Radio-frequency and microwave SETI, including the Allen Telescope Array

Abstract

Since we began to search for alien signals in 1960 we have increased the size of our antennas, increased the sensitivity of our detectors and increased the sophistication of our data processing. Despite the failure to detect a signal at radio frequencies and microwaves, it is the very limitations of the various efforts that enable the search to expand in scope. This is because (as noted in earlier chapters) it is possible that we have found nothing because the originating civilization is using a transmitter power that requires a potential recipient to build an enormous antenna in order to pick up the energy required to pull the signal out of the noise. Even the increase in capability provided by the Allen Telescope Array might not be sufficient. And, of course, there remains the requirement that we point our receiver in the direction of the source as it is transmitting towards us and be in the right part of the electromagnetic spectrum. In this chapter we discuss nine projects which operated in the past or are currently in progress.