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.

In accordance with an embodiment, an RF system includes a transmit path having a first tunable transmit band stop filter, and a power amplifier coupled to an output of the first tunable transmit band stop filter, where the first tunable transmit band stop filter is configured reject a receive frequency and pass a transmit frequency; a receive path comprising an LNA; and a duplex filter having a transmit path port coupled to an output of the power amplifier, a receive path port coupled to an input of the LNA, and an antenna port, where the duplex filter is configured to pass the transmit frequency and reject the receive frequency between the antenna port and the transmit path port, pass the receive frequency and reject the transmit frequency between the antenna port and the receive path port.

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.

In accordance with an embodiment, a method of operating an RF system includes filtering a wideband RF signal using an adjustable center frequency bandpass filter to produce a filtered RF signal; amplifying the filtered RF signal to produce an amplified RF signal; and band stop filtering the amplified RF signal to produce a band stopped RF signal.

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 notch filter includes a first inductor coupled between an input node and an output node, a dual-resonator structure coupled between the input node and the output node, and a second inductor coupled between the dual-resonator structure and ground, and 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.

In accordance with an embodiment, an RF system includes a transmit path having a transmit RF filter and an adjustable transmit phase shifter/matching network coupled between the transmit RF filter and a transmit antenna port, where the adjustable transmit phase shifter/matching network is configured to transform an impedance of the transmit RF filter at a receive frequency from a first lower impedance to a first higher impedance at the transmit antenna port; and a receive path having a receive RF filter and an adjustable receive phase shifter/matching network coupled between the receive RF filter and a receive antenna port, where the adjustable receive phase shifter/matching network is configured to transform an impedance of the receive RF filter at a transmit frequency from a second lower impedance to a second higher impedance at the receive antenna port.

In accordance with an embodiment, a method of operating an RF system includes filtering a first wideband RF signal using a wideband filter bank. Filtering the first RF signal includes separating the first wideband RF signal into frequency cluster signals, where each frequency cluster signal of the frequency cluster signals includes different frequency ranges, the first wideband RF signal includes multiple RF bands, and each of the different frequency ranges comprises a plurality of RF bands of the multiple RF bands. The method further includes band stop filtering at least one of the frequency cluster signals to produce a band stopped frequency cluster 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.

An acoustic wave device includes a first piezoelectric layer including a first main surface and a second main surface, a first support portion including a first support substrate that overlaps the first piezoelectric layer in a first direction, a first resonator provided on at least the first main surface of the first piezoelectric layer, a second piezoelectric layer including a third main surface and a fourth main surface, a second support portion including a second support substrate overlapping the second piezoelectric layer in the first direction, and a second resonator provided on at least the third main surface of the second piezoelectric layer. The first resonator and the second resonator each include a functional electrode. The support portion includes a space portion that overlaps at least a portion of the functional electrode of the resonator in a plan view in the first direction.