Mixer, Multiplier and Passive Components for Low Noise THz Receivers

Doctoral thesis, 2013

This thesis presents the work done in the field of development of low noise instruments for radio astronomy applications, and addresses some of the key components in the receiver. Part of this thesis describes the design and development of a Superconductor-Insulator-Superconductor (SIS) junction mixer covering RF frequencies from 163 to 211 GHz, reaching the quantum limited noise performance. The mixer uses an integrated approach, where an LO coupler and a resistive LO termination are fabricated on the same mixer chip. Another part of the thesis describes the work on the design and development of the Band 5 receiver cartridge for the Atacama Large Millimeter Array (ALMA) project. Details on the development of Band 5 receiver cartridge, sideband separation mixer, and a superconducting IF hybrid is presented. Additionally, this thesis presents first ever experimental demonstration of an SIS device as frequency multiplier, and presents successful off-chip detection of the multiplied signal. The experimental frequency multiplier was designed for the 182 to 192 GHz output frequency band, and uses an array of SIS junctions to boost the total output power. Dependence of multiplier output power on the DC bias voltage and pumping power are investigated. The measurements successfully confirm x2 multiplication, where extremely sharp multiplied signal was detected with no observable spurious signals. The SIS multiplier shows no deterioration of the linewidth of the original pumping signal.