Far-Field Antenna Pattern Measurement Using Near-Field Thermal Imaging

The Active Denial nonlethal weapon system utilizes a large millimeter-wave (mmW) antenna with over 66 dBi of gain operating at 95 GHz. In its final state, the active denial antenna cannot be characterized by conventional measurement techniques including direct far-field pattern characterization or near-field scanning. However, the high power transmitted from Active Denial (100 kW average) provides the means of rapidly recording near-field antenna beam patterns using infrared imaging. Although these thermal images provide a magnitude-only snapshot of the near-field antenna beam, phase can be retrieved from measurements at two different ranges using the iterative Gerchberg-Saxton algorithm. The resulting complex near fields can then be used to compute the antenna far-field pattern and the complex aperture fields. This method has been used to successfully characterize these mmW antennas in both indoor laboratory and outdoor field test environments.