A bandpass filter includes a capacitor coupled between an input node and an output node, and a dual-resonator structure coupled between the input node, the output node, and ground.

A radio frequency identification (RFID) tag includes an antenna operable to receive a radio frequency (RF) signal having a carrier frequency. The RFID tag further includes a tank circuit coupled to the antenna. The RFID tag further includes a tuning circuit operable to determine a received power level of the RF signal at the carrier frequency, determine whether the received power level is lower than a power level threshold. When the received power level is lower than the power level threshold: tuning circuit increases the input impedance of the RFID tag, determines a most recent power level of the received RF signal, and compares the most recent power level with the received power level. When the most recent power level is greater than the received power level, the tuning circuit incrementally increases the input impedance until the received power level is substantially equal to the power level threshold.

A radio frequency identification (RFID) tag includes an antenna operable to receive a radio frequency (RF) signal having a carrier frequency. The RFID tag further includes a tank circuit coupled to the antenna. The RFID tag further includes a tuning circuit operable to determine a received power level of the RF signal at the carrier frequency, determine whether the received power level is lower than a power level threshold. When the received power level is lower than the power level threshold: tuning circuit increases the input impedance of the RFID tag, determines a most recent power level of the received RF signal, and compares the most recent power level with the received power level. When the most recent power level is greater than the received power level, the tuning circuit incrementally increases the input impedance until the received power level is substantially equal to the power level threshold.

In accordance with an embodiment, a method of operating an RF system includes generating a first RF signal having a first frequency; filtering the generated first RF signal to form a first filtered transmitted signal; producing a first coupled signal and a first transmitted signal from the first filtered transmitted signal; transmitting the first transmitted signal; transmitting a second RF signal having a second frequency; bandpass filtering the first coupled signal to form a first tunable bandpass filtered signal; and measuring a parameter of the first tunable bandpass filtered signal.

In accordance with an embodiment, a method of operating an RF system includes generating a first RF signal having a first frequency; filtering the generated first RF signal to form a first filtered transmitted signal; producing a first coupled signal and a first transmitted signal from the first filtered transmitted signal; transmitting the first transmitted signal; transmitting a second RF signal having a second frequency; bandpass filtering the first coupled signal to form a first tunable bandpass filtered signal; and measuring a parameter of the first tunable bandpass filtered signal.

A power detector for use in an RF receiver. The detector includes a power reference generator and a power quantizer. The power reference generator develops a power reference current, voltage, or signal as a function of a power transferred via a received RF signal. The power quantizer is responsive to the power reference current, voltage, or signal to develop a digital field power value indicative of the power reference current, voltage, or signal.

A power detector for use in an RF receiver. The detector includes a power reference generator and a power quantizer. The power reference generator develops a power reference current, voltage, or signal as a function of a power transferred via a received RF signal. The power quantizer is responsive to the power reference current, voltage, or signal to develop a digital field power value indicative of the power reference current, voltage, or signal.

A method includes sending, by a reader, a radio frequency (RF) signal to a wireless sensor that includes an antenna having a tail section and a head section. The tail section is for placement in an RF limited area for sensing moisture in a first location of a vehicle under test and wherein the head section is for placement in a non-RF limited area. The method further includes receiving, by the reader, an RF response to the RF signal from the wireless sensor. The first RF response includes an indication of adjustment of one or more RF characteristics of the wireless sensor, which corresponds to a variance of the one or more RF characteristics from a desired value, which, in turn, corresponds to a level of moisture at the first location. The method further includes outputting, by the reader, a message regarding the level of moisture at the first location.

A method includes sending, by a reader, a radio frequency (RF) signal to a wireless sensor that includes an antenna having a tail section and a head section. The tail section is for placement in an RF limited area for sensing moisture in a first location of a vehicle under test and wherein the head section is for placement in a non-RF limited area. The method further includes receiving, by the reader, an RF response to the RF signal from the wireless sensor. The first RF response includes an indication of adjustment of one or more RF characteristics of the wireless sensor, which corresponds to a variance of the one or more RF characteristics from a desired value, which, in turn, corresponds to a level of moisture at the first location. The method further includes outputting, by the reader, a message regarding the level of moisture at the first location.

A resonator element for use in a filter is provided. The resonator element includes a first resonator acoustically coupled to a second or third resonator or both. The first resonator has terminals for incorporation in a filter structure. A tuning circuit is coupled to the second or third resonator or both to enable tuning of the resonator element. The tuning circuit includes a variable capacitor and an inductor.