A Reflection-type Amplitude Hologram as a Collimating Element in the Compact Antenna Test Range

In this paper, we study the possibility to use an amplitude hologram as a reflection-type collimating element to produce a plane wave in the compact antenna test range (CATR). So far, we have used holograms as transmissiontype elements only. The hologram studied here has a diameter of 600 mm and it operates at the frequency of 310 GHz. It is a computer-generated slot pattern etched on a thin metal-plated dielectric film. We have simulated and measured the plane wave field reflected from the hologram. The maximum measured ripples are only 1.6 dB and 20°, peak-to-peak. The reflection-type hologram has some advantages over the transmission-type one. For example, the power loss is about 4 dB lower for the reflection-type hologram. In addition, a CATR based on the reflection-type hologram can be situated in a much smaller space. To demonstrate the capability of the reflection-type hologram in actual antenna testing, the radiation pattern of a small reflector antenna was measured at 310 GHz.