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Spectrum sensing over a wide bandwidth increases the probability of finding unutilized spectrum for cognitive radios. The hardware realization of wideband sensing is challenging because strong primary users introduce large dynamic range and spectral leakage in adjacent unused bands. This paper proposes a multitap-windowed frequency power detector with adaptive threshold and sensing time to address the above challenges. The suppression of spectral leakage is achieved by multitap-windowed FFT processing, which also enables reduced sensing time. The sensing time and detection threshold are adapted according to the channel-specific spectral leakage, which results in a reliable wideband signal detection within constrained sensing time. Our simulations with a 20 dB interferer-to-noise ratio (INR) indicate a 2× improvement in detection rate compared to conventional power detectors. An order-of-magnitude improvement in sensing time is achieved in the presence of 30-dB INR interferers while maintaining a false-alarm rate of 0.1 and a detection rate of 0.9. The proposed algorithms are realized in an FPGA to demonstrate real-time operation with a latency below 10 μ s. Experimental results from a radio testbed closely match the numerical simulations. An ASIC architecture for a 200-MHz bandwidth is estimated to occupy 0.98 mm2 and dissipate 25 mW from a 1-V supply in a standard 65-nm CMOS technology.