High-Frequency Wave Sources Using Josephson Junction Arrays.

This dissertation presents the results from Josephson junction arrays used as high frequency wave sources. Phase -locked Josephson junction arrays having a large number of junctions have been developed to meet the need for compact submillimeter wave sources for use in such applications as satellite communications and receivers for radioastronomical observation. The design, fabrication processes, and measurements are discussed. Distributed arrays of 40 junctions in which all Josephson junctions are placed at wavelength intervals have been fabricated and tested. Such arrays can deliver about 1 muW of power into a 20-60 Omega load resistor in the frequency range from 100 GHz to 500 GHz, the upper limit being set by the large loss of the superconducting microstrip. Compact arrays have been designed and fabricated to eliminate the loss of the superconducting microstrip. Those arrays have also demonstrated an output power level about 1 muW into a 15 Omega load from 100 GHz up to 620 GHz. Using a similar design and replacing Nb superconducting microstrip with a normal metal such as Au or Cu, an array operating at 1 THz with several microWatts of output power is feasible. Characteristics of the Josephson junction source, including the power level, impedance matching, the tunability, the radiation linewidth, and the tuning rate (or frequency -modulation) will be discussed. Josephson effect sources are expected to have a potential for use as rapidly tunable sources. Measurements of the tuning rate were performed by employing an array of 65 wide junctions, showing that the array remains in the phase-locked coherent state as it is modulated by current at 3.6 GHz. The discussion on the stability in such wide junctions (W/lambda _{J} = 5 - 10) will also be presented.