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IEEE Transactions on Applied Superconductivity

Linewidth measurement of millimeter wave radiation from a Josephson array source coupled to free space

S. Deus, Shogo Kiryu

Published Jun 1, 1999• 2 citations
Publisher

Abstract

Radiation from a linear array oscillator with a spiral antenna has been coupled out of the dewar through a Teflon window. Both its linewidth and its power have been measured after coupling the radiation through free space into a second dewar. The linewidth has been determined using a SIS mixer with a spiral antenna which was pumped with an 88 GHz phase-locked Gunn oscillator, and also by Josephson mixing of the array itself. The array oscillator has a distributed array structure of 300 resistively shunted junctions which are placed in groups of 6 junctions. It was fabricated on a silicon wafer and has a two-arm spiral antenna. The chip was attached to a silicon lens with an anti-reflection coating. The linewidth of the array oscillator was determined between 158 GHz and 194 GHz, far below its design frequency of 400 GHz. The measured linewidth and power data of the oscillator reveal interesting information about its phaselocking behavior in the operating range far below its design frequency.

DOI
10.1109/77.783982

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Radiation from a linear array oscillator with a spiral antenna has been coupled out of the dewar through a Teflon window. Both its linewidth and its power have been measured after coupling the radiation through free space into a second dewar. The linewidth has been determined using a SIS mixer with a spiral antenna which was pumped with an 88 GHz phase-locked Gunn oscillator, and also by Josephson mixing of the array itself. The array oscillator has a distributed array structure of 300 resistively shunted junctions which are placed in groups of 6 junctions. It was fabricated on a silicon wafer and has a two-arm spiral antenna. The chip was attached to a silicon lens with an anti-reflection coating. The linewidth of the array oscillator was determined between 158 GHz and 194 GHz, far below its design frequency of 400 GHz. The measured linewidth and power data of the oscillator reveal interesting information about its phaselocking behavior in the operating range far below its design frequency.
Radiation from a linear array oscillator with a spiral antenna has been measured using an off-chip coupled bolometer. The array oscillator has a distributed array structure with 300 resistively shunted junctions which are placed in the groups of 6 junctions. The array oscillator was fabricated on a Si wafer with a two-arm spiral antenna. The chip was attached to a Si lens with an anti-reflection coating. Rather large power (>100 nW) was detected at a number of array bias voltages V/sub bias/ from 115 mV to 196 mV, which correspond from 185 GHz to 315 GHz. The maximum measured power was 550 nW at V/sub bias/=125 mV (200 GHz).
The power and linewidth of the radiation, near 250 GHz, of small distributed Josephson junction array sources have been measured using a single-chip integrated source and receiver. The intermediate frequency (IF), coupled off the chip to a room-temperature spectrum analyzer, permitted a direct measurement of the oscillator linewidth. The one-dimensional arrays were of a novel design with junctions placed in 1/4 wavelength lumps separated by one half wavelength. The measured power ( approximately=2 mu W) and linewidth ( approximately=10 MHz) for the 10 junction sources were in reasonable agreement with those obtained from computer simulations.>
The radiation linewidth of a phase-locked distributed Josephson junction array source at 250 GHz has been measured as a function of temperature using an integrated submillimeter wave receiver/source. The measured total linewidth (including signal and local oscillator arrays, having 10 junctions each) is 10 MHz at 1.6 K. The measured data agree, within 50% uncertainty, with the linewidth obtained from computer simulation assuming the Nyquist noise current spectral density generated by the junction shunt resistors.
We have developed resistively shunted tunnel junctions with a small parasitic inductance (/spl equiv/100 fH) to improve the high-frequency performance of Josephson array oscillators. Josephson array oscillators with 11 such junctions and Nb microstrip resonators were designed and fabricated to operate at 690 GHz. Shapiro steps induced by Josephson oscillation were clearly observed at the submillimeter frequency region. By comparing the step height with the numerical simulation, we estimated the power of the Josephson oscillator delivered to the load resistor to be about 10 /spl mu/W at 625 GHz. The linewidth of the Josephson array oscillator was also measured using an integrated receiver consisting of two Josephson array oscillators and an SIS mixer. The designed frequency of the receiver was set at 550 GHz. IF output power spectrum was observed when both the oscillators were biased at about 1.17 mV which corresponds to 566 GHz. The composite linewidth of Josephson oscillation was measured about 8 MHz at 4.2 K.
We present experimental results on the emission from phase-locked twodimensional arrays of Josephson junctions. We have coupled the emission from 10 x 10 arrays to a room-temperature mixer throu h a tin-line antenna and WR-12 waveguide. A single voltagetunable peak was detected up to 230 GHz. A stripline resonance in the antenna reduced the array's dynamic resistance and thereby the emission linewidth to as low as 10 kHz. We extract an effective noise temperature of 14 K from the linewidth data. When the array's emission was coupled to an on-chip detector junction through a dc blocking capacitor, we detected voltagetunable emission from 75 GHz up to 300 GHz, and in some circuits emission above 400 GHz. The coherent power spectrum depends primarily on internal resonances.
We present a basic description of Josephson junctions and discuss their use as GHz and THz oscillators. The resistively shunted junction model is used to calculate the available power, linewidth and operating frequency of the oscillators. We discuss how phase-locked arrays of junctions are used to achieve higher power and narrower linewidth. Two experimental examples of phase-locked emission are shown: one from on-chip detection circuits at 150 GHz and one detected off-chip showing a 13 kHz linewidth at 88.8 GHz.>