Summary
International Symposium on Antennas and Propagation
2010
Session Number:3TC2
Session:
Number:3TC2-3
A Radiation Measurement System by Using Optical Feeding
Ryouhei Hosono, Ning Guan, Naoki Kimura,
pp.-
Publication Date:2010/11/23
Online ISSN:2188-5079
Summary:
Recently, as wireless mobile devices become smaller and smaller, antennas used in the devices are required to be very compact. It becomes even more important to measure precisely such compact antennas for antenna development. However, an antenna must be fed when the antenna is to be measured and the feeding is generally made electrically by microstrip lines, coaxial cables, etc. Electrical feeding lines disturb the radiation pattern of the antenna due to their metallic bodies. In addition, there causes unbalanced currents on the feeding lines to excite unwanted radiation which interferes the original one. The influence becomes significant when the antenna under test is small. As a consequence, ripples or unwanted peaks appear in the radiation patterns of the antenna. Using smaller feeding lines, setting a balun by ferrite chokes, cylindrical conductive caps on coaxial cables [1]-[2], or replacing the electrical feeding by optical feeding [3]-[4] are main solutions for suppressing the influence. However, a conventional balun is only available at narrow and low frequency band. The optical feedings proposed in [3]-[4] used expensive laser diodes and only results measured at frequencies lower than 2 GHz were presented. In this paper, we propose a compact measurement system for radiation patterns by using optical feeding. We use direct modulation on a vertical surface emitting laser (VCSEL) and a graded-index (GI) optical fiber as transmission line so as we can realize a cost-effective system and extend the measuring frequency range up to 6 GHz easily. To show the validity of the system, a small antenna operating at ultra-wideband (UWB) is measured by the system. We investigate the influence of the feeding line by changing its wiring. Results are compared with those measured by an electrical feeding and it is demonstrated that our system can be used for precise measurement of small antennas.