Electrooptic Millimeter-Wave–Lightwave Signal Converters Suspended to Gap-Embedded Patch Antennas on Low- $k$ Dielectric Materials

An electrooptic (EO) millimeter-wave (MMW) to lightwave (LW) signal converter suspended to narrow-gap-embedded patch antennas on a low-k dielectric material substrate was proposed for electrical-optical conversion in radio-over-fiber systems. Direct conversion from wireless MMW to LW signals can be obtained using the proposed device with simple and compact structures. The proposed device can be operated with a low MMW loss and no external power supply. By using the low-k dielectric material for the substrate, the antenna size and interaction length become large compared to a device using a high-k EO crystal. As a result, conversion efficiency can be enhanced. Furthermore, effects of the substrate resonant modes can be eliminated since the rather thin EO crystal (<;100 μm) is used. The conversion efficiency of the proposed device can be enhanced about ten times compared to the device fabricated on an EO crystal. Analysis and experimental results of the proposed device in the 60-GHz band are presented in this paper.