Showing papers on "Dipole antenna published in 1984"

Picosecond photoconducting Hertzian dipoles

Abstract: The generation transmission, and detection of extremely rapid electromagnetic pulses have been achieved using fast photoconducting materials as time‐varying Hertzian dipoles. This approach, which has a measured time response of 1.6 ps, overcomes many of the limitations imposed by transmission line structures, and due to its jitter‐free behavior and open geometry is ideally suited for transient electromagnetic measurements of materials.

Fundamental superstrate (cover) effects on printed circuit antennas

Abstract: The fundamental effects of superstrate (cover) materials on printed circuits antennas are investigated. Substrate-superstrate resonance conditions are established which maximize antenna gain, radiation resistance, and radiation efficiency. Criteria are determined for material properties and dimensions for which surface waves are eliminated and a radiation efficiency due to substrate-superstrate effects of e_{s} = 100 percent is obtained. Criteria for nearly omnidirectional \bar{H} -plane patterns and nearly omnidirctional \bar{E} -plane patterns are presented. Finally, a general criterion is given for choosing a superstrate to optimize efficiency for the important case of nonmagnetic layers with the antenna at the interface.

Accurate transmission-line model for the rectangular microstrip antenna

Abstract: An accurate and numerically efficient model for the rectangular microstrip antenna is presented. It concerns a transmission-line model which features the following three major improvements with respect to earlier such models: the mutual radiative coupling (both real and imaginary parts) between the equivalent slots is fully taken into account; the influence of the side slots on the radiation conductance is taken into account implicitly; simple analytic expressions are introduced for all relevant model parameters. By way of illustration, the new model is applied to antennas with a single microstrip feed line. Excellent agreement is shown with available experimental and theoretical results for the input impedance of a rectangular antenna. The improvements with respect to previous transmission-line models are illustrated for a square antenna.

On the modeling of electromagnetically coupled microstrip antennas--The printed strip dipole

Abstract: A generalized solution for a class of printed circuit antennas excited by a strip transmission line is presented. The strip transmission line may be embedded inside or printed on the substrate. As an example, microstrip dipoles electromagnetically coupled (Parasitically excited) to embedded strip transmission line have been analyzed accurately, and design graphs are provided for a specific substrate material. These graphs permit the establishment of a design procedure which yields the microstrip dipole length, overlap, offset, and substrate thickness with the goal of a desired input match for a given substrate material. The method accounts for conductor thickness and for arbitrary substrate parameter. Comparison with experiment shows excellent agreement.

Directive properties of antennas for transmission into a material half-space

Abstract: The directive properties of antennas for transmission into a material half-space are investigated. In a practical situation, the antennas might be located in air with the directive transmission into the earth. The field of a general antenna over the half-space is expressed as a spectrum of plane waves. The integrals representing the field are evaluated asymptotically to obtain the "geometrical optics" field of the antenna, and this field is used to define quantities that describe the directive properties of the antenna (pattern function, gain, and directivity). Numerical results are presented for infinitesimal electric and magnetic horizontal dipole antennas in a dielectric half-space, region 1, with directive transmission into the adjacent dielectric half-space, region 2, and the ratio of permittivities \epsilon_{2}/\epsilon_{1} greater than one. The theory for the infinitesimal dipoles completely explains the directive properties previously obtained for the resonant circular-loop antenna over a material half-space. Measured field patterns and gains for dipole and loop antennas near an interface between air and fresh water are in good agreement with the theory.

Shortening ratios of modified dipole antennas

Abstract: Two types of modified dipole antennas, zigzag and meander-line types, are analyzed and the shortening ratios are calculated. A zigzag dipole antenna with a wire length of 0.58 wavelengths has a shortening ratio of 24 percent with a resonant resistance of 46 \Omega . A meander-line dipole antenna with a wire length of 0.70 wavelengths has a shortening ratio of 30 percent with a resonant resistance of 43 \Omega . It is found that the radiation patterns of these two types of antennas are similar to the radiation pattern of a conventional half-wave linear dipole antenna.

Dual band transceiver antenna

Abstract: A dual band antenna (11) for a radio transceiver includes a conductor of a predetermined length with a feedpoint (24) located substantially central of the conductor. Radiator elements (26, 28) terminate the ends of the conductor and ground plane (30) terminates the radiator elements. An impedance matching circuit (32) is coupled to the feed point whereby the high impedance part of the antenna is confined to the center. Dual banding elements (42, 44) coupled to the impedance matching circuit with a high Q resonant circuit element. Input/output circuits (46) are also coupled to the dual banding elements. The design minimizes the effect on the antenna by the proximity of user's hands, head and body.

