The invention discloses an ultra wide band low power radiofrequency signal generator and a method thereof. The signal-generator comprises a baseband signal source used for generating continuous baseband signals, a switch used for controlling the segmentation of the baseband signals into a plurality of portions in terms of time domain, a quadrature modulator which modulates the baseband signals which have been segmented into the plurality of portions to make the baseband signals become a plurality of radiofrequency signals through the utilization of different radio frequency local oscillators, and a synthesizer used for synthesizing the plurality of radiofrequency signals a channel of ultra wide band low power radiofrequency signals in terms of time domain. The signal-generator is mainly used for a radar exciter.