Small Phased Array Research Articles

Difference pattern synthesis in small planar phasedarrays

A pattern synthesis technique for low sidelobe arbitrarily scanned difference beams in small planar phased arrays is presented. The approach is based on adaptive array theory and is the development of a technique used for radiation pattern synthesis in linear arrays. The method has been applied to measured element pattern data from a small planar array, which includes the effects of pattern corruption by mutual coupling. The successful synthesis of low sidelobe difference beams is demonstrated, with arbitrary difference plane and scan angle.

Improvement of coupling corrected difference beamsin small phased arrays

The corrupting effects of mutual coupling between radiating elements of small phased arrays means that conventional aperture weighting schemes (Taylor, Chebyshev etc.) cannot be applied to small phased array antennas to form low sidelobe sum and difference beams. The corrupting effects of mutual coupling can be removed by the determination of an inverted coupling matrix. This description of the couplings is not perfect. The imperfect coupling matrix description means the synthesised beams are degraded, particularly difference beams where a deep look direction null is an important characteristic of the beam. The results of applying an adaptive algorithm to the coupling corrected array weight vector in order to enhance difference beam nulls is presented.

Pattern synthesis in small phased arrays using adaptivearray theory

A pattern synthesis technique for low sidelobe difference and scanned beams in small phased arrays is presented. The approach is based on adaptive array theory and is a development of a technique used for beam synthesis in an ideal, λ/2 spaced, isotropic array. The method has been applied to measured element pattern data from a five element linear array, which includes the effects of pattern corruption by mutual coupling. The successful synthesis of low sidelobe sum and difference beams are demonstrated, with the look direction on and scanned off boresight.

Application of retrodirective beams to achieve lowsidelobe levels in small phased arrays

Synthesis of beams with low sidelobe levels is a difficult problem for the case of small phased arrays with few elements. Mutual coupling between elements means that conventional weighting algorithms are not applicable. A technique is presented that calculates a complex weight vector for a five element linear array, giving a reduced sidelobe beam pattern. Sidelobes are reduced by the addition of retrodirective beams to the quiescent beam pattern. No knowledge of the coupling coefficients or element radiation patterns is required.

Derivation of orthogonal beams and their application to beamforming in small phased arrays

It is a difficult problem to synthesise beams with the desired characteristics (low sidelobe levels, narrow main beam) from small phased arrays with few elements. Mutual coupling between elements means that conventional tapering algorithms are corrupted. In the paper a technique is presented whereby weights are calculated by point matching measured element radiation patterns to an ideal sinc function. It is found that a very close approximation to an ideal sinc beam can be synthesised by point matching to the nulls and main beam peak value of the ideal. Moreover, an orthogonal set of sinc beams can be synthesised using this technique, which in turn are used to construct a low sidelobe beam using the main beam gain of orthogonal sinc beams as sampling points. This technique gives insight into the limits of how far sidelobe levels can be reduced in arrays with few elements. No knowledge of the coupling coefficients of the array is required.

Hybrid antenna synthesis for reconfigurable contoured beams

A reflector illuminated by a small phased array is an attractive antenna configuration for systems requiring reconfigurable contoured beams. The use of a shaped reflector can provide control of the feed power distribution and antenna geometry. A systematic reflector synthesis technique based on geometric optics is formulated, using complex coordinate notation and illustrated by application to a simple design requirement. Results demonstrate that geometric shaping can be successfully applied to systems with distributed sources, and that significant beam reconfiguration can be achieved by phase-only control of the feed array.

Analysis of near-field Cassegrain reflector: plane wave versus element-by-element approach

A near-field Cassegrain reflector (NFCR) is an effective way to magnify a small phased array into a much larger aperture antenna for limited scan applications. Traditionally the pattern wave approach, i.e. the field from the feed array incident on the subreflector is approximated by a truncated collimated beam with planar phase and tapered amplitude distribution. This approach simplifies the computation tremendously, but fails to provide design information about the most critical component of the whole antenna system, namely, the feed array. With the help of today's computers, it is now feasible to calculate the pattern of a NFCR by a more exact element-by-element approach. Each element in the feed array is considered individually and the diffraction pattern from the subreflector is calculated by the geometrical theory of diffraction (GTD). The field contributions from all elements are superimposed at the curved main reflector surface, and a physical optics integration is performed to obtain the secondary pattern. >

Bandwidth capabilities of array-fed parabolic cylinders

The bandwidth of hybrid phased-array/reflector antennas, in which a large parabolic cylinder reflector is fed by a relatively small phased array, is investigated. Two types of array feeds are considered: one employs only phase-amplitude matching, the other employs amplitude and time-delay matching. In the case of phase-amplitude matching, the on-axis hybrid array/reflector designs are shown to have substantially higher bandwidth than pure phased arrays. A form of time-delay compensation is described which removes the bandwidth limitations of hybrid array/reflectors, but introduces interfering signals. This interference can be avoided by either locating the feed outside the caustic zone or by using off-axis array feeds.

Moment method analysis of finite rectangular waveguide phased arrays

A method of moments formulation for small finite planar phased arrays of rectangular waveguides in an infinite ground plane is investigated. Piecewise sinusoidal-uniform surface patches are used as the basis and testing functions for the unknown equivalent magnetic currents of each aperture. The block-Toeplitz symmetry property for rectangular grid arrays is utilized in the solution of the system of equations. Data are presented for 11 \times 11 arrays with various element sizes, element spacings, and scan angles. Good agreement with data in the literature is shown. The analysis is particularly efficient for E - plane and H -plane scans for arrays having rectangular waveguide-fed apertures excited by the dominant mode.

Imaging Reflector Arrangements to Form a Scanning Beam Using a Small Array

To obtain the performance of a large aperture phased array, a small phased array is combined with a large main reflector and an imaging arrangement of smaller reflectors to form a large image of the small array over the main reflector. An electronically scanable antenna with a large aperture is thus obtained, using a small array. An attractive feature of the imaging arrangement is that the main reflector need not be fabricated accurately, since small imperfections can be corrected efficiently by the array. As an application, a 4.2-m diameter antenna is discussed for a 12–14 GHz satellite with a field of view of 3 degrees by 6 degrees required for coverage of the continental United States.