An enabling technology for cognitive radio is expeditious wideband spectrum sensing. A major challenge for implementing wideband spectrum sensors is fitting a wideband antenna within a given form factor. Scanning a narrowband antenna is an attractive alternative to using a wideband antenna in situations where constraints on the allowable antenna dimensions make designing a sensitive wideband antenna a challenge. However, scanning the antenna through a wide spectrum extremely rapidly can induce significant nonlinear effects. This work explores the nonlinear effects of rapidly scanning a narrowband antenna in order to enable the design of devices that scan the antenna extremely rapidly. The frequency spread due to the amplitude modulation effect due to tuning and detuning the antenna is characterized. The frequency shift due to the rapidly changing phase associated with rapidly tuning an antenna is calculated. The limit on how rapidly the antenna may be tuned effectively is explored. The nonlinear effects of rapid antenna tuning are observed experimentally and replicated in simulation.
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Wideband spectrum sensing using rapidly tuned antennas