A class of reconfigurable microwave antennas now undergoing development comprise fairly conventional printed-circuit feed elements and radiating patches integrated with novel switches containing actuators of the microelectromechanical systems (MEMS) type. In comparison with solid-state electronic control devices incorporated into some prior printed microwave antennas, the MEMS-based switches in these antennas impose lower insertion losses and consume less power. Because the radio-frequency responses of the MEMS switches are more nearly linear, they introduce less signal distortion. In addition, construction and operation are simplified because only a single DC bias line is needed to control each MEMS actuator.

Figure 1. The Two Independent MEMS Actuators in this patch antenna can be used to change the operating frequency. When both actuators are off, the frequency is about 25.0 GHz. When one of the actuators is on, the frequency is 24.8 GHz. When both actuators are on, the frequency is 24.6 GHz.

The incorporation of the MEMS switches makes it possible for an antenna of this class to operate over several frequency bands without undergoing changes in its dimensions other than the small deflections associated with opening and closing gaps between switch contacts. In addition, the polarization of the radiation emitted or received by the antenna can be switched between linear and circular. The ability to change frequency and polarization makes these antennas attractive for inclusion in planar phased antenna arrays.

The upper part of Figure 1 shows the layout of one such antenna containing two MEMS actuators, while the lower part of this figure presents an enlarged view of one of the actuators. Each actuator includes a flexible metal overpass suspended over a metal stub. The overpass is supported at its ends by metal vias electrically connected to the antenna patch. A dielectric film occupies part of the gap between the stub and the overpass. The overpass is free to bend up and down and is actuated in bending by electrostatic attraction by a DC bias voltage applied between the overpass and the metal stub. A metal strip of length L and width W attached to metal stub behaves as a parallel-plate capacitor.

When an actuator is in the “off” state (voltage not applied, overpass not bent), the antenna patch operates at a nominal frequency determined by the dimension b. When the actuator is in the “on” state (voltage applied, overpass bent down), the capacitance of the metal strip appears in shunt with the input impedance of the antenna patch. This capacitance tunes the antenna to a lower operating frequency. During the design-synthesis process, the inductances and capacitances of the actuators and their locations in the patch should be taken into account in order to ensure constant input impedance.

Figure 2. This Patch Antenna radiates in circular polarization when the actuator is off and in dual linear polarization when the actuator is on.

The antenna depicted in Figure 2 is designed to support two degenerate orthogonal modes when excited at a corner. When the MEMS actuator in this antenna is in the “off” state, the perturbation of the modes is negligible and the patch radiates a circularly polarized wave. When the actuator is in the “on” state, the phase relation between the two modes is perturbed to a degree that causes the patch to radiate dual linearly polarized waves.

This work was done by Rainee N. Simons of Glenn Research Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Electronics/Computers category.

Inquiries concerning rights for the commercial use of this invention should be addressed to

NASA Glenn Research Center, Commercial Technology Office, Attn: Steve Fedor, Mail Stop 4-8, 21000 Brookpark Road, Cleveland Ohio 44135.

Refer to LEW-17389.


NASA Tech Briefs Magazine

This article first appeared in the February, 2005 issue of NASA Tech Briefs Magazine.

Read more articles from the archives here.