ABSTRACT
One recent project that has advanced the state of THz technology is the Atacama Large Millimeter/Submillimeter Array (ALMA), a photograph of which is shown in Figure 5.1. ALMA is an ambitious astronomy project consisting of an array of 66 telescopes covering all the atmospheric windows between 84 GHz and 950 GHz. The astronomical signals are detected using heterodyne mixers based on cryogenic (4 K) superconducting-insulator-superconductor (SIS) junctions that have state-of-the-art detection sensitivity [7, 8]. The frequency range is divided into a series of discrete bands, as shown in Figure 5.1. The local oscillators (LOs) for the mixers were developed at the National Radio Astronomy Observatory (NRAO) and consist of GaAs monolithic microwave integrated circuit (MMIC) amplifiers driving Schottky diode frequency multipliers [9].
