To address the issues of flexible electronics needed for surface-to-surface, surface-to-orbit, and back-to-Earth communications necessary for manned exploration of the Moon, Mars, and beyond, a room-temperature printing process has been developed to create active, phased-array antennas (PAAs) on a flexible Kapton substrate.

Field effect transistors (FETs) based on carbon nanotubes (CNTs), with many unique physical properties, were successfully proven feasible for phased-array antenna systems. The carrier mobility of an individual CNT is estimated to be at least 100,000 cm2/V·s. The CNT network in solution has carrier mobility as high as 46,770 cm2/V·s, and has a large current-density carrying capacity of ≈ 1,000 mA/cm2 , which corresponds to a high carrying power of over 2,000 mW/cm2 . Such high carrier mobility, and large current carrying capacity, allows the achievement of high-speed (>100 GHz), high-power, flexible electronic circuits that can be monolithically integrated on NASA’s active phased-array antennas for various applications, such as pressurized rovers, pressurized habitats, and spacesuits, as well as for locating beacon towers for lunar surface navigation, which will likely be performed at S-band and attached to a mobile astronaut.

A fully printed 2-bit 2-element phased-array antenna (PAA) working at 5.6 GHz, incorporating the CNT FETs as phase shifters, is demonstrated. The PAA is printed out at room temperature on 100-μm thick Kapton substrate. Four CNT FETs are printed together with microstrip time delay lines to function as a 2-bit phase shifter. The FET switch exhibits a switching speed of 0.2 ns, and works well for a 5.6-GHz RF signal. The operating frequency is measured to be 5.6 GHz, versus the state-of-the-art flexible FET operating frequency of 52 MHz. The source-drain current density is measured to be over 1,000 mA/cm2, while the conventional organic FETs, and single carbon nanotube-based FETs, are typically in the μA to mA/cm2 range. The switching voltage used is 1.8 V, while the state-of-the-art flexible FET has a gate voltage around 50 V. The gate voltage can effectively control the source-drain current with an ON-OFF ratio of over 1,000 obtained at a low Vds bias of 1.8 V. The azimuth steering angles of PAA are measured at 0°, –14.5°, –30°, and 48.6°. The measured far-field patterns agree well with simulation results. The efficiency of the 2-bit 2-element PAA is measured to be 39 percent, including the loss of transmission line, FET switch, and coupling loss of RF probes. With further optimization, the efficiency is expected to be around 50–60 percent.

This work was done by Yihong Chen of Omega Optics, Inc. and Xuejun Lu of UMass Lowell for Glenn Research Center. For more information, download the Technical Support Package (free white paper) at under the Manufacturing & Prototyping category.

Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steve Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. Refer to LEW-18428-1.

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This article first appeared in the June, 2010 issue of NASA Tech Briefs Magazine.

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