|Authors: ||O. Caytan, L. Bogaert, H. Li, J. Van Kerrebrouck, S. Lemey, G. Torfs, J. Bauwelinck, P. Demeester, S. Agneessens, D. Vande Ginste, H. Rogier|
|Title: ||Passive Opto-Antenna as Downlink Remote Antenna Unit for Radio Frequency over Fiber|
|Format: ||International Journal|
|Publication date: ||12/2018|
|Journal/Conference/Book: ||Journal of Lightwave Technologies
A novel remote antenna unit, intended for application in the downlink of an analog radio frequency over fiber system, is proposed, whose radiated power originates entirely from the optical signal supplied by a single multi-mode fiber. By operating the photodetector of the optical receiver at zero bias voltage, while omitting typical active components, such as transimpedance amplifiers, a fully passive unit, requiring no external power supply, is obtained. Instead, a careful co-design is performed to maximize the power transfer from photodetector to antenna within the frequency range of interest using an impedance matching network. A wideband cavity-backed slot antenna is implemented in air-filled substrate-integrated-waveguide technology. The antenna feed plane serves as integration platform for the optical receiver. The resulting downlink remote antenna unit is compact, cost-effective, energy-efficient and extremely reliable. Therefore, it is an ideal building block for novel, highly specialized, ultra-high density wireless communication systems, which require massive amounts of remote antenna units, deployed in attocells as small as 15cmx15cm. A prototype operating in a wide frequency bandwidth ranging from 3.30GHz to 3.70GHz is constructed and validated. In free-space conditions, a broadside gain of -0.2dBi, a front-to-back ratio of 8.8dB and linear polarization with a cross-polarization level of -28.8dB are measured at 3.50GHz. Furthermore, a -3dB gain bandwidth of 500MHz is observed. Finally, the prototype is deployed in a unidirectional data link, achieving a symbol rate of 80MBd over a distance of 20cm.
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