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.

Embodiments of an acoustic filter are disclosed. In some embodiments, a bandpass filter is included in a passband signal path, the passband signal path is connected between a first terminal and a second terminal. A first bandstop filter is located in a first stopband signal path, the first stopband signal path connected at the first terminal. Additionally, a second bandstop filter is located in a second stopband signal path, the second stopband signal path is connected at the second terminal.

Acoustic resonators and filter devices, and method of making acoustic resonators and filter devices. An acoustic resonator includes a substrate having a surface and a piezoelectric plate having front and back surfaces, the back surface attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm that spans a cavity in the substrate. An interdigital transducer (IDT) is formed on the front surface of the piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm. The interleaved fingers have an irregular hexagon cross-sectional shape.

A multiplexer includes a first filter on a first path connecting a common terminal and a first terminal and defined by a band pass filter, a low pass filter, or a high pass filter, and a second resonator on a second path connecting the common terminal and a second terminal and defined by a band elimination filter including at least one elastic wave resonator. A pass band of the first filter and an attenuation band of the second filter overlap with each other, and a ripple of a first resonator closest to the common terminal is generated only outside pass bands of the first filter and the second filter.

A filter module includes filters. Each of the filters is configured to control communications bands having overlapping bandwidths each with the other. Each of the communications bands, allocated to any one of the filters, has a different limit frequency from the other.

Provided are a band-stop filter and a multi-frequency band-stop filter. The band-stop filter includes at least one band-stop filtering unit; the at least one band-stop filtering unit includes an input port, an output port, at least two resonators, and at least one inductive element; and the first terminal of the first resonator is connected between the input port and the inductive element, and the first terminal of the second resonator is connected between the output port and the inductive element.

A filter module comprises a first terminal, a second terminal, and a filter disposed along each signal path extending from the first terminal to the second terminal, the filter including a plurality of series resonators and a plurality of shunt resonators disposed between the series resonators and a ground, at least one resonator among the plurality of series resonators and the plurality of shunt resonators being a first type of resonator with a temperature compensating layer for better temperature coefficient of frequency, at least one resonator among the plurality of series resonators and the plurality of shunt resonators being a second type of resonator without a temperature compensating layer.