An Antenna Measurement System Based on Optical Feeding

A radiation measurement system by using optical feeding is proposed. The system replaces conventional electrical feeding toantennas by the optical feeding which is composed of an electrical/optical (E/O) converter, a graded-index (GI) optical fiber, and an optical/electrical (O/E) converter. The GI fiber is used so as the O/E converter becomes very compact by using a simple means of coupling between the fiber and the photo-diode in the converter. A vertical surface emitting laser (VCSEL) is used in the E/O converter to make the system available till 6 GHz. This combination also makes the system cost-effective. The validity as well asthe advantage of the system is demonstrated by measuring an ultra-wideband (UWB) antenna both by the optical and electrical feeding systems and comparing with a calculated result. Ripples in radiation pattern due to the electrical feeding are successfully suppressed by the optical feeding. For example, in a radiation measurement on the azimuth plane at 3 GHz, ripple amplitude of 1.0 dB that appeared in the electrical feeding is reduced to 0.3 dB. In addition, a circularly polarized (CP) antenna is successfully measured by the proposed system to show that the system is available not only for amplitude but also phase measurements