This review of array antennas highlights those elements of theory and hardware that are a part of the present rapid technological growth. The growth and change in array antennas include increased emphasis on "special-purpose" array techniques such as conformal and printed circuit arrays, wide angle scanning arrays, techniques for limited sector coverage, and antennas with dramatically increased pattern control features such as low sidelobe, adaptively controlled patterns. These new topics have substantially replaced large radar arrays in the literature and constitute a major change in the technology. The paper presents a tutorial review of theoretical developments emphasizing techniques appropriate to finite arrays, but indicating parallel developments in infinite array theory, which has become the useful tool for analysis of large arrays. A brief review of the theory of ideal arrays is followed by a generalized formulation of array theory including mutual coupling effects, and is appropriate to finite or infinite arrays of arbitrary wire elements or apertures in the presence of a conducting ground screen. Some results of array tolerance theory are summarized from the literature and retained as reference throughout discussions of array component requirements and device tolerance for low sidelobe arrays. Examples from present technology include conformal and hemispherical coverage arrays, lightweight printed circuit arrays, systems for use with reflectors and lenses in limited sector coverage applications, and wide-band array techniques.

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Phased array theory and technology

The equivalent paraboloid is derived for classical offset Cassegrain and Gregorian antennas. The important practical case of systems with circular exit apertures is discussed in detail, and a condition for a symmetric equivalent paraboloid is derived. For such systems, diffraction effects are investigated using tapered and scanned feeds to illuminate the equivalent paraboloid and the two-reflector system. >

Derivation and application of the equivalent paraboloid for classical offset Cassegrain and Gregorian antennas

Two methods of scanning large parabolic cylinder antennas are examined: one method moves a small array across the focal plane to form a scanning beam; the other method employs a larger stationary array which is capable of electronically scanning the beam. With conventional single-element feeds, the maximum possible scan angle decreases with increasing reflector size. With array feeds, however, the scan limits are shown to be independent of reflector size and antenna gain. Antennas with movable array feeds are found to have high performance (high gain and low sidelobes) even when scanned more than ten degrees off axis; antennas with stationary array feeds degrade rapidly beyond about one degree of scan because of aperture blockage. Off-axis designs which eliminate the aperture blockage are shown to extend the coverage of antennas with stationary feeds to about \pm 5 degrees.

Scanning capabilities of large parabolic cylinder reflector antennas with phased-array feeds

An offset antenna and feed combination for use in a satellite communication system is disclosed wherein an array of adjacent microwave energy feed elements is disposed within a predetermined shape on the focal surface of the antenna for delivering electromagnetic energy to a remote, correspondingly shaped zone. Electromagnetic energy beams are selectively radiated towards predetermined areas of the overall remote zone by associated cluster groups of feed elements typically arranged as a minimum of one central and six surrounding feed elements. Additionally, each surrounding type of feed element of a cluster may be shared by two or more overlapping clusters, the overlapping clusters generating contiguous beams of electromagnetic energy in different frequency subbands.

Array feed for offset satellite antenna

A computer simulation is described for the production of multiple beams by a dual-offset reflector antenna with a feed consisting of a circular waveguide array. It is shown that acceptable efficiencies and low crosspolar levels can be achieved for two sample beams of a multibeam configuration by deriving the array excitation from the focal-region fields of the double-offset antenna.

Multiple-beam dual-offset reflector antenna with an array feed

A receive-mode analysis of a dual-offset reflector antenna consisting of an offset paraboloid and an offset hyperboloid is presented. In this analysis the field scattered from the offset paraboloid is determined using a g.t.d. formulation involving two edge points and a reflection point, if one exists. A method is described for deciding whether there is a reflection point from the gradient of the path length at the edge points. The focal-region fields and the radiation characteristics are computed by numerical integration of the physical optics current on the offset hyperboloid. An experimental antenna operating at 35 GHz is described Results of measurements of radiation patterns and of the power coupled into a circular waveguide array feed are compared with theory. In each cae reasonable agreement is achieved for copolarised directed components. However, the experimental antenna produced higher crosspolarisation than expected.

J.L. Boomars

Papers

Multiple-beam dual-offset reflector antenna with an array feed

Evaluation of focal fields and radiation characteristics of a dual-offset reflector antenna