MANUFACTURING OF LARGE-SIZED AMPLITUDE HOLOGRAMS FOR A SUBMM-WAVE CATR Anne Lönnqvist*, Juha Ala-Laurinaho, Janne Häkli, Tomi Koskinen, Ville Viikari, Jussi Säily, Juha Mallat, Jussi Tuovinen 1 , Antti V. Räisänen MilliLab, Radio Laboratory, Helsinki University of Technology P.O. Box 3000, FIN-02015 HUT, FINLAND Tel: + 358 9 4515971; Fax: +358 9 451 2152 e-mail: alonnqvi@cc.hut.fi 1 Millilab, VTT Information Technology ABSTRACT An amplitude hologram is a novel alternative as the focusing element in a CATR at submm-wavelengths. The amplitude hologram can be manufactured using printed circuit board technology. However, for tests of high-gain antennas, the required size of the hologram may be several square meters. In this paper, details concerning manufacturing of the holograms and the following tests are discussed. Potential methods for manufacturing and joining of holograms are identified and measured results at 310 GHz are shown. 1 COMPACT ANTENNA TEST RANGE BASED ON A HOLOGRAM Testing of electrically large antennas operating in the submillimeter wave region is difficult with the traditional antenna testing methods. The compact antenna test range (CATR) based on a hologram is one possible way to solve the problem [1]. A hologram is an interference pattern of two wavefronts. When it is illuminated with a spherical wave, a planar wavefront comes out. In the hologram CATR, a computer-generated binary amplitude hologram is used. An example of a hologram pattern and a photograph of the hologram CATR test setup are presented in Figure 1. The absorbers are surrounding the hologram to prevent reflections and direct radiation from the feed to the quiet-zone (QZ). Receiver Hologram Transmitter Absorbers Figure 1. Measurement setup (left) and a binary amplitude hologram (right). The hologram pattern is generated and optimized with computer simulations. The simulations are done using the finite-difference time-domain (FDTD) and physical optics (PO) methods. Both phase and amplitude can be modified in the iterative optimization process. To avoid disturbances caused by the unwanted wavemodes which propagate straight through the structure, the hologram is designed so that the 0-7803-7330-8/02/$17.00 ©2002 IEEE 394 © 2002 IEEE. Reprinted with permission from Digest of 2002 IEEE Antennas and Propagation Society International Symposium, vol. 4, 2002, pp. 394-397.