| With the rapid development of wireless communication, the shortage of spectrum resources becomes one of the major urgent problems. Cognitive Radio (CR) can senses and utilizes the unoccupied spectrum which have been authorized automatically, then CR improves the utilization rate of spectrum resources. CR has been developed for decade, the spectrum sensing and resource management techniques for CR have been matured. On the contrary, the researches of hardware which support these algorithms are lesser. Therefore, the researches of CR hardware are the key for CR applications from theory.This research comes from Huawei Technology Foundation "The Key Technology of Cognitive Radio". This paper research on the key issues of Radio Frequency (RF) front-end for CR. This paper analyzes the requirement of RF front-end, and analyzes the design requirement of RF filter, low noise amplifier, local oscillator, mixer and power amplifier (PA), and summarizes the related researches status. The innovations of this paper are mainly embodied in the following two aspects:1. In allusion to the issue that LO harmonics will down-convert the unwanted signals to the baseband in the CR receiver, this paper propose a novel Adjustable Harmonic Rejection Mixer (AHRM) which utilizes the nonlinearity of mixer and changes the number of operation-paths to satisfy the variable harmonic rejection requirement of CR. The simulation results show that the harmonic rejection ratio of the AHRM can reach about295dB for the required harmonics, and the AHRM can suppress seven-order harmonic and ninth-order harmonic which can’t be prevented by the traditional HRM.2. To meet the operation band and performance requirement of PA for CR, this paper present a concurrent dual-wideband PA, in which negative feedback and transformer techniques are employed to design the matching network. The simulated results indicate that the gains exceed 25dB over the two frequency bands, and the proposed PA has excellent flatness and linearity. |
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