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Microstrip Antenna Arrays on Multilayer LCP Substrates

The diagonal orientation of the microstrip patches in Figure 1 is not inherent in the LCP implementation: instead, it is part of an example design for a typical intended application in radar measurement of precipitation, in which there would be a requirement that both the 14- and the 35-GHz arrays exhibit similar orthogonal-polarization characteristics, including high degrees of polarization purity. The diagonal orientation helps in realizing a symmetrical feed network for both polarizations with similar impedance characteristics and radiation patterns. RF MEMS switches would be included in a production model but are not included in the prototype: Instead, to simplify computational simulation and testing, switching of polarizations is represented by the presence of hard-wired open and short circuits at switch locations.

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Figure 2. MEMS Switches are used to connect the input/output ports to one of the two delay lines to obtain one or the other of two different amounts of phase shift.
Figure 2 is a plan view of a switchable phase shifter — in this case, one that can be switched between two different phase shifts. The device includes electrostatically actuated RF MEMS switches that are used to make and break connections to eight microstrip delay lines having different lengths (e.g., 1 wavelength versus 3/4 wavelength). Necessarily omitting details for the sake of brevity, each MEMS switch includes a microscopic flexible electrically conductive member that, through application of a suitably large DC bias voltage, can be pulled into proximity with microstrip conductors on opposite sides of the gap. The flexible member is covered to prevent direct electrical contact with the microstrip conductors, but the effect of the proximity is such as to enable substantial capacitive coupling of the microwave signal across the gap. The measured loss of the four-bit packaged phase shifter is only 0.24 dB per bit with a phase error less than 4° at 14 GHz. At the time of this reporting, this is the first package flexible organic RF MEMS multibit phase shifter ever documented.

This work was done by Dane Thompson, Ramanan Bairavasubramanian, Guoan Wang, Nickolas D. Kingsley, Ioannis Papapolymerou, Emmanouil M. Tenteris, Gerald DeJean, and RongLin Li of Georgia Institute of Technology for Glenn Research Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Semiconductors & ICs 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- 17980-1.

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