Development of Widely Tunable RF Frontend: Challenge for Realization of Cognitive Radio

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This project was aimed at developing the software defined radio using a radio frequency (RF) recursive filter.First, auto tuning of the recursive filter was investigated. It is shown that the oscillation behaviors can be expressed well by the van der Paul equation, and this fact enables us to adjust the center frequency. We can also set the filter Q factor by storing the relation of the amplifier gain and its control voltage to the embedded micro-controller.Next, higher-order filters were synthesized combining multiple recursive filters. The auto-setting procedure allows us to compose a quasi-continuously tunable filter for the 300-500 MHz range.