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 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 radio frequency filter module includes: an antenna package including patch antennas and having first and second frequency passbands different from each other; an integrated circuit (IC) package including an IC; and a connecting member disposed between the antenna package and the IC package, and having a laminated structure configured to electrically connect the patch antennas and the IC to each other. The connecting member includes: a first radio frequency filter pattern having the first and second frequency passbands, and including a first port electrically connected to the IC and a second port electrically connected to at least one of the patch antennas; and a second radio frequency filter pattern having the first and second frequency passbands, and including a third port electrically connected to the IC and a fourth port electrically connected to at least another one of the patch antennas.

A radio frequency filter module includes: an antenna package including patch antennas and having first and second frequency passbands different from each other; an integrated circuit (IC) package including an IC; and a connecting member disposed between the antenna package and the IC package, and having a laminated structure configured to electrically connect the patch antennas and the IC to each other. The connecting member includes: a first radio frequency filter pattern having the first and second frequency passbands, and including a first port electrically connected to the IC and a second port electrically connected to at least one of the patch antennas; and a second radio frequency filter pattern having the first and second frequency passbands, and including a third port electrically connected to the IC and a fourth port electrically connected to at least another one of the patch antennas.

A noise suppressor includes a first differential-mode transmission module, a second differential-mode transmission module and a common-mode absorption module. The first and second differential-mode transmission modules are configured to receive a differential signal at one of the first and second differential-mode transmission modules, and output the differential signal at the other of the same. The common-mode absorption module is electrically connected to a reference node, and is configured to absorb common-mode noise of the differential signal from at least one of the first differential-mode transmission module or the second differential-mode transmission module.

An electrical filter structure for forwarding an electrical signal from a first port to a second port in a frequency selective manner, wherein the filter is an edge-coupled filter, the filter comprising: a plurality of coupled line sections coupled in a series, comprising at least a first coupled line section and a last coupled line section; wherein the first port is connected with the first of the coupled line sections using a first transmission line; wherein the second port is connected with the last of the coupled line sections using a second transmission line; wherein the electrical filter comprises an open stub; wherein a length of the open stub is chosen such that an electrical length of the open stub is equal, within a tolerance of +/20 percent, to a fourth of a wavelength of a signal having a frequency of twice a passband center frequency of the filter.

An electrical filter structure for forwarding an electrical signal from a first port to a second port in a frequency selective manner, wherein the filter is an edge-coupled filter, the filter comprising: a plurality of coupled line sections coupled in a series, comprising at least a first coupled line section and a last coupled line section; wherein the first port is connected with the first of the coupled line sections using a first transmission line; wherein the second port is connected with the last of the coupled line sections using a second transmission line; wherein the electrical filter comprises an open stub; wherein a length of the open stub is chosen such that an electrical length of the open stub is equal, within a tolerance of +/20 percent, to a fourth of a wavelength of a signal having a frequency of twice a passband center frequency of the filter.

A circuit interrupter including a busbar, a Rogowski coil disposed around the busbar and structured to sense current having a first frequency flowing through the busbar, a test injector circuit structured to input a test signal having a second frequency to the Rogowski coil, high or band pass filter circuitry structured to receive an output of the Rogowski coil, the output including a first component having the first frequency and being proportional to the current through the busbar and a second component having the second frequency and being proportional to a temperature of the Rogowski coil, and to attenuate the first component of the Rogowski coil output, and an electronic trip unit including a temperature measurement unit structured to receive an output of the high or band pass filter circuitry and to estimate the temperature of the busbar based on the output of the high or band pass filter circuitry.

A circuit interrupter including a busbar, a Rogowski coil disposed around the busbar and structured to sense current having a first frequency flowing through the busbar, a test injector circuit structured to input a test signal having a second frequency to the Rogowski coil, high or band pass filter circuitry structured to receive an output of the Rogowski coil, the output including a first component having the first frequency and being proportional to the current through the busbar and a second component having the second frequency and being proportional to a temperature of the Rogowski coil, and to attenuate the first component of the Rogowski coil output, and an electronic trip unit including a temperature measurement unit structured to receive an output of the high or band pass filter circuitry and to estimate the temperature of the busbar based on the output of the high or band pass filter circuitry.