A 660 GHz local oscillator subsystem: Design, testing and alignment

A 660 GHz local oscillator (LO) sub-system for the submillimeter array is designed, tested and aligned in the laboratory by optical and radio alignment. The LO unit employs a cascade tuneless frequency doubler-tripler based on the planar GaAs Schottky diode technology. It is found that a phase shifter inserted between the first and second multiplier stages can improve the frequency response of the unit, reduce the ripples due to the impedance mismatch between the 2 stages. A new technique for the optical and radio alignment of the beam emerging from the unit is also introduced. A near-field scanner which measures the complex beam pattern facilitates the final alignment and helps to verify proper focusing of the LO output beam.