Multibeam Optical Signal Processing Array Antenna Using Optical Waveguide Arrays and Lens

Phased array antennas are expected to be effective for use in advanced wireless communications for mobile radio communication, wireless LAN, and satellite communication [1]. Recently, the application of photonics technology to microwave array antennas has been studied [2-5]. An optically controlled phased array antenna is very well-suited for fiber-optic microwave or millimeter-wave links. Optical components such as a lens and optical fibers can be combined to form a beam forming network (BFN) using the spatial optical signal processing (OSP) method. In addition, a high-quality RF signal can be generated from the frequency offset between the lights by using a heterodyne technique. By using a Fourier transform (FT) lens, beam scanning and beam forming can be carried out by simply arranging the light source in the front focal plane of the FT lens. ATR has proposed a variety of functions for OSPBFNs, such as beam shaping, beam scanning, and multibeam formation [2]; we have experimentally demonstrated the achievements of beam steering and multibeam formation in the Ku-band [3]. However, these OSP-BFNs mainly consist of optical fibers, so they have some problems with miniaturization and stability. Furthermore, the use of light in OSP-BFNs is inefficient because the area of the core is quite small compared with the clad of the optical fiber. NTT uses a slab waveguide and has confirmed the OSP-BFN function [4]. An optical waveguide would greatly reduce the light transmission loss, the size of the optical processing feed part, and the optical alignment difficulties. A two-dimensional beam forming method using only a slab-waveguide was proposed [5], however, the relationship of the light and the RF beam direction is difficult to determine. We applied optical waveguide arrays and a micro lens to the emitting and sampling of laser light parts in an OSP-BFN in order to solve the above mentioned problems. In the case of this structure, if a multilayered waveguide arrays are applied, a two-dimensional OSP-BFN can be easily constructed. In this report, we describe the design concept of a one-dimensional OSP-BFN using waveguide arrays, and show the system, which we constructed. The efficiency of an OSP array antenna system, which including an optical RF sources, an OSP-BFN, and a linear array antenna, was demonstrated in experiments on multibeam formation in the X-band.