Indirect holographic imaging of antennas using an electronically synthesised "slow-wave"

The use of indirect holographic techniques, where radiation characteristics and antenna aperture fields can be obtained from simple intensity measurements made in the near field, has traditionally been restricted to the measurement of large antennas with small angular spread. The following work describes how this limitation can be overcome by synthesising a reference wave with wave vector in excess of the free space wave vector. This enables the radiation characteristics and complex aperture fields of much smaller antennas to be determined. Results are included to show how this technique can be applied to a standard gain pyramidal horn antenna.