# US 10,122,478 B2 · Methods and devices for real-time monitoring of tunable filters > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,122,478 B2 - Document ID: US10122478B2 - Status: Granted - Kind: B2 - Application number: 15/057,072 - Filed: 2016-02-29 - Published: 2017-07-13 - Granted: 2018-11-06 - Earliest claimed: 2015-02-27 - Assignees: Purdue Research Foundation - Applicants: Purdue Research Foundation - Inventors: Mohammad Abu Khater; Dimitrios Peroulis - Web page: https://patentgrep.com/patent/US10122478B2 ## CPC - H04B 17/22: {for calibration of the receiver components} - G01R 1/24: Transmission-line, e.g. waveguide, measuring sections, e.g. slotted section - G01R 23/02: Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage - G01R 23/10: by converting frequency into a train of pulses, which are then counted {, i.e. converting the signal into a square wave} - H01P 1/219: Evanescent mode filters - H03H 7/1775: {Parallel LC in shunt or branch path (H03H7/1791 takes precedence)} - H03K 19/21: EXCLUSIVE-OR circuits, i.e. giving output if input signal exists at only one input; COINCIDENCE circuits, i.e. giving output only if all input signals are identical - H01P 1/2136: {using comb or interdigital filters; using cascaded coaxial cavities (H01P1/2131, H01P1/2135 take precedence)} - H03H 2007/013: {Notch or bandstop filters} - H04B: TRANSMISSION - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - H01P: WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE (operating at optical frequencies G02B) - H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P) - H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M) ## Abstract Methods and devices suitable for monitoring the frequency of microwave tunable filters in real time. The frequency readout relies on the natural response of such a filter when excited by a pulse. Methods of measuring an operating frequency of a pole in a tunable filter include measuring a number of cycles in a natural response in the filter when the filter is excited by an electric current pulse, and determining a resonance frequency based on the number of cycles measured in the natural response. Such a method can provide the operating frequency information in a binary digital format, making it relatively easy to read and process. A measuring resonator may be mounted to the filter resonator and connected by a common actuator. ## Claims ### Claim 1 An evanescent-mode RF filter, comprising: an RF filter resonator having a first membrane enclosing a first cavity; a monitoring resonator having a second membrane enclosing a second cavity, the monitoring resonator mounted opposing the filter resonator such that the first and second membranes are facing one another; a planar actuator mounted between the first and second membranes, wherein the planar actuator comprises a piezoelectric element, wherein the piezoelectric element is electrically isolated from the first membrane and the second membrane by an electrically insulating material; and a power supply configured to apply a voltage bias signal to the actuator, the voltage bias signal causing the actuator to increase or decrease the operating frequency of the filter resonator; a pulse injection circuit operatively connected to an input of the monitoring resonator, the pulse injection circuit configured to supply a pulse signal to the monitoring resonator; a readout circuit connected to an output of the monitoring resonator, the readout circuit configured to determine a number of pulses from the output having a voltage greater than a predetermined threshold in a predetermined time period, the number of pulses corresponding to a natural response frequency of the filter resonator in response to the pulse signal, wherein the readout circuit outputs a value in a binary digital format, the value corresponding to said number of pulses; and a feedback control circuit, the feedback control circuit having an input configured to receive output from the readout circuit and an output operatively connected to the power supply, the feedback control circuit configured to tune the filter to a desired operating frequency. ### Claim 2 (depends on 1) The filter of claim 1, wherein the piezoelectric element comprises a disk, and wherein the filter resonator and the monitoring resonator are circular. ### Claim 3 (depends on 1) The filter of claim 1, wherein the filter comprises a plurality of filter resonators and monitoring resonators, each of the filter resonators connected to a corresponding monitoring resonator. ### Claim 4 (depends on 1) The filter of claim 1, wherein the filter is a band-stop filter. ### Claim 5 (depends on 1) The filter of claim 1, further comprising: an antenna connected to an input of the filter resonator; and an RF receiver connected to an output of the filter resonator.