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This paper presents two-stage detectors for spectrum sensing in cognitive radio networks. The first stage consists of multiple energy detectors, where each energy detector (ED) has a single antenna with fixed threshold for making a local binary decision. If required, the second stage comprised of ED with adaptive double threshold is invoked. The detection performance of the proposed scheme is compared with a cyclostationary-based sensing method and adaptive spectrum sensing scheme. The numerical results show that the proposed scheme improves detection performance and outperforms the cyclostationary-based sensing method and adaptive spectrum sensing by 12.3% and 14.4% at signal-to-noise ratio (SNR) setting of as low as -8 dB, respectively. Performance was also measured in terms of sensing time and scheme has smaller sensing time than cyclostationary detection and adaptive spectrum sensing scheme in the order of 4.3 and 0.1 ms at -20-dB SNR, respectively. Furthermore, the scheme was analyzed in conjunction with cooperative spectrum sensing (CSS), where each cognitive radio (CR) user used two-stage spectrum sensing detectors for local detection and sent detection decisions to the fusion center to give the final decision based on hard decision OR rule. It is further found that the proposed two-stage spectrum sensing scheme with CSS achieves spectrum detection performance in the order of 0.9 for an SNR value of as low as -19 dB as the number of CR users (K) is 10.