In this letter, a new ultra- wideband receiving antenna used in the field of radio monitoring is proposed, which uses FR-4 flexible substrate to design the proposed antenna. The radiation frequency range of the antenna is 700MHz to 6GHz, fed by coplanar waveguide (CPW), and has a huge bandwidth to meet the needs of modern wireless communication. In order to enhance the performance of the antenna in the low frequency band and realize the ultra wideband characteristics, we constructed a composite structure, which includes a pair of symmetrical power divider like structures, a central serpentine structure, a gradual microstrip feeder, an impedance conversion node, and a M-shaped feeder structure. The working frequency range of the antenna is extremely wide, covering 8 times of ultra wideband from 700MHz to 6GHz. As a radio monitoring antenna, it can effectively receive multiple communication bands, showing excellent performance.