Wifi-UHF transceiver design for 650-680 MHZ television white space (TVWS) spectrum application

Abstract

Studies have sparked an interest to look further into the possibility of research to make beneficial of underutilized Television White Space (TVWS) frequency band of 470 MHz-770 MHz to substitute the 2.4 GHz Wi-Fi which has been running out of frequency spectrum. The design, simulation, fabrication, experimental validation and optimization of a Wi-Fi-UHF Transceiver (WUT) circuit to achieve a capability of up and down-conversion between frequency of 2.4 GHz and UHF band are presented in this thesis. The WUT which is consisted of subsections like filters, mixers, amplifiers and attenuators are comprehensively designed with an architecture of utilizing a single VCO-PLL to perform up-conversion and down-conversion of RF signals between 2.4 GHz and 650-680 MHz correspondingly. The down-conversion from 2.4 GHz to 650- 680 MHz is performed during the RF transmission while up-conversion is the other way around. By programming VCO-PLL to certain frequency as local oscillator (LO), the 2.4 GHz RF signal can be down-converted to any frequency within 650-680 MHz which will be transmitted out from the antenna into the air. On the receiver path, preadjustment of the VBPF through potentiometer enabled WUT to receive any frequency within 650-680 MHz which will be mixed-up with certain LO frequency from the same VCO-PLL to generate the 2.4 GHz. Such unique design mechanism has paved the way for WUT to work as a transceiver without any change or modification required to the existing Wi-Fi modem. ADS is used as a tool to design and simulate the subsection circuits separately towards specific design goals prior to integration as complete WUT system. The simulation results shows that WUT is able to down-convert 2.4 GHz to 650-680 MHz with gain of 9.8 dB meanwhile the up-convert of 650-680 MHz to 2.4 GHz managed to have gain of 5.6 dB. Also the physical WUT is able to perform similarly, but with up-conversion gain of -42.7dB and down-conversion gain of -22.6dB.