GB1277004A - Improvements in antennae - Google Patents

Abstract

1277004 Aerials NATIONAL RESEARCH DEVELOPMENT CORP 1 Aug 1969 [15 May 1968] 23145/68 Heading H4A An aerial comprises a reflector having a surface which is parabolic in at least one crosssection, operational means, having a plurality of discrete ports or a continuous port, for performing a spatial Fourier transformation on radiation received from, or transmitted to, a predetermined region between it and the reflector, and phase shift means coupled between the operational means and power summing means. A spatial Fourier transformation is performed by the reflector in respect of an outgoing or an incoming plane wave. During transmission, an input signal to the summing means results in the appearance of equal amplitude signals at the discrete ports or over the continuous port of the operational means, and the phase relationships thereof can be so adjusted that the plane wave is radiated in a predetermined direction from the reflector. During reception, the phase relationships of the signals can be so adjusted as to give maximum output from the summing means. As described, an aerial comprises a parabolic-cylinder type reflector 10, Fig. 1, and a primary feed 11 consisting of a linear array of eight horn radiators, terminating waveguides. The other ends of said waveguides are coupled to a Butler matrix 12, which is coupled through a bank 13 of variable phase shifters to a summing network 14 having a single port for the aerial input or output. Steering means are provided for moving the feed 11 relative to the reflector 10 to provide scanning so that, as shown in Fig. 3, the locus of its centre is a circle of diameter F[1 + (D/4F)<SP>2</SP>] sec #, where F, D and # are, respectively, the focal length of, the width of, and half the angle subtended at the centre of the feed by, the reflector. The steering means also maintains the normal at the centre of the feed so that it bisects the angle 20. A Fourier transformation is carried out between the reflector 10 and the feed 11, and a spatial Fourier transformation is performed by the Butler matrix 12 upon signals which pass through. Thus, considering reception, equal amplitude signals are consequently presented to the phase shifters in the bank 13, and said phase shifters may be so adjusted that the signals presented to the summing network 14 are in phase, and its output is maximized. Comma phase error effects are thus reduced, so that the angular range of scanning may be increased. In another embodiment, a paraboloidal reflector is used with a primary feed means distributed in two dimensions and arranged in two parts. A two-dimensional Fourier transformation is performed upon the signals received or transmitted, in which a onedimensional Fourier transformation is performed upon the signals associated with each part of the feed means. Two phase-shifting and summing means are provided, and each summing means is coupled to a common combining means with a single input or output. The Butler matrix may be replaced by a microwave lens, when the discrete output parts of the matrix are replaced by a continuous output port.