Six-port digital radio communications at VHF band

Digital communications in VHF band have been increasing over the recent years. The goal of this thesis is to develop a direct digital Six-Port QPSK modem(modulator and demodulator) at VHF band using discrete components, namely, surface mount devices (SMD) which are widely used in RF and microwave systems such as transceivers, up and down-converters. A new architecture of Six-Port modem is proposed which superior to the conventional direct conversion architecture in terms of circuit's simplicity, system performance and operating bandwidth.; To properly realize the system, circuit simulations using CAD tools such as Agilent advanced design system (ADS) and adequate models of the components are necessary. The modeling method of the power detectors is presented in this thesis.; Simulation results do not always agree to the measurement results all time. This work addresses this issue with analysis for the demodulator implementation results.; Another significant contribution of this research work is a new architecture for the direct Six-Port QPSK modulator. As the Six-Port modulator has wide-spread spectrum because of the lack of pulse shaping in the baseband data. A new spectrum shaping approach is proposed using half wavelength transmission line load.; The proposed digital Six-Port QPSK modem (modulator and demodulator) has been implemented and fabricated in the Poly-Grames research center. The performance tests are promising, indicating that they are the good candidate for VHF band digital communications.