The foundation of a satisfactory Rotman lens design is geometric. The effects of seven design parameters (focal angle, focal ratio, beam angle ratio, maximum beam angle, beam port curve ellipticity, array element spacing, and focal length/ lambda ) on the shape, and on the geometric phase and amplitude errors of a Rotman lens are described. The advantage of beam port shaping to reduce phase error, and of pointing port horns at the opposite apex (instead of normal to the curve) to reduce off-axis beam amplitude asymmetries, are shown numerically. A design procedure for selecting these parameters is given, and a calculation of lens gain is presented. >

Design trades for Rotman lenses

As various enabling technologies advance, conformal phased arrays are finding more numerous applications. Because a conformal array is curved, new far field pattern behaviors emerge and many of the traditional linear and planar phased array synthesis methods are not valid. This paper starts by reviewing the equations for the far field of a curved phased array, and provides a generalized definition of aperture efficiency appropriate for conformal arrays. A modified Bernstein polynomial, defined with just five parameters, is introduced which provides a flexible method to specify a variety of smooth unimodal amplitude distributions that are shown to give good sidelobe levels and aperture efficiencies. By using particle swarm optimization of the modified Bernstein polynomial parameters constrained to provide a specified aperture efficiency, a family of aperture distributions and corresponding far field patterns is produced that allows aperture efficiency to be traded for sidelobe level.

Efficiency-constrained particle swarm optimization of a modified bernstein polynomial for conformal array excitation amplitude synthesis

A synthesis method based on differential evolution algorithm is proposed for conformal antenna arrays in the presence of platform. With the desired phase weights determined by the scan angle and array geometry, the amplitude weights of elements are optimized by differential evolution algorithm to drive down the side-lobes. Both the effect of platform on radiation pattern of conformal array and the mutual coupling between the elements are taken into account by calculating the antenna array and platform simultaneously using the method of moment. Application of adaptive integral method reduces the storage and computation time needed by the method of moments.

Pattern Synthesis of Conformal Array Antenna in the Presence of Platform Using Differential Evolution Algorithm

Sparsening conformal arrangements is carried out through a versatile Multi-Task Bayesian Compressive Sensing (MT-BCS) strategy. The problem, formulated in a probabilistic fashion as a pattern-matching synthesis, is that of determining the sparsest excitation set (locations and weights) fitting a reference pattern subject to user-defined geometrical constraints. Results from a set of representative numerical experiments are presented to illustrate the key-features of the proposed approach as well as to assess, also through comparisons, its potentials in terms of matching accuracy, element saving, and computational costs.

Sparsening Conformal Arrays Through a Versatile $BCS$ -Based Method

This paper presents a new design to realize a compact Rotman lens-fed antenna array. The lens-fed antenna has the form of two layers, which is a new approach to reducing the size of the Rotman lens. The approach is demonstrated at 24 GHz aiming for an automotive sensing radar. The lens consists of a top metal layer, a dielectric, a common ground, a dielectric, and a bottom metal layer, in sequential order. The layout of the lens body is placed on the bottom layer and the antennas are placed on the top layer. Both of them are electrically connected through slot transitions. This two-layer structure reduces not only the total size of the lens, but also the loss of the delay lines because the lines can be designed to be as short and straight as possible. The two-layer Rotman lens-fed antenna array is measured in terms of scattering parameters and beam patterns. From the scattering parameters, the power efficiencies of the beam port 1, 2, and 3 at 24 GHz are obtained as 32.3%, 48.5%, and 50.8%, respectively. The measured beam patterns show that the beam directions are -28.1°, -14.9°, 0°, 15.5°, and 28.6° and the beamwidths are 13.4°, 13.2°, 12.8°, 13.5°, and 13.0°. The measurements confirm that the compact two-layer Rotman lens has been successfully demonstrated.

Compact Two-Layer Rotman Lens-Fed Microstrip Antenna Array at 24 GHz

A Rotman lens is used to feed a linear array antenna for wideband use. A relationship between design parameters for realizing a Rotman lens has been derived by introducing a new design variable. The design method which minimizes the phase error on the aperture of the linear array antenna has been shown. For large array length, the above phase error due to this method becomes considerably smaller than that due to a conventional method. This improved method makes it possible to design small and low-loss Rotman lens antennas.

An improved design method of Rotman lens antennas

The authors present a novel method for the analytical determination of the amplitude distribution providing the low sidelobe pattern of conformal array antennas. The proposed projection method considers both the nonuniform element density and element patterns on the aperture. Numerical results are given as well as results of experimental verification for an X-band, half-spherical array with 60 rectangular microstrip antennas. >

A projection method providing low sidelobe pattern in conformal array antennas

For original paper by Katagi, Mano, and Sato see ibid., vol.32, no.5, p.524 (1984). Corrections to this paper were suggested by Leonakis (see ibid., vol.34, no.8, p.1067, 1986) and by Singhal and Sharma (see ibid., vol.42, no.7, p.1037, 1994). Katagi et al. here comment on the corrections to their paper. Singhal and Sharma reply to the comments. >

S. Mano

Papers

An improved design method of Rotman lens antennas

A projection method providing low sidelobe pattern in conformal array antennas

Comments on corrections to "An improved design method of Rotman lens antennas"