GENERALLY, RADAR and imaging systems call for antennas with large apertures and fast beam-scanning capabilities. Although phased-array antennas have been accepted as a rather natural "fit" for such applications, electronically reconfigurable reflectarray antennas are now being considered an option as well. One large one in particular featuring 160 x 160 reflecting elementshas been designed, fabricated, and evaluated for a millimeter-wave system at 60 GHz. This antenna is the work of Hirokazu Kamoda, Jun Tsumochi, Takao Kuki, and Toru Iwasaki from Japan Broadcasting Corp. together with Osamu Hashimoto from Japan's Aoyama Gakuin University.

In such an antenna, the illuminated elements reflect the incident field with phase shifts to obtain the required phase front over the array aperture. The reflectarray is spatially fed, so it does not require complex, high-loss power dividers/combiners. As a result, insertion loss is minimized at the feed. For such a large array to be constructed, the reflecting element structure had to be both simple and easy to control. The researchers therefore used a reflecting element comprising a microstrip patch and a single-bit digital phase shifter using a PIN diode for each element. The team fabricated the large reflectarray antenna using reflecting elements that it had designed as part of a previous project. Measured radiation patterns and antenna gain were in agreement with computer predictions. However, the use of PIN diodes for such a large reflectarray did result in large direct-current (DC) power dissipation due to the current required to bias the diodes. See "60-GHz Electronically Reconfigurable Large Reflectarray Using Single-Bit Phase Shifters," IEEE Transactions On Antennas And Propagation, July 2011, p. 2524.