An acoustic wave device includes an acoustic wave filter configured to filter a radio frequency signal and a loop circuit coupled to the acoustic wave filter. The loop circuit is configured to generate an anti-phase signal to a target signal at a particular frequency. The loop circuit includes a Lamb wave resonator having a piezoelectric layer and an interdigital transducer electrode disposed on the piezoelectric layer. The piezoelectric layer includes free edges. An edge of the piezoelectric layer is configured to one of suppress or scatter reflections of acoustic waves generated by the interdigital transducer electrode from the edge of the piezoelectric layer.

To realize a compact device that detects phase or controls phase or an amplitude with high sensitivity, a signal controller includes: a linear conductor having a first end fixed to a negative electrode and a second end serving as a free end; a positive electrode facing the free end with a small gap therebetween; a first signal source that applies a voltage between the negative electrode and the positive electrode, the voltage applied being variable; a driving electrode that applies an electric field to a space around the conductor, the electric field having a component perpendicular to the lengthwise direction of the conductor; and a second signal source that applies an AC signal to the driving electrode. The signal processor can be a device for controlling or modulating phase or amplitude.

To realize a compact device that detects phase or controls phase or an amplitude with high sensitivity, a signal controller includes: a linear conductor having a first end fixed to a negative electrode and a second end serving as a free end; a positive electrode facing the free end with a small gap therebetween; a first signal source that applies a voltage between the negative electrode and the positive electrode, the voltage applied being variable; a driving electrode that applies an electric field to a space around the conductor, the electric field having a component perpendicular to the lengthwise direction of the conductor; and a second signal source that applies an AC signal to the driving electrode. The signal processor can be a device for controlling or modulating phase or amplitude.

A notch filter includes an inductor 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 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.