All-solid-state, room-temperature, multipixel, sub milli meter-wave re ceiv ers are in demand for efficient spatial mapping of a planet’s atmosphere composition and wind velocities for future NASA missions to Venus, Jupiter, and its moons. Roomtemperature operation based on Schottky diode technology is a must in order to avoid cryogenic cooling and enable long-term missions. This technology is also being successfully applied for very-high-resolution imaging radars for standoff detection of concealed weapons. For submillimeter-wave radar imaging, the main issue is that, in order to reach video frame rates with high image pixel density, multi-pixel focal plane transceiver arrays are needed to illuminate targets with many radar beams simultaneously.

Close-up view of the on-chip power-combined 105- to 120-GHz balanced frequency tripler.
Ultra-high-power, high-performance Schottky-diode-based frequency triplers able to handle up to 800-1000 mW input power and produce up to 200 mW output power at W-band (70 to 110 GHz) and F-band (90 to 140 GHz) with a single chip were developed. This corresponds to a conversion efficiency of 20 to 25% and sets a new state-of-the-art in power generation at these frequency bands. The frequency bandwidth of these multipliers is 15 to 20%, which is larger than that of power amplifiers at W-band. This solution also incorporates a novel topology called on-chip power combining that allows it to increase by a factor of two or four the power handling of traditional frequency multipliers.

The epi-structure and anode size of the devices have been, for the first time, optimized to reach the limits of the GaAs Schottky diode technology in terms of power handling and efficiency at these frequency bands. The improvement with regard to the state-of-the-art is a factor of four to five in both power and efficiency. These devices can operate up to 120 GHz (commercially available high-power amplifiers do not operate beyond 105 GHz), and can be pumped with low-cost, high-power amplifiers at Ka-band. Hence, this solution considerably reduces the cost of high-power sources.

Test results for 500-mW input power.
With these high-power multipliers, all the power dissipation is at Ka-band instead of W-band or F-band. There is no need for W-band or F-band amplifiers with these new devices. The connection between the high-power Ka-band amplifiers and the rest of the multiplied LO source is via coaxial cables, which provide a very good thermal break to the LO chain. This will considerably simplify the thermal management of terahertz LO sources.

Reaching the highest possible powers is critical to operate radars at the longest standoff range, or for building radars using multiple transmitters and receivers. Sources above 110 GHz can also be used in emerging high-throughput communications systems and emerging space-based applications such as high-resolution altimetry. Finally, high millimeter-wave sources can be used in academic research work, such as molecular spectroscopy.

This work was done by Jose V. Siles, Choonsup Lee, Goutam Chattopadhyay, Ken B. Cooper, Imran Mehdi, Robert H. Lin, and Alejandro Peralta of Caltech for NASA’s Jet Propulsion Laboratory. For more information, contact This email address is being protected from spambots. You need JavaScript enabled to view it.. Refer to NPO-49351.


NASA Tech Briefs Magazine

This article first appeared in the January, 2016 issue of NASA Tech Briefs Magazine.

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