floquet modes of the infinite array Green's function, to excite only a few specific low-order Floquet modes. Results from this idealized model, in the form of reflection coefficient magnitudes and input resistance, are compared with rigorous moment method solutions for specific elements (dipoles and microstrip patches). It is shown how the dominant scanning characteristics of a printed phased array, such as reflection coefficient and input resistance trends, scan blindnesses, and grating lobe effects, are dictated more by factors such as element spacing and substrate parameters than by the particular element type itself.

Antenna apparatus for scanning hyperthermia

Abstract: An arrangement for heating includes an antenna which has at least one convolution of conductor centered on an axis. The antenna is adapted for receiving electrical power for heating a surface. A noncontacting temperature sensor is centered on the axis of the antenna with its field of view directed along the axis.

Criteria for nearly omnidirectional radiation patterns for printed antennas

Abstract: Radiation from printed antennas is investigated with emphasis placed on producing \bar{E} - and \bar{H} -plane radiation patterns that are as nearly omnidirectional as possible. This is achieved using criteria which are derived for a nonzero radiation field extending down to the layer surface (radiation into the horizon). It is determined that this phenomenon arises when a surface wave pole coincides with a branch point in the complex plane. A simple ray optics interpretation is given for the phenomenon, and graphs are presented to easily enable design of printed antenna geometry to achieve nearly omnidirectional \bar{E} - or \bar{H} -plane patterns.

Active antenna in the rear window of a motor vehicle

Abstract: An active antenna for the reception of long-, medium-, short-and ultra-short wave broadcasts is arranged in a rear window of a motor vehicle equipped with a boundary conductor enclosing an array of heating elements. The reception of long-, medium- and short-wave signals is made by means of an elongated flat antenna element which is arranged in the window on a free area above or below the heating elements, and the reception of the ultra-short wave signals is effected by the array of heating elements. An antenna amplifier includes a linear amplifying stage connected to the flat antenna element, an amplifying branch circuit connected to the array of heating elements and a common ground terminal connected to the boundary conductor. A frequency separator has two inputs connected, respectively, to the output of the amplifying stage and of the branch circuit, and an output connected via an antenna cable to a conventional radio receiver.

Electromagnetic applicator for localizing hyperthermia heating in a system

Abstract: An electromagnetic applicator (10) is provided for heating internal biological tissue, such as cancerous tumors, where applicators generate an electromagnetic field propagating across a gap (20) for forming a relative maximum power density adjacent the internal tumor volume. Conductive elements (12, 14) are spaced a predetermined distance to form a gap (20) and power is applied at radio frequencies through a balancing and matching circuit to generate the electromagnetic field which propagates across the gap (20). A plurality of applicators (10) may be placed about a body location to enable the maximum relative power density to be placed at a selected location within the body portion. A radiating dipole antenna (46) may be used to radiate a signal from which transmitted signal parameters are derived for forming a local power density maximum at a location approximated by the radiating dipole antenna (46). A controller (42) provides power source (40) outputs to applicators (10) having the same relative amplitudes and opposite phase angles of signals received from the transmitting dipole antenna (46) at locations approximating the locations of applicators (10) at the desired body location.

Multiple-source, multiple-frequency error of an electric field meter

Abstract: Electric field meters (EFM's) are typically calibrated using single-frequency, single-source standard fields. The response to multiple sources or nonsinusoidal time dependence may be different, however. Possible errors in a multiple-source, multiple-frequency environment are analyzed for an EFM consisting of an electrically short dipole antenna with a diode load and a radio-frequency (RF) filter transmission line. Also considered are errors in the assumption of equal electric and magnetic energy densities in a multiple plane-wave environment. Typical errors of field-intensity measurements are about one to 3 dB, but in some circumstances they can exceed 10 dB.

Microstrip patch antenna system

Abstract: A microstrip antenna system (10) is comprised of either a single antenna element (patch) (16) or a plurality of stacked antenna elements (16,36 and 40) having one or more feedpins (30) connected to a corresponding number of conductive elements (fiags) (28) capacitively coupled to the antenna element or elements. The one or more feedpins (30) have an inductive reactance which is canceled by trimmed flags (28) to provide the capacitance necessary to cancel the inductance for tuning the one or more antennas (16, 36 and 40) and providing maximum gain and minimum VSWR.

