Phase Spoiling Technique for High Power and Wide Beam in Alos-4

Abstract

ALOS-4 succeeds the concepts of ALOS-2[1] except for improvements in mission performance. ALOS-4 utilizes digital beam forming on receive to improve observation swathwidth [2]. PALSAR-3 on-board ALOS-4 has an onboard digital beam forming processor in order to increase the swathwidth of the 3m resolution Stripmap mode to 200 km. Transmit signal with a wide beam-width in the elevation direction is generated in order to cover the wider swathwidth. The reflected signal from the ground is received by several independent receive channels, which are processed in order to form several antenna patterns. There is an inverse relationship between the beam-width and the antenna length. It is necessary that the antenna length should be short in order to obtain the wide beam-width.One way of downsizing the antenna length is to turn off the Transmit/Receive Modules (TRMs), which are connected to each antenna element of Active Phased Array Antenna (APAA). However, this will cause the NESZ to get worse due to the reduction of transmit power.The phase spoiling technique is utilized to solve this problem. Even with a long antenna, wide beam-width can be obtained with this technique. In this paper, the principle of the phase spoiling technique with various phase distributions and the simulation results applied to APAA installed on ALOS-4 are presented.