RF Feedforward Interference Cancellation For Wide-band Signals using Adjustable Band-stop Resonators

This dissertation is focused on developing RF feedforward cancellation systems for wideband interference signals appearing at close proximity from the receiver. The system is designed to target high interference risks in the Upper-700 MHz band (746-805 MHz) following the congestion in the spectrum between public safety land mobile radios, LTE broadband public safety and LTE commercial mobile. New low-profile planar band-stop resonators are designed to obtain a wide-band and a high roll-off rejection (> 1dB per MHz). Two new design methodologies of band-stop resonators are presented in this work. The first approach incorporates the use of power splitters and large delay transmission lines, and the second methodology uses finite cell artificial left-hand transmission lines. The two structures are used in separating the receiver wanted signal from the interferer, and this separation is required to generate a replica of the interferer, which later becomes an input to the cancellation phase of the system. The system is tested using two generated LTE modulated signals, modeling the interference and the wanted signals, which are 20, 15 and 10 MHz apart. The test results have shown successful cancellation for 9 MHz wide interference signals. The cancellation can be further improved over a wide band, by increasing the linearity of the phase shifters used in the feedforward system. Therefore, new RF MEMS switch based phase shifters are designed, implemented and measured. Measurements of the new phase shifters have successfully reduced the RMS amplitude deviation, which is calculated between all the phase states over a 100 MHz bandwidth, by 66% when compared to the phase shifter used in the above interference cancellation tests