Tunable multi-band direct conversion receiver for cognitive radio systems

A low-cost frequency-agile dual-band direct conversion receiver is proposed and experimentally validated for cognitive radio systems. The receiver is composed of a varactor-tuned six-port front-end module as a unique tunable device. Two tunable types of receiver architectures are also proposed and analyzed. The architecture based on a tunable six-port demodulator shows a better sensitivity. In order to demodulate phase-shift-keying (PSK) modulated signals at multiple operating frequency of a transmit signal at a high bit rate of 40 Mbps, the receiver makes use of a wideband power detectors in connection with a high speed quad comparators. An experimental prototype has been fabricated and a complete measurement test bench has been realized in order to obtain the receiver performances in a more realistic application environment. Consequently, the proposed electronically controlled system will therefore be used to operate at multi-band frequency ranges including GSM cellular and IEEE802.11a.