Linear Dipole Array Research Articles

Analysis and design of a leaky-wave EMC dipole array

An analysis of an electromagnetically coupled (EMC) dipole array is presented, in which a microstrip line is coupled to an infinite periodic linear array of microstrip dipoles, arranged perpendicular to the line. The spectral-domain immittance method is used to obtain the periodic Green's function for the two-layered structure, and the method of moments with a Galerkin testing procedure is then used to enforce the electric field integral equation (EFIE) on the line and the dipole within a unit cell of the structure to obtain the determinantal equation for the unknown leaky-wave propagation constant. One of the interesting features of this analysis is the path of integration in the complex plane used to compute the moment method reactions, which must be partly on the improper sheet for the m=-1 space harmonic when it radiates in the forward direction. Measured radiation patterns for a 10-element EMC dipole array are presented and compared with the corresponding theoretical ones. >

Low sidelobe arrays of parallel dipoles with finite reflector

The effects of a finitely sized reflecting plane on the radiation patterns and on the input impedances of linear low sidelobe arrays of parallel dipoles are analysed. The differences between arrays with a finite reflector and those with an infinite one are studied and the design criteria are discussed.

Radiation Characteristics of Linear Log-Periodic Dipole Array Antennas Placed Near a Lossy Ground

The radiation properties of linear log-periodic dipole array antennas placed near a finite conductivity earth is investigated analytically. A method of moment solution is developed to solve the integral equation associated with the log periodic antenna array. The effect of finite ground conductivity is taken into account by using the appropriate Green's function which is derived from the well known Sommerfeld solution of the finite conductivity semi-infinite space. Piecewise sinusoidal pulse functions are employed as describing and testing functions. In computing the mutual impedance matrix elements, Sommerfeld type integrals are encountered which are computed by applying a numerically efficient technique. After computing the current distributions on the dipole elements of the log-periodic array the far field of the antenna is computed by employing the stationary phase integration technique. Several type log-periodic dipole arrays placed near a finite conductivity ground are computed. The effects of condu...

Pattern synthesis using reactive loads and transmission line sections for a singly fed array

A feed network design is presented for an array antenna fed by a single source. A specified radiation pattern from the array, with a set of known terminal voltages, can be synthesized by choosing the appropriate characteristic impedance and length of feed transmission-line sections and reactive loads at the terminals of each element. Two configurations, a series feed and a parallel feed, are described. As an example, this method is applied to the feed network design of a singly fed linear dipole array, but the method is general enough to be applied to any type of array which can be characterized by a multiport terminal admittance matrix. Some results are shown for the bandwidth of the radiation pattern and input impedance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Determination of the Location and Extent of Karst in Limestone with the use of Geophysical Methods

Field studies for testing the usefulness of geophysical methods in the mapping of karst in the northern part of the 'Rheinischen Schiefergebirge' yielded the following results: (1) Geoelectrical resistivity profiling, gravimetry and refraction seismic can be used for the detection of karstified zones. Low apparent resistivities, low p-wave velocities and negative gravity anomalies characterise the loose fill material or highly jointed limestone in these zones; (2) Rapid detection of karstified zones can be carried out with the resistivity profiling technique. The approximate extent of these zones can be mapped. The double dipole (linear) array gives the best results; (3) A more exact determination of the size of the karstified zones can be carried out using refraction seismic and gravimetry. Gravimetry enables an approximate volume estimate whereas refraction seismic allows a more precise volume estimate as well as the determination of the internal structure, nature of material present and boundaries to non-karstified areas.

Antenna designer's notebook

Small linear arrays of dipoles, with and without reflecting screen, are sometimes used for hf broadcasting, or at higher frequencies for ECM and other applications. When the scan is in the plane in which the element pattern has directivity, or when a backscreen is used, the element pattern will affect the angle of the maximum radiation, especially for very small arrays. This item presenrtess ults for collinear Eplane arrays of half-wave dipoles, with and without a backscreen.

