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 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 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.

A multiplexer includes: a substrate having a surface; another substrate having another surface facing the surface across an air gap; a filter that is located on the surface, and includes first series resonators in a first series pathway from a common terminal to a terminal, and first parallel resonators in first parallel pathways; another filter that is located on the another surface, and includes second series resonators in a second series pathway from the common terminal to another terminal, and second parallel resonators in second parallel pathways, a second parallel resonator closest to the another terminal and a second series resonator closest to the another terminal not overlapping with the first series pathway, at least a part of the second parallel pathways overlapping with at least a part of first pathways between the first series pathway and the first parallel resonators, the first parallel resonators, and the first series pathway.

A multiplexer includes: a substrate having a surface; another substrate having another surface facing the surface across an air gap; a filter that is located on the surface, and includes first series resonators in a first series pathway from a common terminal to a terminal, and first parallel resonators in first parallel pathways; another filter that is located on the another surface, and includes second series resonators in a second series pathway from the common terminal to another terminal, and second parallel resonators in second parallel pathways, a second parallel resonator closest to the another terminal and a second series resonator closest to the another terminal not overlapping with the first series pathway, at least a part of the second parallel pathways overlapping with at least a part of first pathways between the first series pathway and the first parallel resonators, the first parallel resonators, and the first series pathway.

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.

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, 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.

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 duplexer includes a duplexer package having a transmit terminal, an antenna terminal, a receive terminal and at least one package ground terminal, a transmit filter disposed within the duplexer package, and a receive filter disposed within the duplexer package. Coupled first and second inductors, the first inductor connected to the transmit filter and the second inductor connected to the receive filter, are configured to cancel, at least in part, RF signal leakage between the transmit filter and the receive filter.