An overview of beamforming from a signal-processing perspective is provided, with an emphasis on recent research. Data-independent, statistically optimum, adaptive, and partially adaptive beamforming are discussed. Basic notation, terminology, and concepts are included. Several beamformer implementations are briefly described. >

Beamforming: a versatile approach to spatial filtering

Phased Arrays in Radar and Communication Systems. Pattern Characteristics and Synthesis of Linear and Planar Arrays. Patterns of Nonplanar Arrays. Elements, Transmission Lines, and Feed Architectures for Phased Arrays. Summary of Element Pattern and Mutual Impedance Effects. Array Error Effects. Special Array Feeds for Limited Field of View and Wideband Arrays.

Phased Array Antenna Handbook

The physical limitations of omni‐directional antennas are considered. With the use of the spherical wave functions to describe the field, the directivity gain G and the Q of an unspecified antenna are calculated under idealized conditions. To obtain the optimum performance, three criteria are used, (1) maximum gain for a given complexity of the antenna structure, (2) minimum Q, (3) maximum ratio of G/Q. It is found that an antenna of which the maximum dimension is 2a has the potentiality of a broad band width provided that the gain is equal to or less than 4a/λ. To obtain a gain higher than this value, the Q of the antenna increases at an astronomical rate. The antenna which has potentially the broadest band width of all omni‐directional antennas is one which has a radiation pattern corresponding to that of an infinitesimally small dipole.

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Physical Limitations of Omni-Directional Antennas

We show that magnetic response at terahertz frequencies can be achieved in a planar structure composed of nonmagnetic conductive resonant elements. The effect is realized over a large bandwidth and can be tuned throughout the terahertz frequency regime by scaling the dimensions of the structure. We suggest that artificial magnetic structures, or hybrid structures that combine natural and artificial magnetic materials, can play a key role in terahertz devices.

http://science.sciencemag.org/content/sci/303/5663/1494.full.pdf

Terahertz magnetic response from artificial materials.

A one-parameter family of current distributions is derived for symmetric broadside arrays of equally spaced point sources energized in phase. For each value of the parameter, the corresponding current distribution gives rise to a pattern in which (1) all the side lobes are at the same level; and (2) the beam width to the first null is a minimum for all patterns arising from symmetric distributions of in-phase currents none of whose side lobes exceeds that level. Design curves relating the value of the parameter to side-lobe level as well as the relative current values expressed as a function of side-lobe level are given for the cases of 8-, 12-, 16-, 20-, and 24-element linear arrays.

A Current Distribution for Broadside Arrays Which Optimizes the Relationship between Beam Width and Side-Lobe Level

Antennas: Theory and Practice

A MATHEMATICAL theory, suitable for appraising and controlling directive properties of linear antenna arrays, can be based upon a simple modification of the usual expression for the radiation intensity of a system of radiating sources. The first step in this modification is closely analogous to the passage from the representation of instantaneous values of harmonically varying quantities by real numbers to a symbolic representation of these quantities by complex numbers. The second step consists in a substitution which identifies the radiation intensity with the norm1 of a polynomial in a complex variable. The complex variable itself represents a typical direction in space. This mathematical device permits tapping the resources of algebra and leads to a pictorial representation of the radiation intensity.

A mathematical theory of linear arrays

A form of circuit which is of considerable interest for the transmission of high frequency currents is one consisting of a cylindrical conducting tube within which a smaller conductor is coaxially placed. Such tubes have found application in radio stations to connect transmitting and receiving apparatus to antennae. As a part of the development work on such coaxial systems, it has been necessary to formulate the theory of transmission over a coaxial circuit and of the shielding against inductive effects which is afforded by the outer conductor. This paper deals generally with the transmission theory of coaxial circuits and extends the theory beyond the range of present application both as regards structure and frequency.

The electromagnetic theory of coaxial transmission lines and cylindrical shields

In this paper it is explained how Maxwell's field equations together with the appropriate boundary conditions may be converted into equations analogous to those for coupled transmission lines. This makes it possible to use the well-known techniques of dealing with transmission lines to solve certain field problems in those cases in which either the method of separating the variables fails or the boundary conditions are too complicated for the conventional method. For example, this method may be applied to studying waveguide to horn junctions, bending of waveguides, propagation of waves over an imperfect earth in the vicinity of the source, etc. Other applications are suggested in the course of the paper. On the theoretical side, this conversion of field equations into transmission line equations brings together two heretofore independent theories of wave propagation on wires, namely, Lord Kelvin's theory based on circuit concepts and Kirchhoff's laws and Mie's theory based on field concepts and Maxwell's equations. The “Generalized Telegraphist's Equations” derived in this paper differ from Kelvin's classical Telegraphist's Equations in two respects. Firstly, for a pair of conductors Kelvin obtained one pair of differential equations implying the existence of only one mode of propagation. For the same pair of conductors we obtain an infinite set of equations implying an infinite number of modes, from which Kelvin's equations are obtained by neglecting the

S. A. Schelkunoff

Papers

Antennas: Theory and Practice

A mathematical theory of linear arrays

The electromagnetic theory of coaxial transmission lines and cylindrical shields

Conversion of Maxwell's equations into generalized Telegraphist's equations

Advanced antenna theory