Antenna engineering handbook /2nd edition/

Abstract: Essential principles, methods, and data for solving a wide range of problems in antenna design and application are presented. The basic concepts and fundamentals of antennas are reviewed, followed by a discussion of arrays of discrete elements. Then all primary types of antennas currently in use are considered, providing concise descriptions of operating principles, design methods, and performance data. Small antennas, microstrip antennas, frequency-scan antennas, conformal and low-profile arrays, adaptive antennas, and phased arrays are covered. The major applications of antennas and the design methods peculiar to those applications are discussed in detail. The employment of antennas to meet the requirements of today's complex electronic systems is emphasized, including earth station antennas, satellite antennas, seeker antennas, microwave-relay antennas, tracking antennas, radiometer antennas, and ECM and ESM antennas. Finally, significant topics related to antenna engineering, such as transmission lines and waveguides, radomes, microwave propagation, and impedance matching and broadbanding, are addressed. Bibtex entry for this abstract Preferred format for this abstract

Finite periodic structure approach to large scanning array problems

Abstract: There are two conventional techniques dealing with mutual coupling problems for antenna arrays. The "element-by-element" method is useful for small to moderate size arrays. The "infinite periodic structure" method deals with one cell of infinite periodic structures, including all the mutual coupling effects. It cannot, however, include edge effects, current tapers, and nonuniform spacings. A new technique called the "finite periodic structure" method, is presented and applied to represent the active impedance of an array, it involves two operations. The first is to convert the discrete array problem into a series of continuous aperture problems by the use of Poisson's sum formula. The second is to use spatial Fourier transforms to represent the impedance in a form similar to the infinite periodic structure approach. The active impedance is then given by a convolution integral involving the infinite periodic structure solution and the Fourier transform of the equivalent aperture distribution of the current over the entire area of the array. The formulation is particularly useful for large finite arrays, and edge effects, current tapers, and nonuniform spacings can also be included in the general formulation. Although the general formulation is valid for both the free and forced modes of excitation, the forced excitation problem is discussed to illustrate the method.

Apparatus for microinductive investigation of earth formations

Abstract: A wall-engaging apparatus for microinductively investigating a characteristic of an earth formation traversed by a borehole includes an antenna set mounted in a sensing body adapted for sliding engagement with the wall of the borehole. The antenna set includes first, second and third antenna elements. The second and third elements, being structurally identical but differentially coupled, are positioned in electromagnetic symmetry about the first antenna element. Either the first antenna element or the differentially coupled second and third antenna elements may be energized by suitable circuits, while the other is coupled to circuits for receiving signals indicative of a set characteristic. In another wall-engaging apparatus for microinductively investigating a characteristic of earth formations traversed by a borehole, a transmitter antenna is mounted in a conductive wall-engaging body, within a volume bounded in part by an integral conductive backplane and conductive side wall and opening to the wall-engaging face of the body, for coupling focused electromagnetic energy into a formation. The volume preferably is conformal with the transmitter antenna. Circuits are provided for energizing the transmitter antenna and for detecting a magnetic field from the engaged formation arising from the coupled electromagnetic energy.

Dipole antenna for portable radio

Abstract: A dipole antenna for a portable radio is contained completely within the insulated housing (10) of the transceiver. The dipole antenna is formed as two conductive surfaces (12, 13) electrically isolated from each other but disposed on the same printed circuit board (11) of the transceiver circuit which supports the circuit modules (14, 15). The two dipole halves are connected to each other by means of a dipole tuning circuit (29). The conductive tracks (23, 26, 27) of the transceiver circuit are interrupted at a location which divides as few tracks as possible. The interrupted tracks are bridged together by high-impedance resistors (22).

Theory of antennas of arbitrary size and shape

Abstract: In this paper there are presented (1) a quite general method of antenna analysis; (2) a physical picture of transmission phenomena in antennas, based on this method; and (3) an expression for the input impedance of antennas of any shape, whose transverse dimensions are small compared with the wavelength. In a brief historical sketch of the antenna problem the factors which must be taken into consideration in solving the problem are discussed. While in ordinary transmission lines the voltage is proportional to the charge, this is not the case in antennas. The explanation lies in the fact that antennas are multiple transmission lines (like wave guides) and not simple, that is, single-mode transmission lines. Our present theory is based on the voltage-current equations since these appear to be considerably simpler than charge-current equations. The latter are considered only briefly. In the absence of dissipation and in so far as the total voltage wave and the "principal" current wave are concerned, radiation is strictly an end effect. In so far as the total current and the total charge waves are concerned, radiation effects are distributed (nonuniformly) along the entire antenna. In the first approximation, regardless of the shape of the wire the charge is proportional to the voltage and waves are sinusoidal, the current wave having nodes while the voltage wave and the charge wave antinodes at the ends of the antenna. The second approximation depends on the shape of the longitudinal cross section of the antenna as well as on the size of the transverse cross section. Our analysis is based on Maxwell's equations but the final results are quite simple and the physical picture growing out of this mathematics is attractive to an engineer. It is permissible to think that a wave emerging from a generator in the center of an antenna is guided by an antenna until it reaches its "boundary sphere" passing through the ends of the antenna and separating the antenna region from the external space; at the boundary sphere some energy passes into the external space and some is reflected back--a situation existing at the juncture between two transmission lines with different characteristic impedances. We may also think of the antenna as the wall of an electric horn with an aperture so wide that one can hardly see the horn itself--just like a Cheshire Cat: only the grin can be seen. In fact, the mathematics that we use is that appropriate to wave guides and electric horns. The antenna problem is stated in Section I and its history is briefly discussed in Section II; Section III contains a summary and a discussion of the results for antennas with uniformly distributed capacitance (conical antennas); Section IV is devoted to antennas with non-uniformly distributed capacitance; Section V presents a derivation of the formulas contained in Section III; Section VI reviews the induced-electromotive-force method of computing radiation and its use in the present problem; Section VII is devoted to the current-charge equations; Section VIII is devoted to wave propagation along parallel wires; in Section IX an expression is given for the impedance of an infinitely long cylindrical wire, and Section X deals with an approximation needed in our discussion of the problem.

