BALANCED RADIO FREQUENCY ELECTRICALLY TUNABLE BAND-PASS FILTER WITH CONSTANT ABSOLUTE BANDWIDTH

摘要

Disclosed in the present invention is a balanced radio frequency electrically tunable band-pass filter with constant absolute bandwidth. The band-pass filter comprises a micro strip structure at an upper layer, a medium substrate at a middle layer and grounding metal at a lower layer. The micro strip structure at the upper layer adopts a balanced circuit and comprises four half-wavelength resonators, two input feed networks, two output feed networks, two input ports and two output ports; each of the four half-wavelength resonators comprises a micro strip and a variable capacitance diode with two connected ends; capacitors are loaded at the middles of the first half-wavelength resonator and the third half-wavelength resonator; the second half-wavelength resonator and the fourth half-wavelength resonator are bent and arranged symmetrically; and the whole filter structure is in mirror symmetry. The balanced radio frequency electrically tunable band-pass filter provided by the invention realizes constant absolute bandwidth during centre frequency tuning and can restrain common mode interference and can be used for a reconstructed radio frequency front end of wireless communication.