A facility that includes a probe station and a scanning open-ended waveguide probe for measuring near electromagnetic fields (see figure) has been added to Glen Research Center's suite of antenna-testing facilities, at a small fraction of the cost of the other facilities. This facility is designed specifically for nondestructive characterization of the radiation patterns of miniaturized microwave antennas fabricated on semiconductor and dielectric wafer substrates, including active antennas that are difficult to test in traditional antenna-testing ranges because of fragility, smallness, or severity of DC-bias or test-fixture requirements. By virtue of the simple fact that a greater fraction of radiated power can be captured in a near-field measurement than in a conventional far-field measurement, this near-field facility is convenient for testing miniaturized antennas with low gains.

ImageThis facility makes it possible to test a complete set or any subset of a multiplicity of antennas on the same substrate in one session. The multiple antennas can all be of the same design or different designs. Unlike in prior antenna-testing facilities, there is no need for wafer-level dicing or packaging to isolate individual antennas from a multiple-antenna substrate before testing, and no need for special text fixtures. Hence, alternative prototype antenna designs can be evaluated in rapid succession to converge on an optimum design in less time (and, hence, at less cost) than in prior antenna-testing facilities.

In this facility, radio-frequency (RF) signals and DC bias voltages and currents are supplied to an antenna under test (AUT) through RF and DC probes, respectively, that are parts of the probe station. The equipment in this facility includes a commercially available RF probe station, a coplanar-waveguide ground-signal-ground microwave probe that makes contact with the AUT, the aforementioned scanning open-ended waveguide probe, an automatic network analyzer (more specifically, a vector network analyzer)/microwave receiver, and a computer.

The mechanisms for scanning the open ended waveguide probe are a three-axis slide mechanism and a rotation mechanism that, under computer control, positions this probe for acquisition of data at prescribed grid points on a plane very close to the AUT. This near-field scanning scheme enables capture of a maximum amount of energy radiated by one or multiple small antennas while they are DC biased, without need for any special fixture.

The system is controlled by user friendly operational, data-acquisition, and data-analysis software. The dimensions of the near-field scan area and the distance between grid points are specified by the user via the computer keyboard as inputs to a software-generated control panel. After each scan, the data analysis software processes the measurement data and displays the far-field radiation pattern of the AUT, computed from the near-field measurements.

This work was done by Afroz Zaman, Richard Q. Lee, William G. Darby, Philip J. Barr, and Félix A. Miranda of Glenn Research Center; and Kevin Lambert of Analex Corp. For further information, access the Technical Support Package (TSP) free online 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, Innovative Partnerships Office, Attn: Steve Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. Refer to LEW-17877-1.