Investigations on the performance of RF circuits and beamforming techniques for wireless systems

Abstract

The wireless systems demand increased performance and low power consumption. Many efforts are being carried out to increase the performance of wireless systems. This leads to research in implementation of RF circuits and new design techniques like beamforming in the physical layer of the wireless system. In this thesis, performance of RF circuits and active beamforming techniques in the front-end of wireless systems operating in the 900MHz and 2.4GHz band is studied. The Intermediate frequency (IF) is 70MHz in the receiver and the IF is 45MHz in the transmitter of 900MHz systems. The IF is 45MHz in transmitter and receiver of 2.4GHz systems. Band Pass Filters (BPFs) are used in the intermediate frequency range of wireless systems to reject the noise components from the signal source on the transmitter and to reject the noise in receivers before signal enters the baseband circuits. In this thesis, BPFs operating in the 45MHz and 70MHz IF ranges are implemented to provide a bandwidth of 3MHz. BPFs are implemented with Operational Transconductance Amplifiers (OTAs). In this research work, vector modulators are implemented for center frequencies of 902.5MHz, 947.5MHz and 2.4GHz. The control element in the vector modulator is a variable attenuator. In active beamforming, beam steering is performed by applying necessary phase shifts along with excitation to the antenna elements. The excitation coefficients are calculated using non uniform amplitude distributions. In passive beamforming, RF switched beamforming system is proposed. The RF switched beamforming system is constructed with PAA, Butler matrices and Single Pole Eight Throw (SP8T) switches. Beamforming techniques proposed perform better by forming a unidirectional beam with high directivity and gain. Hence the circuits and beamforming techniques proposed and studied are found to be suitable for improving the performance of wireless systems. newline newline newline