A Variable Phase Shifter with an Improved Linearity for the Adaptive Interference Cancellation System Application
vii, 42 p.
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A variable phase shifter with an improved phase linearity is fabricated for the adaptive interference cancellation system (ICS) application. The theory of an adaptive interference cancellation system is that if a reference-interference signal (which is used to reduce the interference received into the system or antenna and has an equal amplitude but opposite phase polarity to that of the receive-interference signal.) and the receive-interference signal are combined, the interference signal is cancelled and a resultant desired signal is retained. The adaptive interference cancellation system can cancel effectively interference signals, so that it can guarantee better quality service for the mobile user and save system. A key components to build the variable phase shifter for the adaptive interference cancellation system application are that a phase shifter requires phase and amplitude flatness characteristics to achieve a high cancellation level over a broad bandwidth. In addition, the insertion loss of a phase shifter is minimal. The variable phase shifter is designed as a reflected type phase shifter. It is produced using a quadrature coupler (90˙hybrid) and varactor diodes. The toroid type inductor technique for improvement of phase flatness and phase linearity are applied to design of a variable phase shifter. A frequency range is 1,750~1,780 MHz. As the results of an experiment, the phase variation of 135°(-5.4 8°~130.36°), the insertion loss of –1.03~-1.19 dB and phase flatness and phase linearity of ±3.47°or 6.94°(at a center frequency 1,765 MHz with 30 MHz bandwidth) are achieved, as a variation in the reverse bias voltage up to 11 V.