This invention provides a lower-cost means for verifying the scanning functionality of an electronically steerable (i.e. phased array) antenna (PAA) compared to existing methods that use a scanning probe or scanning test fixture and surrounding anechoic enclosure. This design is comprised of a standard test hat that has been modified to include additional probes located in the positive and negative directions of each scan axis. RF measurements taken from these additional probes provide an estimate of the beam-pointing angle. This solves the problem of verifying the platform-installed antenna’s beam-pointing functionality without the relatively high cost of a conventional anechoic chamber with a scanning probe or scanning test fixture.

An interior view of the prototype multiport test hat.
Beam-steering measurements are obtainable from this configuration because the radiated power received by each antenna probe will change with respect to the other probes as the beam is scanned towards or away from it.

A vector network analyzer (VNA) was used to measure the insertion loss of the PAA and test hat, although a scalar measuring instrument such as a spectrum analyzer or RF power meter could be used in conjunction with an RF signal generator. The insertion loss is measured on each antenna probe port for each pointing angle tested. Each antenna probe must be terminated with its characteristic impedance to prevent reflections. For the prototype characterization, one probe was measured with the 50-ohm load terminations placed on the unconnected probes. Production-level testing should make use of a terminated RF switch to minimize the number of mates/demates and streamline the testing.

The multiport test hat must be characterized with a set of reference measurements before it can be used to measure pointing angles. These measurements are made on an antenna that has recently had its pointing performance verified in an antenna test range. Characterization of the three-port prototype test hat revealed that pointing angle estimation accuracy is best when the antenna scan vector is oriented towards an antenna probe. This was expected, and the production multiport couplers will therefore have five antenna probes (+X, -X, +Y, -Y, and +Z).

This work was done by Joseph Moran, Nicholas Mullins, and Timothy Becker of Lockheed Martin for Johnson Space Center. For further information, contact the JSC Technology Transfer Office at (281) 483-3809. MSC-25482-1