Under Sampling Technique For Downsizing In Alos-4

ALOS-4 succeeds the concept of ALOS-2 and hence the system design of ALOS-4 satellite basically follows on that of ALOS-2, except for improvements in mission performance. The swath width is drastically improved in ALOS-4 by applying DBF (Digital Beam Forming) technique.DBFU (DBF Unit) is newly designed for ALOS-4 SAR sensor. In ALOS-4 system, receiving channels are divided into 6 sub-arrays in elevation, and received signals are converted into digital data independently by ADCs for DBF processing.In conventional radar systems, high frequency signals, such as L-band signals, are down-converted by local and COHO (COHerent Oscillator) signals by mixers in RF front-end to make sampling frequency lower. In DBF systems composed of multiple receiving channels, the number of local and COHO signals must be increased to match the number of channels.To overcome this issue, under sampling technique is applied. This technique allows band-pass filtered signals to be sampled at a rate below the Nyquist frequency of the target signal. With under sampling, COHO signals can be eliminated, so downsizing of H/W scale of DBFU can be achieved.This paper describes the under sampling system design result for ALOS-4.