Wideband reflectarray antenna using true-time delay lines

Reflectarray antennas show a narrow bandwidth as a result of two factors: the narrow bandwidth of the radiating elements and the differential spatial phase delay. The last factor is specially important in large aperture reflect arrays. In this contribution, the bandwidth of reflect arrays is increased significantly by the inclusion of radiating elements with very linear response which allows true-time delay (TTD) without limiting the phase. These elements are based on patches aperture-coupled to delay lines allowing a wide range of phase with several cycles of 360°. An example of wideband reflectarray antenna in X-band is shown. Two identically- sized reflect arrays have been designed using different phase distributions to collimate the same pencil beam. In the first case the phase distribution is truncated to 360° and in the second case is expanded to at least 3 cycles of phase delay. The gain patterns of these reflect arrays are compared demonstrating a considerable improvement in the bandwidth when TTD elements are used.