Synthesis of near-field patterns of a nonuniformly spaced array

A technique of synthesis of near-field patterns of a nonuniformly spaced linear array of point dipoles with identical direction of current flow for each array element, or a uniformly spaced array of point dipoles with variation in direction of current flow for each dipole is presented. Further, it is described how one should prescribe the near-field (NF) pattern and how one should sample the same, while performing the NF pattern synthesis. Also discussed is how NF pattern synthesis should be performed so that the synthesized NF amplitude pattern closely follows a prescribed far-field amplitude pattern of the same array. Numerical computations are performed to demonstrate the validity of the physical concepts made use of in the technique proposed for performing the NF pattern synthesis successfully.

A new technique of synthesis of the near- or far-field patterns of arrays

A unified approach for synthesizing the near- or far-field radiation patterns of an array of uniformly or nonuniformly spaced point sources or directive elements located on a planar contour of arbitrary shape is presented. The synthesis problem is formulated employing the free-space Green's dyadic as well as the translational and rotational addition theorems for spherical vector wave functions. A similar unified approach for synthesizing the near- or far-field radiation patterns of a uniformly or nonuniformly spaced linear array of point dipoles is also presented. The validity of the technique presented is established with several typical numerical illustrations.

Antenna, load, and field effects on the bistatic scattering patterns from a linear dipole array

Scattering from a terminated antenna structure is studied and evaluated by modeling and computing its characteristics for linear dipole arrays and a variety of field, structure, and load conditions. Specific current distributions and effective load terminations are established that separate and compare the surface- and load-reflected contributions to the scattered field. The level and spatial distribution of the resulting fields and cross sections are determined as well as the relationship of these fields to the antenna gain pattern and their dependence on termination network effects that include waveguide phase delays and interdipole connections. The results presented illustrate the character of the bistatic scattering and its dependence on array structure, mutual coupling, conducting plates, incident field variations, and the internal and termination impedances.

Near fields of wire antennas by matrix methods

The method of moments [1], [2] is applied to wire antenna near-field problems. Within the general method, two computational procedures are developed. Results of these are compared with those of certain approximate analytical techniques and also with those of other investigators. A treatment for junctions is outlined. Examples are included for a single dipole antenna, for linear arrays of dipoles and also for loop and T -junction radiators.

On linear parasitic array of dipoles with reactive loading

Center loaded linear parasitic arrays of dipoles are examined. It is shown that capacitive loading increases the phase velocity of the slow wave on the structure while inductive loading reduces it. For the infinite array, used as a transmission line, this has the effect of modifying the cutoff frequency and the bandwidth. This is experimentally verified for the capacitive loading. For a simple finite array without a reflector, due to end effects only a small bandwidth widening is observed. However, when the finite array is attached with a suitable reflector, a significant widening of bandwidth is observed. In both these cases the loading causes a significant shifting of the center operating frequency. This effect is utilized to build a tunable Yagi array with varactor loading. With variable bias this loading can effectively be adjusted to double the operational bandwidth. Also it is shown that it is possible to sustain the optimum array directivity over a very wide bandwidth without bias adjustments, by a special loading network.

Mutual coupling effects in semi-infinite arrays

An analysis of mutual coupling in linear and planar uniformly spaced semi-infinite arrays is presented. The currents under arbitrary excitations at the array ports are obtained by solving an infinite order difference equation with the aid of an extension of the Wiener-Hopf factorization procedure to finite Fourier transforms. The solution for mutual coupling coefficients as well as for the active reflection coefficients in a phased semi-infinite array is expressed explicitly in terms of the active impedance in a phased infinite array. The analytical results are directly applicable to the evaluation of edge effects in large phased arrays. Numerical results for active reflection coefficients and element patterns are presented for a semi-infinite array of slots in a perfectly conducting ground plane and for a linear dipole array.