Miniature radio transceiver antenna

Abstract: A compact, lightweight, printed circuit card antenna which is adaptable to a wide range of frequencies, including very low frequencies. The antenna includes a three-dimensional inductor formed on the card, a peripheral conductor stripe on one side of the card which provides a distributed capacitance to the end of the antenna (to cancel inductive effects and broaden its bandwidth), and a peripheral conductor on the opposite side of the card which provides a capacitance to ground (to tune the antenna to frequency), and a transmission line feed point which provides an impedance match to the associated printed circuit flat cable transmission line without the use of impedance matching circuits.

Broad-band half-wave dipole

Abstract: An ultrahigh frequency (UHF) fan-dipole is optimized for wide-band operation near the first resonance in order that the antenna could be used in a planar array of half-wavelength spaced elements operating over a conducting ground plane. The resultant voltage standing-wave ratio (VSWR) of the optimized dipole (with a 50 \Omega coax input) is less than 2:1 over a 37 percent bandwidth.

NMR antenna and method for designing the same

Abstract: An antenna system for nuclear magnetic resonance (NMR) imaging or spectroscopy devices which produce a uniform magnetic field in an object under examination includes transmit and receive antenna arrays each comprising a group of loop antennas. A signal generating circuit produces a set of input antenna signals which are applied to the loop antennas of the transmit array which transmits RF signals of a frequency that perturbs the magnetic moment of nuclei in a volume of the object. The receiving antenna array is responsive to NMR signals produced by the relaxation of perturbed nuclei in said volume for producing a set of output antenna that are applied to a signal processing circuit. A control circuit selectively controls the relative phases and amplitudes of at least one set of antenna signals to control the size and location of the region of the volume in which excitation of nuclei occurs, or from which NMR signals are processed. The relative phases and amplitudes can be controlled in such a way that nuclei in only a preselected region of the volume are excited, and that NMR signals from nuclei in only a preselected region of the volume are processed.

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.

Monopole antenna on circular disk

Abstract: The sinusoidal-Galerkin moment method is developed for the impedance of a monopole antenna at the center of a circular disk in free space. Numerical results are presented for the impedance and current distributions as a function of the disk radius.

Low profile array antenna system with independent multibeam control

Abstract: An array antenna system has been described incorporating a plurality of antenna elements each having two quarter wave patches or monopoles for radiating microwave energy in a forward and reverse direction, a first and second beam forming network coupled to a coupler for each antenna element, wherein microwave energy coupled to the antenna element from one beam forming network couples lagging phase to one of the two quarter wave patches and from the second beam forming network couples lagging phase to the other quarter wave patch. The invention overcomes the problem of antenna utilization by providing two autonomous beam patterns with independent control or for overcoming the problem of antenna pattern performance by providing a second pattern which may be combined with the first pattern to provide, for example, an improved front-to-back ratio.

Bistatic Radar Cross Sections of Chaff

Abstract: Bistatic cross sections applicable to scattering from a cloud of randomly positioned and randomly oriented resonant dipoles, or chaff, are found. The chaff cloud can have an arbitrary location relative to an illuminating radar and the radar antenna can have an arbitrarily specified polarization. The receiver can be located arbitrarily in relation to the radar and chaff cloud and can also have arbitrary polarization (different from the transmitter antenna). Average cross sections are found for a preferred receiver polarization and the corresponding orthogonal polarization. Results are reduced to simple, easily applied expressions, and several examples are developed to illustrate the ease with which the general results can be applied in practice.

