Frequency-Agile Dual-Band Direct Conversion Receiver for Cognitive Radio Systems

A frequency-agile dual-band direct conversion receiver is proposed and experimentally validated for cognitive radio system applications. Two types of tunable receiver architectures are presented and analyzed in this work; one structure relying on a tunable bandpass filter, and a second system based on a varactor-based tunable six-port demodulator, with the latter showing better sensitivity and dynamic range. In order to demodulate phase-shift-keying modulated signals at multiple operating frequencies at a high bit rate of 40 Mb/s, the receiver is designed using a wideband power detector in connection with a high-speed quad comparator. An experimental prototype and a complete measurement test bench have been realized in order to obtain the bit error rate performance of the receiver in a more realistic application environment. In summary, the proposed electronically tunable system allows for an operation in multiband frequency ranges including global system for mobile communications cellular networks (1900 MHz) and IEEE802.11 a/b/g applications (2.4 and 5.8 GHz).