Mutual coupling in linear dipole arrays

A Hallen's type integral equation is formulated for the current distribution on a dipole which can assume an arbitrary tilt angle in an infinite periodic phased array. The active impedance of the dipole is calculated for various combinations of spacing, tilt angle, scan angle, and frequency.

Optimum scattering from an array of half-wave dipoles

Optimization of the field scattered by an antenna has important applications in radar systems and as elements in passive communication links. A method is presented of optimizing the scattering from a linear array of half-wavelength dipoles at a prescribed bistatic angle. The array is excited by a plane wave incident at an arbitrarily specified angle. The field scattered by the array is maximized or minimized as a function of the parameters of a network connected to the accessible antenna terminals. The result is a matrix eigenvalue equation of order <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N = \frac{1}{2}M(M + 1)</tex> for the optimum parameters of an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> -element array. It is known that <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N - 1</tex> solutions of this equation exist, which yield a prescribed zero in the bistatic scattering pattern but they do not correspond to physical networks. Using linear combinations of these, we construct a family of optimum admittance matrices that satisfy necessary and sufficient conditions that they be admittance matrices of passive networks. The form of the matrices is such that the corresponding passive regions in the bistatic plane are easily determined. The corresponding network can then be realized using existing network synthesis procedures. The essential features of the theory are illustrated by synthesizing an optimum network for a two-element array. It is also shown that backscatter at any angle can be minimized independently of the receiving pattern of the array.

Transient performance of array antennas

The transient performance of a uniformly excited, equal-spaced linear dipole array is evaluated under the assumption of constant radiated power over a finite frequency band. This approach permits the implicit evaluation of the effects of mutual coupling between array elements on transient performance. It is shown that the transient response depends on the array directivity as a function of frequency. Approximation techniques are used to evaluate the transient performance at boresight, within the main antenna beam, and beyond the main beam for small and large array element, spacing. At boresight, the far field signal may be approximated by the weighted sum of the Hilbert transform of the input signal and its time derivative.

The Radiation Patterns Produced by a Linear Array of Half-Wave Dipoles Coupled Electromagnetically to a Two-Wire Transmission Line

AbstractThe radiation patterns produced by a linear array of half-wave dipoles coupled electromagnetically to a two-wire transmission line are analysed by an idealized theory. The effects of the various physical parameters on the radiation pattern are studied from theoretical and physical considerations. The theoretical conclusions are verified by actual measurements. In general, the radiation pattern of the antenna contains four major lobes, two in the end-fire and two in the broadside directions. The levels of the end-fire and broadside radiation can be controlled by simple means. The electromagnetic coupling principle used in this antenna array provides more flexibility for controlling the radiation pattern than in the case of the usual method of coupling the dipoles to a two-wire transmission line. A step-by-step design procedure is outlined in the end; this can be used in order to obtain the desired radiation pattern from the antenna.

Ground-Controlled Approach---Its Development and Early Operational Use

Ground-Controlled Approach (GCA) was developed to meet military requirements for a "universal" blind-landing system, needing no additional airborne equipment or pilot indoctrination beyond short-range voice radio and basic instrument training. The talk-down principle, previously discredited in favor of beam-approach systems, was proved feasible when accurate information was available. The requirements of rapid radar scanning, at low angles to the horizon, with a high degree of accuracy at short range, were met by linear dipole arrays at 3-cm wavelength, with mechanical variation of waveguide width varying the angle of radiated power to the array. Half-power beamwidth for the elevation antenna was 0.1°; for the azimuth antenna, 0.8°. To translate range/angle data into a linear relationship of range vs deviation in feet from a selected approach path, a new type of indication was developed, i.e., Expanded Partial PPI Indicator (EPI). This permitted direct interpretation and immediate transmission of the data to the pilot by the controller. GCA's wartime service record, beginning late in 1944, proved its effectiveness under all conditions and led to further modifications and simplification for postwar commercial as well as military use.