Antenna synthesis and optimization using weighted Inagaki modes

Abstract: Inagaki modes represent a new modal formalism for problems of radiation and scattering from arbitrary discrete and continuous structures. These modes can be generalized to be orthogonal over any sector of the sphere at infinity, as well as the source region itself. Theory and application of these modes to problems of pattern synthesis and array optimization, including constraints, are presented. Examples are given for a line source, an array of printed dipoles, and a dipole array in free space.

The design of a slot array in nonradiating dielectric waveguide, part II: Experiment

Abstract: Measurement procedures for obtaining the self-impedance of an isolated inclined radiating slot in the metal wall of a nonradiating dielectric (NRD) waveguide are discussed. The design procedure for an antenna array fed by NRD-waveguide and making use of this information is described. As an example, the design, construction and evaluation of a ten-element input-matched broadside linear array is described.

Infinite planar arrays of arbitrarily bent thin wire radiators

Abstract: A plane wave expansion moment method is presented for computing active impedances and current distributions of infinite planar arrays of thin wire radiating elements. The array lattices can be rectangular or triangular. The excitations can be plane waves or progressively phased voltage sources. Each radiating element, including feedline, can be any collection of bent thin wires. Results are given for arrays of straight dipoles with straight feedlines, straight dipoles with bent feedlines, and swept back dipoles (arms inclined with respect to the array planes) with straight feedlines. The experimentally observed phenomenon of array blindness as a consequence of feedline scattering is verified theoretically. The absence of this effect when the dipole arms are inclined with respect to the array plane also is verified.

Integrated oscillator antenna for low power, low harmonic radiation

Abstract: A low-power transmitter for garage door operator systems and the like wherein harmonics of the fundamental frequency are suppressed by class A or AB oscillator operation and fundamental radiation is enhanced by way of a combined inductor/radiator having conductive printed circuit extrusions on the ends thereof to effectively form a center-fed dipole antenna.

Equivalent line current for cylindrical dipole antennas and its asymptotic behavior

Abstract: The concept of an equivalent line source for representing the current on a cylindrical dipole antenna is introduced. It is shown that the Fourier series coefficients of this equivalent line source are related to those of the actual antenna current by exponentially growing factors that grow rapidly for the higher order harmonics. This is used to explain why Hallen's integral equation using an approximate kernel does not have an exact solution. The asymptotic behavior of the Fourier coefficients is established. An explanation of why approximate solutions to the approximate integral equation often provide good results for the current and input impedance is also given.

Characteristics of TV transmitting batwing antennas

Abstract: All of the characteristics of the batwing radiator, which is the heart of the superturnstile antenna system, are theoretically calculated by using the moment method. The matching condition is obtained on the basis of the characteristics in the cases of changing the shape of the jumper and of changing the distance between the support mast and the antenna elements. In this paper, a comparative study on the results of theoretical analysis and actual measurements was conducted as to whether or not the construction of the batwing antenna could be simplified by eliminating the element at its central part, without detracting its favorable characteristics. Next, regarding the mutual radiation impedance when arranged as a broadside array, a theoretical analysis was made according to the moment method, and the results were compared with measured values. As a result, in the case where this antenna was positioned at a distance exceeding full wavelength, the value was in the order of a few ohms, and it was found that mutual radiation coupling effect was small.

Microstrip patch array antenna

Abstract: A microstrip array with mutual coupled rectangular patch radiators is described. By the avoidance of a corporate feeding network, advantages in the antenna performance and design are realisable. Experimental results are presented for both linearly and circularly polarised antennas which demonstrate the usefulness of this special antenna configuration.

The effect of a dielectric cover on the current distribution and input impedance of printed dipoles

Abstract: The effect of the thickness and relative permittivily of a dielectric cover on a printed microstrip dipole has been analyzed. It is shown that the current distribution and the input impedance are, in general, very sensitive to variations of the cover parameters. For a dielectric plate with a constant thickness the dipole resonant length decreases substantially with an increase of the relative permittivity. Because of the limited bandwidth presented by single-element microstrip antennas the effects of the dielectric cover on the design of these antennas have to be carefully considered. For the calculation of the current distribution, the Hertz vector potential associated with the problem was determined for an element of current located in a stratified medium with four layers. Pocklington's integral equation was solved for the currents, using Galerkin's method with piecewise-sinusoidal expansion and weighting functions.

The optimum transient radiation from an arbitrary antenna

Abstract: Bounds on the optimum transient radiation from an arbitrary antenna enclosed by a spherical surface of specified size are presented. The optimization criterion is either maximization of the radiated electric field amplitude at a specified time and far-zone position, or maximization of the radiated energy density in a specified time interval for a particular far-zone position. The latter optimization results in the prolate spheroidal wave functions. In both cases, the total energy radiated by the antenna is constrained to be 1 J, and the antenna excitation is assumed to be bandlimited. The performance of the optimum arbitrary antenna is compared to that of optimized practical antennas, such as dipoles and arrays of dipoles. The effect of a sidelobe constraint is also studied.