Study And Implementation Of The Ultra-Wide Bandwidth Wireless Receiver System Based On Electro-Optic Modulator

Ultra-wideband (UWB) communication systems, with the ultra-wide bandwidth(3.1GHz~10.6GHz) and the high-speed data transmission, have been wildly used in theshort distance wireless communication systems. In order to increase the signaltransmission distance and coverage area, optical fiber is the powerful solution toprovide the long-range UWB communications, with the advantages including GHzbroadband transmission, low loss and no channel crosstalk. UWB signals transmit overfiber (UWBoF) technology has great value in high-speed broadband wirelesscommunication system in the future.In the paper, the UWBoF communication system based on Mach-Zehnder (M-Z)modulator is designed and implemented. In this system, the wireless signal of bandwidth with7GHz has been received first, and then this received UWB signal isconverted into optical signal by Mach-Zehnder modulator, finally, the UWB signaltransmitted over fiber has been implemented. Two main parts are studied: one is thetheoretical study of the high-speed electro-optic (E-O) modulator, another is the studyand implementation of the UWB receiver system. In the theoretical study of themodulator, optical waveguide and electrode have been analyzed. The effective indexmethod (EIM) and finite difference-beam propagation method (FD-BPM) are used tosimulate and optimize the optical waveguide structure. Two structures of theasymmetric M-Z modulators are designed which can make the initial phase differencereach π/2. The expressions of the electrode characteristic and structure parameters areobtained by the extended multilayer wheeler's function. In the comparison with finiteelement method (FEM), the extended multilayer wheeler's function has the samecomputational precision, but has higher computational efficiency. The compensationlayer of the microstripe line (MSL) electrode structure, the compensation layer of thecoplanar waveguide (CPW) structure and the multilayer CPW structure with shield areput forward for the first time. Combining with the optimized results of the waveguideand the electrode, the velocity matching and the impedance matching for the E-O modulator can be both achieved simultaneously, so the modulator could get thehigh-speed and wide bandwidth modulation.UWB wireless receiver system is divided into two sub-systems, one is the designof the UWB antenna system, and the other is the investigation and implementation ofthe UWB receiver. For the first sub-system, by analyzing and simulating the currentdistributions of rectangle patch antenna, an improved patch structure is given, and a newUWB antenna is implemented. The measurement of the band width for the implementedantenna can achieve3GHz~14GHz, which can match the standard3.1GHz~10.6GHzdefined by Federal Communications Commission (FCC). For the second sub-system,according to the UWB frequency ranges, the UWB receiver based on thesuperheterodyne structure is studied, including design and implementation of thelow-noise amplifier and low pass filter structure. In our experiment, the receivingsensitivity of the UWB receiver can achieve-80dBm when the CNR is around40dB.Finally, the UWB over fiber experimental system is established successfully. Afterthe UWB signal is processed by the UWB receiver, the output signal is transmitted intoRF port of the E-O modulator, meanwhile, the optical signal is input to the opticalsource port. The UWB signal has been carried by optical wave and transmitted byoptical fiber. The experiments show that the UWBoF receiving system can achieve largebandwidth reception, which can match the standard of UWB signal. The receivingsensitivity of our system is around-80dBm, when the CNR is around40dB, and thehalf-wave voltage is about3.9V.