Vandalism-resistant UHF antenna

Abstract: A vandalism-resistant antenna for the UHF band comprises a ring-shaped radiator printed on a dielectric board or disc mounted within a shallow enclosure of insulating material having high impact strength. The radiator is approximately 1/4 wavelength long at the operating frequency and is located at a constant spacing above a ground plane. A coaxial RF connector fastens the radiator-board assembly to a mounting surface serving as the ground plane, and couples the antenna to a transmitter or receiver.

Fundamental surface-wave effects on microstrip antenna radiation

Abstract: The spectral domain approach is used to determine the influence of surface waves on the radiation efficiency of a rectangular patch antenna. The effects on the radiation patterns due to the dielectric truncation are computed and compared with experiment.

Automatic control using proximity sensors

Abstract: Proximity sensor apparatus has at least first and second antenna strips arranged along the edge of a structure. The antenna strips receive signals reflected by an object whose proximity is to be detected. Signal processing circuitry is coupled to the antenna strips for receiving and processing the signals picked up by the antenna strips. Proximity detection may occur when the difference in signal strength received by the two antenna strips exceeds a threshold level. In one embodiment, the difference between the maximum and minimum signals is determined and increases the threshold as the difference between signals decreases. In another embodiment, the difference in signal strength is used to determine the position of the object on one side or another of the antenna strips. In yet another embodiment, a bootstrap electrode is positioned behind a single antenna strip and is electrically connected to follow the voltage induced on the antenna strip by the received signal.

Measurements of distributed polarized radio sources from spinning spacecraft - Effect of a tilted axial antenna ISEE-3 application and results

Abstract: An analysis is presented of the system response of a satellite receiver-antenna system to locate a radio source when the satellite is tilted on its axis. The satellite is spin stabilized but experiences a tilt due to either a mechanical misalignment or a shift in the electrical axis caused by parasitic currents in other spacecraft structures. The shorter the antenna, the more significant the effects. Numerical techniques are developed for obtaining the Stokes parameters and the angular parameters of a uniform conical source sensed by a linear antenna in order to derive the average power response of a synthesized dipole to a point on a distributed polarized source. Relative gains are calculated along the antenna at different angles to the source. The techniques are applied to sample ISEE-3 satellite data for Type III solar radio bursts which were sensed by an axial and an equatorial antenna. The two antennas permit localization of the source and quantification of the polarization and angular extent of the source. The resulting high precision in calculations of all three source parameters commends use of the model in analyses of data from the planned ULYSSES mission.

Exact image method for impedance computation of antennas above the ground

Abstract: The principle of exact images recently developed by two of the present authors for the Sommerfeld problem is here applied for the classical impedance problem of antennas above the ground. In the present method, the effect of the ground is taken into account with an image source, which is located in complex space, leading to a modified Green function for the antenna current integral equation. The image of the antenna can be effectively determined through new expressions evaluated for the image current function. The stationary functional for the antenna impedance is extended to take into account the effect of the ground. As examples of the theory, impedance expressions for small dipoles and half-wave dipoles are formulated with numerical results calculated and compared with previous results. A simple method applicable for small microcomputers is suggested for calculating the impedance of wire antennas with finite thickness from that of infinitesimally thin antenna if the height of the antenna from the ground is not too small. Also, a practical method is suggested for the determination of ground parameters from horizontal \lambda/2 dipole minimum resistance and height measurements.

Optimization of the transient radiation from a dipole array

Abstract: The optimum solution for the transient radiation from a dipole array is derived in terms of the time-domain voltages which are required at the input terminals of dipoles in an array so that the amplitude of the transient radiated field at a specified time t_{0} and far-field position r_{0} , \theta_{0}, \phi_{0} is maximized. Constraints are placed on the energy and bandwidth of the input signal voltages with current restricted by Pocklington's equation. Further constraints on the sidelobe level are used to obtain a modified solution for suppressed sidelobes in the radiation pattern. Results of numerical optimization are presented, and the effects of scan angle, element spacing, and a sidelobe constraint on the optimization are discussed.