# US 2020/0403602 A1 · Correction unit for radio frequency filter > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2020/0403602 A1 - Document ID: US20200403602A1 - Status: Published application - Kind: A1 - Application number: 16/975,073 - Filed: 2019-03-08 - Published: 2020-12-24 - Earliest claimed: 2018-03-08 - Assignees: Kongsberg Defence & Aerospace AS - Applicants: Kongsberg Defence & Aerospace AS - Inventors: Bjørn Holst PETTERSEN; Stig ROOTH - Web page: https://patentgrep.com/patent/US20200403602A1 ## CPC - H03H 9/6489: {Compensation of undesirable effects} - H03H 9/6496: {Reducing ripple in transfer characteristic} - H01P 3/08: Microstrips; Strip lines - H03H 7/0115: {comprising only inductors and capacitors (H03H7/075, H03H7/09, H03H7/12, H03H7/13 take precedence)} - H03H 9/25: Constructional features of resonators using surface acoustic waves {(devices for manipulating acoustic surface waves in general G10K11/36)} - H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P) - H01P: WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE (operating at optical frequencies G02B) ## Abstract The present invention relates to a filter correction unit (203a) as well as an RF filter including the correction unit for use in radio frequency transmission lines including a band pass filter (201) having input and output interfaces mounted in the signal transmission line. The filter (201) is chosen so as to transmit signals within a predetermined frequency range, the quality factor of the filter having predetermined limitations generating a known distortion to the signal. The correction unit (203a) has a first bus connected to said transmission line and to said filter, wherein the correction unit comprises at least one surface acoustic wave (SAW) transducer (204a-n), each transducer having two electrodes on a piezoelectric substrate where a first electrode is connected to said first bus and the other electrode connected to a second bus, the SAW transducer being adapted to distort a transmitted signal with a factor being the inverse of said known distortion of the filter (201). ## Claims ### Claim 1 A filter correction unit for use in radio frequency transmission lines, the transmission lines including a band pass filter having input and output interfaces mounted in the signal transmission line, the band pass filter being chosen so as to transmit signals within a predetermined frequency range having a filter passband response, the quality factor of the filter's resonators having predetermined limitations generating a known passband distortion of the filter to the signal, wherein the correction unit has a first bus connected to the transmission line and to the filter, wherein the correction unit comprises at least one surface acoustic wave (SAW) transducer, each transducer having two electrodes on a piezoelectric substrate where a first electrode is connected to the first bus and the other electrode connected to a second bus, the SAW transducer being adapted to distort the amplitude of a transmitted signal with a factor being the inverse of the known distortion of the filter. ### Claim 2 (depends on 1) The filter correction unit according to claim 1, wherein the second bus is connected to ground. ### Claim 3 (depends on 1) The filter correction unit according to claim 1, wherein the band pass filter is produced on a piezoelectric substrate material, and the SAW transducers are produced on the same substrate. ### Claim 4 (depends on 1) The filter correction unit according to claim 1, wherein the first bus is connected to a first input and output interface of the filter correction unit, where one interface is connected to a first interface of the transmission line and the other interface to a first filter interface. ### Claim 5 (depends on 1) The filter correction unit according to claim 1, wherein the second bus is connected to a second input and output interface of the filter correction unit, where one interface is connected to a second interface of the transmission line and the other interface to a second filter interface, the filter being a balanced four port band pass filter. ### Claim 6 (depends on 1) The filter correction unit according to claim 1, wherein the dominant acoustic wave mode to which the SAW transducer couples is a pseudo-SAW mode. ### Claim 7 (depends on 1) The filter correction unit according to claim 1, wherein the dominant acoustic wave mode to which the SAW transducer couples is a leaky wave mode bound to the surface. ### Claim 8 (depends on 1) The filter correction unit according to claim 1, including inductive and capacitive elements, the capacitive elements having one end connected to a first transmission line or filter interface and the other end to ground, whereas the inductive elements are connected between the first bus and the transmission line or filter interface, the elements being chosen so as to improve the impedance matching of the correction unit to the transmission line and filter. ### Claim 9 (depends on 1) The filter correction unit according to claim 1, including inductive and capacitive elements, the capacitive elements being connected between a first and second transmission line or filter interface, whereas the inductive elements are connected between the first or second bus and the first or second transmission line or filter interface, the elements being chosen so as to improve the impedance matching of the correction unit to the transmission line and filter, the filter being a balanced four port band pass filter. ### Claim 10 (depends on 1) The filter correction system including two filter correction units according to claim 1, being connected on both sides of the band pass filter. ### Claim 11 (depends on 1) A radio frequency filter including a filter correction unit according to claim 1, wherein the band pass filter is constituted by grounded capacitive filter elements, the capacitive filter elements being realized through at least one of the SAW transducers, each having two electrodes on a piezoelectric substrate where the first electrode is connected to the interior of the band pass filter and the second electrode to ground, the SAW transducer being adapted both to distort a transmitted signal with a factor being the inverse of the know distortion of the filter, and also realizing the capacitance required to define the band pass filter response. ### Claim 12 (depends on 11) The radio frequency filter according to claim 11, wherein the filter is a LC filter. ### Claim 13 (depends on 11) The radio frequency filter according to claim 11, wherein the filter comprises coupled transmission lines in a comb-line structure. ### Claim 14 (depends on 11) The radio frequency filter according claim 11, wherein transmission lines incorporated in the radio frequency filter are microstrip lines. ### Claim 15 (depends on 11) The radio frequency filter according claim 11, wherein transmission lines incorporated in the radio frequency filter are strip lines. ### Claim 16 (depends on 11) The radio frequency filter according to claim 11, wherein the SAW transducers and the transmission lines incorporated in the band pass filter are located on a single piezoelectric substrate. ### Claim 17 (depends on 11) The radio frequency filter according to claim 11, wherein the dominant acoustic wave mode to which the SAW transducer couples is a pseudo-SAW mode. ### Claim 18 (depends on 11) The radio frequency filter according to claim 11, wherein the dominant acoustic wave mode to which the SAW transducer couples is a leaky wave mode bound to the surface.