No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
A general scheme of extracting the optimum pattern nulls for monopulse array antennas with arbitrary sidelobe levels
Abstract
In this paper, a generalized Fourier transform pair is newly presented for the relationship between the patterns and the corresponding line source distribution functions in the monopulse tracking array antenna synthesis problem. This pair enables the desired patterns and the distributions to be simultaneously extracted by the optimum perturbation of pattern null positions. And the difference patterns with the individually specified sidelobe levels are optimally synthesized by appropriately updating the Taylor line source sum pattern formula. Furthermore the method can be extended to the synthesis of the discrete linear array antennas. The schemes for extracting the excitation current weights are also based on the perturbations of pattern nulls which are represented by the complex root locations on Schelkunoff's unit circle. Examples are given for both the sum and difference patterns with arbitrary sidelobe levels, showing the validity of the proposed method.
ResearchGate has not been able to resolve any citations for this publication.
The flexibility of modern monopulse radar antenna systems makes possible the independent optimization of sum and difference patterns. The two parameter difference pattern, developed here for the circular aperature antenna, is designed to have nearly equal sidelobes similar to those of the Taylor sum pattern. The difference pattern is asymptotic to a model difference pattern which has the greatest slope (angle sensitivity) for a given sidelobe level. The model function is unrealizable because it has uniform sidelobes which are infinite in extent. The two parameter difference pattern is realizable and is expressed in a Fourier—Bessel series of N terms in a manner similar to Taylor's treatment of the sum pattern. The other parameter, A, controls sidelobe level.
Comprehensive tables of the Fourier—Bessel coefficients are given for both the circular aperture series and the difference pattern series. Directivity and angle sensitivity are investigated and found to have maximum values that decrease as sidelobe level decreases. The monopulse system performance using the asymptotic difference pattern and the Taylor sum pattern compares favorably with a maximum likelihood angle estimation system. Development of a line source difference pattern is presented in the appendix.
It is well known that the phenomenon of radiation from line-source antennas is very similar to that of the diffraction of light from narrow apertures. Unlike the optical situation, however, antenna design technique permits the use of other-than-uniform distributions of field across the antenna aperture. Line source synthesis is the science of choosing this distribution function to give a radiation pattern with prescribed properties such as, for example, narrow angular width of the main lobe and low side lobes. In the present article the mathematical relationships involved in the radiation calculation are studied from the point of view of function theory. Some conclusions are drawn which outline the major aspects of synthesis technique very clearly. In particular, the problem of constructing a line source with an optimum compromise between beamwidth and side-lobe level (analogous to the Dolph - Tchebycheff problem in linear array theory) is considered. The ideal pattern is cos π √ {u /sup 2/ - A/sup 2/} , where u = (2a/λ) cos θ, a is the half-length of the source, and cosh π A is the side-lobe ratio. Because of theoretical limitations, this pattern cannot be obtained from a physically realizable antenna; nevertheless its ideal characteristics can be approached arbitrarily closely. The procedure for doing this is given in detail.
The constrained least squares (CLS) distribution is a method for obtaining distribution functions that yield low sidelobe patterns with specified constraints on the aperture efficiency, and are especially useful for the transmit patterns of active array antennas. The widely used Taylor distribution optimizes only pattern performance while the CLS distribution optimizes pattern performance while taking into account the constraints on both the peak element amplitude and the total effective radiated voltage (ERV) of the aperture distribution. The paper compares the pattern characteristics of linear arrays with CLS and Taylor distributions. The results help to establish guidelines on when a CLS distribution would be preferable over a Taylor distribution when a specified aperture efficiency is important.
A design method previously developed to give a sum pattern with arbitrary sidelobe topography is shown to be applicable to difference patterns as well. The basis is Bayliss patterns (Taylor-type patterns for the difference mode) which are transformed through an iterative procedure to the desired result. For practical cases the convergence is rapid and a previously developed do-loop computer program has been modified to facilitate the computations and provide final patterns and aperture distributions.
Antenna array distributions and their associated patterns are now
designed on physical principles, based on placement of zeros of the
array polynomial. An overview of the synthesis processes is given.
Robust and low Q distributions for linear arrays and circular
planar arrays that provide variable sidelobe level pencil beam patterns
are treated in detail. Associated difference patterns are included.
Individual sidelobes or groups of sidelobes may be adjusted in level.
The same technique allows synthesis of an efficient shaped beam, with or
without sidelobe adjustment. The ultimate pencil beam array, the
superdirective array, is evaluated
Antenna theory and design, Englewood Cliffs
- R S Elliot
R. S. Elliot, Antenna theory and design, Englewood Cliffs, N.J.: Prentice Hall, Inc., 1981.