Reconfigurable RF front-end for frequency-agile direct conversion receivers and cognitive radio system applications

A reconfigurable direct conversion receiver front-end for GSM and WLAN bands (1.9 and 2.4 GHz) is proposed and demonstrated for cognitive radio system applications. The RF front-end platform makes use of a silicon varactor-tuned bandpass filter in connection with a tunable six-port demodulator. Varactor diodes of both of the tunable structures are independently biased using two different sets of supply voltage. The demodulation of phase-shift-keying (PSK) signals at a bit rate of 40 Mbps is achieved by using wideband power detectors. An experimental test bench of the proposed receiver is realized, and QPSK and 8PSK signal constellations are measured at the center-operating frequencies of 1.9 and 2.4 GHz for different noise levels.