An apparatus and technique have been devised for measuring the radiation pattern of a microwave patch antenna that is one of a number of identical units that have been fabricated in a planar array on a high-resistivity silicon wafer. The apparatus and technique are intended, more specifically, for application to such an antenna that includes a DC-controlled microelectromechanical system (MEMS) actuator for switching the antenna between two polarization states or between two resonance frequencies.

Figure 1. RF and DC Probes are applied to the transmission line of one of several identical patch antennas on a silicon wafer of 3-in. (7.62-cm) diameter.

Prior to the development of the present apparatus and technique, patch antennas on wafers were tested by techniques and equipment that are more suited to testing of conventional printed-circuit antennas. The techniques included sawing of the wafers to isolate individual antennas for testing. The equipment included custom-built test fixtures that included special signal launchers and transmission-line transitions. The present apparatus and technique eliminate the need for sawing wafers and for custom-built test fixtures, thereby making it possible to test antennas in less time and at less cost. Moreover, in a production setting, elimination of the premature sawing of wafers for testing reduces loss from breakage, thereby enhancing yield.

Figure 2. The Spinning Open-Ended Rectangular Waveguide samples the radiation from a patch antenna on the wafer. The antenna is positioned along an arc by use of the stepping motor.

The apparatus includes (1) a commercial coplanar-waveguide ground-signal-ground radio-frequency (RF) probe, through which microwave excitation is applied to a microstrip transmission line that is part of the integrated circuitry of the patch antenna under test; (2) DC probes for biasing the microelectromechanical actuator; (3) a spinning linearly polarized antenna for sampling the linearly and circularly polarized radiation from the patch antenna as a function of angle relative to the perpendicular to the plane of the wafer; and (4) an automatic network analyzer/microwave receiver for measuring the sampled signal. The microwave probe is a commercial unit of the coplanar-waveguide (CPW) ground-ground-signal-ground type. The microwave and DC probes (see Figure 1) are installed in a commercial RF wafer probe station that has been modified to accommodate the rotating sampling antenna.

The sampling antenna (see Figure 2) is an open-ended rectangular waveguide that is spun by use of a small DC motor mounted on poly (methyl methacrylate)arm. The signal acquired by the sampling antenna is coupled through a coaxial rotary joint to a detector that is also mounted on the arm. The arm, in turn, is attached to the shaft of a stepping motor, which is used to position the sampling antenna, in increments of a few degrees, along an arc that extends from -90° to +90° relative to the perpendicular to the plane of the wafer.

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 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-17462.

NASA Tech Briefs Magazine

This article first appeared in the September, 2004 issue of NASA Tech Briefs Magazine.

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