A Rotman lens fed ridge-element multibeam array demonstrator

For most shipborne and airborne communication, radar or EW applications, there are limited space and locations to deploy the various antenna systems optimally. Shared-aperture, multi-function systems have been proposed to reduce the number of apertures required. A broadband and wide scan antenna with multibeam performance would satisfy the requirements of such a system. A 1D multibeam antenna array demonstrator has been built around a ridge antenna element and a Rotman lens. The system has an octave bandwidth and scans ±51° in the azimuth plane. With supporting structures included, the array weighs 17 kg. It is a dual polarized array; the horizontally polarized elements are not used for the present series of tests and are terminated in 50 Ω loads. There are 8 vertically polarized (VP) elements in total in each column, but the top and bottom elements of each column are parasitic elements. The 6 innermost VP elements in each column are combined to give a fixed beam in the elevation plane. There are a total of 32 columns but the two outermost columns at each end of the array are parasitic. The centre 28 columns are connected to the Rotman Lens via semi-rigid phased matched cables. The planar lens has 28 array ports and 18 beam ports. The beams can point in the fixed direction and 18 other directions. They remain invariant with frequency since the lens provides true time delay beam steering.